Railways: surface track – Rail seats – Cushions
Reexamination Certificate
2000-11-20
2002-11-19
Le, Mark T. (Department: 3617)
Railways: surface track
Rail seats
Cushions
C238S382000
Reexamination Certificate
active
06481637
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention, in general relates to rail pads and, more particularly, to rail pads that lessen abrasion of a concrete railroad tie.
Rail pads are typically placed intermediate each of the rails and each railroad tie. The railroad ties may be concrete or steel or other material. In general, the use of rail pads is well known in the railroad arts.
They are used to dampen the changes in loading that occur on the rails. This is sometimes referred to in the industry as “strain attenuation”. Rail pads are also used to provide electrical isolation sufficient to electrically insulate the rail from the railroad tie and they also serve to lessen abrasion of the railroad ties. The industry term for this detrimental phenomenon is “rail-seat abrasion” and it is discussed in greater detail hereinafter.
These types of benefits are well known and are not elaborated herein other than to state that rail pads are generally required devices and that an improvement appertaining to any of these areas is desirable.
The railroad industry has, over time, increased the use of concrete railroad ties (over pressure treated types of wood and other materials, such as steel) to support the rails thereon. Concrete railroad ties have advantages over their wood counterparts and over other possible types of materials that may be used to form the railroad tie that appertain, primarily, to issues of durability, availability, environment, toxicity, consistency, and especially, longevity (i.e., life-cycle cost) matters.
However, their use is not now without problems. Previous types of rail pads that are placed intermediate the rail and the tie were designed to absorb and dampen the changes in the loading that are experienced by the rails that they support. This change is known as dynamic loading and rail pads must effectively dampen dynamic loads.
Some of the prior art patents mentioned hereinafter describe the design and construction of such types of rail pads. These prior types of rail pads, while providing many benefits, fail to adequately solve the problem of rail-seat abrasion. This problem exists whenever a rail pad is placed intermediate a rail and any type of a railroad tie.
If a rail makes direct contact with a railroad tie, movement of the rail in response to changes in dynamic loading directly abrades the tie. If the railroad tie is made of concrete this problem is worsened.
Rail-seat abrasion also occurs when a rail pad is placed intermediate the rail and the tie. One of the factors that exacerbates rail-seat abrasion includes the effects of greater axle loading. Heavier and more powerful locomotives as well as the trend toward having railroad cars with a greater carrying capacity means a greater axle loading. Accordingly, the potential magnitude of change in the dynamic loading that the rail pad can experience is increasing.
Another factor is that sand from locomotives (for improving traction) settles down and further abrades the ties. This is discussed in greater detail hereinafter.
Another factor affecting rail-seat abrasion by increasing the effective dynamic loading is known as “rail roll” and this occurs on curves.
Rail-seat abrasion is affected as well by many other factors, such as the speed of the train, the trend toward greater annual tonnage, the radius of the curve, and other elements. In general, rail-seat abrasion is a vexing problem in the railroad arts.
Former types of rail pads, which are elastomeric, deform and then recover under the changing stress of dynamic loading, such as occurs when the numerous axles of a train apply a compressive loading to the pads and then as each axle successively passes by until the next axle once again repeats the loading process.
The deformation of an elastomer (within the elastic limit) is well known in the mechanical arts. Compression of an elastomer inevitably results in its lateral deformation. The amount of this deformation is mathematically expressed by Poisson's ratio where Poisson's ratio is equal to the unit lateral deformation divided by the unit longitudinal deformation. Average values of Poisson's ratio may then be calculated for any type of material.
When an elastomeric object, such as a rail pad, experiences a downward (i.e., a vertical) force applied thereto, such as when an axle of a rail car applies a load to the pad, it undergoes compression due to the load being vertically applied and it must, accordingly, expand in other directions. Therefore the pad will deform horizontally.
When the compressive force is withdrawn, that is when the axle of the rail car passes beyond the rail pad, the additional (i.e., dynamic) loading is removed causing the elastomeric rail pad to both rise (i.e., to decompress) and also to retract horizontally, again in reverse compliance with Poisson's ratio.
As there are many axles in both passenger and freight trains that periodically pass over each rail pad there is considerable back and forth horizontal motion of the rail pad that is occurring. Multiply this event times all of the railroad ties and then multiply that number by two, because there are two railroad pads per tie, (i.e., one at each rail) to obtain an idea of the scope of the problem, which extends to all railroad pads.
This type of motion in the railroad industry is known as “scrubbing” or sometimes as “scuffing”. The rail pad literally scrubs that portion of the railroad tie upon which it rests. This scrubbing action eventually abrades the top of the rail tie at the rail-seat area.
Due to scrubbing, the concrete is abraded (i.e., worn) into a dust that is sloughed off and carried away by rain and wind, thereby forming an ever deepening (in depth) pocket in the railroad tie at the rail-seat into which the rail pad increasingly descends. Scrubbing abrades the rail pad as well, thereby also contributing to premature rail pad disintegration.
The scrubbing action of the railroad pad upon the tie, if allowed to persist unchecked, eventually reduces the concrete section at the rail-seat which in turn dramatically decreases the life expectancy of the concrete railroad tie. This necessitates the premature replacement of many such railroad ties.
Eventually, if left unattended, the rail itself may begin to make contact with the tie during times of maximal loading. This subjects the tie to unacceptable levels of stress and must be avoided. It also compromises the electrical insulation of the rail. It also has a deleterious influence on the longitudinal and lateral restraint aspects of the rail fastening system which are, in particular, essential for the proper securance of long-welded rails.
As the rail pad is required and as its dimensions are limited (i.e., its thickness is predetermined), the ties themselves must be replaced or repaired when they become sufficiently abraded (i.e., worn) by the scrubbing action of the rail pads.
It is a well known problem in the railroad industry to replace or repair an otherwise perfectly good concrete railroad tie that is no longer serviceable simply because it has been abraded by the horizontal scrubbing action of the rail pads. Attempts at rail-seat repair are also costly. In summary, rail-seat abrasion is a pervasive problem in the industry.
A satisfactory solution has not been forthcoming because it has been heretofore believed that there is no ideal way around the deleterious effects associated with Poisson's ratio. Various types of railroad pads attempt to ameliorate the problems of dynamic loading via compression of the elastomer but no satisfactory solution to the problem of “scrubbing” is presently known or available.
Pads of composite materials, dual-durometer materials, pads that are laminated and which include a steel-layer therein (three-layer pads), as well as pads having various other shapes, such as protrusions or embedded dimples, also do not completely solve the problem.
Certain of these rail pads, while they do lessen rail seat abrasion, are considerably more expensive to manufacture, for example dual-durometer and s
Le Mark T.
Rinne, Jr. Risto A.
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