The present invention is related to stock delivery systems for papermaking equipment, and in particular to a stock distributor and headbox arrangement to provide uniform consistency stock across a width of a papermaking machine.
Prior known headbox and stock delivery systems for papermaking machines all attempt to varying degrees to distribute the stock flow evenly and uniformly across the width of the papermaking machine. The amount of fiber per unit area (basis weight) is ideally constant across the width of the machine and along the machine direction.
The first step in transforming stock flow from a round pipe, which provides an initial delivery of the stock white water, to a thin rectangular shaped flow from the headbox (the stock jet) is to use a manifold device to distribute or feed the flow evenly into the headbox. Prior to the 1960's, a number of different types of flow spreaders were used, utilizing different piping arrangements. The primary problem with these prior art designs was that the flow was not uniform across the machine as the pipes closest to the incoming connection often received the most flow, starving the others. In the early 1960s, a tapered manifold system was developed for more uniform flow distribution. This system is still widely used today, but there often can be flow distribution issues.
A design where the tapered header is no longer used is also known, with the flow being supplied by a set of separate hoses to the headbox. Flow uniformity is achieved by using a cylindrical tank as the feed source with the hoses connected at a substantially similar height and in a symmetrical radial pattern to ensure uniform inflow conditions. These hoses are of equal length to ensure similar throughput. See U.S. Pat. No. 3,296,066.
To maintain a uniformity of paper in the machine direction, pressure pulsation dampening devices are often used in the stock delivery systems. Many of these incorporate a pressurized air chamber as the dampener and this chamber may be directly in contact with the stock flow (for example, as provided in U.S. Pat. No. 4,146,052) or may utilize a diaphragm interface (for example, as provided in U.S. Pat. No. 4,262,700).
So that a separate pulsation attenuator is not required, cylindrical stock feed tanks with radially distributed outlet hoses have also been combined with air chambers (such as disclosed in DE 431840 C2, EP 0631011 B1). With the advent of dilution profiling for basis weight control (for example, see U.S. Pat. No. 4,897,158; U.S. Pat. No. 4,909,904; and U.S. Pat. No. 5,196,091), this later design was also adapted by adding dilution water addition into the feed hoses (such as disclosed in DE 4005281 C1, U.S. Pat. No. 5,958,189).
The stock is then delivered from the headbox tube bank to the slice lip where it is directed onto the fabric of the papermaking machine, for example as provided in U.S. Pat. No. 4,137,124 or U.S. Pat. No. 4,783,241.
It would be desirable to provide an apparatus for the delivery of stock to the headbox of a papermaking machine, and from there onto a moving forming fabric, whereby non-uniformities in the resulting web are minimized and the physical properties of the web, especially with respect to basis weight and fiber orientation, are rendered as uniform as possible across the sheet.
The present invention provides, in combination, a headbox including a stock dilution profiling arrangement and associated stock delivery systems which together deliver to the forming section of a papermaking machine a uniform stock flow with more consistent basis weight and fiber orientation profiles than has previously been possible. These improvements in basis weight uniformity and fiber orientation profile provide benefits in paper sheet formation and related paper properties. The invention comprises a radial stock distributor, a stock dilution assembly, and a headbox which includes a stilling chamber, a tube bank and nozzle with turbulence control vanes, as well as a slice adjustment system to allow for adjustment of the stock slice at the headbox nozzle. A diverging channel can optionally be provided between the stock dilution assembly and the headbox. Edge flow controls to adjust stock flow at the lateral edges can also be provided. The invention has applicability in both single wire fourdrinier papermaking environments, as well as twin wire gap or hybrid type papermaking machines.
In one aspect, the invention includes a stock feed tank of the type generally known in the art, such as disclosed in U.S. Pat. No. 4,146,052. It includes a generally circular cross-sectional shape stock receiving tank. In the preferred embodiment, the stock feed tank further includes a conical diffuser located within the stock receiving tank through which fluid flow from the stock source is directed. The stock receiving tank further includes internal flow separator plates to dampen undesired secondary flows and swirls. A stock distributor block having a radial manifold is preferably also provided in communication with the receiving tank, to evenly distribute flow and increase pressure. A plurality of stock delivery tubes are provided, with each being located in the distributor block and profiled to include a step (internal diameter/cross-sectional area change) to provide a pressure drop and even out stock flow over the face of the block. A perforated plate may also be used as the distributor block. An air pressurized chamber is preferably in communication with the stock receiving tank, opposite the stock distributor block as a pressure fluctuation dampening device. The tank preferably also includes a stock level and air pressurization control. This helps to provide a stable, uniform flow of stock to the headbox.
Connector hoses are attached to the perimeter of the stock feed tank to distribute stock from the tank to a stock dilution system. The connector hoses are each approximately the same length to provide equal pressure and stock flow to the stock dilution system.
