Note: Descriptions are shown in the official language in which they were submitted.
CA 02654476 2009-02-17
RESTORING WORN RAIL CLIP SHOULDERS ON CONCRETE RAIL TIES
BACKGROUND
This relates to methods and materials for restoring worn rail clip shoulders
located on concrete rail ties.
Conventionally, rails are held to concrete rail ties by rail clips or
fasteners
that bear down on the rail flange. These rail clips or fasteners are typically
fabricated of metal and include a shoulder portion.
Concrete rail ties have been found to be prone to wear particularly in
sandy and wet locations or on steep grades where locomotives use sand for
traction. More specifically, a rail shoulder is disposed on a rail tie. The
tie is
surrounded by ballast. The rail clip shoulders are embedded in the concrete
tie
and adapted to hold the rail clips that bear down on the flange of the rail.
Worn shoulders on concrete rail ties need to be repaired quickly enough to
limit hold up of train traffic to an acceptable time. Worn shoulders also need
to be
restored to their original dimensions.
Conventionally, when a rail clip shoulder has become unduly worn, the
entire shoulder is removed and replaced with a new shoulder. The new shoulder
is secured in place, typically by a curable epoxy resin material. However,
even
when applied in a relatively thin layer, the cure time for epoxy resins can
take 12
to 36 hours at typical ambient temperatures. This is completely unacceptable
from a train operator's point of view.
If the trains are running even slowly over the freshly replaced rail
shoulders, and if the epoxy is still in a plastic state, it will run-off. This
results in
improper bonding of the new shoulder to the concrete rail tie.
SUMMARY
As stated above, in the past worn rail clip shoulders are replaced by new
rail clip shoulders. When epoxy resins are used in the new rail clip shoulder
replacement process, a number of problems will result. Conducting the rail tie
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CA 02654476 2009-02-17
shoulder repair in the field by laborers who are not trained for conducting
this
epoxy material application work is arduous at best. Curing an epoxy resin over
a
wide range of humidity's, temperatures and pressures is difficult to
implement.
Therefore, replacing a rail tie shoulder in a commercial time frame is hard to
consistently accomplish. Restoring a worn shoulder presents an even bigger
problem. This is because the shoulder is a vertically-extending member and
quite
problematical to restore.
Pre-catalyzed mercaptan-based epoxy hardeners are commonly required in
epoxy formulations. It is difficult for these products to cure under cold
climatic
conditions. These mercaptan-based hardeners also have a very obnoxious odor
and workers often complain of becoming nauseous when working with these
products. Repairing a rail tie with an epoxy resin does not result in a
refurbished
product wherein superior performance under dynamic operating condition can be
maintained. The use of an epoxy resin does not result in a rail tie that
exhibits a
high level of durability under load so that maintaining the gauge of a rail
assembly
is a problem. The use of an epoxy resin does not result in a rail tie that
exhibits a
high level of fracture resistance under load so that maintaining the gauge of
a rail
assembly cannot be accomplished. The high viscosity of an epoxy resin makes
handling more complicated when it is dispensed, particularly in the field.
It has now been determined that polymeric materials can be employed to
restore a worn rail clip shoulder. In an embodiment herein the polymeric
materials can comprise, and in another embodiment can consist essentially of,
at
least one of a polyurethane, a polyurea and/or a poly(urethane-urea) polymer.
Thus, when these polymeric materials are use a number of advantages will
result.
The method comprises applying a polymeric material as described above to the
worn rail clip shoulder located on the concrete rail tie. Then, the polymeric
material is cured so it adheres to the worn rail clip shoulder where it is
restored.
The polymeric material is substantially sag resistant and exhibits excellent
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pseudoplasticity. Therefore, the polymeric material maintains its shape
without
substantial runoff from the concrete rail tie during the restoration
operation.
In an embodiment, the damaged rail shoulder is restored using non-ambient
heat.
In one embodiment the damaged rail shoulder is restored using non-ambient
heat for curing the polymeric material. Furthermore, in another embodiment,
the
worn rail clip shoulder is restored without requiring the use of non-ambient
pressure.
