Patent Application
20070187522
1. Field of the Invention
The present invention relates to an improved railroad tie and process of manufacture. More particularly, the improved railroad tie is fabricated out of various thermoplastic resins and fillers using an injection molding and cooling process. Part of the cooling is accomplished using a cooling cavity located in the mold. Further the present invention uses a unique automated system for molding the ties. Further, the improved railroad tie has one or more cavities on at least one side of the tie to provide a lighter and less expensive railroad tie and to provide more lateral stability for resistance to sliding around railroad curves. Even more particular the improved tie uses an improved insert designed to add strength while reducing the amount of required thermoplastics and resins for the tie. The insert also includes features which enable the use of an automated production line. The same improvements in the mold and automated system as well as the improved insert can be used to mold structural members other than railroad ties.
2. Prior Art
Railroads are typically constructed out of two steel rails fastened to a plurality of wooden railroad ties using a bracket and/or railroad spikes. The railroad ties run perpendicular to the rails and are held in place by a rail bed of gravel. When the train rolls down the track, the wheels ride on the rail. The weight from the wheel is transferred through the rail onto the railroad tie and into the gravel rail bed. Most of the forces exerted on the railroad tie are in compression. The railroad tie is held in place by the gravel rail bed surrounding the bottom and sides of the railroad tie. This gravel helps resist the vibration and forces exerted on the railroad tie.
One of the primary concerns in the operation of a railroad is safety. A major safety problem is derailment. Derailments can cost millions of dollars in damage and loss of use of a railway. On average, there is one derailment in the U.S. every day. The leading cause of this problem is a lack of lateral stability. This is caused when the railroad ties allow the track to move from side to side. This happens when the gravel on either end of the tie, as well as the friction between the gravel and the sides and bottom of the tie, cannot restrain the forces exerted on the tie by the train rolling over the rails above it.
Historically, the railroad ties are constructed out of timber. A standard railroad tie is 7 inches tall by 9 inches wide by 108 inches long. The surfaces of the tie are typically flat. The increased demand for wood in today's economy, coupled with the limited supply, has driven up the cost of wooden railroad ties.
When the railroad ties are in use they are subjected to conditions which greatly reduce the useful life of the railroad tie. These include exposure to moisture, wood destroying insects, and freezing and thawing. These, coupled with the forces and vibrations exerted on the ties by the trains, lead to a limited useful life for the railroad ties. Currently in the United States various railroad companies replace 10 to 15 million ties per year.
Due to the shortcomings and cost of the wooden railroad ties and recent advances in various composites, other materials have been used to fabricate railroad ties. U.S. Pat. No. 6,604,690 issued to Hartley Frank Young on Aug. 12, 2003 discloses a concrete railroad tie. While concrete provides a solid material for a tie, it can tends to be excessively heavy and hard to move.
U.S. Pat. No. 5,055,350 discloses a composite railroad tie made from sand and recycled thermoplastic containers. The sand is coated with an adhesive and then mixed with the thermoplastic. Using sand as the filler in this thermoplastic mix has the same draw back as concrete in that it is excessively heavy. The sand also increases the wear on the die used to extrude the tie.
U.S. Pat. No. 5,799,870 issued to John C. Bayer discloses a railroad tie made from a gypsum filler and a thermoplastic resin. Much of the material in a railroad tie is not necessary in order to support the load placed upon it. The railroad ties disclosed in the Bayer patent are formed using an extrusion process. Due to the way they are formed, they must have a solid cross-sectional shape. This means that the railroad tie is heavier than necessary. It is also more expensive than necessary because it contains more material than is needed for its application. The solid cross-sectional shape and excess material increase the cooling time by reducing the surface area and increasing the mass and heat density of the hot freshly extruded ties. This means that the production must either have a larger cooling bath or a slower production rate, either which adds to the cost of the ties.
Other features of prior art for molding large structural members similar to ties require cumbersome cooling processes. U.S. Pat. No. 5,766,711 issued to Andrew Barmakian on Jun. 16, 1998 discloses a Composite Camel Structure and Method for Manufacture. The method of molding requires a core be molded into the center of the structure. During the molding process cooling water is circulated through the core to remove heat from the injected plastic. After the molded object is cooled the core must then be drained and filled with buoyant material. This designs adds to the material cost of the structure as well as the labor and manufacturing cost due to the additional necessary steps.
