Railways: surface track – Ties
Reexamination Certificate
1998-11-12
2001-01-30
Stormer, Russell D. (Department: 3617)
Railways: surface track
Ties
Reexamination Certificate
active
06179215
ABSTRACT:
BACKGROUND OF THE INVENTION
Railroad crossties have been made almost exclusively of wood from the beginning of the railroad age. The wooden crossties are held in place by ballast rock, and the rails are attached using tie plates and cut spikes. This is a readily available and commonly used system. The wooden ties accept and hold spikes, so that the rail and tie plate fastening systems may be secured to the ties. A wood tie will flex under load. The resulting flexing is beneficial only in that it helps to provide for a softer ride. However, the flexing also increases the displacement of, or “pumpinpg” of, the supporting ballast out and away from the tie. This increases maintenance cost. The flexing also “pumps” or works the spikes up and loosens them, resulting in additional maintenance cost. Wooden ties deteriorate and must be replaced at regular intervals, resulting in high maintenance costs.
Railroad ties made of material other than wood have been proposed. For example, U.S. Pat. No. 5,238,734 to Murray discloses a railroad tie made from a mixture of recycled tire fragments and an epoxy mixture. Other patents disclosing railroad ties made out of composite materials include U.S. Pat. No. 4,150,790 (Potter) and U.S. Pat. No. 4,083,491 (Hill). Although ties made out of composite materials provide significantly longer life than conventional wooden ties, it has not been possible to provide composite ties that are durable enough to withstand the heavy repeated loads of main line railroad tracks. Both wooden and composite railroad ties tend to pump ballast rock away from the rails, thus requiring frequent reballasting.
Concrete crossties that are reinforced with various materials are also known in the prior art, such as the crosstie disclosed in U.S. Pat. No. 1,566,550 (McWilliam). However, conventional concrete crossties are too hard and brittle to use conventional and standard fastening systems (tie plates and cut spikes). Concrete ties use pre-casted fasteners that are attached during the curing stage in the tie manufacturing process. Furthermore, each tie must be individually loaded and obstructed from the mold. The concrete crossties are stiff and non-flexible, this is advantageous and provides a stiffer track module, improved lateral stability and gauge control, increased rail life, and greater locomotive fuel economy. What should have been a significantly lower maintenance cost due to the lack of “pumping” of the ballast rock, has actually become another maintenance cost. The concrete tie is so hard that it pulverizes the ballast rock beneath it which results in a sand like or soft support system.
SUMMARY OF THE INVENTION
The railroad crosstie according to the present invention combines the best features of the wooden and concrete crossties. The present invention offers all the benefits of the concrete tie while adding “shock absorbing” and “impact resistance” features with the outer composite shell. This helps to eliminate the pulverizing of the ballast rock. The ballast rock actually imbeds itself into the composite helping to keep it in place.
Accordingly, an outer casing is provided which is made out of, preferably, a 50/50 mixture of high density polyethylene (such as from recycled household containers) in which reinforcing beams have been mounted in the cavity within the casing. The new system also uses traditional fastening systems. Inserts are placed within the beams that are made out of the same composite material from which the casing is made, and the upper surfaces of the beams define apertures so that spikes can be driven through the casings, the apertures, and into the inserts. The rubber and plastic mixture is sufficiently yieldable so that spikes can be driven through the casing and into the inserts in much the same way as spikes can be driven in conventional wooden crossties. The rubber gives the composite a “gripping feature” that has been proven to hold the spike better than wood, resulting in higher spike pull testing. The cavity is then filled with concrete, including the portions of the cavity within the beams and between the inserts. The beams, which are preferably made of steel, stiffen the cross tie and prevent pulverizing of the concrete. If heavier axle loads are to be accommodated, tubular beams made out of a heavier gauge of steel may be used, which stiffens the beam, resulting in a higher positive bending moment. The higher the bending moment the better the track modules.
Accordingly, crossties made according to the present invention have a bending moment that can be manipulated to best fit the end user's needs while having a cross section of the standard 7″×9″ size that any concrete tie which meets the railroads requirements must be 8″×10″ in cross section. Any tie other than a 7″×9″, can not be used as a replacement tie for the 14,000,000 ties that are replaced each year. The ability to adjust the bending moment and remain within the 7″×9″ cross section is unique to this invention.
Accordingly, a railroad crosstie is provided that combines the benefits of conventional wooden ties and concrete ties. The cross tie has the durability and load carrying capacity of a concrete tie, but the composite material has shock absorbing and vibration dampening qualities such that the ride of trains on the tracks supported by the tie is smooth. Ballast rock embeds in the casing material, just as in wooden ties, so that the ballast is not pulverized or displaced. Since the stiffness of the cross tie may be controlled, the cross tie may be optimized to provide a smooth ride, but yielding and movement of the tie can be limited so that the tie will not pump ballast rock away from the rails as is the case with wooden ties.
REFERENCES:
patent: 3951384 (1976-04-01), Hildreth, Jr.
patent: 3957250 (1976-05-01), Murphy
patent: 4083491 (1978-04-01), Hill
patent: 5030662 (1991-07-01), Banerjie
patent: 5053274 (1991-10-01), Jonas
patent: 5238734 (1993-08-01), Murray
patent: 5271203 (1993-12-01), Nagle
patent: 5320794 (1994-06-01), Holmes
patent: 5609295 (1997-03-01), Richards
patent: 5675956 (1997-10-01), Nevin
Baker & Daniels
McCarry, Jr. Robert J.
Primix International, LLC
Stormer Russell D.
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