U.S. patent application number 11/678166 was filed with the patent office on 2007-08-30 for ozone and chemical resistant coating for railway line elastomeric components.
Invention is credited to Bradford G. JR. Corbett, James Richard Hirst.
Application Number | 20070200005 11/678166 |
Document ID | / |
Family ID | 38443064 |
Filed Date | 2007-08-30 |
United States Patent
Application |
20070200005 |
Kind Code |
A1 |
Corbett; Bradford G. JR. ;
et al. |
August 30, 2007 |
Ozone and Chemical Resistant Coating for Railway Line Elastomeric
Components
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; Bradford G. JR.;
(Fort Worth, TX) ; Hirst; James Richard; (Fort
Worth, TX) |
Correspondence
Address: |
Charles D. Gunter, Jr.;Whitaker, Chalk, Swindle & Sawyer, LLP
STE 3500
301 Commerce Street
Fort Worth
TX
76102-4186
US
|
Family ID: |
38443064 |
Appl. No.: |
11/678166 |
Filed: |
February 23, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60776380 |
Feb 24, 2006 |
|
|
|
Current U.S.
Class: |
238/283 |
Current CPC
Class: |
E01B 19/003 20130101;
E01C 9/04 20130101; E01B 3/28 20130101 |
Class at
Publication: |
238/283 |
International
Class: |
E01B 9/38 20060101
E01B009/38 |
Claims
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: TABLE-US-00007 Appearance
Clear Liquid with Orange Hue Viscosity, cps @ 77.degree. F.
(25.degree. C.) 20-100 Density Lb/gal 6.72-6.92 (kg/m.sup.3)
(805.23-829.20) Solids Content, % by Weight 10.6 by Volume 7.7-8.8
Flash Point (Seta), .degree. F. (.degree. C.) 60 (15.6) Solvents
Methyl Ethyl Ketone (MEK)
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] 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
[0002] 1. Field of the Invention
[0003] 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.
[0004] 2. Description of the Prior Art
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] Another specific application for the present invention
relates to railroad tie "boots." In many parts of the world,
Sonneville.RTM. 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.
[0010] The Sonneville.RTM. 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.
[0011] 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.
[0012] 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.
[0013] 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.
[0014] 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.
[0015] 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
[0016] 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.
[0017] 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.RTM. 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.TM. 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.
[0018] Another particularly preferred coating is manufactured by
Lord Chemical Products, as the LORD HPC-5C.TM. 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.TM.
primer plus a single coat of HPC-5C.TM. topcoat. The addition of
the HPC-5C.TM. 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.
[0019] Additional objects, features and advantages will be apparent
in the written description which follows.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] 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.
[0021] FIG. 2 is an isolated view of a railroad tie and tie boot as
used in the practice of the present invention.
[0022] 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
[0023] 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.
[0024] 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.
[0025] 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.
[0026] 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.
[0027] 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.
[0028] 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.
[0029] 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.RTM.. 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.
[0030] 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.
[0031] 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.
[0032] 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.RTM.
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.
[0033] The Manufacturers Technical Data for the CHEMGLAZE.RTM.
product is as follows: TABLE-US-00001 Mix ratio A/B by volume 3/1
supplied in premeasured kits Percent solids (by weight) 56 Volatile
Organic compounds 3.5 lb/gal Tack Free time 30 min. Physical
Properties of Cured Coatings: Tensile strength ASTM D 412 5000 psi
(Method A, Die C) Percent Elongation ASTM D 412 500 percent (Method
A, Die C) Taber Abraser No loss CS17 1000 g/1000 cycles Durometer
Shore A 110 Mixing and recommending spray application techniques
are given in the manufacturer's REMR Material Data Sheet,
CM-SE-1.9.
[0034] Another coating which has been evaluated is the Lord
Elastomeric Coating manufactured by Lord Mechanical Products
Division and marketed under the tradename ENDURALAST.TM. Tire
Coating. This product also has excellent adhesion properties and
environmental resistance and is capable of strains of several
hundred percent.
[0035] The particularly preferred coating used in the present
invention is manufactured by Lord as the HPC-5C.TM. coating. Lord
HPC-5C.TM. is one-part, room temperature curing hydrogenated
nitrile butadiene rubber (HNBR) coating which features robust
adhesion and exceptional mechanical properties. The HPC-5C.TM.
coating enhances fluid and ozone resistance for elastomeric
substrates of the type under consideration, as will be described in
greater detail below. HPC-5C.TM. is clear and colorable, and is
composed of a mixture of polymers, organic compounds and fillers
dissolved or dispersed in an organic solvent system.
[0036] The Lord HPC-5C.TM. has been found to offer the required
characteristics for a coating used on railway line elastomeric
components. HPC-5C.TM. 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.TM. 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.TM. provides excellent resistance to
lubricating oils and transmission fluids. In addition, HPC-5C.TM.
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).
[0037] Manufacturers Technical Data for the Lord HPC-5.TM. coating
is as follows: TABLE-US-00002 Appearance Clear Liquid with Orange
Hue Viscosity, cps @ 77.degree. F. (25.degree. C.) 20-100 Density
Lb/gal 6.72-6.92 (kg/m.sup.3) (805.23-829.20) Solids Content, % by
Weight 10.6 by Volume 7.7-8.8 Flash Point (Seta), .degree. F.
(.degree. C.) 60 (15.6) Solvents Methyl Ethyl Ketone (MEK)
[0038] The method of applying the coatings of the invention will
now be described. Before applying the HPC-5C.TM. 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.
