Title:
Ozone and Chemical Resistant Coating for Railway Line Elastomeric Components
Kind Code:
A1


Abstract:
Elastomeric pads are shown for positioning on top of railroad ties. Pre-cast concrete panels that are commonly provided at railway grade crossings between and alongside the rails rest on the pads. The pads may be extruded from a variety of natural or synthetic elastomeric materials. The pads include a panel or body formed of the elastomeric material with an exterior surface. A synthetic, polymeric coating is applied to at least selected portions of the exterior surface of the elastomeric body. The coating provides improved properties which allow more standard elastomers to be utilized for the main body of the component. The coatings can also be applied to railroad tie boots to provide increased ozone resistance.



Inventors:
Corbett Jr., Bradford G. (Fort Worth, TX, US)
Hirst, James Richard (Fort Worth, TX, US)
Application Number:
11/678166
Publication Date:
08/30/2007
Filing Date:
02/23/2007
Primary Class:
International Classes:
E01B9/38
View Patent Images:
Related US Applications:
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20070012794Anti-mud pumping railroad ties, pre-plated railroad ties and related methodsJanuary, 2007Ollendick et al.
20090121035Fixed carriageway for rail vehiclesMay, 2009Kowalski
20040232253RECYCLED RUBBER CROSSTIENovember, 2004Hansen
20070108308STACKED RAILWAY TIEMay, 2007Keightley
20070283838TOUR AND LEISURE CART MANAGEMENT SYSTEM AND RAIL TRACK MAINTENANCE METHODDecember, 2007Hwang
20090301343Bogie Lateral Movement-Limiting SystemDecember, 2009Sakanoue et al.
20080142611Railway Ground CrosstieJune, 2008Scobie
20010048034DRIVING CIRCUIT FOR TOY CARSDecember, 2001Epping
20030164403Elastomeric railroad crosstieSeptember, 2003Fitch et al.



Primary Examiner:
SMITH, JASON C
Attorney, Agent or Firm:
WHITAKER CHALK SWINDLE & SCHWARTZ PLLC (FORT WORTH, TX, US)
Claims:
I claim:

1. An elastomeric component used in a railway line emplacement, the elastomeric component comprising: an elastomeric body having an exterior surface; a synthetic, polymeric surface coating applied to at least selected portions of the exterior surface of the elastomeric body, the surface coating comprising a one-part, room temperature curing hydrogenated nitrile butadiene rubber base coating.

2. The elastomeric component of claim 1, wherein the component is a railway tie pad.

3. The elastomeric component of claim 1, wherein the component is a railway line boot or shoe.

4. The elastomeric component of claim 1, wherein the surface coating is selected from the family of coatings sold commercially by the Lord Corporation as the HPC family of coatings.

5. A tie pad of elastomeric material for use atop an elongate tie of a track having rails supported by a plurality of said ties, the tie pad comprising: (a) a main panel locatable on said tie and having a length, width, and a first side margin extending longitudinally along said main panel, the top surface of said main panel generally defining a plane; (b) a first flange, adjacent said first side margin of said main panel and engagable with said tie, said first flange having an inner margin connected to said first side margin of said main panel; and (c) a first shoulder projectable above said plane and located proximate said interconnection of said first side margin of said main panel and said inner margin of said first flange, said first shoulder extending longitudinally for at least a portion of said main panel; and a synthetic, polymeric surface coating applied to at least selected portions of the exterior surface of the main panel, the surface coating comprising a one-part, room temperature curing hydrogenated nitrile butadiene rubber base coating.

6. A railroad tie emplacement, comprising: a rail supported atop a railroad tie; a railroad tie boot formed of a resilient elastomer, the boot having an initially open interior, a bottom, surrounding sidewalls and an open top; a railroad tie located within the railroad tie boot, the tie having an exposed upper surface which is peripherally surrounded by an upper exposed lip of the railroad tie boot; a concrete substrate surrounding the bottom and sidewalls of the railroad tie boot; and wherein a synthetic, polymeric surface coating is applied to at least the exposed tip portion of the railroad tie boot, the surface coating comprising a one-part, room temperature curing hydrogenated nitrile butadiene rubber base coating.

