This invention is directed to methods and materials for restoring damaged rail seats located on concrete rail ties.
Conventionally, rails are held to rail ties by rail clips or fasteners that bear down on the rail flange. A rail seat insulates the rail from the rail ties. The rail seat can be fabricated of an elastomeric material such as rubber, polyurethane, ethyl vinyl acetate or high-density polyethylene
U.S. Pat. No. 5,173,222 (“US '222”), which is incorporated herein by reference, relates to a method and apparatus for repairing damaged concrete rail ties. Concrete rail ties have been found to be prone to wear particularly in sandy and wet locations or on steep grades where the locomotives use sand for traction. US '222 explains the cause of this wear. US '222 provides a method and apparatus for repairing rail tie damage utilizing an abrasion resistant composition and an abrasion plate as described therein.
As shown in the drawings of US '222, a rail seat 4 is disposed on a rail tie 1. The tie 1 is surrounded by ballast 2. The rail seat 4 is defined by the edges of the rail tie 1 and the rail clamp shoulders 3, which are embedded in the concrete tie 1 and adapted to hold the rail clamps (not shown) that bear down on the flange of the rail (not shown). The damaged rail seat is repaired by filling the worn recess 5 with a rail seat epoxy composition. An abrasion plate 6 (also referred to as an attenuating pad) can be bonded to the repaired rail seat.
US '222 identifies two problems. First, abraded rail ties need to be repaired quickly enough to limit hold up of train traffic to an acceptable time. Second, badly abraded rail seats need to be restored to their original dimensions.
The paste of US '222 employs an abrasion resistant material and a curable epoxy resin material. This epoxy resin is used for repairing damaged rail seats and also for reducing further abrasion. However, even when applied in a relatively thin layer, the cure time can take 12 to 36 hours at typical ambient temperatures. This is completely unacceptable from a train operator's point of view.
If the trains are running even slowly over the freshly repaired rail seats, and if the epoxy is still in a plastic state, it will run-off. This will disrupt the true level of the rail seat, causing cavities to form in the rail seat material. This results in improper bonding to the abrasion plate. All of these factors will lead to subsequent failure of the rail seat.
US '222 attempts to overcome these problems by providing a method of repairing a rail tie comprising applying an abrasion resistant composition which includes a curable epoxy binder to the eroded area of the rail tie, pressing the composition into place, and then heating the applied composition for a period sufficient to cure the epoxy binder. The rail plate can be placed on to the rail seat over the area to be repaired so that it becomes bonded using the epoxy binder repair composition to the rail tie with the application of heat and pressure using the hot box device 10 described in detail in US '222.
USPTO Backgrounds
USPTO Backgrounds