Patent Grant
11224990
This invention discloses a method of producing fiber reinforced cementitous materials in a continuous process.
U.S. Pat. No. 6,986,812 to Dubey et al., incorporated herein by reference in its entirety, features a slurry feed apparatus for use in a structural cement panel (SCP) production line or the like application where settable slurries are used in the production of building panels or board. The apparatus includes a main metering roll and a companion roll placed in close, generally parallel relationship to each other to form a nip in which a supply of slurry is retained. Both rolls preferably rotate in the same direction so that slurry is drawn from the nip over the metering roll to be deposited upon a moving web of the SCP panel production line. A thickness control roll is provided in close operational proximity to the main metering roll for maintaining a desired thickness of the slurry.
U.S. Pat. No. 7,524,386 B2 to George et al., incorporated herein by reference in its entirety, discloses a process employing a wet mixer having a vertical mixing chamber for forming a wet slurry of a cementitous powder and liquid. The vertical mixing chamber is designed to provide the required amount of mixing to provide thoroughly mixed, uniformly thin slurry within a mixing residence time that allows for adequate supply of slurry to ensure continuous operation of an associated cement panel production line. Gravity feed means for supply of cementitous powder and water to the slurry mixing area of the chamber is also disclosed. In preparing the SCP panels, an important step is mixing cementitous powder to form slurry. The slurry is then withdrawn from the bottom of the chamber and pumped through a cavity pump to the slurry feeding apparatus. A typical conventional continuous cement mixer is the DUO MIX2000 continuous cement mixer from M-TEC GmbH, Neuenburg, Germany used in the construction industry to mix and pump concrete slurry.
U.S. Pat. No. 7,513,963 B2 to George et al., incorporated herein by reference in its entirety, discloses a wet mixer apparatus and method for its use, the mixer having a vertical mixing chamber for forming a wet slurry of a cementitous slurry and water. The vertical mixing chamber is designed to provide the required amount of mixing to provide thoroughly mixed, uniformly thin slurry within a mixing residence time that allows for adequate supply of slurry to ensure continuous operation of an associated cement panel production line. Gravity feeding for separate supply of cementitous powder and water to the slurry mixing area of the chamber without pre-mixing of the powder and water is also disclosed.
U.S. Pat. No. 8,038,790 to Dubey et al., incorporated herein by reference in its entirety, discloses structural cement panel for resisting transverse and shear loads equal to transverse and shear loads provided by plywood and oriented strain board, when fastened to framing for use in shear walls, flooring and roofing systems. The panels provide reduced thermal transmission compared to other structural cement panels. The panels employ one or more layers of a continuous phase resulting from curing an aqueous mixture of calcium sulfate alpha hemihydrate, hydraulic cement, coated expanded perlite particles filler, optional additional fillers, active pozzolan and lime. The coated perlite has a particle size of 1-500 microns, a median diameter of 20-150 microns, and an effective particle density (specific gravity) of less than 0.50 g/cc. The panels are reinforced with fibers, for example alkali-resistant glass fibers.
US Patent Application Publication No. 2005/0064164 to Dubey et al., incorporated herein by reference in its entirety, discloses a multi-layer process for producing structural cementitous panel which includes: (a) providing a moving web; (b) one of (i) depositing a first layer of individual, loose fibers upon the web, followed by depositing a layer of settable slurry upon the web and (ii) depositing a layer of settable slurry upon the web; (c) depositing a second layer of individual, loose fibers upon the slurry; (d) actively embedding said second layer of individual, loose fibers into the slurry to distribute said fibers throughout the slurry; and (e) repeating steps (ii) through (d) until the desired number of layers of settable fiber-enhanced slurry is obtained and so that the fibers are distributed throughout the panel. Also provided are a structural panel produced by the process, an apparatus suitable for producing structural cementitous panels according to the process, and a structural cementitous panel having multiple layers, each layer created by depositing a layer of settable slurry upon a moving web, depositing fibers upon the slurry and embedding the fibers into the slurry such that each layer is integrally formed with the adjacent layers.
US Patent Application Publication No. 2006/0061007 to Chen et al. discloses a method and apparatus for extruding cementitous articles. The extruder includes a casing with a pair of inter-meshing self-wiping screws rotatably mounted therein. The screws continuously mix and knead the components of the fiber cement provided through various feed means to form a substantially homogeneous paste and force the paste through a die to form a green cementitous extrudate suitable for casting. Cementitous mixtures for extruding are very viscous and not suitable for uses such as shotcrete or deposition through a forming assembly on a cementitous panel production line.
The current state-of-the-art mixing technology for producing fiber reinforced cementitous slurry typically involves use of industry standard batch mixers into which all raw materials including reinforcing fibers are first added and then mixed for several minutes to yield a slurry mixture with randomly dispersed fibers. Rotating drum and rotating pan mixers are examples of concrete mixers that are commonly used for preparing fiber reinforced cementitous slurry mixtures. Some major limitations and drawbacks of the current state-of-the art concrete mixers and mixing technologies for producing fiber reinforced cementitous slurry mixtures include:
The mixing operation in a batch mixer is not continuous thus making their use more difficult in applications where a continuous supply of slurry is needed such as in the case of a continuous panel production line.
The mixing time in a batch mixer is typically very long, in the order of several minutes, to obtain a well-blended, homogeneous slurry mixture.
Since a large amount of fibers are added at a time in a batch mixer, that leads to fiber lumping and balling during the mixing operation.
Longer mixing times involved with the batch mixing process tend to damage and break the reinforcing fibers.
Batch mixers are not very useful and practical with respect to handling rapid setting cementitous materials.
There is a need for a single-layer process for producing slurry for cementitous panels having high reinforcing fiber concentrations. Thus, there is a need for an improved wet mixing apparatus that ensures supply of sufficient mixed fluid cementitous slurry which contains reinforcing fibers such as glass fibers or polymeric fibers to supply a continuous panel production line. It is desired to provide a degree of mixing of the cementitous reactive powder, reinforcing fibers, and water in the mixer to result in a slurry of proper rheology and sufficient fluidity to provide a slurry for use in the continuous cementitous panel manufacturing line.
The present invention features methods for preparing a fiber reinforced concrete (FRC) panel, also termed by this specification as a fiber reinforced cement panel, or a fiber reinforced cementitious panel. Considering the limitations and drawbacks of the current state-of-the-art some objectives of the present invention are as follows:
Develop a manufacturing process that facilitates formation of fiber reinforced concrete panel products which is a continuous method.
Develop a manufacturing process that facilitates formation of fiber reinforced concrete panel products in a single homogenous layer.
Develop a manufacturing process that facilitates formation of fiber reinforced concrete panel products to correct thickness and surface tolerance, thus eliminating the need for time consuming and expensive panel finishing operations.
Develop a manufacturing process that facilitates formation of fiber reinforced concrete panel products in which the discrete reinforcing fibers are randomly and uniformly distributed throughout the panel.
Develop a manufacturing process that facilitates formation of fiber reinforced concrete panel products at much faster line speeds.
Develop a manufacturing process that facilitates formation of fiber reinforced concrete panel products having different and unique composite designs and reinforcing options including the ability to add surface reinforcements such as scrims, fabrics, and structural laminates.
Develop a manufacturing process that facilitates formation of fiber reinforced concrete panel products at significantly lower cost compared to the current state-of-the-art manufacturing processes.
The invention provides a continuous method for preparing a fiber reinforced cement panel comprising:
mixing water and cementitous powder to form a cementitous slurry;
mixing the cementitous slurry and reinforcement fibers in a single pass horizontal continuous mixer to form a fiber-slurry mixture,
the horizontal continuous mixer comprising
wherein the cementitous slurry and reinforcement fibers are mixed in a part of the mixing chamber for mixing the reinforcement fibers and cementitous slurry and moving the cementitous slurry and reinforcement fibers being mixed to the fiber-slurry mixture outlet;
wherein the shaft in the part of the mixing chamber for mixing the reinforcement fibers and cementitous slurry and moving the cementitous slurry and reinforcement fibers being mixed to the fiber-slurry mixture outlet comprises at least one mixing element selected from the group consisting of (1) an auger and (2) a plurality of mixing paddles mounted on the shaft at regular intervals and different circumferential locations to extend from the shaft, wherein the at least one mixing element rotates about the shaft within the housing;
wherein the cementitous slurry and fibers are mixed in the mixing chamber of the horizontal fiber-slurry mixer for an average mixing residence time of about 5 to about 240 seconds, preferably 10 to 180 seconds, more preferably 10 to 120 seconds, most preferably 10 to 60 seconds while the at least mixing element applies shear force, wherein the central rotating shaft rotates at 30 to 450 RPM, more preferably 40 to 300 RPM, and most preferably 50 to 250 RPM during mixing;
discharging the fiber-slurry mixture from the horizontal mixer;
wherein fresh water, cementitous powder, and fibers are fed to the mixer simultaneous with the discharging of the mixture of water, cementitous powder, and fibers in the fiber-slurry mixture from the mixer;
feeding the fiber-slurry mixture to a forming assembly (preferably a “headbox”) which deposits the fiber-slurry mixture on a moving surface of a panel production line uniformly as a layer 0.25 to 2 inches thick, preferably 0.25 to 1 inches thick, more preferably 0.4 to 0.8 inches thick, typically 0.40 to 0.75 inches thick;
leveling the fiber-slurry mixture on the moving surface;
allowing the fiber-slurry mixture to set on the moving surface;
cutting the set fiber-slurry mixture into panels and removing the panels from the moving surface, wherein an additional layer of fiber-slurry mixture is not deposited on the deposited layer of fiber-slurry mixture.
The horizontal continuous mixer shaft is connected to a drive mechanism and a drive motor to accomplish shaft rotation when the horizontal continuous mixer is in operation, wherein the horizontally oriented shaft is externally connected to the drive mechanism and the drive motor
The method disclosed herein is a continuous method as opposed to a batch method. In a continuous method the raw materials required to make the end product are metered and fed continuously at a rate that equals the rate (mass balance) at which the end product is being produced, that is, the raw material feed flows in the process and the end product flows out of the process simultaneously. In a batch method, the raw materials required to make the end product are first combined in large amounts to prepare a large batch of mixture for storage in appropriate vessel/s; this batch of mixture is then subsequently drawn from the storage vessel/s to produce multiple pieces of the end product.
The method of the present invention continuously produces a cementitous panel having at most a single layer of fiber reinforced cementitous composition on a conveyor-type frame supporting a moving web. The horizontal mixer is in operational relationship to the frame and configured for discharging the fiber-slurry mixture to a first slurry feed station (preferably a headbox) which is in operational relationship to the frame and configured for depositing the layer of settable fiber-containing cementitous slurry upon the moving web. Preferably the moving surface (moving web) moves at a speed of 1 to 100 feet per minute, more preferably 5 to 50 feet per minute. This is substantially faster than the conventional cement extrusion processes utilizing viscous cementitious mixtures. Typically the fiber-slurry mixture is deposited at a rate of about 0.10-25 cubic feet per minute for a panel 4 to 8 feet wide. This method of producing cementitious products is also much faster than the typical extrusion manufacturing processes employed in the industry. The fiber-slurry mixture levels and sets as it travels on the moving web. Downstream is an apparatus for cutting the set fiber-slurry mixture into cement boards.
The fiber-slurry mixture discharged from the horizontal mixer has a slump of 4 to 11 inches as measured according to a slump test using a 4 inch tall and 2 inch diameter pipe. The fiber-slurry mixture discharged from the horizontal mixer also has a viscosity less than 45000 centipoise, preferably less than 30000 centipoise, more preferably less than 15000 centipoise, and most preferably less than 10000 centipoise when measured using a Brookfield Viscometer, Model DV-II+ Pro with Spindle HA4 attachment running at 20 RPM speed. Typically the resulting fiber-slurry mixtures have a viscosity of at least 1500 centipoise.
The fiber-slurry mixtures typically also include plasticizers and superplasticizers. Plasticizers are commonly manufactured from lignosulfonates, a by-product from the paper industry. Superplasticizers have generally been manufactured from sulfonated naphthalene condensate or sulfonated melamine formaldehyde, caseins, or based on polycarboxylic ethers. The present fiber-slurry mixtures preferably lack thickeners or other additives that substantially increase material viscosity.
The resulting fiber-slurry mixtures of the present invention distinguish over cementitous mixtures used in extrusion processes. Such extrusion mixtures have a slump of 0 to 2 inches as measured according to the slump test using a 4 inch tall and 2 inch diameter pipe and have a viscosity greater than 50000 centipoise, more typically greater than 100000 centipoise, and most typically greater than 200000 centipoise. The extrusion mixtures also generally do not include water reducers and superplasticizers which are present in fiber-slurry mixtures of the present invention. As mentioned above, plasticizers are commonly manufactured from lignosulfonates, a by-product from the paper industry. Superplasticizers have generally been manufactured from sulfonated naphthalene condensate or sulfonated melamine formaldehyde, or based on polycarboxylic ethers.
In the method the mixing of water and cementitous material may occur in a first mixer which forms cementitous slurry. Then the mixing of the cementitous slurry and the fibers occurs in a second fiber-slurry mixer.
Alternatively, the mixing of water and cementitous material and fibers may be combined in a single unit operation using a combination continuous mixer where the first section of the mixer produces a cementitous slurry mixture by combining all dry powders, chemical additives, and water; and the second section of mixer produces a fiber reinforced cementitous slurry mixture by introducing and combining the reinforcing fibers with the incoming cementitous slurry mixture produced in the first section of the combined mixer.