A plurality of connector tubes are provided to receive the stock from the connector hoses. Each connector tube has a step expansion followed by a circular cross-section that tapers to a generally rectangular cross-sectional shape. The rectangular-shaped ends are located at regular intervals in the cross-machine direction (CD) across an inlet duct which is attached to the stock dilution assembly.
The stock dilution assembly receives the stock from the inlet duct and includes a source of lower consistency fluid distributed from a tapered header (or similar device) oriented in the CD of the machine and providing fluid to a plurality of dilution feed pipes. The dilution feed pipes convey fluid from the source of lower consistency fluid to individual stock feed pipes in a dilution mixing module. The flow of fluid from each dilution feed pipe is controlled by a valve and an actuator associated with each pipe, which can be adjusted responsive to product quality requirements. Dilution basis weight profiling decouples fiber orientation effects from basis weight control while ensuring an even basis weight profile. Modular construction of the dilution profiling module provides for independent selection of the profiling resolution (i.e. the fineness of the dilution profile) in accordance with grade specification requirements.
The plurality of stock feed pipes receive the stock from the inlet duct and fluid from the dilution feed pipe and deliver the dilution profiled stock to the headbox, preferably through a diverging channel which carries the stock to a stilling chamber in the headbox. The diverging channel, which is preferably a hydraulic elbow, has a flange for attachment to the stock dilution assembly. Alternatively, a straight diverging channel can be utilized in place of the elbow to direct the adjusted stock flow from the dilution assembly to the stilling chamber in the headbox. A perforated plate preferably connects the diverging channel to the stilling chamber. The perforated plate includes a plurality of regularly spaced and uniformly sized openings to allow controlled movement of the now dilution profiled stock from the diverging channel to the stilling chamber.
The headbox preferably includes the stilling chamber, noted above, as well as a tube bank and a nozzle with turbulence vanes to control stock turbulence and minimize streaks. Slice adjustment systems allow for movement of the slice in both the horizontal and vertical directions. The stilling chamber comprises an open area located downstream of the diverging channel and upstream of the tube bank, through which the dilution profiled stock passes towards the tube bank. The stilling chamber allows the pressure to equalize and motions in the fluid stock to dissipate. The tube bank is comprised of a plurality of shaped tubes through which the stock passes as it progresses downstream towards the nozzle and vanes to control turbulence. The tubes are mounted at regular intervals in at least one row and shaped so that their cross-sectional profile transitions from generally circular at their upstream ends to generally square at their downstream ends. The tubes include inserts to create the desired level of pressure drop. Shear is induced in the stock flow as it passes through the tube bank so as to disperse and fluidize the fiber suspension and deliver a controlled scale of motion to the headbox nozzle.
Turbulence vanes are preferably located downstream of the tube bank and are positioned so that stock exiting the tube bank passes either over, or under at least one vane. The geometry of the headbox vanes, including the length, thickness and/or surface characteristics, is selected to provide a desired shear and flow characteristics to meet specific grade and furnish requirements. As requirements change, vanes can be replaced to maintain optimal performance. At the nozzle, turbulence levels and the low contraction design permit low tensile ratio capability with good formation. Vanes in the nozzle maintain flow control for the suspension to be delivered streak-free to the former. High internal stock velocities over polished surfaces of the vanes and the headbox act to provide a high degree of cleanliness.
The slice adjustment system allows movement of the headbox slice in either, or both, the horizontal and vertical directions so as to adjust the speed and direction of stock exiting the headbox slice.
The edge flow control system includes providing for an initial increased flow rate through the edge tubes relative to the interior tubes in the tube bank and valves to control the flow rate of stock through the edge tubes to be either greater or less than that through the interior tubes after valve adjustment. Fiber orientation is separately controlled through slice opening and edge flow rate adjustments.
A robust structural design is preferably provided along with a hot water chamber thermal compensation system at the headbox to ensure maximum stability and cross machine uniformity. Preferably, easy access is provided to all headbox components for inspection and maintenance, including full width internal access, at both the dilution module and inlet face to the tube bank.
The foregoing summary, as well as the following detailed description of the preferred embodiment of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, the presently preferred embodiment of the invention is shown. It should be understood, however, that the invention is not limited to the precise arrangements shown. In the drawings:
Certain terminology is used in the following description for convenience only and is not considered limiting. The words “lower” and “upper” designate directions in the drawings to which reference is made. “CD” refers generally to the cross-direction of the equipment extending across a moving fourdrinier fabric for receiving stock, and “MD” refers to the machine direction or direction of travel of the moving belt in the papermaking machine. The terms “pipes,”, “tubes,” and “hoses” are used interchangeably herein to refer to a hollow elongated body for conveying fluid, which can be flexible or rigid. Additionally, the terms “a” and “one” are defined as including one or more of the referenced item unless specifically noted.