7. The tie emplacement of claim 6, wherein the railroad tie is formed from a material selected from the group consisting of concrete and wood.

8. The tie emplacement of claim 6, wherein the resilient elastomer which is coated with the surface coating is a styrene butadiene rubber.

9. The tie emplacement of claim 8, wherein the surface coating is selected from the family of coatings sold commercially by the Lord Corporation as the HPC family of coatings.

10. The tie emplacement of claim 8, wherein the surface coating has the following published specifications:
AppearanceClear Liquid with Orange Hue
Viscosity, cps @ 77° F. (25° C.) 20-100
Density
Lb/gal6.72-6.92
(kg/m3)(805.23-829.20)
Solids Content, %
by Weight10.6
by Volume7.7-8.8
Flash Point (Seta), ° F. (° C.)60 (15.6)
SolventsMethyl Ethyl Ketone (MEK)


Description:

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority from the earlier filed provisional application, serial number 60/776,380, filed Feb. 24,2006, entitled “Impact, Abrasion and Chemical Resistant Coating For Railway Line Pads and Boots.”

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to surface coatings which provide enhanced performance properties for elastomeric components used in railway line emplacements including railway line pads and boots and to goods produced with such coatings. Specifically preferred coatings are used to provide improved weathering, anti-vibration, abrasion and oil and chemical resistance characteristics for such goods. The invention also relates to assemblies of rails, pads, boots and rail foundation members when secured together in a railway line emplacement.

2. Description of the Prior Art

A variety of rubber or elastomeric type goods are used in the railroad industry including railway emplacements. For example, rail pads are interposed between the lower surface of a railway rail and a foundation member on which the rail stands and to which it is usually secured. The rail foundation member may be a concrete or steel sleeper extending across the railway track, or a slab or plate, for example, running along the length of the rail. The purpose of the rail pad is to protect the foundation member from impulsive and other loads from passing rail traffic, to compensate for any unevenness in the foundation member and, where the rail is electrical, to provide some electrical insulation between the rail and the foundation member.

One application of the present invention relates to the construction of railway grade crossings where railroads intersect vehicular roads, and in particular to such grade crossings where a portion of the vehicular roadway includes concrete panels that are supported atop the railroad ties of the railroad track. In railway emplacements of this type, cast concrete “filler” panels or slabs are used to fill the spaces between the rails and along the outer side of each rail to provide a roadway surface. Such concrete panels rest on top of the railroad ties, with each panel covering several ties and having its top surface aligned with the roadway surface to establish a smooth crossing for vehicles. Despite having been engineered to withstand the weight of vehicular traffic, these panels are subject to wear and can fail prematurely.

The concrete filler panels used in grade crossings are typically not loaded other than by their own weight. When a heavy truck passes over the crossing, the panels are subjected to bending stresses, tending to deflect downward where the tires of vehicles pass over areas of the panels that are not directly supported by the ties. If the tops of the ties are not even with each other, a panel might bridge the distance between several ties without actually contacting the tops of intermediate ties. If a panel is flexible enough, under a heavy road-traffic load it might deflect so that the undersurface of the panel is brought into contact with the tops of low-standing intermediate ties. Once the panel touches the top of a low-standing tie, it is then supported by that tie and does not deflect further. In some cases, it is not the bending stress sustained by the entire panel that causes the panel to fail. Rather, it is the fact that the undersurface of the panel is in tension as it repeatedly strikes against the upper surface of the tie so that tiny chips are broken away from the bottom surface of the panel, leading to eventual surface cracks and propagation of the cracks. Premature failure of a panel in such railway crossings is most likely to occur when the ties are unusually uneven. Although the tops of all the ties should be at the same height at the rail-attachment point, the top surfaces of the ties are often not at exactly the same heights except at the rail-attachment points.

Variation in ties and concrete filler panels is taken into account when the panels are designed, and the amount of bending stress the panel might experience should not ordinarily cause the panel to fail. However, the panels still do fail, and in order to counter premature failure of the concrete panels, pads of rubber or rubberlike materials have been used atop the ties to distribute the loads of motor vehicle traffic more evenly. The presence of rubber tie pads between the ties and the panels distributes the forces caused by projecting irregularities on the tops of the ties, helps compensate for uneven ties, reduces the pressure applied to the bottom surfaces of the panel when it is in tension and protects the panel from repeated impact on the ties.

