Elastomeric pad between railroad rail and railroad tie

Abstract

In a railroad track comprising a railroad rail having a lower flange and a railroad tie made from concrete, a polyurethane pad is mounted between the lower flange of the rail road rail and an upper surface of the railroad tie. A bonding layer at least as flexible as the polyurethane pad is bonded to a lower surface of the polyurethane pad. An adhesive layer is bonded to the upper surface of the railroad tie. The bonding and adhesive layers are bonded to each other, whereby the polyurethane pad and the railroad tie are bonded to each other via the bonding and adhesive layers. Preferably, the adhesive layer comprises a methacrylate ester composition, and the bonding layer comprises either a product of polymerizing a solution of methyl methacrylate copolymer in n-butyl acrylate monomer with an addition of cumene hydroperoxide to the solution or a product of curing or drying a water-based acrylic emulsion. Alternatively, the bonding layer is a product of polymerizing a solution of a thermoplastic elastomer in methyl methacrylate monomer. The solution may have an addition of 1% (by volume) of cumene hydroperoxide to catalyze polymerization. The solution may have a sprayed coat of a dispersion of benzoyl peroxide in a plasticizer or in water to catalyze polymerization.

Description

TECHNICAL FIELD OF THE INVENTION

This invention pertains to an elastomeric pad, such as a polyurethane pad, which is mounted between a lower flange of a railroad rail and a railroad tie, for example a tie made of concrete. A bonding layer interposed between the elastomeric pad and the railroad tie is bonded to the elastomeric pad and an adhesive layer interposed therebetween is bonded to the bonding layer and to the railroad tie, whereby the elastomeric pad and the railroad tie are bonded to one another via the bonding and adhesive layers. Preferably, an acrylic and a methacrylate ester are used for the respective layers.

BACKGROUND OF THE INVENTION

Commonly, metal clips or clamps that engage embedded supports are used for securing steel railroad rails to concrete railroad ties, and non-conducting insulators are used to insulate the clips or clamps from the railroad rails. Metal clips or clamps of a type exemplified in Leeves U.S. Pat. No. 4,757,945, which when issued was assigned to Pandrol Limited of London, England, and metal clips or clamps of a type exemplified in Young U.S. Pat. No. 5,110,046, which when issued was assigned to McKay Australia Limited of Maidstone, Australia, are used widely in North America.

Commonly, when such clips are used, elastomeric pads are disposed between the lower flanges of the railroad rails and the railroad ties for cushioning the railroad rails and for insulating the rails electrically from the ties and from other underlying structures. Although ethylene vinyl acetate (EVA) rubber and other pads have been used widely for many years, polyurethane pads offering superior performance have become available commercially from ITW Irathane (a unit of Illinois Tool Works Inc.) of Hibbing, Minn., under its IRATHANE trademark.

Deterioration of the elastomeric pads and erosion of the concrete ties can occur if water infiltrates and freezes between the pads and the ties or if sand, which is used commonly to increase traction on grades, or debris infiltrates therebetween. Such deterioration and erosion problems can be quite severe, particularly under high loadings, in regions where weather conditions vary widely from summer to winter, at sharp curves, and at steep grades. Such deterioration and erosion problems can result in so-called "tie seat abrasion", which if severe can result in a railroad tie being judged unsafe for further service in a railroad track and having to be replaced.

Prior efforts to address such deterioration and erosion problems are disclosed in Buekett U.S. Pat. No. 4,925,094. As disclosed therein, a stainless steel or other non-corrodible metal or plastic plate is cast into an upper surface of a concrete tie. A rubber or plastic pad is interposed between the lower flange of a railroad rail and the plate that has been cast into the tie. The pad merely rests upon the plate and is free to move relative to the cast-in-place plate, held only by the clips.

Other efforts to address such deterioration and erosion problems are disclosed in Young U.S. Pat. No. 5,110,046. As disclosed therein, either an abrasion-resistant plate of an unspecified material is bonded to the upper surface of a concrete tie by an adhesive layer, epoxy resin adhesives being preferred, or a high density polyethylene (HDPE) closed cell foam is interposed between the abrasion-resistant plate and the upper surface of the concrete tie. In either instance, a rubber, polyurethane, or other elastomeric pad is interposed between the lower flange of a railroad rail and the upper surface of the concrete tie. Again the elastomeric pad merely rests upon the plate, held in place by clips, and is free to move relative to the adhesively bonded or foam-separated plate.