Other prior art on molding large structural members avoid the additional cost of using these cooling cores. U.S. Pat. No. 6,244,014 issued to Andrew Barmakian discloses a Steel Rod-Reinforced Plastic Piling. In manufacturing these pilings cooling of the part is achieved by submersing the part in a cooling bath while still in the mold. While this presents certain advantages over using a cooling core, the process of submerging the entire mold presents its own set of problems such as having to maintain a cooling tank large enough to accommodate the molds, handling of the molds with the added weight of the piling inside and the cost of having multiple molds on hand to keep production going while the molds are cooling.
One of the problems that has plagued the injection molding industry is the inability to use a split mold on these extra large structures. Typically large molds that bolt together or have a tubular shape are used. This leads to problems in removing the completed part from the mold, which in turn leads to low production rates and higher production costs.
In the field of injection molding liquid cooled molds are known for use in making objects much smaller than a tie. However, they rely on one or more cylindrical holes drilled through the block of the mold. These cooling passages are operated completely filled with cooling fluid. The heat is therefore only removed via a conductive heat transfer. The cooling passages also provide little surface area for heat transfer. Thus further limiting the efficiency of this arrangement.
Other suppliers of plastic composite ties on the market today inject a plastic into a long rectangular tube. The tie must then cool completely in the rectangular tube mold to avoid having the tie swell. Finally, each tie is removed by production workers using a forklift and chain to pull attached to lag bolt inserted into the end of the tie. In other applications a pneumatic or hydraulic cylinder was used in lieu of a forklift. All in all this proves to be a very inefficient process.
Due to the shortcomings of the prior art, it is an objective of the present invention to provide a railroad tie which is formed using an injection molding and post cooling process using various thermoplastics and fillers.
Another objective of the present invention is to provide a railroad tie which has one or more cavities formed into at least one of the faces to provide a lighter railroad tie and one that can be better gripped by the material of the roadbed for improved lateral stability.
It is a further objective of the present invention to provide a thermoplastic railroad tie which can be cooled quicker than the prior art due to the increase of surface area and the decrease in mass and volume.
Yet another objective of the present invention is to provide an improved composite railroad tie with increased strength and reduced weight and cost through the use of reinforcing materials.
A further objective of the present invention is to provide an improved composite railroad tie with a structural insert molded into the web of the tie. The insert provides increased stiffness and quality, thus permitting the use of a wider range of polymers for a ductile skin or shell of the tie.
The present invention also includes an improved insert which provides additional strength to the improved composite tie while helping to minimize weight and maintain strength. This same insert has improved features which allow it to be used in an automated production line.
Another object of the present invention is an improved split mold and vault with each half having an interior cooling cavity in which cooling water is sprayed onto the back side of the mold cavity maximizing the cooling rate of the molded tie and in turn maximize the production rate. The improved split mold and vault allow for using it to mold extra large structural elements
It is another object of the invention to provide an automated system which can provide high production rates for large structural elements in a relatively small area. Thus reducing manufacturing costs, overhead and labor.
It is a further object of the present invention to provide an improved process and system for injection molding composite ties. The system being highly automated to help lower labor and production costs while producing high quality ties of the present design.
The objects of the present inventions can also be applied to large structural members other than ties.
Other objects, features, and advantages will be apparent to persons of ordinary skill in the art in view of the following detailed description of preferred embodiments and the accompanying drawings.
For a more complete understanding of the present invention, the needs satisfied thereby, and the features and advantages thereof, reference now is made to the following descriptions taken in connection with the accompanying drawings in which:
When the tie 20 is in use, the weight and force from the train is transferred through the rails generally into the area indicated as 32, the majority of these forces are in compression. As such, the railroad tie 20 does not need to be a solid rectangular block in order to handle these loads. Therefore, the cavities 30 are located in those areas where the material would otherwise be underutilized.
The cavities 30 provide several benefits. When the tie 20 is installed, it is surrounded by gravel from the rail bed. This gravel helps hold the tie 20 in place. It also fills the cavities 30 providing a better grip on the tie 20 than would be provided with a traditional flat sided tie, thus increasing the lateral stability of the tie. The cavities 30 also remove material which is not needed when the tie 20 is in use. This provides a lighter tie 20 than one with continuous flat sides 28. It also reduces the amount of material needed and thus reduces the cost.