Another specific application for the present invention relates to railroad tie “boots.” In many parts of the world, Sonneville® low-vibration track (LVT) and floating slab track with soft baseplates are being used to reduce vibration transmission to stations and to cut re-radiated noise from structures. These two major trackforms provide different levels of attenuation at various frequencies across the noise spectrum found along the tunnels and viaducts. For example, a 60 kg/m flat bottom tunnel rail which is commonly used in Europe, especially on French high speed routes, may be held in place with sprung bolts holding the rail to the sleeper blocks. Due to the relative constant temperature of the tunnel the rails do not have expansion joints and are continuously welded for their entire length except at the emergency crossovers. In the open the rails are provided with expansion joints to reduce the effect of buckling.

The Sonneville® system, which is used to support the rails, comprises of pairs of reinforced concrete blocks to support the rails at 600 mm intervals. For resilience, the rails sit on ‘H’ shaped pads of microcellular ethyl-vinyl-acetate (EVA) with a grooved surface. Screw fastenings attach the pads to the blocks. Nylon clips and EVA pads provide electrical insulation to ensure the proper operation of the track circuits in the tunnel conditions which are damp and salty. A rubber boot surrounds the bottom of the sleeper block providing further insulation.

At the present time, natural rubber, e.g., styrene butadiene rubber (SBR), is often used in railway pad, boot and component installations of the above type because its dynamic stiffness is relatively frequency insensitive. However, natural rubber or other existing elastomer compounds are not satisfactory to meet the requirements in all applications. There are various materials that will solve one problem, but not all combinations of problems. In the case of railway pads of the type described, the elastomer must be elastic so as to be able to withstand impact forces, must be strong and rugged enough to withstand the physical contact typically encountered without being torn or ruptured, and must be impervious and resistive to oil and other contaminants which are encountered.

Particularly in Europe, new railway line standards require that the railroad tie boots, for example, be ozone resistant. The raw SBR materials which have been used in the past will not meet the new standards for ozone resistance. A need exists, therefore, for a replacement product for the various elastomeric railway line components discussed above which will meet the increased performance characteristics now be imposed.

Despite the various improvements which have occurred in materials and manufacturing techniques applied to railway boots, pads, shoes and other elastomeric components, a need exists for a manufacturing technique which will allow the use of traditional elastomeric compounds while providing enhanced properties for these particular end applications.

A need also exists for such a technique which is economical to implement so that elastomeric goods are provided which are impact, ozone and oil resistant and yet are manufactured from more economical starting materials.

A need also exists for such a technique which can be implemented by dipping or spraying a coating on an exposed exterior surface of an elastomeric railway line component to give the goods enhanced performance and endurance characteristics.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a railway pad, boot or other elastomeric component used in a rail pad assembly which component has improved weatherability, ozone, impact, abrasion and oil and chemical resistance characteristics when in place in a railway installation.

The preferred elastomeric components of the invention include an elastomeric body having an exterior surface which is coated with a synthetic polymeric coating. One preferred coating is a synthetic polymer, preferably thermoplastic, most preferably a polyurethane high performance coating that will withstand severe temperature, chemical attack and abrasion. One such coating is manufactured by Lord Chemical Products of Erie, Pa., as the CHEMGLAZE® polyurethane coating. This is a high performance coating that will withstand severe temperature, chemical attack and abrasion. Another version of the coating is the Lord Elastomeric Coating manufactured by Lord Mechanical Products Division and marketed under the tradename ENDURALAST™ Tire Coating. The synthetic polymeric coatings of the invention can be applied by any technique generally used in the industry. For example, the coatings can conveniently be applied by spraying or dipping on at least selected external surfaces of the elastomeric element followed by a drying period as recommended by the manufacturer. In some cases, the coating may be strategically applied to only selected exposed areas of the elastomeric component under consideration.