In particular the method which mixes water and cementitous material in a first mixer to form cementitous slurry and then mixes the cementitous slurry and the fibers in a second fiber-slurry mixer comprises the following steps:
feeding a liquid stream comprising water, into a continuous slurry mixer through a liquid stream inlet and feeding a stream of a dry cementitous powder into the continuous slurry mixer to form a cementitous slurry, said continuous slurry mixer having a horizontally or vertically mounted impeller;
passing the cementitous slurry from the continuous slurry mixer into a single pass horizontal fiber-slurry continuous mixer and passing a stream of reinforcement fibers into the horizontal fiber-slurry continuous mixer and mixing the cementitous slurry and the reinforcement fibers to form a fiber-slurry mixture,
the horizontal fiber-slurry continuous mixer comprising
a plurality of mixing and conveying paddles mounted on the horizontally oriented shaft of the mixer at regular intervals and different circumferential locations, the paddles rotated about the horizontally oriented shaft within the horizontal housing, the paddle assemblies extending radially from a location on the shaft, the paddle assemblies comprising a pin engaged to a paddle head, the pin pivotally engaged to the horizontally oriented shaft and/or the paddle head to permit pivotal rotation of the paddle head relative to the respective location on the horizontally oriented shaft, wherein the plurality of paddles are arranged to mix the reinforcement fibers and cementitous slurry and move the cementitous slurry and reinforcement fibers being mixed to the fiber-slurry mixture outlet;
wherein the horizontally oriented shaft is externally connected to a drive mechanism and a drive motor, for example, powered by electricity, fuel gas, gasoline, or other hydrocarbon, to accomplish shaft rotation when the mixer is in operation;
wherein the cementitous slurry and fibers are mixed in the mixing chamber of the horizontal fiber-slurry mixer for an average mixing residence time of about 5 to about 240 seconds, preferably 10 to 180 seconds, more preferably 10 to 120 seconds, most preferably 10 to 60 seconds while the rotating paddles apply shear force, wherein the central rotating shaft rotates at 30 to 450 RPM, more preferably 40 to 300 RPM, and most preferably 50 to 250 RPM during mixing, to produce a uniform fiber-slurry mixture having a consistency that will allow the fiber-slurry mixture to be discharged from the fiber-slurry mixer;
discharging the fiber-slurry mixture from the fiber-slurry mixer.
In particular the method which mixes water and cementitous material and the fibers in a single unit operation comprises the following steps:
feeding a dry cementitous powder into a horizontal continuous mixer through at least one dry cementitous powder inlet port;
the horizontal continuous mixer comprising
wherein each horizontally mounted impeller within the upstream end feed section of the elongated mixing chamber comprises an auger, wherein the dry cementitous powder is fed into the upstream end feed section of the elongated mixing chamber and conveyed by the auger to the first mixing section,
feeding a liquid stream comprising water into the elongated mixing chamber of the continuous slurry mixer through at least one liquid stream inlet port downstream of the at least one dry cementitous powder inlet port and mixing the dry cementitous powder and the liquid stream in the first mixing section to form a cementitous slurry;
wherein each horizontally mounted impeller within the first mixing section comprises a first plurality of mixing paddles mounted on a horizontally oriented shaft of the impeller at regular intervals and different circumferential locations, the paddles rotated about the horizontally oriented shaft within the horizontal, preferably cylindrical housing, the paddles extending radially from the shaft,
feeding a stream of reinforcement fibers through at least one reinforcement fiber inlet port into the second mixing section, and mixing the cementitous slurry and the reinforcement fibers in the second mixing section to form a fiber-slurry mixture,
wherein at least a portion of each horizontally mounted impeller within the second mixing section of the elongated mixing chamber comprises at least one member selected from the group consisting of:
an auger, and
discharging the fiber-slurry mixture from the mixer through a fiber-slurry mixture outlet port at a downstream end portion of the second mixing section, wherein the cementitous slurry and fibers are mixed in the mixing chamber of the horizontal continuous mixer for an average mixing residence time of about 5 to about 240 seconds, preferably 10 to 180 seconds, more preferably 10 to 120 seconds, most preferably 10 to 60 seconds, while the rotating paddles apply shear force, wherein the central rotating shaft rotates at 30 to 450 RPM, more preferably 40 to 300 RPM, and most preferably 50 to 250 RPM during mixing, to the fiber-slurry mixture to produce a uniform fiber-slurry mixture.
In both alternatives the fiber-slurry mixture discharged from the horizontal mixer has a slump of 4 to 11 inches as measured according to a slump test using a 4 inch tall and 2 inch diameter pipe. The fiber-slurry mixture discharged from the horizontal mixer also has a viscosity less than 45000 centipoise, preferably less than 30000 centipoise, more preferably less than 15000 centipoise, and most preferably less than 10000 centipoise when measured using a Brookfield Viscometer, Model DV-II+ Pro with Spindle HA4 attachment running at 20 RPM speed. Typically the resulting fiber-slurry mixtures have a viscosity of at least 1500 centipoise.
A distinctive feature of the mixer and mixing method of the present invention disclosed herein is the ability of this mixer to blend reinforcing fibers with the rest of the cementitous components in a continuous operation without unduly damaging the added fibers. Furthermore, the mixer and mixing method of this invention allow production of a fiber reinforced cementitous slurry mixture having a desirable working consistency. The slurries with favorable rheological properties produced by this mixer can beneficially be utilized for producing products using a variety of manufacturing processes. For instance, a workable slurry consistency facilitates further processing and formation of panel products on a continuous forming line running at high line speeds.
The present invention also provides an apparatus for preparing the above-described composite fiber-slurry mixtures comprising:
a slurry mixer for having a liquid stream inlet and a dry cementitous powder stream inlet for mixing a liquid stream comprising water and a stream of a dry cementitous powder comprising cement, gypsum and aggregate, said slurry mixer having a horizontally or vertically mounted impeller;
a single pass horizontal fiber-slurry continuous mixer;
a conduit for passing the cementitous slurry from the slurry mixer into the single pass horizontal fiber-slurry continuous mixer and
a conduit for passing a stream of reinforcement fibers into the horizontal fiber-slurry continuous mixer,
a single pass horizontal fiber-slurry continuous mixer for mixing the cementitous slurry and the reinforcement fibers to form a fiber-slurry mixture,
the horizontal fiber-slurry continuous mixer comprising
a plurality of mixing and conveying paddles mounted on the horizontally oriented shaft of the mixer at regular intervals and different circumferential locations, the paddles extending radially from a location on the shaft, the paddles comprising a pin engaged to a paddle head, the pin pivotally engaged to the horizontally oriented shaft and/or the paddle head to permit pivotal rotation of the paddle head relative to the respective location on the horizontally oriented shaft, wherein the plurality of paddles are arranged to mix the reinforcement fibers and cementitous slurry and move the cementitous slurry and reinforcement fibers being mixed to the fiber-slurry mixture outlet.
The term paddles means any structure extending radially from the shaft for rotating about the shaft. Paddles may have any of a variety of shapes. For example, preferred paddles are flat paddles, helical paddles, or paddles made of a pin having opposed ends, one end for attaching to the shaft and the other end for attachment to a broad paddle head. The pins used without the paddle head are also considered paddles within the scope of the invention.
One distinctive feature of the novel manufacturing process disclosed herein is that it permits blending of reinforcing fibers with the rest of the cementitous components in a continuous operation to produce a fiber reinforced cementitous slurry mixture. Furthermore, the manufacturing process disclosed herein allows production of a fiber reinforced cementitous slurry having a workable and flowable consistency using continuous mixing processes. A workable slurry consistency facilitates further processing and formation of the product on the forming line. One key aspect of this manufacturing process innovation is the novel unit operation that combines the reinforcing fibers with the rest of the cementitous components in a continuous process to produce a fiber reinforced cementitous slurry mixture that is easily workable and formable on a continuous production line. Another key aspect of this manufacturing innovation is a method of extruding a layer of slurry that has a uniform profile (thickness).
The fiber reinforced cementitious products formed using this manufacturing process have various uses including:
The fiber-slurry mixture produced by the methods and apparatus of the present invention is fed to a forming assembly (preferably a “headbox”) which deposits the fiber-slurry mixture on a moving surface of a panel production line uniformly as a layer 0.25 to 2 inches thick, preferably 0.25 to 1 inches thick, more preferably 0.4 to 0.8 inches thick, typically 0.40 to 0.75 inches thick;
leveling the fiber-slurry mixture on the moving surface;
allowing the fiber-slurry mixture to set on the moving surface;
cutting the set fiber-slurry mixture into panels and removing the panels from the moving surface, wherein an additional layer of fiber-slurry mixture is not deposited on the deposited layer of fiber-slurry mixture.
The invention also provides methods and apparatus for making its fiber reinforced concrete (FRC) panels with edges wrapped in a surface reinforcing web such as a nonwoven fiber mat, on the panel production line. Typically the nonwoven fiber mat is a polypropylene mat or a fiberglass mat. This includes depositing the fiber-slurry mixture of the invention on a layer of nonwoven fiber mat on the moving surface of the panel production line and applying another layer of nonwoven fiber mat over the setting board. The layer of nonwoven fiber mat on the moving surface of the panel production line extends from the right and left sides of the setting board so it can be wrapped around the board to wrap the right and left edges when the board is not entirely set so it is still sufficiently tacky to hold the flipped web in place. Then the edges are flipped to wrap around the right and left edges and then the invention applies a top web of nonwoven fiber material and glues the top web to the setting panel and then the setting panel is run under a forming plate. These webs are applied to provide a smooth surface and help with the stacking of the panels of the invention. Rather than having to be in a rack separately during curing, if they are sufficiently set the wrapped fiber reinforced concrete (FRC) panels can be put directly on one another while curing. These webs also help to provide structural strengthening to the fiber reinforced concrete panels of the invention. The nonwoven fiber mat can be permeable, semi-impermeable or non-impermeable to liquids. Preferably, the nonwoven fiber mat does not completely embed into the fiber reinforced cementitious material slurry material. Preferably the mat is not permeable to the slurry or it is at most slightly permeable to the slurry. Thus, it is sufficiently impermeable that the slurry does not bleed through the mat. Thus, the mat provides sufficient impermeability to not let fiber-slurry mixture of the invention seep through to the exposed surface even when the fiber-slurry mixture of the invention is vibrated and/or goes under forming plates on the production line. The surface reinforcing web is preferably applied on both major faces of the panel but alternatively it can be applied only on one major face of the panel depending upon the product application and desired surface aesthetics.
In the figures, like reference numerals indicate like elements unless otherwise indicated.
The basic steps and key features of the manufacturing process of this invention for producing fiber reinforced concrete (FRC) panel (also termed a fiber reinforced cementitous panel) products are shown in
Step 1: Accurately meter raw materials including cementitous materials, fillers, chemical additives, and water using continuous feeders and convey these raw materials to a continuous slurry mixer.
Step 2: Mix raw materials including cementitous materials, fillers, chemical additives, and water using a continuous slurry mixer to form a cementitous slurry mixture.
Step 3: Convey the cementitous slurry mixture to a continuous fiber-slurry mixer.
The conveying of the cementitous slurry mixture to the continuous fiber-slurry mixer can be carried out using a suitable positive displacement pump such as a progressive cavity pump or a peristaltic pump, or alternatively, the cementitous slurry mixture can be dropped (gravity drop) directly from the mouth of the continuous slurry mixer into the continuous fiber-slurry mixer.
Step 4: Accurately meter reinforcing fibers using suitable continuous fiber feeders and convey to the fiber-slurry mixer.
The conveying of the reinforcing fibers to the continuous fiber-slurry mixer can be carried out using a suitable conveying mechanism such as air-veying, or alternatively, the reinforcing fibers can be dropped (example, gravity drop) directly from the mouth of the fiber feeder/s into the continuous fiber-slurry mixer. Fibers may be sprayed with water or other additives (accelerators or dispersants) in this step.
Step 5: Add reinforcing fibers to the prepared cementitous slurry mixture in a continuous fiber-slurry mixer and mix the ingredients to form a fiber reinforced cementitous slurry mixture having a workable consistency.
Step 6: Convey the fiber reinforced cementitous slurry mixture to a panel forming assembly such as a headbox assembly (or a forming screed roll assembly or a vibrating plate assembly) located on a conveying line. The conveying of the fiber reinforced cementitous slurry mixture to the forming assembly can be carried out using a suitable positive displacement pump such as a peristaltic pump or a piston pump, or alternatively, the fiber reinforced cementitous slurry mixture can be dropped (gravity drop) directly from the mouth of the continuous fiber-slurry mixer in to the forming assembly located on the conveying/forming line.
Step 7: Add secondary composite reinforcements (if desired) such as continuous scrims, continuous rovings, continuously chopped fibers from rovings, structural composite reinforcing laminates as part of the panel formation process on the conveying and forming line.
The operations carried out in Steps 2, 3, 5 and 6 may alternatively be combined in a unit operation using a combination continuous mixer where the first section of the mixer produces a cementitous slurry mixture by combining all dry powders, chemical additives, and water; and the second section of mixer produces a fiber reinforced cementitous slurry mixture by introducing and combining the reinforcing fibers with the incoming cementitous slurry mixture produced in the first section of the combined mixer.
The combination continuous mixer can either be a single shaft continuous mixer or a dual-shaft continuous mixer. The fiber reinforced cementitous slurry mixture so produced using the combination continuous mixer can then be conveyed to the forming assembly using a suitable positive displacement pump such as a peristaltic pump or a piston pump, or alternatively, the fiber reinforced cementitous slurry mixture can be dropped (gravity drop) directly from the mouth of the combination continuous mixer in to the forming assembly located on the conveying/forming line.
Vibrations produced by a vibrating table located right under the forming assembly 40 (below the forming belt) is typically used to facilitate embedment of the laid bottom layer of chopped fibers into the layer of fiber reinforced cementitous slurry deposited by the forming assembly. If a layer of chopped fibers is introduced on top of the deposited layer of fiber reinforced cementitous slurry after the forming assembly, the embedment of this laid layer of fibers can be achieved, for example, by utilizing one or more vibrating screed plates located on the top surface of the formed panels on the conveying line.