As a matter of related interest, Brown U.S. Pat. No. 5,261,599 discloses an elastomeric pad having resiliently deformable sealing portions, which are intended to form a watertight seal between the pad and the upper surface of a railroad tie, such as a concrete tie.

In U.S. patent application Ser. No. 08/333,522, supra, a composite pad is disclosed, which addresses such deterioration and erosion problems. The composite pad comprises an elastomeric pad, such as a polyurethane pad, to underlie the rail flange and a bonding member, such as a galvanized, organically coated, steel plate, or a rigid, polymeric film or sheet to overlie the railroad tie. An adhesive layer, for which a methacrylate ester composition is preferred, is employed for bonding the composite pad to the railroad tie. Preferably, a polyurethane pad is cast onto a steel plate, whereby the steel plate is bonded directly to the polyurethane pad. Because of differential shrinkage, however, it has been found that undesirable warpage of the composite plate can occur when a polyurethane pad is cast onto a steel plate or rigid, polymeric film or sheet.

SUMMARY OF THE INVENTION

Further addressing such deterioration and erosion problems but avoiding undesirable warpage, this invention contemplates that an elastomeric pad is mounted between the lower flange of the railroad rail and an upper surface of the railroad tie, that a bonding layer at least as flexible as the elastomeric pad is bonded to the elastomeric pad, and that an adhesive layer is interposed between the elastomeric pad and the railroad tie and is bonded to the bonding layer and to the railroad tie, whereby the elastomeric pad and the railroad tie are bonded to one another via the bonding and adhesive layers.

Preferably, the elastomeric pad is a polyurethane pad, and the adhesive layer comprises a methacrylate ester composition. Preferably, the bonding layer comprises an acrylic composition. It is convenient to refer to the elastomeric pad, to which the bonding layer is bonded, as a composite pad.

According to one proposed embodiment, the acrylic composition is a product of polymerizing a solution of methyl methacrylate copolymer in n-butyl acrylate monomer. The solution may have an addition of cumene hydroperoxide to catalyze polymerization. According to another proposed embodiment, the acrylic composition is a product of curing or drying an acrylic emulsion, which may be water-based.

Alternatively, the bonding layer is a product of polymerizing a solution of a thermoplastic elastomer in methyl methacrylate monomer. The solution may have an addition of 1% (by volume) of cumene hydroperoxide to catalyze polymerization. The solution may have a sprayed coat of a dispersion of benzoyl peroxide in a plasticizer or in water to catalyze polymerization.

These and other objects, features, and advantages of this invention are evident from the following description of two alternative embodiments of this invention with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary, cross-sectional view of a railroad rail having a lower flange, a railroad tie made from concrete, and a composite pad, together with associated clips, supports, and insulators, in a first embodiment of this invention.

FIG. 2 is a plan view of the first embodiment shown in FIG. 1.

FIG. 3 is a greatly enlarged, fragmentary sectional view taken along line 3--3 of FIG. 2, in a direction indicated by arrows.

FIG. 4 is a plan view of a second embodiment of this invention.

FIG. 5 is a somewhat enlarged, fragmentary sectional view taken along line 5--5 of FIG. 4, in a direction indicated by arrows.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS

As shown in FIG. 1 in a first embodiment of this invention, a composite pad 10 is mounted between a railroad rail 12 made from steel and a railroad tie 14 made from concrete. As mounted between a lower flange 16 of the railroad rail 12 and an upper surface 18 of the concrete tie 14, the elastomeric pad 10 cushions the railroad rail 12 and insulates the railroad rail 12 electrically from the concrete tie 14.

Two supports 20 are embedded in the concrete tie 14 and extend upwardly from the upper surface 18. Two clamps 22 are provided, each engaging one of the supports 20 and pressing against one side of the lower flange 16 of the railroad rail 12, via an insulator 24 bearing on the composite pad 10, so as to secure the railroad rail 12 to the concrete tie 14.