Another particularly preferred coating is manufactured by Lord Chemical Products, as the LORD HPC-5C™ coating. This coating is a one-part, room temperature curing hydrogenated nitrile butadiene rubber. In use, the base rubber material, such as styrene butadiene rubber, is provided with a single coat of CH7701™ primer plus a single coat of HPC-5C™ topcoat. The addition of the HPC-5C™ coating allows styrene butadiene rubber to meet ozone requirements, meet tensile strength and elongation after aging requirements, minimize flame propagation, decrease fume toxicity, and increase oil and fluid resistance.

Additional objects, features and advantages will be apparent in the written description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial, schematic view showing the use of concrete filler panels at a railway grade crossing, and showing the placement of elastomeric tie pads between the ties and the concrete filler panels.

FIG. 2 is an isolated view of a railroad tie and tie boot as used in the practice of the present invention.

FIG. 3 is a cross sectional view of a railway tie emplacement showing the rubber boot of the invention and the surrounding concrete substrate.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1 of the drawings, there is shown a railway grade crossing, designated generally as 10. The crossing 10 includes a railroad track 12 having parallel rails 14, 16 supported on cross ties 18, which are typically set into ballast. The ties 18 are preferably of concrete but could be of wood or other material. A road 20 for vehicular traffic is shown crossing the railway track 12. Concrete filler panels 24 and 26 have respective upper surfaces 28 and 30 located at substantially the same height as the upper surface 32 of the road 20 on either side of the crossing 10. In the particular grade crossing 10 shown in FIG. 1 the road 20 is sufficiently wide such that two wide panels 24 arranged end-to-end are needed between the rails 14 and 16. Similarly, on each side of the track 12 two smaller side panels 26 have been placed end-to-end outside the rails 14 and 16 with their upper surfaces 30 aligned with the road surface 32 of the road 20. In constructing the grade crossing 10 the concrete filler panels 24 and 26 are lowered into place with a suitable hoist, using hook eyes 34 which are provided in the panels for that purpose. Elastomeric rail boot or seal strips 36 and 38 are installed between the panels 24, 26, and the rails 14, 16, as shown also in FIG. 2. Tie pads 40, 42 are located directly on the tops of the ties 18. The filler panels 24 rest on top of the gauge pads 40 and the field panels 26 rest on top of the field pads 42.

In the description which follows, the invention will primarily be described with respect to the tie pads 40, 42. However, it will be understood that the coating techniques of the invention could be applied to tie pads, boots or seal strips, or other elastomeric components commonly found at railway emplacements. For example, FIGS. 2 and 3 show a concrete tie 11 surrounded by a rubber boot 13 which, in turn is encased in a surrounding concrete substrate 15 (FIG. 3). Note that the top lip 17 of the rubber boot 13 is exposed to the atmosphere and therefore subject to ozone attack.

Returning to FIG. 1, the tie pads 40 and 42 must be correctly located and kept in place on top of the ties 18 so it is important that the pads resist movement once they are installed. Preferably, the tie pads are held in position on the ties by the relationships between the respective shapes of the tie pads and the ties. As shown in FIG. 1, each tie pad 40, 42 can be held in position on the width of each tie 18 by flanges 44, 46 that rest on a diagonal surface 48 of the chamfered upper longitudinal edges of the ties 18. The pads 40, 42 also need to be held in the proper positions along the length of the ties 18. This may be done in a number of ways. For example, the pad 40 can be restrained from longitudinal movement along the length of tie 18 by abutting against the rail attachment hardware 50. Alternatively, shoulders on the tie 18, attachment to the panels 24 and 26 or abutment against adjoining structure such as ballast or the roadway 20 may be used.

As shown in FIG. 1, the pads 40 and 42 support the filler panels 24 and 26 atop the ties 18, preventing direct contact between the tops of the ties and the undersides of the panels. When the bottom surface of panel 24 or 26 is loaded in tension by the weight of a vehicle on the upper surface 28 or 30 of one of the filler panels, surface irregularities such as bumps on the top surface of the ties 18 do not press directly against the bottom surface of the panels, and the forces resulting from such irregularities are spread over a larger area by the elastic deformation of the tie pads 40 and 42 at such points.