Step 8: Deposit a continuous layer of fiber reinforced cementitous slurry mixture having desired thickness from the forming assembly. A screed forming roll may be utilized alternatively instead of the forming assembly to deposit a continuous layer of fiber reinforced cementitous slurry mixture. A forming plate (table) located right under the forming assembly and forming belt is typically used to achieve a true and flat casting surface that facilitates extrusion of an even layer of fiber reinforced cementitous layer that has a uniform thickness and surface profile across the width of the cast panel. The forming table may also be optionally combined with a vibration assembly that further helps to deposit of an even layer of fiber reinforced cementitous layer having a uniform thickness and surface profile across the width of the cast panel. The importance of vibration introduced by the vibrating plate assembly increases with increasing viscosity of the slurry. In other words, the use of a vibrating plate assembly as described above facilitates use of fiber reinforced cementations slurry mixtures that are more viscous with diminished flow properties.
Step 9: Form panels and panel edges using suitable substrates, molds, and edge formation device/s.
Step 10: Screed the top surface of the panel, if required, to achieve desired panel surface finish.
The top surface of the formed panel may optionally be touched and finished with one or more vibrating screeds located at various places along the continuous forming line. A vibrating finish screed installed right after the forming assembly is useful for embedding visible fibers and occasional fiber-slurry lumps thus creating a more homogeneous panel surface. Vibrating screeds installed at locations where the panel has achieved partial set are useful in further homogenizing panel surface and improving panel appearance. These latter vibrating screeds are also useful in knocking down the raised slurry meniscus typically observed at the panel edges when the edge is formed against a surface. If required, the vibrating screeds may also be accompanied with vacuum air suction to remove dislodged particles and lumps accumulating at the back end of the screed plate. The location of the screed along the length of the forming line may be adjusted depending upon the material set characteristics and environmental conditions. The importance of the use of top vibrating screed on the production line to achieve a more uniform surface profile increases with increase in viscosity of the fiber reinforced cementitous slurry.
Step 11: Cut the continuous formed panel ribbon to correct panel length. Different methods for cutting panels on the line may be employed. These include, circular cutting saws, water-jet cutters, rotating knife cutters, etc.
Step 12: Stack and cure formed panels.
Special curing methods such as high humidity-high temperature curing chambers may be employed to accelerate the curing process thus facilitating rapid strength development and release of the panels for sale.
Step 13: The panels formed on the forming line after curing may optionally be coated with special coatings and/or paints to impart desirable properties required for specific product applications.
Method Employing a Separate Slurry Mixer and Fiber-Slurry Mixer
The resulting fiber-slurry mixture is suitable for a variety of uses. For example, the resulting slurry is suitable for being deposited and used as statuary, shotcrete, consolidation of loose rock, soil stabilization, pre-cast concrete products, pavement, repair application, or as a layer on a moving surface of a panel production line uniformly as a layer 0.125 to 2 inches thick, preferably 0.25 to 1 inches thick, typically 0.40 to 0.75 inches thick on the moving surface of the panel production line to produce a fiber reinforced concrete (FRC) panel. The resulting fiber-slurry mixture has a viscosity less than 45000 centipoise, more preferably less than 30000 centipoise, and most preferably less than 15000 centipoise. The resulting fiber-slurry mixture also has a slump according to the slump test using a 4 inch tall 2 inch diameter pipe is from 4 to 11 inches. The resulting fiber-slurry mixture is not suitable for extrusion manufacturing processes that typically rely on slurry mixture compositions have extremely high viscosity.
The slump test characterizes the slump and flow behavior of the cementitious compositions produced by the method and apparatus of this invention. The slump test used herein utilizes a hollow cylinder about 5.08 cm. (2 in.) diameter and about 10.16 cm. (4 in.) length held vertically with one open end resting on a smooth plastic surface. The cylinder is filled up to the top with the cementitious mixture followed by striking off the top surface to remove the excess slurry mixture. The cylinder is then gently lifted up vertically to allow the slurry to come out from the bottom and spread on the plastic surface to form a circular patty. The diameter of the patty is then measured and recorded as the slump of the material. As used herein, compositions with good flow behavior yield a larger slump value.
Slurry Mixer
Any of a variety of continuous or batch mixers may be employed as the slurry mixer 2. For example, the mortar mixers described in ICRI Guideline No. 320.5R-2014, Technical Guidelines, Pictorial Atlas of Concrete Repair Equipment, International Concrete Repair Institute, May 2014, incorporated by reference, can be used in this invention for preparing cementitious slurry 3. These include horizontal shaft mixers, tumble mortar mixers, rotating-drum stationary mixers, pan-type mixers, rotating-tub rotating paddle mixers, planetary paddle mixers, horizontal shaft mixer-pump combinations, and vertical shaft mixer-pump combinations. The horizontal shaft mixer-pump combinations and vertical shaft mixer-pump combinations are continuous mixers. In addition, continuous slurry mixers disclosed in U.S. Pat. No. 7,513,963 B2 to George et al, incorporated by reference, may also be used in the present invention. Continuous slurry mixers disclosed in U.S. Pat. No. 7,347,895 to Dubey (column 6, lines 36 to 56), incorporated by reference, may also be used to prepare slurry in a continuous manner.
For example, the continuous slurry mixer 2 may be a single shaft or dual shaft horizontal mixer.
The term horizontal when used with mixers means generally horizontal. Thus, a mixer oriented with a variation of plus or minus 20 degrees from horizontal would still be considered a horizontal mixer.
Volumetric feeding systems would discharge powder from the storage hopper bin 60 at a constant rate (volume per unit time, e.g., cubic feet per minute). Gravimetric feeding systems generally use a volumetric feeder associated with a weighing system to control the discharge of powder from the storage hopper bin 60 at a constant weight per unit of time, e.g., pounds per minute. The weight signal is used via a feedback control system to constantly monitor the actual feed rate and compensate for variations in bulk density, porosity, etc.
Volumetric feeding systems discharge powder from the storage hopper bin 60 at a constant rate (volume per unit time, e.g., cubic feet per minute. Gravimetric feeding systems generally use a volumetric feeder associated with a weighing system to control the discharge of powder from the storage hopper bin 60 at a constant weight per unit of time, e.g., pounds per minute. The weight signal is used via a feedback control system to constantly monitor the actual feed rate and compensate for variations in bulk density, porosity, etc.
Aqueous medium, such as water, from liquid pump 6 feeds the horizontal chamber 62 through a nozzle 68. The powder and water slurry mixture is then discharged from the horizontal chamber 62 and then feeds the fiber-slurry mixer 32.
Horizontal Fiber-Slurry Continuous Mixer
The fiber-slurry continuous mixer of the present invention preferably achieves the following results:
Allows continuous blending of fibers with the rest of the cementitious components to produce a uniformly mixed fiber reinforced cementitious slurry mixture.
Reduces the required mixing time from several minutes to less than 60 seconds, preferably less than 30 seconds, to produce a uniformly blended fiber reinforced cementitious slurry mixture. Generally the chamber provides an average slurry residence time of about 5 to about 240 seconds, preferably 10 to 180 seconds, more preferably 10 to 120 seconds, most preferably 10 to 60 seconds, typically 20 to 60 seconds.
Does not cause fiber balling and lumping during the mixing operation.
Does not cause damage to the reinforcing fibers as a result of the mixing action.
Allows use of rapid setting cementitious materials useful in manufacturing and construction applications.
The horizontal fiber-slurry continuous mixer disclosed as part of this invention comprises:
an elongated mixing chamber defined by a horizontal (typically cylindrical) housing having an interior side wall,
a central rotating shaft mounted in the elongated mixing chamber traversing from one end of the mixer to another, wherein the central shaft is externally connected to a drive mechanism and a drive motor, for example, powered by electricity, fuel gas, gasoline, or other hydrocarbon, to accomplish shaft rotation when the mixer is in operation;
a plurality of mixing and conveying paddles mounted on the central shaft of the mixer at regular intervals and different circumferential locations, the paddles extending radially from a location on the central shaft, the paddles comprising a pin having a paddle head, the pin pivotally engaged to the shaft and/or the paddle head pivotally engaged to the pin to permit pivotal rotation of the paddle relative to the respective location on the shaft, wherein the plurality of paddles are arranged to mix the cementitious slurry and move the cementitious slurry and reinforcement fibers being mixed to the fiber-slurry mixture outlet,
at least one fiber inlet port to introduce reinforcement fibers into the chamber in a first feed section of the horizontal housing;
at least one cementitious slurry inlet port to introduce cementitious slurry mixture into the chamber in the feed section of the horizontal housing;
a fiber-slurry mixture outlet port at a second discharge end section of the horizontal cylindrical housing to discharge the fiber reinforced cementitious slurry mixture produced by the mixer, and
a venting port to remove any air introduced into the mixing chamber from raw material feed.
The fiber-slurry mixer can have additional inlet ports to introduce other raw materials or other performance enhancing additives into the mixing chamber.
The cementitious slurry and fibers are mixed in the mixing chamber of the horizontal fiber-slurry mixer for an average mixing residence time of about 5 to about 240 seconds, preferably 10 to 180 seconds, more preferably 10 to 120 seconds, most preferably 10 to 60 seconds while the rotating paddles apply shear force, wherein the central rotating shaft rotates at 30 to 450 RPM, more preferably 40 to 300 RPM, and most preferably 50 to 250 RPM during mixing, to the fiber-slurry mixture, wherein the fiber-slurry mixture discharged from the mixer has a slump of 4 to 11 inches, preferably 6 to 10 inches, as measured according to a slump test using a 4 inch tall and 2 inch diameter pipe and a viscosity less than 45000 centipoise, preferably less than 30000 centipoise, and more preferably less than 15000 centipoise. The resulting fiber-slurry mixture also has a slump according to the slump test using a 4 inch tall 2 inch diameter pipe is from 4 to 11 inches. The resulting fiber-slurry mixture is not suitable for extrusion manufacturing processes that typically rely on slurry mixture compositions have extremely high viscosity. The resulting fiber-slurry mixture is a uniform fiber-slurry mixture that has a consistency that will allow the fiber-slurry mixture to be discharged from the horizontal fiber-slurry mixer and be suitable for being deposited as a continuous layer on a moving surface of a panel production line uniformly as a layer 0.25 to 2.00 inches thick, preferably 0.25 to 1 inches thick, more preferably 0.4 to 0.8 inches thick, typically 0.5 to 0.75 inches thick on the moving surface of the panel production line to produce a fiber reinforced concrete (FRC) panel. Typically the fiber-slurry mixture is deposited at a rate of about 0.10-25 cubic feet per minute for a panel 4 to 8 feet wide. This is faster than conventional extrusion manufacturing processes that utilize extremely viscous slurries to facilitate product formation as the viscous slurry is extruded through a die to for product shape. Extrusion manufacturing processes are typically used to form three-dimensional hollow-shaped thin-walled articles where the high slurry viscosity is useful in holding product shape during and after material extrusion.
The central shaft is externally connected to a drive mechanism and a drive motor, for example, powered by electricity, fuel gas, gasoline, or other hydrocarbon, to accomplish shaft rotation when the mixer is in operation. Typically an electrical motor and drive mechanism will drive the central shaft in the mixing chamber.
A distinctive feature of the mixer and mixing method disclosed herein is the ability of this mixer to blend reinforcing fibers with the rest of the cementitious components in a continuous operation without unduly damaging the added fibers. Furthermore, the mixer and mixing method of this invention allow production of a fiber reinforced cementitious slurry mixture having a desirable working consistency. The slurries with favorable rheological properties produced by this mixer can beneficially be utilized for producing products using a variety of manufacturing processes. For instance, a workable slurry consistency facilitates further processing and formation of panel products on a continuous forming line running at high line speeds.
As depicted in
The rotatable shaft 88 rotates about its longitudinal axis “A” to mix the fed ingredients and convey them as fiber-slurry mixture to the discharge outlet 78A.
The reinforcement fibers and cementitious slurry and other ingredients will be fed to the mixer 32 at respective rates to leave an open space in the mixer above resulting mixture to facilitate mixing and conveying. If desired, a liquid level control sensor is used to measure the level of the slurry in the horizontal chamber of the mixer.
The rotatable shaft 88 may include a first end assembly 70 and a second end assembly 72. First end assembly 70 and second end assembly 72 may take any of a wide variety of forms known to one of skill in the art. For example, first end assembly 70 may include a first end engagement portion that operatively engages a first end of the rotatable shaft 88, a first cylindrical proportion 74 extending from the first end engagement portion, an intermediate cylindrical portion 76 extending from the first cylindrical portion 74, and an end cylindrical portion 78, extending from the intermediate cylindrical portion 76 and including a slot 90. The second end assembly 72 may include a second end engagement portion that operatively engages a second end of the rotatable shaft 88, a first cylindrical portion 72 extending from the second end engagement portion, and an end cylindrical portion 74 extending from the first cylindrical portion. In at least one embodiment, first end engagement portion of first end assembly 70 may be engaged to the rotatable shaft 88 proximate to first cylindrical proportion 74. In one or more embodiments, end cylindrical portion 78 may be operatively engaged to a motor or engine 92 capable of imparting rotation (e.g., high-speed rotation) to rotatable shaft 116 and the one or more paddle assemblies 100 engaged therewith to mix the reinforcement fibers and cementitious slurry. In at least one embodiment, second end engagement portion of second end assembly 72 may be engaged to a second end (e.g., an end opposing the first end) of rotatable shaft 88 proximate to first cylindrical portion 92. In one or more embodiments, end cylindrical portion 94 of second end assembly 72 may be preferably engaged to a bearing assembly, which may be integral to an exterior wall of the horizontal fiber-cementitious slurry mixer 32, to permit the rotation of rotatable shaft 88.
In one or more embodiments, as may be seen in
The rotatable shaft 88, in one or more embodiments, may be constructed to rotate at a predetermined rate of 30 to 450 RPM, more preferably 40 to 300 RPM, and most preferably 50 to 150 RPM during mixing
Paddle pin 114 has a width W1 which is less than a width W2 of paddle head 116 (See
The above mentioned features and parameters of the fiber-slurry continuous mixer of this invention are further described as follows:
Elongated Mixing Chamber
The elongated mixing chamber is typically cylindrical in shape.