In each illustrated embodiment, the composite pad 10 is configured so as to coact with metal clips or clamps known for securing railroad rails to railroad ties and comprises a polyurethane pad 30 and a bonding layer 40, which is bonded to the polyurethane pad 30 so as to cover the lower surface of the polyurethane pad 30. Preferably, the polyurethane pad 30 is a similar to the polyurethane pads that have become available commercially from ITW Irathane, supra, and is cast in an orientation that is inverted from its orientation in use (see FIGS. 3 and 5) except that a curable composition to provide the bonding layer 40 when cured is applied to the upper surface of the polyurethane pad 30, as cast, before the polyurethane pad 30 has been cured completely, whereupon the curable composition to provide the bonding layer 40 and the polyurethane pad 30 are cured together until cured completely.

Moreover, an adhesive layer 50 is used to bond the composite pad 10 to the concrete tie 14, at the bonding layer 40 and at the upper surface 18 of the concrete tie 14, so as to resist relative movement between the polyurethane pad 30 and the concrete tie 14 and so as to retard infiltration of sand, water, or debris between the composite pad 10 and the concrete tie 14.

Preferably, the adhesive layer 50 in its uncured state is deposited on the upper surface 18 of the concrete tie 14, whereupon the composite pad 10 is pressed onto the adhesive layer 50 so as to spread the adhesive layer 50 until the adhesive layer 50 covers the exposed surface of the bonding layer 40 bonded to the polyurethane pad 30. It is permissible for some of the adhesive layer 50 to be thus extruded beyond the margins of the composite pad 10. Thereupon, the adhesive layer 50 is allowed to cure so that the adhesive layer 50 is bonded not only to the bonding layer 40 bonded to the polyurethane pad 30 but also to the concrete tie 14, whereby the composite pad 10 and the concrete tie 14 are bonded to one another via the bonding layer 40 and the adhesive layer 50.

According to one proposed embodiment, the bonding layer 40 comprises an acrylic composition that is a product of polymerizing a 20% (by volume) solution of methyl methacrylate copolymer in n-butyl acrylate monomer. The solution has an addition of 1% (by volume) cumene hydroperoxide to catalyze polymerization and is applied by air spraying, which is preferred, or by coating, printing, or pouring. After the solution is applied to the polyurethane pad 30 while the polyurethane pad 30 is partially cured, the bonding layer 40 is cured (polymerized) by activation of the peroxide during further curing of the polyurethane pad 30 (at 250.degree. F.) until the bonding layer 40 and the polyurethane pad 30 are cured completely.

According to another proposed embodiment, the bonding layer 40 comprises an acrylic composition that is a product of curing or drying a water-based acrylic emulsion, which is cured by drying. Either of two water-based acrylic emulsions available commercially from Johnson Wax of Racine, Wis., under trade designations "Joncryl 74" and "Joncryl SCX 2660" respectively are suitable.

Alternatively, the bonding layer 40 is a product of polymerizing a solution of a thermoplastic elastomer in methyl methacrylate monomer. As an example, the bonding layer may be a product of polymerizing a solution of 20% (by volume) of Kraton D1117 thermoplastic elastomer available commercially from Shell Chemical Co. of Houston, Tex., either with an addition of 1% (by volume) of cumene hydroperoxide to catalyze polymerization, whereupon heat curing is employed, or with a sprayed coat of a dispersion of benzoyl peroxide in a plasticizer or in water to catalyze polymerization, whereupon either ambient curing or heat curing is employed. The dispersion may comprise AFR400 benzoyl peroxide available commercially from Elf Atochem North America, Inc. of Philadelphia, Pa.

Preferably, the adhesive layer 50 is comprised of a methacrylate ester composition, namely the methacrylate ester composition disclosed in a copending application, U.S. patent application Ser. No. 08/310,709 (ITW Case 7046) which was filed on Sep. 21, 1994, by Fred A. Kish et al. for A METHACRYLATE ESTER COMPOSITION FOR ANCHORING MATERIALS IN OR TO CONCRETE OR MASONRY, which is assigned commonly herewith, and the disclosure of which is incorporated herein by reference.

