Patent Application
20060086817
1. Field of the Invention
The present invention relates to a composite material that can be used to manufacture railroad ties and other extra large structural objects. The present invention also provides a use for post-consumer waste which can be used to make the railroad ties, other extra large structural objects and a replacement for treated wood products such as ties, pilings, poles, etc.
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. 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 tends to be excessively heavy and hard to install. Typically, concrete ties are not used to replace wood ties due to the difficulty of installation and incompatibility of the two materials.
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. 5,094,905, and its continuation-in-part, U.S. Pat. No. 5,238,734, issued to Kevin N. Murray, disclose the use of recycled tire fragments for use in making railroad ties. The vulcanized rubber from the tire fragments creates a rather brittle tie. This can lead to problems during shipping, installation and use of 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. The railroad ties disclosed in the Bayer patent are formed using an extrusion process. The gypsum filler and thermoplastic composition used in Bayer is abrasive. This causes wear on the die used for extruding. Once cooled the composition used in Bayer is relatively brittle. This leads to problems in the shipping, installation and use of the ties.
U.S. Pat. No. 6,191,228, issued to Thomas Nosker et al. discloses the make-up of a preferred plastic composite for manufacturing railroad ties. While most of the components of the Nosker plastic can be obtained from recycled or post-consumer products, it requires that each of the components of the composite be obtained in relatively pure form or waste stream, thus limiting the source of the components to those which are highly segregated. The composite used in the Noskar patent has a relatively low melting point. This makes it difficult to machine. The heat generated by the cutting tool during machining melts the plastic as it cuts. This can gum up and dull the tool which leads to increased machine time and cost. It also makes it difficult to maintain the correct tolerances on the finished product. Finally once cooled the composition used in Nosker is relatively brittle. This causes breakage problems during shipment and installation and premature failure under certain use conditions.
Every year approximately 200 million tons of post-consumer, remnant and scrap carpet are generated in the U.S. Currently there is no market for the use of this product, so the carpet must be land filled, thus taking up valuable space. Most carpet is made up of nylon and polypropylene. With rising oil prices the costs of virgin nylon and polypropylene have greatly increased. Every ton of carpet that is recycled reduces the amount of oil that must be imported and increases the useful life of existing landfills.
Post-consumer carpet can be particularly problematic in a landfill. It has a tendency to get caught in the tracks of bulldozers used to move the refuse and dirt in the landfill. When the carpet gets caught in the tracks, it tends to ball up and cause the track to come off of the bulldozer. This in turn adds to maintenance costs for the landfill and slows production.
The U.S. government has recently become aware of the increasing problems of post-consumer carpet. They have set up an organization Carpet America Recovery Effort (CARE) whose purpose is to foster interest in finding uses for the tons of post-consumer carpet that are otherwise wasted in the U.S.
The present invention is a composition for a polymer composite. It can be manufactured using virgin ingredients.
The present invention also can be manufactured using post-consumer ingredients including, but not limited to, recycled carpet.
The present invention provides a process to make a polymer composite for use in railroad ties and other extra large structural objects.
Further, the present invention contains a process for using post-consumer carpet for the manufacture of railroad ties and other extra large structural objects, such as light poles or utility poles.
A better understanding of the invention will be obtained from the following detailed description of the preferred embodiments taken in conjunction with the drawings and the attached claims.
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:
It is to be understood that the invention that is now to be described is not limited in its application to the details of the construction and arrangement of the parts illustrated in the accompanying drawings. The invention is capable of other embodiments and of being practiced or carried out in a variety of ways. The phraseology and terminology employed herein are for purposes of description and not limitation.
The present invention includes the formulation of a composite material for manufacturing composite railroad ties and other objects needing structural integrity. The composite material comprises 25% to 60% recycled carpet, 5% to 15% polystyrene and 25% to 70% polyolefin. The polyolefin can be any member of that chemical family including but not limited to low density polyethylene, high density polyethylene and polypropylene. While both the polystyrene and polyolefin can be obtained in a virgin form and included in the composite material, in an alternate embodiment of the present invention, post-consumer polystyrene and polyolefin can be used.