The length of the mixing chamber typically ranges anywhere from about 2 to 8 feet. The preferred length of the mixing chamber is from about 3 to 5 feet.
The diameter of the mixing chamber typically ranges anywhere from about 4 to 24 inches. The preferred diameter of the mixing chamber ranges from about 6 to 12 inches.
Central Rotating Shaft
The central rotating shaft diameter is typically from about 1 to 8 inches. The preferred central shaft diameter ranges from about 2 to 6 inches.
The central rotating shaft rotates at a speed, preferably ranging from about 30 to 450 RPM, more preferably ranging from about 40 to 300 RPM, and most preferably ranging from about 50 and 150 RPM. It has been discovered that relatively lower mixer speeds are preferable to meet the objectives of the present invention. It has been surprisingly found that excellent fiber dispersion in the cementitious slurry mixture can be obtained even at relatively low mixer speeds. Furthermore, another important benefit of using lower mixing speeds is that it results in reduced fiber breakage and superior material working and flow properties useful in further processing of the fiber reinforced cementitious slurry mixture. A variable frequency drive is preferably used with the mixer for turning the central rotating shaft when the mixer is in the operational mode. The variable frequency drive is helpful for adjusting and fine-tuning the mixer speed for a given combination of raw materials involved in the production process.
The continuous mixers of the present invention can either be a single-shaft mixer, a dual-shaft mixer, or a multi-shaft mixer. This disclosure describes the single-shaft mixers of the present invention in greater detail. However, it is contemplated that dual-shaft or multiple-shaft mixers in accordance to the present invention can also be beneficially employed for producing fiber reinforced cementitious slurry mixtures possessing desirable properties that are useful in a variety of applications including continuous production processes.
Mixing and Conveying Paddles
The mixing and conveying paddles 100 mounted on the central shaft can have different shapes and dimensions to facilitate mixing and conveying of the added components in the mixer. The mixing and conveying paddles include paddles with a pin and a relatively wider head to help move the material forward. In addition to the paddles having one type of pin and head, the fiber-slurry mixer may include more than one type of paddle having a pin and a relatively wider head, or just pins, to achieve desirable characteristics for further processing of the material. However, as seen in
The quality of mixing and conveying of the components in the mixer is also dictated by the orientation of the paddles in the mixer. A parallel or perpendicular paddle orientation with respect to the cross-section of the central shaft diminishes the conveying action of the paddles thus increasing the residence time of the material in the mixer. An increased residence time of the material in the mixer can lead to significant fiber damage and production of fiber reinforced cementitious slurry mixture having undesirable characteristics. The orientation of the longitudinal axis “LH” of the paddle head 116 with respect to the longitudinal axis “A” of the central shaft 88 is preferably at an angle “B” (
The set of paddles in the mixer are typically configured in a spiral form on the central shaft from one end of the mixer to another. This arrangement of paddles further facilitates conveying action of the material inside the mixer. Other configurations of paddle arrangement in the mixer are possible and are contemplated as part of this invention.
The paddles can be made of variety of materials including metals, ceramics, plastics, rubber, or a combination thereof. Paddles with softer lining materials are also contemplated as they tend to minimize material and fiber breakage.
The paddles and/or inner walls of the elongated mixing chamber may be coated with a release material, to minimize buildup of the cementitious slurry on the paddles and/or shell.
Furthermore,
Inlet Ports
The size, location, and orientation of raw material inlets ports (inlet conduits) of the fiber-slurry mixer are configured to ease introduction of the raw material into the fiber-slurry mixer and to minimize potential for blocking of ports from the slurry mixture in the mixer.
The cementitious slurry from the slurry mixer is preferably conveyed using a slurry hose to the fiber-slurry mixer and introduced into the fiber-slurry mixer through an inlet port setup to accept the slurry hose. Alternatively, the cementitious slurry from the slurry mixer may be gravity fed to the fiber-slurry mixer.
The fibers can be introduced into the fiber-slurry mixer gravimetrically or volumetrically using a variety of metering equipment such as screw feeders or vibratory feeders. Fibers can be conveyed from a fiber feeder to the fiber-slurry mixer by a variety of conveying devices. For example, fibers can be transferred using screws (augers), air conveying, or simple gravity deposition. Discrete or chopped fibers can be made of different reinforcing fiber materials including fiberglass; polymeric materials such as polypropylene, polyethylene, polyvinyl alcohol, etc; carbon; graphite; aramid; ceramic; steel; cellulosic or natural fibers such as jute or sisal; or a combination thereof. The fiber length is about 2 inches or lower, more preferably less than 1.5 inches or lower and most preferably less than 0.75 inches or lower.
Panel Production Using the Fiber-Slurry Mixture from the Slurry Mixer and Fiber-Slurry Mixer System
In this embodiment, a web 26 of release paper, polymer film or a plastic carrier, slip sheet or forming mold, for supporting a slurry prior to setting, may be provided and laid upon the carrier 14 to protect it and/or keep it clean. However, it is also contemplated that, rather than the continuous web 26, individual sheets (not shown) of a relatively rigid material, e.g., sheets of polymer plastic, may be placed on the carrier 14. These carrier films or sheets may be removed from the produced panels at the end of the line or they may be incorporated as a permanent feature in the panel as part of the overall composite design. When these films or sheets are incorporated as a permanent feature in the panel they may provide enhanced attributes to the panel including improved aesthetics, enhanced tensile and flexural strengths, enhanced impact and blast resistance, enhanced environmental durability such as resistance to water and water vapor transmission, freeze-thaw resistance, salt-scaling resistance, and chemical resistance.
Continuous reinforcement 44 such as a roving or a web of reinforcing scrim such as fiberglass scrim may be provided for embedding in the slurry prior to setting and reinforcing the resulting cementitious panels. The continuous rovings and/or reinforcing scrim roll 42 are fed through the headbox 40 to be laid upon the carrier 14. However, it is also contemplated to not employ continuous reinforcement 44. The continuous scrim or rovings can be made of different reinforcing fiber materials including fiberglass; polymeric materials such as polypropylene, polyethylene, polyvinyl alcohol, etc; carbon; graphite; aramid; ceramic; steel; cellulosic, paper, or natural fibers such as jute or sisal; or a combination thereof. A roving is an assemblage of continuous reinforcing monofilaments. Scrim is a web of continuous fibers running in the machine direction and the cross-direction. Reinforcement may also be provided as a nonwoven fiber web made of discrete reinforcement fibers. The nonwoven fiber web may be made of organic fibers such as polyolefin fibers or inorganic fibers such or fiberglass or a combination thereof. Fibrous webs made of metal fibers are also contemplated as part of the present invention.
It is also contemplated to form the cementitious panels produced by the present line 10 directly upon the carrier 14. In this situation, at least one belt washing unit 28 is provided. The carrier 14 is moved along the support frame 12 by a combination of motors, pulleys, belts or chains which drive the main drive roll 16 as is known in the art. It is contemplated that the speed of the carrier 14 (forming belt) of the forming line may vary to suit the product being made. The fiber-slurry mixture travels in direction “T”.
The present production line 10 includes a continuous slurry mixer 2. The slurry mixer may be a single shaft or dual shaft mixer. Dry powder feeder 4 (one or more may be employed) feeds dry components of the cementitious composition, except for reinforcing fibers, to the slurry mixer 2. Liquid pump 6 (one or more may be employed) feeds to the slurry mixer 2 aqueous medium, such as water, with liquid or water soluble additives. The slurry mixer mixes the dry components and the aqueous medium to form a cementitious slurry 8. The cementitious slurry 31 feeds a first slurry accumulator and positive displacement pump 30 which pumps the slurry to a fiber-slurry mixer 32. A fiber feeder 34 (one or more may be employed) feeds fibers to the fiber-slurry mixer 32. Thus, in the fiber-slurry mixer 32 the fibers and slurry are mixed to form a fiber-slurry mixture 36. Fiber-slurry mixture 36 feeds a second slurry accumulator and positive displacement pump 38 which pumps the fiber-slurry mixture 36 to a forming assembly 40 (forming headbox).
Forming assembly 40 deposits the fiber-slurry mixture on the web 26 of release paper, continuous reinforcement, rovings, and/or reinforcing scrim, and/or nonwoven fiber web (if present) on the moving carrier. If present, continuous reinforcement 44 provided by rovings and/or scrim roll and/or nonwoven fiber web 42 may be deposited on the fiber-slurry mixture traveling on the moving carrier 14. To assist in leveling the fiber-slurry mixture 46 a forming vibrating plate 50 may be provided under or slightly downstream on the location where the forming assembly 40 deposits the fiber-slurry mixture 46.
The slurry 46 sets as it travels along the moving carrier 14. To assist in leveling the fiber-slurry mixture 46 as the slurry 46 is setting the slurry 46 passes under one or more vibrating screed plates 52. At the distal end 18 of the support frame 12 a cutter 54 (panel cutting device) cuts the set slurry into boards 55. The boards (panels) 55 are then placed on an unloading and curing rack 57 (See
The fiber-cement mixtures produced by the method and apparatus of this invention contain cement, water, and other cement additives. However, to achieve the desired viscosity the cementitious compositions preferably avoid thickeners or other high viscosity processing aids at high dosage rates as commonly used with conventional fiber cement extrusion processes. For example, the present slurries avoid high viscosity cellulose ethers addition at high dosage rates. Examples of high viscosity cellulose ethers which the present slurries avoid are methyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl methylcellulose.
The fiber-cement mixtures produced by the method and apparatus of this invention are aqueous slurries which may be from a variety of settable cementitious slurries. For example, compositions based on hydraulic cements. ASTM defines “hydraulic cement” as follows: a cement that sets and hardens by chemical interaction with water and is capable of doing so under water. Examples of suitable hydraulic cements are Portland cement, calcium aluminate cements (CAC), calcium sulfoaluminate cements (CSA), geopolymers, magnesium oxychloride cements (sorel cements), and magnesium phosphate cements. A preferred geopolymer is based on chemical activation of Class C fly ash.
While calcium sulfate hemihydrate sets and hardens by chemical interaction with water, it is not included within the broad definition of hydraulic cements in the context of this invention. However, calcium sulfate hemihydrate may be included in fiber-cement mixtures produced by the method and apparatus of this invention. Thus, also such aqueous slurries may be based on calcium sulfate cements such as gypsum cements or plaster of Paris. Gypsum cements are primarily calcined gypsum (calcium sulfate hemihydrate). It is customary in the industry to term calcined gypsum cements as gypsum cements.
The fiber-cement mixtures contain sufficient water to achieve the desired slump test value and viscosity in combination with the other ingredients of the fiber-cement mixtures. If desired the composition may have a weight ratio of water-to-reactive powder of 0.20/1 to 0.90/1, preferably 0.20/1 to 0.70/1.
The fiber-cement mixtures may contain pozzolanic material such as silica fume, a finely divided amorphous silica which is the product of silicon metal and ferro-silicon alloy manufacture. Characteristically, it has very high silica content and low alumina content. Various other natural and man-made materials have been referred to as having pozzolanic properties, including pumice, perlite, diatomaceous earth, tuff, trass, metakaolin, microsilica, and ground granulated blast furnace slag. Fly ash also has pozzolanic properties. The fiber-cement mixtures may contain Ceramic microspheres and/or Polymer microspheres.
However, one use of the fiber-cement slurries made by the present method is to produce structural cement panels (SCP panels) having reinforcing fibers such as fiberglass, particularly alkali resistant glass fibers. As such, the cementitious slurry 31 is preferably comprised of varying amounts of Portland cement, gypsum, aggregate, water, accelerators, plasticizers, superplasticizers, foaming agents, fillers and/or other ingredients well known in the art, and described in the patents listed below which have been incorporated by reference. The relative amounts of these ingredients, including the elimination of some of the above or the addition of others, may vary to suit the intended use of the final product.
Water reducing admixture additives optionally can be included in the fiber-cement mixture, such as, for example, superplasticizer, to improve the fluidity of a hydraulic slurry. Such additives disperse the molecules in solution so they move more easily relative to each other, thereby improving the flowability of the entire slurry. Sulfonated melamines and sulfonated naphthalenes, and polycarboxylate based superplasticizers can be used as superplasticizers. Water reducing admixture additive can be present in an amount from 0% to 5%, preferably 0.5 to 5%, by weight of the wet finish fiber-slurry mixture.
U.S. Pat. No. 6,620,487 to Tonyan et al., incorporated herein by reference in its entirety, discloses a reinforced, lightweight, dimensionally stable structural cement panel (SCP) which employs a core of a continuous phase resulting from the curing of an aqueous mixture of calcium sulfate alpha hemihydrate, hydraulic cement, an active pozzolan and lime. The continuous phase is reinforced with alkali-resistant glass fibers and containing ceramic microspheres, or a blend of ceramic and polymer microspheres, or being formed from an aqueous mixture having a weight ratio of water-to-reactive powder of 0.6/1 to 0.7/1 or a combination thereof. At least one outer surface of the SCP panels may include a cured continuous phase reinforced with glass fibers and containing sufficient polymer spheres to improve nailability or made with a water-to-reactive powders ratio to provide an effect similar to polymer spheres, or a combination thereof.
If desired the composition may have a weight ratio of water-to-reactive powder of 0.20/1 to 0.90/1, preferably 0.20/1 to 0.70/1.