[0039] 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.TM.. The part
can be dipped as long as no metal portions come in contact with the
Chemlok 7701.TM.. Alternatively, Chemlok7701.TM. 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.degree. F. (121.degree. 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.
[0040] In order to mix the HPC-5.TM., 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.
[0041] 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.
[0042] As mentioned, there are several conventional techniques for
applying the HPC-5C.TM. coating:
[0043] 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.
[0044] 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.degree. F.
(66.degree. C.) in between dips.
[0045] 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.degree. F. (66.degree.
C.) once or twice during spraying may be necessary to build film
the desired film thickness and avoid running.
[0046] 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.
[0047] 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.
[0048] 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.TM. 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.TM. and HPC-6C.TM. were compared during the test. The
following results were obtained, wherein .sigma. (sigma) represents
the standard deviation: TABLE-US-00003 Coating Coating Thickness
Pass/fail None(control) 0.000 failed at 48 hours Coated with 1 coat
of HPC-6C .TM. 0.400 mils, .sigma. = 0.068 mils pass Coated with 2
coats of HPC-6C .TM. 0.859 mils, .sigma. = 0.172 mils pass Coated
with 1 coat of HPC-5C .TM. 0.235 mils, .sigma. = 0.033 mils pass
Coated with 2 coats of HPC-5C .TM. 0.448 mils, .sigma. = 0.077 mils
pass
[0049] The test results show that the proposed HPC-5C.TM. coating
of the SBR material meets the above ozone requirement, whereas an
uncoated control sample fails after 48 hours. HPC-5C.TM. was chosen
as the preferred coatings because it dries faster and is a tougher,
more abrasion resistant coating.
[0050] 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/mm.sup.2 before aging and
.+-.30% after aging for 60 days at 80.degree. 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-US-00004 TABLE I Gotthard LP-30-33
Test Tribeton Physical Property Method DOC 13/04/06 Results Shore A
Hardness D2240 60 to 80 74 IRHD Hardness -- -- 73 Tensile Strength
D412 12 min 16.1 (Longitudinal or Transversal), N/mm.sup.2 Ultimate
Elongation D412 250 min 334 (Longitudinal or Transversal), %
Compression Set 22 h at -- -- 7.2 70.degree. C. Ozone Resistance 96
h at ISO1431 No Cracks No 40.degree. C., 200 pphm, Apperance Cracks
Rat. 20% E Accelerated Aging, 72 h at D573 100.degree. C. Hardness
Change, points -- 2 Tensile Strength 10 min 16.3 (Longitudinal or
180 min 286 Transversal), N/mm.sup.2 Ultimate elongation
(Longitudinal or Transversal), % Accelerated Aging, 60 d at D573
80.degree. C. Hardness Change, points -- 6 Tensile Change, % 30 max
6.2 Elongation Change, % .+-.70 max -25.1 Ash Content, % D297 10
max 1.9 Abrasion of 50% of the boot -- 10 Mio Cycles Not tested in
complete system, Tested load applied in angle 22.degree. F.
[0051] 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.TM. coated SBR material and in all cases the concentration
of gases generated in the BSS 7239 test fall well under the
maximums allowable. TABLE-US-00005 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 and 800C spec
Boeing M-7 spec Gas HPC-5C (ppm) (ppm max) (ppm max) CO 350.0 3500
3500 HCN 0.6 100 150 SO.sub.2 12.5 100 100 HCL 0.0 500 500 HF 0.0
100 200 NO.sub.2 3.5 100 100
[0052] As has been noted, a major increase in chemical resistance
can be imparted to the elastomeric component by the application of
the HPC-5C.TM. 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-US-00006 TABLE III Coating Designation Control
HPC-5C Fluid Resistance of Coated and Uncoated Rubber Base
Elastomer NR/BR Blend Uncoated Fluid Age, 2 Coats Applied by
Dipping Jet A Fuel, 168 hrs. @ 21.degree. C.: volume 204.6 35.0
change (%) Unleaded Gasoline, 22 hrs. @ 21.degree. C.: 103.6 1.1
volume change (%) Mineral Spirits, 22 hrs. @ 21.degree. C.: 181.1
1.7 volume change (%) IRM-930 Oil 70 hrs. @ 21.degree. C.: volume
change (%) 62.5 0.5 70 hrs. @ 70.degree. C.: volume change (%)
184.0 14.8 70 hrs. @ 100.degree. C.: volume change (%) 256.2 41.5
1000 hrs. @ 21.degree. C.: volume change (%) 180.1 --
Mil-PRF-23699F Exxon Turbo Oil 2380 70 hrs. @ 100.degree. C.:
volume change (%) 105.7 54.6 Mil-PRF-5606 AeroShell Fluid 41 70
hrs. @ 21.degree. C.: volume change (%) 188.7 0.4 Resistance to
IRM-903 Reference Oil Base Elastomer NR/BR Blend Uncoated Fluid
Aging in IRM-903 Reference Oil Original Physical properties of
substrate Hardness (Shore A) 58 55 Tensile (mPa) 23.33 22.48
Elongation (%) 575 570 Aged 70 hrs. @ 70.degree. C. in IRM-903 Oil
Hardness (pts) 28 43 Tensile 3.27 17.06 Elongation 145 435 Change
in Hardness (points) -30 -12 Change in Tensile (%) -86 -24.1 Change
in Elongation (%) -74.8 -23.7 Change in Volume (%) 184 14.8
[0053] 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.
[0054] 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.
* * * * *