A typical pad is at least about 6 mm in overall thickness and may have an overall thickness of about 7 and 15 mm, preferably between 6.5 and 12 mm. The pad body is preferably formed of a high resilient elastomer (between 30 and 90% rebound value, preferably between 55 and 75); and is typically between 45 and 95 shore A hardness (preferably between 60 and 90). The pad bodies have, in the past, been formed primarily of a natural or synthetic rubber, or other type elastomer having the desired performance characteristics.

For example, tie pads 40 and 42 have been formed in the past by extruding a suitable thermoplastic elastomeric material from a suitable tool or die. A suitable material for the main body of the tie pads 40 and 42 is a rubber or rubberlike material with an ability to withstand weather conditions and to remain elastic throughout the expected range of temperatures in the environment of the grade crossing 10. For example suitable materials would preferably have a hardness in the range of about 25 to 80 Shore A Durometer.

In order to meet the increased performance standards, particularly ozone attack, one possible solution to the problem would be to substitute a new material for the natural rubbers, (SBR's, etc.) used in the past. For example, one more exotic material which has been used in the past in the railway environment is an extrudable thermoplastic synthetic rubber material called SANTOPRENE®. This material has a typical hardness of 65A and is a combination of highly crosslinked rubber particles in a continuous matrix of thermoplastic material, available from Advanced Elastomer Systems, L. P., of Akron, Ohio.

Despite the improved performance which can be achieved, such as greater weatherability, such more exotic materials greatly increase the cost of the railway line elastomeric component. This is especially true in the case of commodity components such as the railway tie boot, since a typically installation might involve thousands of such boots.

The present invention offers an alternative solution to the previously described problem by providing a coating method for coating the traditional natural type rubber products with a coating which provides the desired enhanced performance characteristics. In the method of the present invention, the elastomeric tie pad bodies 40, 42 are coated with a synthetic elastomeric coating. One class of materials which has been evaluated is sold commercially by Lord Chemical Products of Erie, Pa., as the “Lord Elastomeric Coatings.” These elastomeric coatings have excellent adhesion properties and environmental resistance, and are capable of strains of several hundred percent. It has been found that these coatings may be applied on elastomeric products of the type described to improve appearance, resistance to fluids and resistance to ozone. The coatings can enable a less expensive material to be used in products with characteristics equivalent to more expensive materials. For example, the tie pad bodies 40, 42 might be formed of a natural or synthetic rubber or other less exotic elastomer. The coatings can be colored as well. These coatings can typically be applied by spraying on or dripping at least selected external surfaces of the gasket followed by a drying period as recommended by the manufacturer.

Another class of coating materials which has been evaluated in a polyurethane high performance coating which is manufactured by Lord Chemical Products of Erie, Pa., as the CHEMGLAZE® polyurethane coating. This is a high performance coating that will withstand severe temperature, chemical attack and abrasion. The coating can be applied to any technique generally used in the industry and is conveniently applied by spraying on or dripping at least selected external surfaces of the elastomeric tie boot, pad, or other component, followed by a drying period as recommended by the manufacturer. The spraying technique can be by conventional air atomized spray coating using a spray gun.

The Manufacturers Technical Data for the CHEMGLAZE® product is as follows:

Mix ratio A/B by volume3/1 supplied in premeasured kits
Percent solids (by weight)56
Volatile Organic compounds3.5 lb/gal
Tack Free time30 min.
Physical Properties of Cured Coatings:
Tensile strength ASTM D 4125000 psi
(Method A, Die C)
Percent Elongation ASTM D 412500 percent
(Method A, Die C)
Taber AbraserNo loss
CS17 1000 g/1000 cycles
Durometer Shore A110

Mixing and recommending spray application techniques are given in the manufacturer's REMR Material Data Sheet, CM-SE-1.9.

Another coating which has been evaluated is the Lord Elastomeric Coating manufactured by Lord Mechanical Products Division and marketed under the tradename ENDURALAST™ Tire Coating. This product also has excellent adhesion properties and environmental resistance and is capable of strains of several hundred percent.