Accordingly, the subject restoration method is more easily performed in the
field by
laborers who are employed for this purpose.
The worn rail clip shoulder in an embodiment herein has an extremely short
Gel Time. In a further embodiment, the gel time of the polymeric material is
not
more than about five seconds, and in still a further embodiment not more than
about
three seconds, and in still another embodiment not more than about one second.
This
allows for placement and retention of the rail shoulder components on the
repair site
without substantial run-off of the polymeric material from the repair site. In
other
words, the worn rail clip shoulder and the polymeric material can be
maintained in a
fixed position on the surface of the concrete rail tie during the course of
the worn rail
clip shoulder restoration procedure.
The Set Time of the polymeric material can also be sufficient to permit
contouring of the worn rail clip shoulder in situ in the repair area using
application
techniques that can be readily performed by workers in the field. In an
embodiment
herein, the Set Time of the polymeric material is sufficient for contouring
the
restored worn rail clip shoulder without requiring the use of non-ambient
pressure.
Set Time is typically dependent upon temperature conditions and the thickness
of
applied polymeric material.
The rail tie properties can be maintained over a wide range of ambient
temperatures during use. These ambient temperature are preferably up to at
least
about 120 more preferably to at least about 140 F, and most preferably
up to at
least about 160 F, and as low as -50 F, more preferably as low as about -25
F, and
most preferably as low as about 0 'F.
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CA 02654476 2009-02-17
In the method of this invention, curing of the polymeric material during
repair of the worn rail clip shoulder can be accomplished over a wide range of
humidity's, temperatures and pressures. Therefore, an effective rail tie
shoulder
can be produced in a commercial time frame.
There is no substantial obnoxious odor emitted with the subject polymeric
material. Thus, a worker in the field does not have to deal with odor problems
which plague prior art repair products.
Repairing a worn rail clip shoulder with the subject polymeric material
results in a refurbished product wherein superior performance under dynamic
operating conditions is maintained so that a high level of durability under
load can
be provided while maintaining the gauge of a rail assembly. The modulus of the
polymeric material used to repair the rail clip shoulder can also be increased
to a
level which will resist compressive loading and maintain the rail gauge of the
rail
assembly.
The polymeric material displays a high degree of toughness and ductility.
Material toughness is indicated by area under stress-strain curve developed
during
tensile testing. Toughness-ductility classifications depend on the Elastic
Modulus
(Young's Modulus), tensile strength, and elongation. Rigid materials have an
Elastic Modulus (E) that is defined as E> 700 Mpa. Brittle materials have an
elongation less than 10%, in the case of epoxy materials an elongation of
about
5%. Ductile materials have an elongation as defined below of at least about
10%
or higher. The percent elongation value of the restored rail clip shoulder can
be
increased to a level that results in increased brittle fracture morphology. In
one
embodiment, the restored rail clip shoulder can provide an increased percent
elongation value that results in substantially improved material durability.
Verification of the structural differences in durability of conventional epoxy
resins
and the subject polymeric material can by established by, for example,
comparing
the elongation ("Elongation") of each of the respective materials under
tensile
loading (ASTM D 638). Typically, conventional epoxy polymers show poor
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CA 02654476 2009-02-17
elongation properties (Elongation > 5%) and exhibit a corresponding brittle
fracture morphology. Contrarily, the Elongation of the polymeric material
employed herein is preferably at least about 10%, more preferably at least
about
15%, and most preferably at least about 20%.
The subject polymeric material also has a modulus that is in the rigid class
of materials, a greater area under the stress strain curve, a substantial
plastic
energy of deformation term, and a lower filler loading that is enhanced by
excellent bonding of the polymer matrix to the filler, minimizing internal
defects
and the size of the internal defect. Typical epoxy systems are highly filled
and
have nominal matrix-filler bonding resulting in numerous internal defects of
considerable size.
The restored rail clip shoulder forms a rail tie, which can exhibit a high
level of fracture resistance under load while maintaining the gauge of a rail
assembly. This improved fracture resistance is evidenced by the presence of a
higher level of mechanical properties, better SEM image analysis results, and
an
enhanced Griffith fracture analysis.