This composition of material provides a synergistic combination. When extruded and molded according to the process outlined below the polyolefins will melt and provide flexibility which helps the composite flow into the mold and fill it. The polyolefins also add ductility and impact strength to the final product. The polystyrene adds stiffness to the composition. The nylon found in the recycled carpet does not melt during extrusion and molding and remains in a reinforcing fiber state. The calcium carbonate from the carpet backing provides a foaming agent which helps fill the mold. If one of the components is not present or the molding and extrusion process outlined below is not followed, the performance characteristics of the composition will decline.
The preferred embodiment of the present invention comprises 40% recycled carpet, 10% polystyrene and 50% polyolefin.
The process for using recycled carpet to manufacture composite railroad ties or any other extra large structural object is comprised of the steps of obtaining recycled carpet 10 from the sources known in the art. The carpet is then shredded 12 and pelletized 14. The components of the composite material are then mixed 16 together to obtain a generally homogenous mixture. The mixture is then extruded 18, molded 20 and cooled 22. Post-consumer carpet can also be purchased in a pelletized form and used in this process.
One of the drawbacks of using recycled carpet is that it contains nylon, a hygroscopic polymer which can retain water. Many times used carpet is stored outside. This introduces moisture into the nylon in the carpet. If the moisture is not removed, it turns into steam during extrusion. The steam causes voids and deformities in the object being molded. In order to overcome the problems during extrusion associated with moisture in the composite material, the recycled carpet can be dried 24. The drying 24 can be done when the carpet is shredded 12 to manageable sized parts or once it is pelletized 14.
When the pelletized material having a desired moisture content is achieved, it can be fed into an extruder 18. The extruder melts and liquefies the pelletized material so that it can be pumped in a molten blend into a die, mold or other forming cavity to form 20 a composite railroad tie or other extra large structural objects. Other extra large structural components could include but are not limited to light poles, utility poles, parking blocks and parking curbs.
One of the more critical factors in the process outlined in the present invention is the operating temperature of the extruder. If the extruder is operated at too high of a temperature, the rubber in the carpet begins to burn or smolder. The smoldering continues once the composite material is in the form. This leads to porosity in the product being formed and causes problems with the strength and structural integrity of the item being formed. If the temperature is too low, the components of the composite material do not melt and do not combine with one another sufficiently. This leads to a low strength. It also becomes problematic in getting the mold to completely fill. Therefore, the items being molded come out with deformations and defects.
The primary constituent of some recycled carpet is nylon. Nylon has a melting point of 480° F. to 500° F. The polystyrene has a melting point of approximately 380° F. The polyolefins typically melt around 390° F. For the composite material to perform in an optimum manner the operating temperature of the extruder and, in turn the composite material in the extruder, must be within a range of 390° F. to 470° F., with the preferred embodiment being 400° F. This is above the melting points of the polystyrene and polyolefin and below the melting point of the nylon. Operating at these temperatures allows the polystyrene and polyolefins to melt and mix while the nylon remains as a fiber and enters the mold as a fiber. This nylon fiber provides a reinforcing strength in the composite material once it has cooled and set. While the polyolefin component provides ductility, the styrene component adds stiffness and hardness to the bonding matrix. The nylon fibers provided increased tensile strength, maintain mechanical properties at extreme temperatures and increase the workability of the composite material.
When the railroad tie or other object is formed, it must be cooled 22. The cooling 22 can be done at room temperature or using chilled liquid in a bath or shower. The object is removed from the mold once it has cooled so the outer skin of the object can support its weight. The object is then allowed to continue to cool outside of the mold.
The co-inventors of the present invention currently have a pending patent application entitled “Improved Composite Railroad Tie and Method of Manufacture,” Ser. No. 10/837,978, which is incorporated herein by reference. The method of manufacture disclosed in the '978 patent application can be used to form the composite railroad ties.
While the invention has been described with a certain degree of particularity, it is manifest that many changes may be made in the details of construction and the arrangement of components without departing from the spirit and scope of this disclosure. It is understood that the invention is not limited to the embodiments set forth herein for purposes of exemplification, but is to be limited only by the scope of the attached claims, including the full range of equivalency to which each element thereof is entitled.
This application is a continuation-in-part and claims the benefit of the filing of U.S. Provisional Patent Application Ser. No. 60/622,032, entitled “Composite Material and Method of Manufacture”, filed Oct. 26, 2004 and the specification thereof is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 60622032 | Oct 2004 | US |