It should be noted that any of the dimensions and/or the size, location and number of cavities 30 can be changed to meet varying needs while still falling within the scope of this invention.
The improved composite railroad tie 20 can be fabricated out of various thermo plastic resins and fillers commonly known in the field using an injection molding process. In the preferred embodiment, the material used would be comprised of recycled or wide-spec thermoplastic polymer, low cost fillers, and additives, such as foaming agents, black color, and extrusion aiding ingredients. In the preferred embodiment, the tie 20 is formed using a structural foam process.
The performance of the improved composite tie 20 can be compared to that of an I-beam.
Use of the reinforcing material will add strength and rigidity to the improved tie 20. This allows for the size of the cavities 30 to be increased while maintaining the same strength of the improved tie 20. This in turn means that the total weight of the improved tie 20 is decreased. This also means that the cost of materials in the improved tie 20 can be decreased. The increased size of the cavities 30, while using the reinforcing material 40, also provides more surface area and less volume for the improved tie 20, which in turn decreases the cooling time and in turn reduces the production costs. The increased stiffness and quality provided by the reinforcing material also permit using a wider range of soft polymers for a ductile skin or shell.
Reinforcing material can also be added to the web 36 to increase strength of the tie 20.
The tie 20 shown in
The insert 40 shown in the tie 20 of
The insert 40 shown in
The insert 81 has a pair of nesting arches 83 and 85. The arches 83 and 85 are attached to the bottom edge 92 of the insert 81. The arches 83 and 85 are also secured to one another directly and by cross links 87. The arches 83 and 85 help concentrate the load on the tie 20 in the center of the tie 20 in the event the ballast washes out from under the ends 26 of the tie 20. The connections between the nested arches 83 and 85 create openings 89 which pass through the insert 81. In the completed tie 20 these openings are filled with the composite. These openings 89 help ensure a better interlocking between the composite and the insert 81 than an insert having a solid body.
The process for making the improved composite tie 20 is comprised of injecting hot molten resin or resin and fillers into a mold, allowing the resins or resins and fillers sufficient time to cool so they will hold their shape when removed from the mold, then removing the improved composite tie 20 from the mold.
The problem with the traditional shaped tie as shown is
The advantage of the improved tie 20 is further shown by the fact the composite used is a non-Newtonian fluid and is compressed during the injection process. If the traditionally shaped tie is removed from the mold before the majority of the center has solidified, the solidified perimeter 102 will not be thick and strong enough to contain the compressed molten center 104. When this happens the tie swells, throwing the dimensions and planar surfaces out of tolerance. With the 10% increase in surface area and 50% reduction in heat density, the improved tie 20 has a much smaller molten center 108 and a much larger and stronger solidified outer perimeter 108 when it is removed from the mold. This allows the improved tie 20 to retain its shape after the same amount of in mold cooling time as a traditional shaped tie.
The tie 20 is then allowed to further cool either in the air or in a spray or liquid bath. The cooling time is a function of the temperature of the tie 20, the heat density of the tie 20 and the surface area of the tie 20. The improved tie 20 provides the advantage of increasing the surface area of the tie 20 while reducing the mass and heat density. This in turn leads to a shorter cooling time, which in turn leads to a faster production rate if the cooling step is the limiting factor in the production rate. As previously mentioned, the process can be modified to include inserting a stiffening material into the mold prior to injecting the hot molten resin or resins and fillers into the mold.
During the molding process once the mold cavity 116 has been filled with the composite material, the cooling cycle begins. Cooling is aided by a cooling fluid such as water being supplied under pressure to the cooling fluid header 132. The cooling fluid then goes through the nozzles 134 and is sprayed into the cooling cavity 130 where it comes into contact with the interior surface of the cooling cavity 130 including the vault side 122 of the mold half 112. This helps remove heat from the parts located in the cavities 116, thus increasing run speed and decreasing manufacturing costs.