The Tensile Strength (ASTM D638M-89) of the restored rail clip shoulder
is generally at least equivalent to that of epoxy resins used conventionally.
In one
embodiment, the Tensile Strength of the polymeric material employed herein is
at
least about 3,800 psi, in another embodiment at least about 4,200 psi, and in
still
another embodiment at least about 4,500 psi.
The polymeric material of the restored rail clip shoulder is also
characterized by an increase in the Young's Modulus of the polymeric material
of
the restored rail clip shoulder. In one embodiment, the Young's Modulus of the
polymeric material employed herein is at least about 700 Mpa, in another
embodiment at least about 850 Mpa, and in still another embodiment at least
about
1,000 Mpa.
This polymeric material is also characterized by exceptional adhesion to
the materials used to construct the rail clip shoulders on the concrete
railroad ties,
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CA 02654476 2011-10-19
typically, stainless steel or ductile iron. It also shows outstanding adhesive
properties
for binding to shims, typically fabricated of stainless steel, which are used
in the
repair process to reinforce the restored rail clip shoulder. This adhesion
property can
be measured by employing several testing regimes.
For example, the adhesion to stainless steel can be measured using a lap shear
test (ASTM 3631). In this embodiment, the minimum adhesion of the polymeric
material employed herein is at least about 1500 lbs/in2, in another embodiment
at
least about 1800 lbs/in2, and in still another embodiment at least about 2000
lbs/in2.
A pull off test for adhesion to stainless steel or ductile iron can be
employed
according to ASTM D4541. In an embodiment using stainless steel, the minimum
adhesion of the polymeric material employed herein is at least about 1600
lbs/in2, in
another embodiment at least about 1800 lbs/in2, and in still another
embodiment at
least about 2000 lbs/in2 In an embodiment using ductile iron, the minimum
adhesion
of the polymeric material employed herein is at least about 2500 lbs/in2, in
another
embodiment at least about 2800 lbs/in2, and in still another embodiment at
least about
3000 lbs/in2
A lowered viscosity of the subject polymeric material is provided. This
property of the polymeric material makes handling less complicated when it is
dispensed, particularly in the field.
According to one aspect of the present invention, there is provided a method
for restoring a worn rail clip shoulder located on a concrete rail tie, which
comprises
applying a polymeric material to a worn area of the worn rail clip shoulder
located on
the concrete rail tie; and restoring the worn area by curing the polymeric
material so it
adheres to the worn rail clip shoulder, the polymeric material being
substantially sag
resistant, and substantially maintaining the original shape of the rail clip
shoulder,
without substantial runoff from the concrete rail tie during said restoring of
the worn
rail clip shoulder.
According to a further aspect of the present invention, there is provided a
method for restoring a worn rail clip shoulder located on a concrete rail tie,
which
comprises applying a polymeric material to a worn area of the worn rail clip
shoulder
located on the concrete rail tie; and restoring the worn area by curing the
polymeric
material so it adheres to the worn rail clip shoulder, the polymeric material
being
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CA 02654476 2011-10-19
substantially sag resistant, and substantially maintaining the original shape
of the rail
clip shoulder, without substantial runoff from the concrete rail tie during
said
restoring of the worn rail clip shoulder.
According to a further aspect of the present invention, there is provided a
method for restoring a worn rail clip shoulder located on a concrete rail tie,
which
comprises applying a polymeric material comprised of a polyurethane, polyurea
or
poly(urethane-urea) material and introducing a shim to the worn area of the
worn rail
clip shoulder located on the concrete rail tie; and restoring the worn area by
curing the
polymeric material so it adheres to the worn rail clip shoulder and so that it
secures
the metal shim to the worn rail clip shoulder, respectively, the polymeric
material
being substantially sag resistant and maintaining its shape without
substantial runoff
from the concrete rail tie during said restoring of the worn rail clip
shoulder.
DETAILED DESCRIPTION
Polymeric materials particularly useful in this invention can be prepared from
various combinations of amine-terminated and/or hydroxyl-terminated resins
that are
reacted with an isocyanate material. These polymeric materials in one
embodiment
comprise at least one polyol compound and/or at least one amine compound, and
an
isocyanate.