Referring to
Still with reference to
The hoses 32 are radially distributed and are preferably centered on a single vertical level. However, depending on flow requirements, more hoses may be required and the centers may be offset vertically in a zig zag or similar fashion in order to provide generally equal pressure while allowing additional hoses to be connected to the upper tank. The hoses 32 are of generally equal length in order to provide equal pressure drops in the stock flow through the hoses 32 to the headbox. This provides for a more uniform flow through the system. In one preferred embodiment, the hoses 32 have an internal diameter between 7.6 and 10 cm (3 and 4 inches).
Referring to
The open rectangular duct 54 provides a generally uniform flow that is evenly distributed by the hoses 32 from the radial stock distributor 20 to the stock dilution assembly. However, in order to improve the basis weight of the stock across the entire CD of the headbox, the stock dilution assembly 70 operates to provide a dilution basis weight profiling system.
Referring now to
As shown in
An outlet mounting plate 88 is connected to a downstream end of each of the stock feed pipes 76, and is generally parallel to the inlet channel plate 72 such that the entire stock dilution assembly 70 can be slid into or out of the headbox and stock delivery system 10. This also allows retrofitting of the stock dilution assembly 70 into existing equipment or changing out of the stock dilution assembly 70 for a different stock dilution assembly depending upon the particular requirements for a desired application. For example, where a more precise basis weight profile is required, a stock dilution assembly 70 having a greater number of stock feed pipes 76 and injection pipes 78 can be provided for a more precise basis weight profile across the width of the headbox. For example, the pipes 76 could have a more rectilinear shape with about one half the center to center spacing and with about one half of the cross sectional flow area.
Referring now to
A perforated plate 122 is connected at the outlet end of the walls 116, 118 for connection to the headbox 130. The perforated plate 122 may include circular holes spaced at the same spacing as the tube bank spacing or may include more rectangular or other shaped holes having a CD center to center spacing that is the same as the CD center-to-center spacing of the tube bank to provide for generally uniform flow while maintaining the basic weight consistency profile across the headbox opening. In the preferred application, the perforated plate 122 is a structural member and supports the inlet opening of the headbox 130. Three rows of 2.5-3.8 cm (1-1.5 inch) diameter holes are provided with a center-to-center spacing of about 3.8-5 cm (1.5-2 inches). The diverging channel 110 is preferably easily removable to allow for easy access to the headbox and/or the stock dilution assembly 70. This provides for better access than was previously available in the known headbox arrangements and allows for easy access to the headbox tube bank as well.
Referring now to
The tube bank 140, shown most clearly at
The tubes 142 are preferably comprised of an outer shell 144, as shown in
Still with reference to
Referring to
The horizontal slice opening adjustment system 170 includes linear actuators 172 spaced across the CD of the headbox 130. These linear actuators 172 are affixed at a first end to fixed structure on the headbox 130 formed by a box beam 174. The second ends of the linear actuators 172 extend to attachment mounts 176 which are connected to a slidable upper plate 178. The upper plate 178 slides on the upper surface of the tube bank supports 154, 156, 158. As shown in
Hinge knuckles 182 are mounted on the upper surface of the plate 178 and engage a hinge pintle 184 formed on the end of the upper wall 164 of the nozzle of the headbox slice. The linear actuators 172 are actuated via a common drive shaft 186 to allow for synchronous, coordinated movement of the sliding plate 178 forward or rearward to adjust the horizontal slice position.
Referring now to
An upper lip plate 220 is adjustably positioned along the upper edge of the nozzle 160. Adjustable holding rods 222 and clamps 224, shown most clearly in
Still with reference to
It is generally known that slice lip adjustment on headboxes with dilution control can be used to optimize fiber orientation CD profiles, but sometimes lack the degree of desired control. According to the invention, edge flow can significantly and reliably be adjusted to provide fiber orientation CD control. This is preferably accomplished by providing for increased flow rate through the edge flow tube(s) relative to the interior tubes and using valves for controlling the flow rate through the edge flow tubes to a level either greater or less than the flow rate through the interior tubes. In the preferred embodiment of the invention, edge flow rate can be controlled +/−15% relative to the interior tubes. This allows further adjustments to and control of fiber orientation cross machine profiles. Different diameter inserts are provided in the edge tubes 142 in the headbox than for the interior tubes in order to set the flow through the edge tubes into a desired range. It is also possible to provide a further means for adjustment for the flow rate by either a separate injection of stock flow downstream of the insert or by use of a valve mechanism to adjust available cross sectional flow areas in the edge tubes.
The system 10 according to the invention provides heretofore unattainable adjustability to establish a desired basis weight uniformity and fiber orientation in order to allow optimum paper sheet formation which can be tailored to specific sheet products being formed. While the invention has been disclosed in the context of a single wire fourdrinier papermaking machine, it is understood that this can also be adapted for use in connection with a twin wire gap or hybrid type papermaking machine.
Number | Date | Country | |
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60764053 | Feb 2006 | US |