The particularly preferred coating used in the present invention is manufactured by Lord as the HPC-5C™ coating. Lord HPC-5C™ is one-part, room temperature curing hydrogenated nitrile butadiene rubber (HNBR) coating which features robust adhesion and exceptional mechanical properties. The HPC-5C™ coating enhances fluid and ozone resistance for elastomeric substrates of the type under consideration, as will be described in greater detail below. HPC-5C™ is clear and colorable, and is composed of a mixture of polymers, organic compounds and fillers dissolved or dispersed in an organic solvent system.

The Lord HPC-5C™ has been found to offer the required characteristics for a coating used on railway line elastomeric components. HPC-5C™ has excellent adhesion, providing strong adhesion to substrate and elongation of up to 600%. Once properly applied, the coating does not crack or peel prior to substrate cracking. HPC-5C™ is also fluid resistant providing a fluid resistant barrier to external surface of elastomeric parts, allowing bulk of component to be made of less expensive, less fluid resistant material. The resulting system offers low cost, high mechanical properties with high fluid and environmental resistance. For example, HPC-5C™ provides excellent resistance to lubricating oils and transmission fluids. In addition, HPC-5C™ is ozone resistant, and provides a barrier to external surface of elastomeric parts of the type under consideration. Resultant systems offer low cost, high mechanical properties with high ozone resistance. Lastly, the HPC-5C is convenient, as application may be completed by spray, brush, dip or rolling coat methods and the coating can be easily incorporated into existing production lines. The coating cures at room temperature, and with hot air dry, it will cure in ten minutes (with full cure and adhesion develop over 48 hours).

Manufacturers Technical Data for the Lord HPC-5™ coating is as follows:

AppearanceClear Liquid with Orange Hue
Viscosity, cps @ 77° F. (25° C.) 20-100
Density
Lb/gal6.72-6.92
(kg/m3)(805.23-829.20)
Solids Content, %
by Weight10.6
by Volume7.7-8.8
Flash Point (Seta), ° F. (° C.)60 (15.6)
SolventsMethyl Ethyl Ketone (MEK)

The method of applying the coatings of the invention will now be described. Before applying the HPC-5C™ coating, the surfaces of all parts intended for coating must are prepared. For example, if exposed metal surfaces are present, these surfaces are preferably cleared with a solvent such as methanol. Wiping is the preferred method, but dipping or spray washing may also be acceptable. Alkaline cleaners may be substituted for the methanol, as well.

The elastomeric portion of railway line component is also preferably given a surface treatment to help ensure successful adhesion. This surface treatment varies depending upon the elastomer. Natural rubber stocks and styrene butadiene rubber stocks can successfully be treated with Chemlok 7701™. The part can be dipped as long as no metal portions come in contact with the Chemlok 7701™. Alternatively, Chemlok7701™ can be brushed or wiped on. For natural rubber stocks with excessive amounts of antiozonants and other additives which may have bloomed to the surface, wiping with 7701 helps to remove these contaminants more effectively. A heavy red or purple residue on the rag as a result of a reaction between the Chemlok 7701198 and the surface additives is a good indication that there are excessive contaminants on the surface. The Chemlok 7701 is generally allowed to flash for 10 minutes or oven bake up to 250° F. (121° C.) for a few minutes. For very soft natural rubber stocks, utilizing a bake cycle during cure as described below may be necessary to obtain adhesion.

In order to mix the HPC-5™, it should be thoroughly stirred by hand or shaken before use. HPC-5 is normally used full strength for brush, dip and roller coat applications. For spray application, dilution up to 1:1 is recommended with ketone type solvents such as MEK.

As mentioned previously, in the preferred embodiment of the present invention, a less expensive rubber, such as SBR, is substituted for a more expensive rubber stock. SBR has acceptable abrasion, wear and tensile qualities, and maybe readily substituted for more expensive rubber compounds with significant cost savings. However, much like natural rubber, SBR offers little resistance to oils and chemicals, and therefore requires additional resistance to ozone, sunlight, and heat. The present coating technique provides enhanced properties for the elastomeric component in question and provides an economical solution to the problem at hand.