In the preferred embodiment the cooling fluid is sprayed across the entire surface and is evacuated from the cooling cavity 130 via a return or drain 138 so the cooling cavity 130 is at least partially empty. This optimizes conductive, convection and radiant heat transfer as the cooling fluid flows over the surface while containing the cooling fluid in the cooling cavity 130. The known prior art only has channels drilled through the mold which are kept full of cooling fluid. As such the prior art only took advantage of conductive heat transfer for cooling. The mold halves 112 only provide thin shell of metal between the part being cooled and the cooling fluid versus the prior art with a large cross-section of metal between the part being cooled and the cooling fluid flowing through the gun drilled channels. The metal between the part being cooled and the cooling fluid acts like a resistor in an electrical circuit. Just as an electrical resistor reduces to the flow of electricity, so the metal between the part and the cooling fluid slows the transfer of heat out of the part. There is also more surface area to use for cooling with the cooling cavity 130 than was available with the prior art drilled channels. Heat transfer is further aided by using aluminum for the molds 110. Aluminum conducts heat three times faster than the steel previously used for injection molds.
Once removed from the cooling cavity 130, the cooling fluid can either be chilled by means typically known in the field such as a fin fan or other heat exchanger. Once the cooling fluid has been cooled or chilled it can then be reused. In the alternative, the cooling fluid can be discarded without removing additional heat from it.
The inserts 40 for the ties are loaded onto carts 212 which can be rolled into position on a level just below the level of the presses 204.
Once the insert 40 has been loaded onto the robot 216, the robot 216 moves away from the cart 212 and along a pathway 220 underneath the presses until it is located below the press 204 that it intends to load with the insert 40. The robot then extends upward until the inserts 40 are at the proper height to be loaded into one half of the molds 210. Each mold has a permanent magnet 222 which is located to correspond with the landings 94 of the inserts 40. The robot extends the inserts 40 towards the molds 210 until the landings 94 of the inserts 40 become engaged with the permanent magnets 222 of the mold 210. The electromagnets 218 of the robot 216 then turn off allowing the inserts 40 to be held in place in the mold by the magnetic force of the permanent magnets 222 and the shoulders 96 located on the landing 94. The robot 216 then retracts away from the half of the mold 210 holding the insert 40 and moves towards the opposing half of the mold 210 located on the opposing vault 206 or 208 which will hold a tie 20 made on the previous cycle of the system 200. The robot 216 has a plurality of extensions or receptors 224 which engage the tie 20 and remove it from the mold 110. The robot 216 retracts from the second half of the mold 210 and lowers until it can proceed down the pathway 220 below the presses 204 to place the tie on a cooling rack 226 where it will remain until it is removed from the automated molding system 200. The newly molded tie 20 can be further cooled by the ambient air or chilled air. Likewise, a cooling bath using a sprayed cooling fluid or immersion could be used to further cool the tie 20
Once the robot has lowered itself out from the space between the two halves of the mold 210, the dynamic vault 208 moves toward the static vault 206 until the two halves of the mold 210 are closed. The two halves of the mold 210 are locked together by a plurality of wedges 207 on the back side of the dynamic vault 208 which slide to engage locking collars 209 located on the tie rods 211. Once the mold 210 is closed and locked, the flow of the composite material from the extruder 202 is directed to the empty mold 210 through a series of piping and valves 228. The composite is then forced into the cavity of the mold 210 until the cavity is completely filled. The flow of composite material is then stopped.
Once the mold 210 has been filled with composite, the composite material is allowed to cool. The cooling can be aided by the use of a mold 110 as shown in
Once the tie 20 has been cooled sufficiently for the external solidified perimeter 106 to support the molten center 108 of the tie 20. The mold 210 is opened and the tie 20 is retained on one half of the mold 210 until it is removed from the mold 210 by the robot 216 and the process is then repeated.
The foregoing specifications and drawings are only illustrative of the preferred embodiments of the present invention. They should not be interpreted as limiting the scope of the attached claims. Those skilled in the arts will be able to come up with equivalent embodiments of the present invention without departing from the spirit and scope thereof.
This application is a continuation-in-part and claims the benefit of the filing of pending U.S. patent application Ser. No. 11/114,620 which in turn is a continuation-in-part of U.S. patent application Ser. No. 10/837,978 which in turn is a continuation-in-part and claims the benefit of the filing of U.S. Provisional Patent Application Ser. No. 60/516,697, entitled “Improved Composite Railroad Tie and Method of Manufacture”, filed on Nov. 3, 2003, and the specifications of these prior applications are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60516697 | Nov 2003 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11114620 | Apr 2005 | US |
| Child | 11402500 | Apr 2006 | US |
| Parent | 10837978 | May 2004 | US |
| Child | 11114620 | Apr 2005 | US |