If the polymeric material is a poly(urethane-urea), in one embodiment it can
be formed employing (a) at least one polyol compound, typically a hydroxyl
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CA 02654476 2009-02-17
capped polyol and/or a hydroxyl chain extender, in one embodiment an amount
from about 20 %, in another embodiment from about 25 %, and in a further
embodiment from about 30 %, in an embodiment herein up to about 60 %, in still
another embodiment up to about 55 %, and in still a further embodiment up to
about 45 %, (b) at least one amine compound, typically an amine chain
extender,
in one embodiment from about 0.5 %, in another embodiment from about 1.0 %,
and in still another embodiment from about 1.5 %, in one embodiment up to
about
20 %, in further embodiment up to about 15 %, and in still a further
embodiment
up to about 10 %, and (c) an isocyanate compound, typically an isocyanate
prepolymer, in one embodiment an amount from about 20 %, in another
embodiment from about 25 %, and in still another embodiment from about 30 %,
in one embodiment up to about 45 %, in a further embodiment up to about 40 %,
and in still a further embodiment up to about 35 %.
If the polymeric material is a polyurethane, in one embodiment it can be
formed employing (a) at least one polyol compound, typically a hydroxyl capped
polyol and/or a hydroxyl chain extender, in one embodiment an amount from
about 55 %, in another embodiment from about 60 %, and in a further
embodiment from about 65 %, in an embodiment herein up to about 80 %, in still
another embodiment up to about 75 %, and in still a further embodiment up to
about 70 %, and (b) an isocyanate compound, typically an isocyanate
prepolymer,
in one embodiment an amount from about 20 %, in another embodiment from
about 25 %, and in still another embodiment from about 30 %, in one embodiment
up to about 45 %, in a further embodiment up to about 40 %, and in still a
further
embodiment up to about 35 %.
If the polymeric material is a polyurea, in one embodiment it is formed
employing (a) at least one amine compound, typically an amine capped compound
and/or an amine chain extender, in one embodiment an amount from about 55 %,
in another embodiment from about 60 %, and in a further embodiment from about
65 %, in an embodiment herein up to about 80 %, in still another embodiment up
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to about 75 %, and in still a further embodiment up to about 70 %, and (b) an
isocyanate compound, typically an isocyanate prepolymer, in one embodiment an
amount from about 20 %, in another embodiment from about 25 %, and in still
another embodiment from about 30 %, in one embodiment up to about 45 %, in a
further embodiment up to about 40 %, and in still a further embodiment up to
about 35 %.
Typical polyol compounds can be hydroxyl capped di- and tri-functional
polyether oxides, hydroxyl capped polypropylene oxides, hydroxyl capped di-
and
tri-functional polyethylene oxides, hydroxyl capped di- and tri-functional
poly(propylene-ethylene)oxides, and hydroxyl capped di- and tri-functional
polyesters. Examples of polyols which can be employed herein are Bayer LFIT-*
240, PPG-425, Arch 20-280 Dow Voranoi 230-238*, and BASF Quadrot In one
embodiment the polyol compound has a molecular weight of from about 200
grams/mol, and in another embodiment from about 300 grams/mol, and in still
another embodiment from about 400 grams/mol, and in a certain embodiment up
to about 4,000 grams/mol, in another embodiment up to about 3500 grams/mol,
and in still another embodiment up to about 3000 grams/mol.
Typical amine compounds can be amine compounds such as amine chain
extenders including di-and tri-polyoxypropylenediamines, liquid aromatic
diamines, isophronediamine, and diethylenetriamine or amine capped compounds
such as amine capped bi- or tri-functional amine compounds. Examples of amines
which can be employed herein are Shell Epi-Cure 3274 Vestamine IPD,
Huntsman D-230; and Dorf Ketal Unilink 4100.