Various formulations for the composite slurry used in the current process are also shown in published US applications US2006/0185267, US2006/0174572; US2006/0168906 and US 2006/0144005, all of which are incorporated herein by reference in their entirety. A typical formulation would comprise as the reactive powder, on a dry basis, 35 to 75 wt. % (typically 45-65 or 55 to 65 wt. %) calcium sulfate alpha hemihydrate, 20 to 55 wt. % (typically 25-40 wt. %) hydraulic cement such as Portland cement, 0.2 to 3.5 wt. % lime, and 5 to 25 wt. % (typically 10-15 wt. %) of an active pozzolan. The continuous phase of the panel would be uniformly reinforced with alkali-resistant glass fibers and would contain 2-50%, for example 20-50%, by weight of uniformly distributed lightweight filler particles selected from the group consisting of ceramic microspheres, glass microspheres, plastic microspheres, fly ash cenospheres and perlite. An example of a formulation for the composite slurry includes from 42 to 68 wt. % reactive powders, 23 to 43 wt. % ceramic microspheres, 0.2 to 1.0 wt. % polymer microspheres, and 5 to 15 wt. % alkali-resistant glass fibers, based on the total dry ingredients.
U.S. Pat. No. 8,038,790 to Dubey et al provides another example of a preferred formulation for the composite slurry which includes an aqueous mixture of a cementitious composition comprising, on a dry basis, 50 to 95 wt % reactive powder, 1 to 20 wt % of coated hydrophobic expanded perlite particles uniformly distributed as lightweight filler therein, the coated hydrophobic perlite particles having a diameter in the range of about 1 to 500 microns (micrometers), a median diameter of 20 to 150 microns (micrometers) and an effective particle density (specific gravity) of less than about 0.50 g/cc, 0 to 25 wt % hollow ceramic microspheres, and 3 to 16 wt. % alkali-resistant glass fibers for uniformly distributed for reinforcement; wherein the reactive powder comprises: 25 to 75 wt. % calcium sulfate alpha hemihydrate, 10 to 75 wt. % hydraulic cement comprising Portland cement, 0 to 3.5 wt. % lime, and 5 to 30 wt. % of an active pozzolan; and the panel having a density of 50 to 100 pounds per cubic foot.
Although the above compositions for the composite fiber-slurry mixture are preferred, the relative amounts of these ingredients, including the elimination of some of the above or the addition of others, may vary to suit the intended use of the final product.
Method with the Horizontal Multi-Stage Fiber-Slurry Continuous Mixer
As an alternative to using the separate slurry mixer 2 and fiber-slurry mixer 32 to make the fiber-slurry mixture, the mixing of water and cementitous material and fibers may be combined in a single unit operation to make the fiber-slurry mixture using a combination continuous mixer where the first section of the horizontal mixer produces a cementitous slurry mixture by combining all dry powders, chemical additives, and water; and the second section of mixer produces a fiber reinforced cementitous slurry mixture by introducing and combining the reinforcing fibers with the incoming cementitous slurry mixture produced in the first section of the combined mixer.
Horizontal Multi-Stage Fiber-Slurry Continuous Mixer
The multi-stage fiber-slurry continuous mixer of the present invention preferably achieves the following results:
Allows continuous blending of fibers with the rest of the cementitious components to produce a uniformly mixed fiber reinforced cementitious slurry mixture.
Reduces the required mixing time from several minutes to less than 60 seconds, preferably less than 30 seconds, to produce a uniformly blended fiber reinforced cementitious slurry mixture. Generally the chamber provides an average slurry residence time of about 5 to about 240 seconds, preferably 10 to 180 seconds, more preferably 10 to 120 seconds, most preferably 10 to 60 seconds.
Does not cause fiber balling and lumping during the mixing operation.
Does not cause damage to the reinforcing fibers as a result of the mixing action.
Allows use of rapid setting cementitious materials useful in manufacturing and construction applications.
The method of using the horizontal fiber-slurry continuous mixer disclosed as part of this invention comprising the steps of:
feeding a dry cementitious powder into a horizontal continuous slurry mixer through at least one dry cementitious powder inlet port;
the horizontal continuous mixer comprising
wherein each horizontally mounted impeller within the upstream end feed section of the elongated mixing chamber comprises an auger, wherein the dry cementitious powder is fed into the upstream end feed section of the elongated mixing chamber and conveyed by the auger to the first mixing section,
feeding a liquid stream comprising water into the elongated mixing chamber of the continuous slurry mixer through at least one liquid stream inlet port downstream of the at least one dry cementitious powder inlet port and mixing the dry cementitious powder and the liquid stream in the first mixing section to form a cementitious slurry;
wherein each horizontally mounted impeller within the first mixing section comprises a first plurality of mixing and conveying paddles mounted on a horizontally oriented shaft of the impeller at regular intervals and different circumferential locations, the paddles rotated about the horizontally oriented shaft within the horizontal, preferably cylindrical, housing, the paddles extending radially from the shaft,
feeding a stream of reinforcement fibers through at least one reinforcement fiber inlet port into the second mixing section, and mixing the cementitious slurry and the reinforcement fibers in the second mixing section to form a fiber-slurry mixture,
wherein at least a portion of each horizontally mounted impeller within the second mixing section of the elongated mixing chamber comprises at least one member selected from the group consisting of:
an auger, and
a second plurality of mixing and conveying paddles mounted on the horizontally oriented shaft of the mixer at regular intervals and different circumferential locations, the paddles rotated about each respective horizontally oriented shaft within the horizontal (preferably cylindrical) housing, the paddles extending radially from the respective shaft,
discharging the fiber-slurry mixture from the mixer through a fiber-slurry mixture outlet port at a downstream end portion of the second mixing section,
wherein the cementitious slurry and fibers are mixed in the mixing chamber of the horizontal continuous mixer for an average mixing residence time of about 5 to about 240 seconds, preferably 10 to 180 seconds, more preferably 10 to 120 seconds, most preferably 10 to 60 seconds while the rotating paddles apply shear force, wherein the central rotating shaft rotates at 30 to 450 RPM, more preferably 40 to 300 RPM, and most preferably 50 to 250 RPM during mixing, to the fiber-slurry mixture to produce a uniform fiber-slurry mixture, wherein the fiber-slurry mixture discharged from the mixer has a slump of 4 to 11 inches, preferably 6 to 10 inches, as measured according to a slump test using a 4 inch tall and 2 inch diameter pipe and a viscosity less than 45000 centipoise, preferably less than 30000 centipoise, and more preferably less than 15000 centipoise. As with the method employing the separate slurry mixer and fiber-slurry mixer the resulting fiber-slurry mixture is not suitable for extrusion manufacturing processes that typically rely on slurry mixture compositions have extremely high viscosity.
Each horizontally oriented shaft is externally connected to a drive mechanism and a drive motor, for example, powered by electricity, fuel gas, gasoline, or other hydrocarbon, to accomplish shaft rotation when the mixer is in operation.
The paddles of the first and/or second mixing sections may be flat paddles or helical paddles. Flat paddles and helical paddles are unitary paddles having a central opening fitted to the shaft such that the paddle encircles a portion of the shaft. Also, the flat paddles and helical paddles have opposed ends extending in opposite directions from the shaft. Preferably if the flat paddles or helical paddles are employed in the second mixing section they are employed in a paddle portion of the second mixing section and an auger is also employed in the second mixing section before and/or after the paddle section.
However, in the alternative the paddle of the first and/or second mixing sections comprises a pin engaged to a broad paddle head, the pin pivotally engaged to the horizontally oriented shaft and/or the paddle head to permit pivotal rotation of the paddle head relative to the respective location on the horizontally oriented shaft, wherein the paddles are arranged to mix the reinforcement fibers and cementitious slurry and move the cementitious slurry and reinforcement fibers being mixed to the fiber-slurry mixture outlet. Preferably if the paddles of the first and second mixing section each comprise the pin engaged to the paddle head then the second mixing section has an absence of an auger. The second mixing section can optionally have only pins (without paddle head) to mix fibers with the slurry. The cross-sectional shape of the pin can either be round, flat (i.e., square or rectangular), triangular, oval or any other shape. When pins with elongated cross-section are employed (example, rectangular or oval cross-section), the pins are preferably oriented such that they not only help to mix the material but also provide the function of moving the material forward toward the mixer outlet.
The central shaft is externally connected to a drive mechanism and a drive motor, for example, powered by electricity, fuel gas, gasoline, or other hydrocarbon, to accomplish shaft rotation when the mixer is in operation. Typically an electrical motor and drive mechanism will drive the central shaft in the mixing chamber.
A distinctive feature of the mixer and mixing method disclosed herein is the ability of this mixer to blend reinforcing fibers with the rest of the cementitious components in a continuous operation without unduly damaging the added fibers. Furthermore, the mixer and mixing method of this invention allow production of a fiber reinforced cementitious slurry mixture having a desirable working consistency. The fiber-slurry mixtures discharged from the multi-stage fiber-slurry mixer are suitable for a variety of uses, for example statuary, shotcrete, consolidation of loose rock, soil stabilization, pre-cast concrete products, pavement, repair application, or to make a fiber reinforced concrete (FRC) building panel or board. For instance, a workable slurry consistency facilitates further processing and formation of panel products on a continuous forming line running at high line speeds.
The uniform fiber-slurry mixture produced has a consistency that will allow the fiber-slurry mixture to be discharged from the horizontal fiber-slurry mixer and be suitable for being deposited as a continuous layer on a moving surface of a panel production line uniformly as a layer 0.25 to 2.00 inches thick, preferably 0.25 to 1 inches thick, typically 0.5 to 0.75 inches thick on the moving surface of the panel production line to produce a fiber reinforced concrete (FRC) panel.
The multi-stage continuous mixer of this invention can either be a dual-shaft mixer or a multi-shaft mixer. Preferably, the multi-stage continuous mixer of this invention is a dual-shaft mixer.
The multi-stage continuous mixer of this invention has an initial auger section and at least two mixing sections. The dry powders are introduced into the mixer through an inlet port located at one end of the mixer. The augers located in the auger section move the dry powders forward into the first mixing section. The first mixing section is intended for mixing the dry powders with the liquid additives including water to produce a uniform blend of cementitious slurry mixture. The cementitious slurry mixture so produced in the first section of the mixer is conveyed to the second mixer section. The second mixing section is where fibers are blended with cementitious slurry produced and conveyed from the first mixer section. The resultant fiber reinforced slurry mixture exits the mixer through an outlet port located at the end of the second mixer section.
The various key components and features of a multi-stage, dual-shaft (or multi-shaft) continuous mixer disclosed as part of this invention can be highlighted as follows:
An Elongated Mixing Chamber
The elongated double barrel mixing chamber houses the dual rotating shafts (or multi rotating shafts) of the continuous mixer.
The total length of the mixing chamber typically ranges from about 2 to 8 feet. The preferred length of the mixing chamber is typically from about 3 to 6 feet.
The diameter of the mixing chamber typically ranges anywhere from about 3 to 24 inches. The diameter of the mixing chamber preferably ranges from about 5 to 12 inches.
Dual rotating shafts (or multi rotating shafts) mounted in the elongated mixing chamber traversing from one end of the mixer to another. The shafts are externally connected to a drive mechanism and an electrical motor to accomplish shaft rotation when the mixer is in operation. The shafts rotate at a speed, ranging from 30 to 450 RPM, more preferably 40 to 300 RPM, and most preferably 50 to 250 RPM. As part of the mixer development and optimization work, it has been discovered that relatively lower mixer speeds are preferable and provide excellent dispersion of fibers in the cementitious slurry mixture. Furthermore, another important benefit of using lower mixing speeds for the purposes of this invention is that it results in reduced fiber breakage and superior material working properties useful in further processing of the fiber reinforced cementitious slurry mixture. A variable frequency drive along with gearing, chain or a belt arrangement is typically used with the mixer for turning the rotating shaft when the mixer is in operation. The variable frequency drive is helpful for adjusting and fine-tuning the mixer speed for a given combination of raw materials involved in the production process.
An auger section to convey the dry powders from the mixer inlet port to the first mixing section of the continuous mixer. The initial length of the mixer shafts is in the form of an auger that accomplishes movement of the dry powder forward. When dual-shafts (or multi-shafts) are used in the mixer, the individual shafts are positioned in the mixer such that the flights from one auger section are in overlapping position to the flights from the second auger section. This overlapping placement of the two auger sections in the mixer provides self-cleaning action to the auger section of the mixer. The initial auger section (located near the dry powder mixer inlet) in a dual-shaft mixer configuration are shown in
The first mixing section 120 comprises mixing paddles 125 mounted on the individual rotating shafts of the mixer. There are two types of paddles that are typically used in the first mixing section—flat or helical.
Flat paddles 125 and helical paddles 127 are unitary (one piece) paddles having a central opening fitted to the shaft such that the paddle encircles a portion of the shaft. Also, the flat paddles and helical paddles have opposed ends extending in opposite directions from the shaft. Flat paddles 125 and helical paddles 127 have a central hole with key slots cut into them to allow the paddles to slide and mount onto a keyed shaft. The paddles are concentrically mounted and keyed on to the shaft. The orientation of the adjacent paddles mounted on the two shafts of the dual shaft mixer is such that they provide wiping action without any rotational interference,
Other paddle shapes and geometries can also be used in the first mixing section of the mixer. For example, of mixing and conveying paddles which each comprise a pin engaged to a paddle head can be employed in the first and/or second mixing sections as explained in more detail below regarding
The paddles mounted on the individual shafts are in over-lapping but non-interfering orientation when the mixer shafts are in rotational mode during the mixer operation.
The primary purpose of the paddles situated in the first mixing section 122 of the mixer 32 is to blend the dry powder with the water and other liquid additives (if any) to produce a uniform cementitious slurry mixture. Due to the over-lapping but non-interfering orientation of the paddles, the rotation of the paddles 125 mounted on the individual shafts provides a self-cleaning action to the first mixing section 122 of the mixer 132. The flat 125 or helical 127 mixing paddles mounted on the two shafts are particularly useful in this regard. This provides excellent self-cleaning action due to the scraping action of the paddles against each other and against the barrel (shell) of the mixer. Flat paddles are the most preferred paddles, as opposed to helical paddles, for use in the first mixing section 122 for the purposes of this invention. The length of the first mixing section 122 is typically from about 1 to 4 feet. More typically, the length of the first mixing section is about 3 feet or less. The width of the individual flat or helical mixing paddles ranges from about 0.25″ to 4″. More typically, the width of the mixing flat or helical paddles is from 1″ to 3″. The clearance of the mixing paddles, regardless of whether flat, or helical or another shape, from the mixer shell is preferably less than ¼″, more preferably less than ⅛″, and most preferably less than 1/16″.