As mentioned, there are several conventional techniques for applying the HPC-5C™ coating:

Brushing applies a coating for example using a camel hair or foam brush. The coating should be brushed onto the part in single strokes and dried for about 15 minutes at room temperature. Once dried, a second brushing of the coating will be generally necessary to obtain a desired film thickness in the general range from about 0.100 to about 3.00 mils, e.g., on the order of 0.235 mils. After the second coat is dry, it can be oven cured or cured at room temperature. Heat-assisted drying between coats to speed the process is also acceptable.

Dipping refers to the process of dipping the parts into the coating and removing the elastomeric components with a hanger or some method to hang the part vertically. If possible, it is best to reverse the orientation of the part on each dip so that equal film thickness is obtained on the entire surface of the part. It is preferable to allow the coating to dry for 15 minutes in between dips so that the coating thickness builds fully. Alternatively, the part may be oven dried for a few minutes at 150° F. (66° C.) in between dips.

Spraying can also be used to apply the coatings under consideration. Air pressure on the spray gun should generally be kept under about 30 psi. Oven drying at 150° F. (66° C.) once or twice during spraying may be necessary to build film the desired film thickness and avoid running.

The coatings used in the method of the invention can also have a color additive, such as a suitable pigment, dispersed therein which impart a distinctive color to the coated region of the elastomeric element. Color markings of this type can be used for product identification purposes. Pigments are commercially available from a number of sources such as Cleveland Pigment & Color Co., of Akron, Ohio. These pigments include, by way of example, organic, fluorescent, iron oxide, ultramarine pigments as well as chromium oxide greens and barytes. Another source of pigments is the FDA approved dyes and pigments.

In some applications, it may not be necessary to coat the entire outer surface of the rubber component under consideration. For example, with reference to the railway tie boot of FIG. 3, it will be appreciated that only the top lip 17 is exposed to the atmosphere once the tie is set into the surrounding concrete substrate. Thus, it may be possible to strategically apply a coating layer to only the ultimate exposed areas of the elastomeric component.

The following tests were carried out on SBR elastomeric components. SBR products provided by Maloney Technical Products. The SBR pads were tested for ozone cracking resistance per ISO 1431, with test conditions of 200 parts per hundred million (pphm) ozone concentration, 96 hours, 40 degrees C., 20% tension and crack classification 0 required to pass. The samples were wiped with methanol, then dipped for 2 seconds into Chemlok 7701™ adhesion promoter and allowed to dry. Coating was applied by dipping and air-dried for 3 days prior to testing. One and two coatings of both HPC-5C™ and HPC-6C™ were compared during the test. The following results were obtained, wherein σ (sigma) represents the standard deviation:

CoatingCoating ThicknessPass/fail
None(control)0.000failed
at 48
hours
Coated with 1 coat of HPC-6C ™0.400 mils, σ = 0.068 milspass
Coated with 2 coats of HPC-6C ™0.859 mils, σ = 0.172 milspass
Coated with 1 coat of HPC-5C ™0.235 mils, σ = 0.033 milspass
Coated with 2 coats of HPC-5C ™0.448 mils, σ = 0.077 milspass

The test results show that the proposed HPC-5C™ coating of the SBR material meets the above ozone requirement, whereas an uncoated control sample fails after 48 hours. HPC-5C™ was chosen as the preferred coatings because it dries faster and is a tougher, more abrasion resistant coating.

Other characteristics of the product, such as tensile strength after aging, were also tested. More specifically, the Terramix/Hultec R&D Chemical Division Department Laboratory evaluated the performance characteristics of boots used in the GottHard Tunnel low vibration track (LVT) project for Tiibeton. Test conditions were greater than 12 N/mm2 before aging and ±30% after aging for 60 days at 80° C. The results which were obtained, are given in Table I. It can be seen that the SBR material used in the LVT boot manufacture, when coated according to the teachings of the invention, provides an acceptable product for railway line components.