Although the methacrylate ester composition discussed in the immediately preceding paragraph does not bond well to polyurethane, such as that used for the polyurethane pad 30, such methacrylate ester composition bonds well to any of the acrylic compositions specified above.

By this construction, any relative movement between the railroad rail 12 and the concrete tie 14 that is caused by a train rolling over the rail 12 will be between the bottom surface 58 of the rail flange 16 and the top surface 54 of the polyurethane pad 30.

Since the adhesive layer 50 is bonded to the concrete tie 14 below the composite pad 10 so as to retard infiltration of sand, water, or debris between the composite pad 10 and the concrete tie 14, the deterioration and erosion problems discussed above are alleviated, even under high loadings, in regions where weather conditions vary widely from summer to winter, at sharp curves, and at steep grades.

Various modifications may be made in the first and second embodiments described above without departing from the scope and spirit of this invention.

Claims

1. In a railroad track, a combination comprising a railroad rail having a lower flange, a railroad tie, an elastomeric pad mounted between the lower flange of the railroad rail and an upper surface of the railroad tie, the elastomeric pad having an upper surface and a lower surface, the upper surface underlying and being in direct contact with the lower flange of the railroad rail, means comprising a bonding layer and an adhesive layer for bonding the elastomeric pad to the railroad tie, the bonding layer being bonded to the lower surface of the elastomeric pad, the bonding layer being at least as flexible as the elastomeric pad, the adhesive layer bonded to the upper surface of the railroad tie, the bonding and adhesive layers being bonded to each other, whereby the elastomeric pad and the railroad tie are bonded to each other via the bonding and adhesive layers so as to resist relative movement between the elastomeric pad and the railroad tie, the combination permitting relative movement between the railroad rail and the elastomeric pad.

2. In a railroad track, a combination comprising a railroad rail having a lower flange, a railroad tie, a polyurethane pad mounted between the lower flange of the railroad rail and an upper surface of the railroad tie, the polyurethane pad having an upper surface and a lower surface, the upper surface underlying and being in direct contact with the lower flange of the railroad rail, a bonding layer bonded to the lower surface of the polyurethane pad, the bonding layer being at least as flexible as the polyurethane pad, and an adhesive layer bonded to the upper surface of the railroad tie, the bonding and adhesive layers being bonded to each other, whereby the polyurethane pad and the railroad tie are bonded to each other via the bonding and adhesive layers so as to resist relative movement between the polyurethane pad and the railroad tie, the combination permitting relative movement between the railroad rail and the railroad tie.

3. The combination of claim 2 wherein the adhesive layer comprises a methacrylate ester composition.

4. The combination of claim 3 wherein the bonding layer comprises an acrylic composition.

5. The combination of claim 4 wherein the acrylic composition of the bonding layer is a product of polymerizing a solution of methyl methacrylate copolymer in n-butyl acrylate monomer.

6. The combination of claim 4 wherein the acrylic composition of the bonding layer is a product of polymerizing a solution of methyl methacrylate copolymer in n-butyl acrylate monomer with an addition of cumene hydroperoxide to the solution.

7. The combination of claim 4 wherein the acrylic composition of the bonding layer is a product of curing or drying an acrylic emulsion.

8. The combination of claim 4 wherein the acrylic composition of the bonding layer is a product of curing or drying a water-based acrylic emulsion.

9. The combination of claim 3 wherein the bonding layer is a product of polymerizing a solution of a thermoplastic elastomer in methyl methacrylate monomer.

10. The combination of claim 9 wherein the bonding layer is a product of polymerizing a solution of a thermoplastic elastomer in methyl methacrylate monomer with an addition of cumene hydroperoxide.

11. The combination of claim 9 wherein the bonding layer is a product of polymerizing a solution of a thermoplastic elastomer in methyl methacrylate monomer with a sprayed coat of a dispersion of benzoyl peroxide in a plasticizer.

12. The combination of claim 9 wherein the bonding layer is a product of polymerizing a solution of a thermoplastic elastomer in methyl methacrylate monomer with a sprayed coat of a dispersion of benzoyl peroxide in water.