The second mixing section 124 of the mixer 132 is where the reinforcing fibers are typically introduced into the mixer and blended with the cementitious slurry. The second mixing section 124 is essentially a continuation of the first mixing section 122 and utilizes one or more means to blend fibers into the cementitious slurry. The reinforcing fibers through conduit 134 are introduced into the continuous mixer 132 at the beginning of the second mixing section 124. The reinforcing fibers are blended with the cementitious slurry produced in the first mixing section 122 using either mixing paddles or augers or a combination thereof. The mixing paddles and/or augers are mounted on the dual rotating shafts of the mixer and help to blend the reinforcing fibers with the cementitious slurry mixture conveyed from the first mixing section. The mixing paddles (flat paddles 125 and/or helical paddles 127) as described and used in the first mixing section 122 may be used in the second mixing section 124 as well. However, use of such paddles has been found to cause significant fiber damage due to the high shear action provided by these paddles. Therefore, use of such paddles alone in the second mixing section is not preferred, particularly when a large number of such paddles are used. Helical paddles are better suited than the flat paddles in the second mixing section to meet the objectives of this invention.
Augers can also be used for blending of fibers with the cementitious slurry in the second mixing section 124. Augers used on their own provide a rapid conveying action and a relatively less mixing action than that provided by the paddles alone. The augers mounted on the two parallel shafts in overlapping configuration further help with the self-cleaning aspect of the mixer.
Preferably if the flat paddles 125 or helical paddles 127 are employed in the second mixing section 124 they are employed in a paddle portion of the second mixing section 124 and an auger is also employed in the second mixing section 124 before and/or after the paddle section. A combination of augers and a limited number of helical paddles (or less preferably flat paddles) may also be used in the second mixing section 24. Such combination is in fact preferred and recommended for achieving best mixing results for blending of fibers with the cementitious slurry. The use of a limited numbers of helical (or flat) paddles after the augers in the second mixing section 24 causes a resistance to the material flow through the mixer. This resistance to material flow provides for a better mixing and wet-out of fibers with the cementitious slurry in the second mixing section of the mixer.
To summarize, the second mixing section 124 can be configured in one or more ways as highlighted below to facilitate mixing of fibers with the cementitious slurry mixture.
When the adjacent paddles on a shaft are rotated with respect to each other, the angle of rotation of the adjacent paddles may range from 0° to 90°, typically 20° to 90°. A greater number of paddles can be used in the second mixing section when the adjacent paddles have a zero degree rotation with respect to each other. Some of the helical paddles 127 used may also be placed in the reverse direction if desired to increase the resistance to material flow and fiber-slurry mixing action taking place in the augers 129A. When flat or helical paddles are used, the number of paddle sets (paddles per shaft) in the second mixing section 124 preferably ranges from 1 to 20, more preferably 1 to 10. The paddle parameters (type, dimensions, orientation, number, and configuration) are selected to minimize the shearing action the material is subjected to in the mixer 132. The paddles can be made of variety of materials including metals, ceramics, plastics, rubber, or a combination thereof. Paddles with softer lining materials are also contemplated for use in the second mixing section as they tend to minimize material and fiber damage. Paddles with a pin and a head or only pins may alternatively be used in the second mixing section after the auger.
The auger parameters (example, auger pitch, auger length) are selected to maximize material retention and promote a more intimate contact between the fibers and the cementitious slurry in the mixer 132. The total length of the second mixing section ranges from about 1 to 5 feet, more preferably from about 2 to 4 feet. Only a small portion of this length is taken up by the paddles 129B and a majority of the second mixing section 24 is covered by the augers 129A.
The following described
Paddle 100 for this mixer has the same structure and is employed with the same orientation as in the slurry-fiber mixer of
Volumetric feeding systems would use an auger screw conveyor (not shown) running at a constant speed to discharge powder from the storage hopper bin 160A at a constant rate (volume per unit time, e.g., cubic feet per minute. Gravimetric feeding systems generally use a volumetric feeder associated with a weighing system to control the discharge of powder from the storage hopper bin 160 at a constant weight per unit of time, e.g., pounds per minute. The weight signal is used via a feedback control system to constantly monitor the actual feed rate and compensate for variations in bulk density, porosity, etc. by adjusting the speed (RPM) of the auger screw of the auger screw feeder. Such volumetric feeding systems can also be used for any other embodiments of the mixer 132.
Aqueous medium, such as water, from a liquid pump (not shown) feeds the horizontal chamber 163 through a nozzle of at least one aqueous medium stream conduit 107A.
The rotatable shaft 129 rotates about its longitudinal axis “A” to mix the fed ingredients and convey them as fiber-slurry mixture to the discharge outlet 168. The rotatable shaft has an auger in the chamber first feed portion 120, and paddles 100 in both the first mixing section 122 and the second mixing section 124.
The reinforcement fibers and cementitious slurry and other ingredients will be feed to the mixer 132 at respective rates to leave an open space in the mixer above resulting mixture to facilitate mixing and conveying. If desired, a liquid level control sensor is used to measure the level of the slurry in the horizontal chamber of the mixer.
The rotatable shaft 129 may include a first end assembly 160 and a second end assembly 162. First end assembly 160 and second end assembly 162 may take any of a wide variety of forms known to one of skill in the art. For example, first end assembly 160 may include a first end engagement portion that operatively engages a first end of the rotatable shaft 129, a first cylindrical proportion 164 extending from the first end engagement portion, an intermediate cylindrical portion 166 extending from the first cylindrical portion 164, and an end cylindrical portion 168, extending from the intermediate cylindrical portion 166 and including a slot 170. The second end assembly 162 may include a second end engagement portion that operatively engages a second end of the rotatable shaft 29, a first cylindrical portion 172 extending from the second end engagement portion, and an end cylindrical portion 174 extending from the first cylindrical portion. In at least one embodiment, first end engagement portion of first end assembly 160 may be engaged to the rotatable shaft 129 proximate to first cylindrical proportion 164. In one or more embodiments, end cylindrical portion 168 may be operatively engaged to a motor 172 or engine capable of imparting rotation (e.g., high-speed rotation) to rotatable shaft 129 and the one or more paddle assemblies 100 engaged therewith to mix the reinforcement fibers and cementitious slurry. In at least one embodiment, second end engagement portion of second end assembly 162 may be engaged to a second end (e.g., an end opposing the first end) of rotatable shaft 129 proximate to first cylindrical portion 172. In one or more embodiments, end cylindrical portion 174 of second end assembly 162 may be preferably engaged to a bearing assembly, which may be integral to an exterior wall of the horizontal fiber-cementitious slurry mixer 132, to permit the rotation of rotatable shaft 129.
As seen in
The rotatable shaft 129, in one or more embodiments, may be constructed to rotate at a predetermined rate 30 to 450 RPM, more preferably 40 to 300 RPM, and most preferably 50 to 250 RPM during mixing
Paddle pin 114 has a width W1 which is less than a width W2 of paddle head 116 (See
The
In the mixer configurations of the invention employing flat and/or helical paddles in the second mixing section, for example in the mixers of
If desired the flat and/or helical paddles are on the shaft in the second mixing section and all adjacent flat and/or helical paddles on the shaft in the second mixing section have a zero degree rotation with respect to each other.
If desired the flat and/or helical paddles are on the shaft in the second mixing section and all adjacent flat and/or helical paddles on the shaft in the second mixing section have a 30 degree rotation with respect to each other.
If desired the flat and/or helical paddles are on the shaft in the second mixing section and all adjacent flat and/or helical paddles on the shaft in the second mixing section have a 45 degree rotation with respect to each other.
If desired the flat and/or helical paddles are on the shaft in the second mixing section and all adjacent flat and/or helical paddles on the shaft in the second mixing section have a 60 degree rotation with respect to each other.
If desired the flat and/or helical paddles are on the shaft in the second mixing section and all adjacent flat and/or helical paddles on the shaft in the second mixing section have a 90 degree rotation with respect to each other.
The above mentioned features and parameters of the fiber-slurry continuous mixer of this invention are further described as follows. This applies not only to the embodiments of the drawings but the invention in general unless otherwise indicated.
Elongated Mixing Chamber
The elongated mixing chamber is typically cylindrical in shape. The length of the mixing chamber typically ranges anywhere from about 2 to 8 feet. The preferred length of the mixing chamber is from about 3 to 5 feet. The diameter of the mixing chamber typically ranges anywhere from about 4 to 24 inches. The preferred diameter of the mixing chamber ranges from about 6 to 12 inches.
Rotating Shafts
The diameter of the dual or multi-rotating shafts is typically from about 1 to 4 inches. The preferred diameter of the central shafts ranges from about 1 to 3 inches.
The central rotating shafts rotate at a speed, preferably ranging from about 30 to 450 RPM, more preferably 40 to 300 RPM, and most preferably 50 to 250 RPM. It has been discovered that relatively lower mixer speeds are preferable to meet the objectives of the present invention. It has been surprisingly found that excellent fiber dispersion in the cementitious slurry mixture can be obtained even at relatively low mixer speeds. Furthermore, another important benefit of using lower mixing speeds is that it results in reduced fiber breakage and superior material working and flow properties useful in further processing of the fiber reinforced cementitious slurry mixture.
A variable frequency drive is preferably used with the mixer for turning the central rotating shaft when the mixer is in the operational mode. The variable frequency drive is helpful for adjusting and fine-tuning the mixer speed for a given combination of raw materials involved in the production process.
The continuous mixers of the present invention can either be a single-shaft mixer, a dual-shaft mixer, or a multi-shaft mixer. This disclosure describes the single-shaft mixers of the present invention in greater detail. However, it is contemplated that dual-shaft or multiple-shaft mixers in accordance to the present invention can also be beneficially employed for producing fiber reinforced cementitious slurry mixtures possessing desirable properties that are useful in a variety of applications including continuous production processes.
Mixing Paddles
The mixing paddles mounted on the central shaft can have different shapes and dimensions to facilitate mixing and conveying of the added components in the mixer.
As explained above the invention may employ flat paddles and helical paddles.
The mixing paddles suitable for use in the present invention also include paddles with a pin and a relatively wider head to help move the material forward, for example paddle 100. In addition to the paddles having one type of pin and head, the fiber-slurry mixer may include more than one type of paddle having a pin and a relatively wider head, or just pins, to achieve desirable characteristics required for further processing of the material. However, as seen in
The overall dimensions of the paddles are such that the clearance (space) between the inner circumference of the mixer chamber and the paddle's furthermost point from the central shaft is preferably less than ¼″, more preferably less than ⅛″, and most preferably less than 1/16″. Too great a distance between the paddle tips and the inner walls of the chamber would result in slurry build-up. Pins 114 can be substituted for at least some of the paddles 100. For example, the pins may be the pins 114 of the paddles 100 without the broad paddle head 116.
The quality of mixing and conveying of the components in the mixer is also dictated by the orientation of the paddles in the mixer. A parallel or perpendicular paddle orientation with respect to the cross-section of the central shaft diminishes the conveying action of the paddles thus increasing the residence time of the material in the mixer. An increased residence time of the material in the mixer can lead to significant fiber damage and production of fiber reinforced cementitious slurry mixture having undesirable characteristics. When employing paddles having pins and heads, for example paddle 100, the orientation of the longitudinal axis “LH” of the paddle head 116 with respect to the longitudinal axis “A” of the central shaft 118 is preferably at an angle “B” (
For the fiber-slurry mixer
When employing paddles having pins and heads, for example paddle 100, the set of paddles in the mixer are typically configured in a spiral form on the central shaft from one end of the mixer to another. This arrangement of paddles further facilitates conveying action of the material inside the mixer. Other configurations of paddle arrangement in the mixer are possible and are contemplated as part of this invention.
The paddles can be made of variety of materials including metals, ceramics, plastics, rubber, or a combination thereof. Paddles with softer lining (coating) materials are also contemplated as they tend to minimize material and fiber breakage.
The paddles and/or inner walls of the elongated mixing chamber may be coated with a release material, to minimize buildup of the cementitious slurry on the paddles and/or shell.
Other Configurations:
Other combinations of augers and mixing/conveying paddles to achieve the objectives of this invention are possible and contemplated as part of this invention. When employing paddles having pins and heads, for example paddle 100, these types of paddles may be used on their own in the first mixing section 122 and second mixing section 124 as described above and shown in
Inlet Ports
The inlet conduits 105A, 107A, 134A for the raw materials, such as the dry cementitious powder, aqueous liquid medium, and fibers fees into the mixer at inlet ports of the mixing chamber. The size, location, and orientation of raw material inlets ports of the fiber-slurry mixer are configured to ease introduction of the raw material into the mixer and to minimize potential for blocking of ports from the slurry mixture in the mixer.
The multi-stage continuous fiber-slurry mixer has at least one inlet port to introduce dry powders into the mixing chamber. This inlet port is located at the beginning of the first feed section (auger section) of the mixer.
The multi-stage continuous fiber-slurry mixer has at least one inlet port to introduce aqueous medium comprising water into the mixing chamber. The water inlet port is typically located at the end of the first feed section (auger section) of the continuous fiber-slurry. The continuous fiber-slurry mixer can have additional inlet ports to introduce other performance enhancing additives into the mixing chamber. These inlet ports are typically located at the end of the auger section or the beginning of the first mixing section of the co continuous fiber-slurry.