Typical isocyanate compounds are di- and tri-functional aromatic
isocyanates, polymeric modified 4,4-diphenylmethane diisocyanates, and 1,6-
hexamethylene diisocyanates (aliphatic isocyanates). Examples of isocyanates
which can be employed herein are Bayer Desrnodure N 3400*,'ICI Rubinate*I209,
Bayer Mondur ML, Bayer Mondur MR and MR Light. Also, the isocyanate
compound can be a prepolytner isocyanate blend such as Bayer Mondur MA-
*Trade-mark
CA 02654476 2011-10-19
2300, Bayer Mondur*MA-2600, and Baytec*lVIE-040. The functionality of the
isocyanate in one embodiment can be at least about 2.0, in another embodiment
at
least about 2.2, in a further embodiment at least about 2.4, and in still a
further
embodiment up to about 2.6.
The polyurethane, and poly(urethane-urea) reactions can include a catalyst
system to accelerate the reaction between the isocyanate and the hydroxyl
groups
of each polyol. These catalysts can include tin, mercury, lead, bismuth, zinc
and
various amine compounds such as are described in U.S. 5,011,902. A preferred
catalyst employed herein is a metal carboxylate.
In certain instances it may be desirable to add a chain extender to complete
the formulation of polyurethane, polyurea, and poly(urethane-urea) polymers by
reacting isocyanate groups of adducts or prepolymers. Examples of some types
of
polyol and amine chain extenders include 1,3-butanediol, 1,4-butanediol, 2-
ethyl-
1,3-hexanediol, diethylene glycol, trimethylol propane and hydroquinone
di(beta
hydroxyethyl ether). The subject polyurethane, polyurea, and poly(urethane-
urea)
compositions may additionally incorporate diluents, fillers, compatibilizers,
thixotropes, pigments, plasticizers, colorants, de-foaming agents, rheological
modifiers, and anti settling agents. Suitable fillers include barium sulfate,
calcium
sulfate, calcium carbonate, silica, and clay particles, such as aluminum
silicates,
magnesium silicates, ceramic and glass micro-spheres and kaolin. Suitable
compatibilizers are hydroxy containing organic compounds, preferably hydroxy
containing monocyclic arenes such as ethoxylated nonyl phenol, which
compatibilize the polyol and aromatic diisocyanate reactants in the
formulation.
Suitable diluents include hydrotreated paraffinic oils, phthlates, carbonates,
hydrotreated naphthenic oils, petroleum solvents, aliphatic solvents and
propylene
carbonate.
Equipment for dispensing the isocyanate and polyol(s)/amines employed in
producing the polyurethane, polyurea, and poly(urethane-urea) materials, such
as
*Trade mark
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CA 02654476 2009-02-17
the MixusTm dispensing equipment manufactured by Willamette Valley Company
of Eugene, Oregon, is commercially available. Typically, the two components
which form the subject polyurethane, polyurea, and poly(urethane-urea) filler
materials are pumped from storage tanks to a proportioning unit where the
components are measured out according to a specified ratio. A known amount of
each material is then separately pumped to a dispensing unit. The components
are
mixed in the dispensing unit and then introduced into the worn area of the
shoulder of the railroad tie. The components of the polymeric materials can
also
be mixed together using a cartridge system with a static mixing tube along
with
standard proportioning equipment.
The shoulder repair process takes place during normal re-gauging and
maintenance operations or during a dedicated shoulder repair process. The
repair
process is generally as follows:
1. The rail is removed.
2. Pressurized air, either from a compressor or blower, is used to clear the
area of debris.
3. Pads can be removed, though this depends on the extent of the
maintenance operation.
4. The shoulder is cleaned with a wire brush or grinding wheel.
5. A polymeric material such as described above is applied to the recess site
in the rail tie shoulder. Alternately, the polymeric material is applied to a
shim.
6. If a shim is employed, it is put in place on the edge of the shoulder.
7. The rail is re-assembled.
It is to be understood that the above-referenced arrangements are only
illustrative of the application for the principles of the present invention.
Numerous
modifications and alternative arrangements can be devised without departing
from
CA 02654476 2012-05-03
the scope of the present disclosure. While embodiments of the present
invention have been shown in the drawings and fully described above with
particularity and detail in connection with what is presently deemed to be the
most
practical and preferred embodiment(s) of the invention, it will be apparent to
those of
ordinary skill in the art that numerous modifications can be made without
departing
from the principles and concepts as set forth herein.
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