TABLE I
Gotthard LP-30-33
TestTribeton
Physical PropertyMethodDOC 13/04/06Results
Shore A HardnessD224060 to 8074
IRHD Hardness73
Tensile StrengthD41212min16.1
(Longitudinal or
Transversal), N/mm2
Ultimate ElongationD412250min334
(Longitudinal or
Transversal), %
Compression Set 22 h at7.2
70° C.
Ozone Resistance 96 h atISO1431No CracksNo
40° C., 200 pphm, ApperanceCracks
Rat. 20% E
Accelerated Aging, 72 h atD573
100° C.
Hardness Change, points2
Tensile Strength10min16.3
(Longitudinal or180min286
Transversal), N/mm2
Ultimate elongation
(Longitudinal or
Transversal), %
Accelerated Aging, 60 d atD573
80° C.
Hardness Change, points6
Tensile Change, %30max6.2
Elongation Change, %±70max−25.1
Ash Content, %D29710max1.9
Abrasion of 50% of the boot10Mio CyclesNot
tested in complete system,Tested
load applied in angle 22° F.

An analysis of the likelihood of dangerous conditions being caused by ignition of the components of the invention in a railway installation was obtained by a comparison with Bombardier specification SMP 800C and Boeing specification M-7. These standards relate to maximum concentration levels of several toxic gases allowable upon combustion of materials used in railcars and airplanes respectively. Table II tabulates the results for HPC-5C™ coated SBR material and in all cases the concentration of gases generated in the BSS 7239 test fall well under the maximums allowable.

TABLE II
Terramix SBR LVT Rail Boot Material Plus HPC-5C Coating
Compared with Bombardier Spec SMP 800C and Boeing Spec M-7
Bombardier SMP
LVT Material and800C specBoeing M-7 spec
GasHPC-5C (ppm)(ppm max)(ppm max)
CO350.035003500
HCN0.6100150
SO212.5100100
HCL0.0500500
HF0.0100200
NO23.5100100

As has been noted, a major increase in chemical resistance can be imparted to the elastomeric component by the application of the HPC-5C™ coating. Table III below compares various oil and fluid resistances of both coated and uncoated elastomers in various media. Dramatic improvements in oil and fluid resistance are observed.

TABLE III
Coating DesignationControlHPC-5C
Fluid Resistance of Coated and Uncoated Rubber
Base Elastomer NR/BR BlendUncoated
Fluid Age, 2 Coats Applied by
Dipping
Jet A Fuel, 168 hrs. @ 21° C.: volume204.635.0
change (%)
Unleaded Gasoline, 22 hrs. @ 21° C.:103.61.1
volume change (%)
Mineral Spirits, 22 hrs. @ 21° C.:181.11.7
volume change (%)
IRM-930 Oil
70 hrs. @ 21° C.: volume change (%)62.50.5
70 hrs. @ 70° C.: volume change (%)184.014.8
70 hrs. @ 100° C.: volume change (%)256.241.5
1000 hrs. @ 21° C.: volume change (%)180.1
Mil-PRF-23699F Exxon Turbo Oil
2380
70 hrs. @ 100° C.: volume change (%)105.754.6
Mil-PRF-5606 AeroShell Fluid 41
70 hrs. @ 21° C.: volume change (%)188.70.4
Resistance to IRM-903 Reference Oil
Base Elastomer NR/BR BlendUncoated
Fluid Aging in IRM-903 Reference Oil
Original Physical properties of
substrate
Hardness (Shore A)5855
Tensile (mPa)23.3322.48
Elongation (%)575570
Aged 70 hrs. @ 70° C. in IRM-903 Oil
Hardness (pts)2843
Tensile3.2717.06
Elongation145435
Change in Hardness (points)−30−12
Change in Tensile (%)−86−24.1
Change in Elongation (%)−74.8−23.7
Change in Volume (%)18414.8

From the above test results, it is apparent that the application of a high performance coating to the surface of the SBR LVT boot will have a major impact on the performance of the product in service. The coatings of the invention can be applied to a variety of elastomeric elements which are used in railway emplacements. The coatings provide improved physical characteristics for the elastomeric goods allowing the main elastomeric body of such elements to be formed of more traditional elastomeric materials. The particularly preferred coatings provide improved weatherability, ozone resistance, impact and abrasion resistance, as well as improved chemical resistance, while preserving the flexibility of the underlying elastomer.

While the invention has been shown in several of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit thereof.