The multi-stage continuous fiber-slurry mixer has at least one inlet port to introduce reinforcing fibers into the mixing chamber. The fiber inlet port is typically located at the beginning of the second mixing section of the continuous fiber-slurry mixer. The fibers can be introduced into the continuous fiber-slurry mixer gravimetrically or volumetrically using a variety of metering equipment such as screw feeders or vibratory feeders. Fibers can be conveyed from a fiber feeder to the fiber-slurry mixer by a variety of conveying devices. For example, fibers can be transferred using screws (augers), air conveying, or simple gravity deposition. The discrete or chopped fibers can be made of different reinforcing fiber materials including fiberglass; polymeric materials such as polypropylene, polyethylene, polyvinyl alcohol, etc; carbon; graphite; aramid; ceramic; steel; cellulosic or natural fibers such as jute or sisal; or a combination thereof. Preferably the fibers are fiberglass. The fiber length is about 2 inches or lower, more preferably less than 1.5 inches or lower and most preferably less than 0.75 inches or lower.
The multi-stage continuous fiber-slurry mixer has an outlet port to discharge the fiber reinforced cementitious slurry mixture produced by the continuous fiber-slurry mixer. The outlet port is located at the end of the second mixing section of the continuous fiber-slurry mixer.
The multi-stage continuous fiber-slurry mixer has a venting port to remove any air introduced into the mixing chamber from raw material feed.
An electrical motor and drive mechanism to drive the shafts are associated with the mixing chamber.
Panel Production Using a Multi-Stage Fiber-Slurry Mixer
Fiber reinforced cementitious slurry made using this multi-stage continuous fiber-slurry mixer can be used for panel production. In particular, production of fiber reinforced concrete (FRC) panel, also known as fiber reinforced cement panel for use as a structural cement panels (SCP) is one preferred use.
Referring now to
In this embodiment, a web 26 of release paper, polymer film or a plastic carrier, for supporting a slurry prior to setting, may be provided and laid upon the carrier 14 to protect it and/or keep it clean. However, it is also contemplated that, rather than the continuous web 26, individual sheets (not shown) of a relatively rigid material, e.g., sheets of polymer plastic, may be placed on the carrier 14. These carrier films or sheets may can be removed from the produced panels at the end of the line or they may be incorporated as a permanent feature in the panel as part of the overall composite design. When these films or sheets are incorporated as a permanent feature in the panel they may provide enhanced attributes to the panel including improved aesthetics, enhanced tensile and flexural strengths, enhanced impact and blast resistance, enhanced environmental durability such as resistance to water and water vapor transmission, freeze-thaw resistance, salt-scaling resistance, and chemical resistance.
Optionally a layer of discrete reinforcing fibers (not shown) may be deposited directly on the conveying belt (carrier), release paper, or forming sheet upstream of the forming assembly 40.
In this embodiment, continuous reinforcement 44 such as a roving or a web of reinforcing scrim such as fiberglass scrim or nonwoven fiber mat may be provided for embedding in the slurry prior to setting and reinforcing the resulting cementitious panels. The continuous rovings and/or reinforcing web roll 42 are fed through the forming assembly 40 to be laid upon the carrier 14. However, it is also contemplated that, the continuous reinforcement 44 not be employed. The continuous scrim or rovings can be made of different reinforcing fiber materials including fiberglass; polymeric materials such as polypropylene, polyethylene, polyvinyl alcohol, etc; carbon; graphite; aramid; ceramic; steel; cellulosic, paper or natural fibers such as jute or sisal; or a combination thereof. A roving is an assemblage of continuous reinforcing monofilaments. Scrim is a web of continuous fibers typically running in the machine direction and the cross-direction. Reinforcement may also be provided as a nonwoven fiber web made of discrete reinforcement fibers.
It is also contemplated that the cementitious panels produced by the present line 110 are formed directly upon the carrier 14. In the latter situation, at least one belt washing unit 28 is provided. The carrier 14 is moved along the support frame 12 by a combination of motors, pulleys, belts or chains which drive the main drive roll 16 as is known in the art. It is contemplated that the speed of the carrier 14 may vary to suit the product being made.
The present production line 110 includes the continuous multi-stage fiber-slurry mixer 132 described above. The multi-stage continuous fiber-slurry mixer is preferably a dual shaft mixer. Dry powder feeder 104 feeds dry components of the cementitious composition, except for reinforcing fibers, to feed section 120 of the continuous multi-stage fiber-slurry mixer 132. Liquid pump 106 feeds to the first mixing section 122 of the fiber-slurry mixer 132 aqueous medium, such as water, with liquid or water soluble additives. The first mixing section 122 of the fiber-slurry mixer 132 mixes the dry components and the aqueous medium to form a cementitious slurry. The cementitious slurry passes to the second mixing section 124 of the multi-stage continuous fiber-slurry mixer 132. A fiber feeder 134 feeds fibers to the second mixing section 124 of the fiber-fiber-slurry mixer 132. Thus, in the second mixing section 124 of the fiber-slurry mixer 132 the fibers and slurry are mixed to form a fiber-slurry mixture 136. Fiber-slurry mixture 136 feeds a forming assembly 40.
Forming assembly 40 deposits the fiber-slurry mixture on the web 26 of release paper (if present) traveling on the moving carrier 14. Continuous reinforcement in form of rovings or scrim may be deposited on either one or both surface of the panel. If desired, continuous reinforcement 44 provided by fiber rovings or spools and/or scrim roll 42 is also passed through the forming assembly 40 as shown in
The fiber-slurry mixture 46 sets as it travels along the moving carrier 14. To assist in leveling the fiber-slurry mixture 46 as it is setting the fiber-slurry mixture 46 passes under one or more vibrating screed plates 52. At the distal end 18 of the support frame 12 a cutter 54 cuts the set fiber-slurry mixture into boards 55. The boards (panels) 55 are then placed on an unloading and curing rack 57 (See
Optionally, rather than applying scrim 42 or rovings to the top of the deposited fiber-slurry mixture 46, discrete reinforcing fibers (not shown) may be deposited on the surface of the fiber-slurry mixture 46 between the forming assembly 40 and the first screed plate 52. The deposited fibers are then embedded by the screed plates 52.
The fiber-cement mixtures produced by this invention contain cement, water, and other cement additives. However, to achieve the desired viscosity the cementitious compositions preferably avoid thickeners or other high viscosity processing aids at high dosage rates as commonly used with fiber cement extrusion. For example, the present slurries avoid high viscosity cellulose ethers at high dosage rates. Examples of high viscosity cellulose ethers which the present slurries avoid are methyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl methylcellulose.
Conveyor Line Edge Formation and Leakage Prevention Devices
The panel can be formed directly on continuous forming belts 14 as shown in
Various types of forming belts 14 are well known in the art that permit formation of product directly on them. The preferred belts for the purposes of this invention are multilayer engineered composites comprising plies made of materials such as thermoplastic/thermosetting resins (examples, polyester, polyurethane, etc.) reinforced with continuous fibers and/or webs (such as fiberglass and/or other high strength reinforcing materials). When the panel is formed directly on a forming belt, a thin layer of release agent is applied on the forming belt to facilitate quick release of the poured material on the belt. Also, when the panels are formed in this manner, a belt wash station is typically employed to properly clean and dry the belt on its return path to the forming end of the line. After the belt has been cleaned and dried, another layer of release agent is applied on the belt followed by extruding a fresh layer fiber reinforced cementitous slurry at the forming assembly.
Alternatively, the panel can be formed on a continuous release paper or on a forming panel such as a FRC slip sheet 14D as shown in
If desired the production line may also have edge support rails 14E as shown in
The panel can also be formed in a containment mold as shown in
The panels may also be formed on permanent molding sheets or three dimensional permanent forms. These molding sheets or forms become intrinsic part of the panel when the fiber reinforced cementitous slurry cures and hardens. When this aspect is desired, the molding sheets or forms are typically rough textured or they carry shear studs or anchors into which the fiber reinforced cementitous slurry mixture is poured. A rough texture and/or anchors enhance the bond between the panel and the permanent form/mold. Special FRC composite laminates for use as permanent forms or molds are particularly desirable in this regard since they allow formation of a composite FRC panel having special attributes including a significantly enhanced durability, impact resistance, and blast-resistance performance.
Forming Assembly (Slurry Feed Apparatus)
In both panel production using fiber-slurry mixture 36 produced by the separate slurry mixer 2 and fiber-slurry mixer 32 (as for example seen in
Different types of forming assemblies (slurry feed apparatus) are suitable on the forming line to produce the end product. A headbox is a preferred type of forming assembly. Other types of forming assemblies suitable in the present invention include: cylindrical screed rolls, roller coaters, vibrating plates with a gap at the bottom, vibrating plates (top and bottom) with a gap in the middle.
One preferred forming assembly (slurry feed apparatus) for depositing a slurry upon a moving forming web of a structural cementitious panel (SCP panel) production line or the like where settable slurries are used for producing fiber reinforced concrete (FRC) building panels or board having a direction of travel, comprises:
The preferred headbox 40 is disposed transversely to the direction of travel “T” of the carrier 14. The fiber-slurry mixture is deposited in a cavity of the headbox 40 and discharges through a discharge opening of the headbox onto the moving carrier web 14 (conveyor belt).
The preferred headbox 40 consists of a corrosion resistant material (for example, stainless steel) and has specific geometry to provide a reservoir for the slurry, height adjustment and support mounts to adjust slurry gap opening, and a curved transition to a straight lip to smoothly and evenly distribute the flow of slurry. The curved transition also provides a means to introduce a reinforcing fiberglass scrim (if needed) from above the headbox. An adjustable seal is provided at the back of the headbox in order to prevent any leakage. Reinforcing glass fiber scrim may also be added from underneath the headbox. Both scrim systems have adjustment for tracking purposes. The vibration unit is a single mass system consists of a table, springs, and two motors which direct forces directly into the mat and cancel out in other directions. This unit is placed under the headbox and it extends about 2 to 24 inches, or about 3 to 12 inches or about 3 to 6 inches beyond the headbox. The headbox height adjustment and support system can either be manually adjusted, mechanically operated, or electrically driven. The entire forming assembly has several advantages:
The fiber reinforced cementitious slurry can be pumped through a hose and hose oscillator system into the headbox 40 or it may be dropped into the headbox 40 directly from the fiber-slurry mixer 32. The oscillator system would be used in either case to agitate the slurry. Thickness of the product formed using the headbox 40 is controlled by the slurry flow rate in the headbox 40, the amount of slurry elevation head in the headbox 40, and headbox discharge opening gap for a given line speed. The discharge opening gap of the headbox 40 is a transverse opening through which the fiber-slurry mixture discharges from the headbox 40 onto the moving carrier web 14. The fiber-slurry mixture from the headbox deposits onto the moving carrier 14 in one step at close to the desired thickness and finish of the final panel 55. Vibration may be added to improve formation and different forms of continuous reinforcements such as scrims and rovings may be added to improve flexural strength of the formed product. For example, a vibration unit 50 may be located below the headbox 40 under the conveyor belt 14.
The vibration unit 50 is typically a single mass system of a table, springs, and two motors which direct forces directly into the deposited mat of fiber-cement slurry and cancel out in other directions. This unit 50 is placed under the headbox 40 and extends about 3 to 6 inches beyond the headbox.
The headbox 40 deposits an even layer of the fiber-slurry mixture of relatively controlled thickness upon the moving carrier web 14. Suitable layer thicknesses range from about 0.125 to 2 inches thick, preferably 0.25 to 1 inches thick, typically 0.40 to 0.75 inches thick.
The fiber-slurry mixture is completely deposited as a continuous curtain or sheet of slurry uniformly directed down to within a distance of about 1.0 to about 1.5 inches (2.54 to 3.81 cm.) of the carrier web 14.
Referring now to
The preferred headbox 40 is disposed transversely to the direction of travel “T” of the carrier 14. The fiber-slurry mixture is deposited in a cavity 352 of the headbox 40 and discharges onto the moving carrier web 14 (conveyor belt) through a discharge opening defined between the forming plate 364 of the headbox 40 and the moving carrier web 14.
The fiber reinforced cementitious slurry can be pumped through a hose and hose oscillator system into the headbox 40 or it may be dropped into the headbox 40 directly from the fiber-slurry mixer 32. The oscillator system would be used in either case to agitate the slurry. Thickness of the product formed using the headbox 40 is controlled by the slurry flow rate in the headbox 40, the amount of slurry elevation head in the headbox 40, and headbox discharge opening gap for a given line speed. Preferably the line speed is 1 to 100 feet per minute. The size (volume) of the slurry chamber 352 of the headbox is adjusted based on the line speed and product thickness being produced. Preferably the slurry is deposited in the headbox at a rate of about 0.10-25 cubic feet per minute.
The discharge opening gap of the headbox 40 is a transverse opening through which the fiber-slurry mixture discharges from the headbox 40 onto the moving carrier web 14. The fiber-slurry mixture from the headbox deposits onto the moving carrier 14 in one step at close to the desired thickness and finish of the final panel 55.
Vibration may be added to improve formation and different forms of continuous reinforcements such as scrims and rovings may be added to improve flexural strength of the formed product.
For example, a vibration unit 50 may be located below the headbox 40 under the conveyor belt 14. The vibration unit 50 typically vibrates at rate of 500 to 3000 cycles per minute, preferably 1000 to 2000 cycles per minute. The vibration unit 50 is typically a single mass system of a table, springs, and two motors which direct forces directly into the deposited mat of fiber-cement slurry and cancel out in other directions. This unit 50 is placed under the headbox 40 and it extends about 3 to 6 inches beyond the head box.
The headbox 40 deposits an even layer of the fiber-slurry mixture of relatively controlled thickness upon the moving carrier web 14. Suitable layer thicknesses range from about 0.125 to 2 inches thick, preferably 0.25 to 1 inches thick, typically 0.40 to 0.75 inches thick.
The fiber-slurry mixture is completely deposited as a continuous curtain or sheet of slurry uniformly directed down to within a distance of about 1.0 to about 1.5 inches (2.54 to 3.81 cm.) of the carrier web 14.
As the fiber-slurry mixture 46 moves toward the moving carrier web 14, it is important that all of the slurry be deposited on the web.
The headbox 140 has sidewalls 102 (
Scrim 42 passes through the slurry chamber 152A to run along the inside wall of the front forming plate 164. If desired the device of
Forming and Smoothing and Cutting
In both panel production using fiber-slurry mixture 36 produced by the separate slurry mixer 2 and fiber-slurry mixer 32 (as for example seen in
In addition to the above-mentioned vibrating table (forming and vibrating plate) 50 that assists to smooth the slurry being deposited by the forming assembly 40, the production line 10 may include smoothing devices, also termed vibrating screed plates 52, to gently smooth the upper surface of the panel (see
By applying vibration to the slurry 46, the smoothing device 144 facilitates the distribution of the fibers 30, 68 throughout the panel 92, and provides a more uniform upper surface. The smoothing device 144 may either be pivoted or rigidly mounted to the forming line frame assembly.
After smoothing, the layer of slurry has begun to set, and the respective panels 55 are separated from each other by a cutting device 54, which in a typical embodiment is a water jet cutter. The cutting device 54 is disposed relative to the line 10 and the frame 12 so panels are produced having a desired length, which may be different from the representation shown in
Another feature of the present invention is that the resulting cementitious panel 55 is constructed so the fibers 30 are uniformly distributed throughout the panel. This has been found to enable the production of relatively stronger panels with relatively less, more efficient use of fibers. The volume fraction of fibers relative to the volume of slurry in each layer preferably constitutes approximately in the range of 1% to 5% by volume, preferably 1.5% to 3% by volume, of the fiber-slurry mixture 46.
Wrapping a Fiber Reinforced Concrete (FRC) Panel in Nonwoven Fiber Layers
The invention also encompasses to make a board wrapped in nonwoven fiber mat, typically a nonwoven polymer fiber mat such as a polypropylene mat or a substantially inorganic nonwoven fiber mat such as a fiberglass mat, on the panel production line. The inorganic nonwoven fiber mat may optionally be coated with a variety of coating materials that impart handling characteristics to the continuous web and enhance physical and chemical durability. The nonwoven fiber mat is preferably applied on the both major faces of the panel but optionally may be applied only on one of the major faces of the panel.
A first continuous mat of nonwoven (preferably fiberglass or multi-layer polyolefin) fiber 44A from a feed roller 42A passes under a roller 42B onto the surface of the moving belt 14. Then the fiber reinforced cementitious slurry mixture 46 produced with the fiber-slurry mixer of the present invention is deposited on the first mat of nonwoven fiber 44A using the forming headbox 220.
The mat of nonwoven fiber 44A on the moving surface of the panel production line 210 extends from the right and left sides of the setting fiber-slurry mixture 46 for board 55. Folding unit 230 flips the edges 44B, 44C (see
Thus, the method may comprise applying a first web 44A of nonwoven fibers on the moving surface of a panel production line, the first web 44A is sufficiently impermeable to prevent seepage of the fiber-slurry mixture on the panel production line; the first web 44A being wider than the cement board 55 being made; forming a continuous trough by bending outer portions of the first web 44A upright; continuously depositing the fiber-slurry mixture 46 from the headbox 200 on the first web 44A and distributing the fiber-slurry mixture 46 laterally to fill the trough to a substantially uniform depth; folding upright portions of the first mesh 44A inward and over the fiber-slurry mixture such that edges are flipped to wrap around right and left edges of the setting fiber-slurry mixture; applying the second web 44 of nonwoven fibers to an upper surface of the setting fiber-slurry mixture 46 on the panel production line 10 and glue the second web 44 to the setting fiber-slurry mixture 46 for the panel 55 and then the setting panel 55 is run under a forming plate 52. Production line 210 applies the second web 44 of nonwoven fibers to an upper surface of the setting fiber-slurry mixture 46 to overlap the folded over portions of the first mesh 44A as is preferred when applying upper and lower nonwoven fiber mats 44, 44A. In an alternative, shown in
Folding unit 230 may be any suitable folding unit. For example, U.S. Pat. No. 5,221,386 to Esminger et al, incorporated herein by reference, describes an apparatus for wrapping bare surfaces of setting cement panel with woven mesh of reinforcing fibers underlying the top, bottom, and longitudinal edge surfaces (in other words, embedded). The Esminger et al apparatus can be adapted to be folding unit 230 by replacing its cement and woven mesh with setting fiber-slurry mixture 46 for board 55 and nonwoven fiber mats 44, 44A (which do not embed). The Esminger et al apparatus includes a pair of edger rails which slidably rest on a conveyor belt and define the path of the cement board being made on the conveyor belt and a means for folding and pressing outer margins of its bottom mesh comprising first pair of flexed spatulas mounted over the conveyor belt on a cross bar transverse to the direction of travel of the moving fiber-slurry mixture
Thus, to achieve the folding the present invention may employ a first pair of flexed spatulas (not shown) mounted over the fiber-slurry mixture 46. For example, the spatulas can be mounted on a cross bar (not shown, but disclosed in U.S. Pat. No. 5,221,386 to Esminger et al) transverse to the direction of travel of the moving fiber-slurry mixture. As the trough of fiber-slurry mixture 46 approaches the first pair of flexed spatulas the margins of the first mat 44A and the walls of the trough they form contact the spatulas to be tucked under the spatulas to initiate the folding over of the continuously approaching mat 44A. It is preferred to fold the upright edges 44B, 44C of the bottom mat 44A over onto the fiber-slurry mixture 46 and use the pressure of the flexed spatula blades to press the folded over first matt edges 44B, 44C down onto the fiber-slurry mixture 46 before applying the top second mat 44.
Preferably, the mats are not substantially embedded in the cementitious core. Preferably, less than about 50% of the thickness of each mat is embedded in the cementitious core, more preferably less than about 30% is embedded in the cementitious core, furthermore preferably less than about 15%, less than about 5% or less than about 1% of the thickness of the mat is embedded in the cementitious core.
In this production line 210, an optional web 26 of release paper, polymer film or a plastic carrier, for supporting a slurry prior to setting, may be provided and laid upon the carrier 14 to protect it and/or keep it clean. It is also contemplated that, rather than the continuous web 26, individual sheets (not shown) of a relatively rigid material, e.g., sheets of polymer plastic, may be placed on the carrier 14. These carrier films or sheets may be removed from the produced panels at the end of the line or they may be incorporated as a permanent feature of the panel as part of the overall composite design. When these films or sheets are incorporated as a permanent feature in the panel they may provide enhanced attributes to the panel including improved aesthetics, enhanced tensile and flexural strengths, enhanced impact and blast resistance, enhanced environmental durability such as resistance to water and water vapor transmission, freeze-thaw resistance, salt-scaling resistance, and chemical resistance. The nonwoven fiber mat 44, 44A may optionally be used in conjunction with a continuous web 26 (for instance the continuous web 26 could be a release paper that prevents any permeated slurry through the nonwoven fiber mat 44A to reach the forming belt). When employing web 26 as a permanent feature of the panel and employing the relatively impermeable nonwoven fiber mat 44, 44A, the web 26 may be affixed to the nonwoven fiber mat 44, 44A with adhesive (for example web 26 may be provided with pressure sensitive adhesive). However, the web 26 or individual sheets of relatively rigid material (not shown) are optional and preferably not employed in this production line 10 of
Materials and Structures for Nonwoven Fiber Mats which do not Fully Embed
These nonwoven fiber mats in the invention designed for not fully embedding into the fiber-slurry mixture, such as for example mats 44, 44A of
These nonwoven fiber mats are not permeable to the fiber-slurry mixture or they are at most slightly permeable to the fiber-slurry mixture. In particular, the nonwoven fiber mats provide sufficient impermeability to not let fiber-slurry mixture of the invention seep through even when the fiber-slurry mixture of the invention is vibrated and/or goes under forming plates on the production line. Fiber-slurry mixture of the invention can undergo a shear thinning when vibrated or spread on the panel production line. This makes the selection of the proper nonwoven sheet to prevent seepage important. If mats are nonwoven fiber glass mats they are coated nonwoven fiberglass mats so they do not completely embed into the fiber reinforced cementitious slurry material. This aspect of the invention with mats that do not embed does not use woven glass mat because woven glass mat is not tight enough to prevent seepage of the slurry through it. The invention contemplates using upper and/or lower meshes and scrims, for example, woven glass mats, when embedding is desired.
In the alternative the nonwoven fiber mats are preferably made of polyolefin (preferably polypropylene and/or polyethylene).
The nonwoven fiber mats can each be a single layer. For example, the preferred coated fiberglass mats are single layers. However, polymer mats are preferably made of more than one layer. For example, a preferred mat of polymer fibers has a laminate composite structure of one spun bound layer of the fibers and a relatively impermeable melt blown layer of the fibers. More preferably the mat 44 is a polyolefin mat shown in
The fibers used in the nonwoven glass mat should be at least 0.25 inch long or longer, more preferably at least one half inch or three quarters inch long and most preferably at least about one inch long, but mixtures of fibers of different lengths and/or fiber diameters can be used as is known. It is preferred that these fibers be coated with a silane containing size composition as is well known in the industry. A preferred continuous glass fiber for fibrous web is at least one member selected from the group consisting of E, C, and T type and sodium borosilicate glasses, and mixtures thereof. As is known in the glass art, C glass typically has a soda-lime-borosilicate composition that provides it with enhanced chemical stability in corrosive environments, and T glass usually has a magnesium aluminosilicate composition and especially high tensile strength in filament form. The present mat is preferably composed of E glass, which is also known as electrical glass and typically has a calcium aluminoborosilicate composition and a maximum alkali content of 2.0%. E glass fiber is commonly used to reinforce various articles. The chopped fibers of the major portion can have varying lengths, but more commonly are substantially of similar length. E glass fiber has sufficiently high strength and other mechanical properties to produce acceptable mats and is relatively low in cost and widely available. Most preferred is E glass having an average fiber diameter of about 11+/−1.5 μm and a length ranging from about 6 to 12 mm.
The non-woven fiber mats generally comprise fibers bound together by a binder, solvent treatment, or heat. The binder can be any binder typically used in the mat industry. Suitable binders include, without limitation, urea formaldehyde, melamine formaldehyde, stearated melamine formaldehyde, polyester, acrylics, polyvinyl acetate, urea formaldehyde or melamine formaldehyde modified or blended with polyvinyl acetate or acrylic, styrene acrylic polymers, and combinations thereof. Typical polymeric fibers are any of nylon, polyester, polyethylene, or polypropylene. Any suitable amount of binder can be used. However, melt blown nonwoven fiber mats do not need binder.
Typically the fibrous mat can have any suitable weight effective to prevent bleed through during manufacturing. Typically, for glass mat the basis weight will be about 18 lbs/1000 ft2 or greater (e.g., about 18-30 lbs/1000 ft2), equivalent to about 88 g/m2 or greater (e.g., about 88-147 g/m2). In one embodiment, the fibrous mat, especially a glass fiber mat, has a basis weight of about 20 lbs/1000 ft2 or greater (e.g., about 20-26 lbs/1000 ft2, or about 23-26 lbs/1000 ft2), equivalent to about 98 g/m2 or greater (e.g., about 98-127 g/m2 or greater).
Typically, for polymer mat the basis weight will be about 8 lbs/1000 ft2 or greater (e.g., about 8-30 lbs/1000 ft2), equivalent to about 39 g/m2 or greater (e.g., about 39-147 g/m2), preferably a basis weight of about 15 lbs/1000 ft2 or greater (e.g., about 15-20 lbs/1000 ft2), equivalent to about 73 g/m2 or greater (e.g., about 73-98 g/m2 or greater).
The mats are preferably each made of a single layer nonwoven fiberglass. In the alternative, preferably they are each made of nonwoven polymer (preferably polyolefin) mat having a multi-layer laminate structure.
The nonwoven fiber mats applied to the panel surfaces provide a smooth surface to the finish product and also help with the stacking of the fiber reinforced concrete panels during manufacturing. Rather than having to stack the panels in a rack separately during curing, if the panels are sufficiently set, the wrapped panels can be put directly on one another while curing. Casting fiber reinforced concrete panels edges in a nonwoven fiber mat will ease edge formation and clean up. The panel cast with a back, sides and front made of the sufficiently impermeable mat will have the benefit of a better surface, easier clean-up, and simplified board stacking (during manufacturing). This process will also yield a structural cement panel that requires zero finishing. The use of nonwoven glass mat has the advantage of a better bond over nonwoven polymer mats. The use of nonwoven polymer mats has the advantage of better alkali resistance over the nonwoven glass mats.
While a particular embodiment of the present slurry feed apparatus for fiber-reinforced structural cementitous panel production has been shown and described, it will be appreciated by those skilled in the art that changes and modifications may be made thereto without departing from the invention in its broader aspects and as set forth in the following claims.
This application is related to: U.S. Provisional Patent Application No. 62/371,578, entitled CONTINUOUS MIXER AND METHOD OF MIXING REINFORCED FIBERS WITH CEMENTITOUS MATERIALS, filed Aug. 5, 2016; U.S. Provisional Patent Application No. 62/371,569, entitled HEADBOX AND FORMING STATION FOR FIBER REINFORCED CEMENTITOUS PANEL PRODUCTION, filed Aug. 5, 2016; U.S. Provisional Patent Application No. 62/371,590, entitled A METHOD FOR PRODUCING FIBER REINFORCED CEMENTITIOUS SLURRY USING A MULTI-STAGE CONTINUOUS MIXER, filed Aug. 5, 2016; all herein incorporated by reference in their entirety. This application claims the benefit of U.S. Provisional Patent Application No. 62/371,554 entitled CONTINUOUS METHODS OF MAKING FIBER REINFORCED CONCRETE PANELS, filed Aug. 5, 2016 incorporated by reference in its entirety.
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