U.S. patent application number 10/710590 was filed with the patent office on 2004-11-25 for recycled rubber crosstie.
This patent application is currently assigned to HANSEN RUBBER PRODUCTS INC.. Invention is credited to Hansen, Steve.
Application Number | 20040232253 10/710590 |
Document ID | / |
Family ID | 32737903 |
Filed Date | 2004-11-25 |
United States Patent
Application |
20040232253 |
Kind Code |
A1 |
Hansen, Steve |
November 25, 2004 |
RECYCLED RUBBER CROSSTIE
Abstract
A railroad crosstie made from recycled rubber and its method for
making is disclosed. The rubber crosstie has an expected life of
between 30 to 60 years and can be made primarily of rubber crumbs
obtained from stockpiles of discarded rubber tires.
Inventors: |
Hansen, Steve; (Bakersfield,
CA) |
Correspondence
Address: |
RALPH D CHABOT
2310 E PONDEROSA DR
SUITE 4
CAMARILLO
CA
93010
US
|
Assignee: |
HANSEN RUBBER PRODUCTS INC.
10212 Planebrook Avenue
Bakersfield
CA
|
Family ID: |
32737903 |
Appl. No.: |
10/710590 |
Filed: |
July 22, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10710590 |
Jul 22, 2004 |
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10275665 |
Nov 7, 2002 |
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6766963 |
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10275665 |
Nov 7, 2002 |
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PCT/US01/15296 |
May 11, 2001 |
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60204342 |
May 15, 2000 |
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Current U.S.
Class: |
238/29 |
Current CPC
Class: |
E01B 3/44 20130101 |
Class at
Publication: |
238/029 |
International
Class: |
E01B 003/00 |
Claims
1. A crosstie made substantially from recycled rubber comprising:
10-35% by weight recycled rubber from natural rubber tires; 65-90%
recycled vulcanized rubber; and, a strength enhancing polymer of no
more than 5% by weight.
2. The recycled rubber crosstie of claim 1 wherein said crosstie
has at least one longitudinal side which has a plurality of
indentations.
3. A method for producing a crosstie made substantially from
recycled rubber comprising the steps of: providing vulcanized
recycled crumb rubber and natural recycled crumb rubber; mixing by
weight 10-35% said natural recycled crumb rubber and 65-90% said
vulcanized crumb rubber to form a blend; and adding a strength
enhancing polymer to said blend, the amount of polymer to add
between 0-5% of the total weight of said blend; milling said blend
at between 240 degrees F. and 370 degrees F. (116-188 deg C.) to
form an intermediate product; extruding said intermediate product
at between 240 degrees F. and 370 degrees F. (116-188 deg C.) to
form an extrusion having a specific width and depth; and,
thereafter cutting said extrusion at intervals to yield a crosstie
having the desired length.
4. The method of claim 3 further comprising after said thereafter
cutting said extrusion at intervals to yield a crosstie of the
desired length step: creating a plurality of pre-holes on one
longitudinal side of said crosstie, the position of said pre-holes
corresponding to the position that spikes will be driven into said
crosstie.
5. The method of producing a crosstie according to claim 3 wherein
said strength enhancing polymer is selected from the group
comprising neoprene, polyethylene, urethane and ABS.
6. The method of claim 5 further comprising after said thereafter
cutting said extrusion at intervals to yield a crosstie of the
desired length step: creating a plurality of concave-type pre-holes
on one longitudinal side of said crosstie, the position of said
pre-holes corresponding to the position that spikes will be driven
into said crosstie.
7. The method of producing a crosstie according to claim 3 further
including a means to form a plurality of indentations in at least
one side of said extrusion.
8. A crosstie comprising: an extruded product made from a blend of
recycled natural crumb rubber and recycled vulcanized crumb rubber
where 10-35% of the crosstie weight is recycled natural rubber,
65-90% of the crosstie weight is recycled vulcanized rubber and a
strength enhancing polymer accounts for no more than 5% of the
crosstie weight.
9. The recycled rubber crosstie of claim 6 wherein said crosstie
has at least one longitudinal side has a plurality of indentations.
Description
CLAIM OF PRIORITY
[0001] This application claims priority to U.S. application bearing
Ser. No. 10/275,665 filed Nov. 7, 2002 which in turn claims
priority to PCT/US01/15296 filed May 11, 2001 which in turn claims
priority to U.S. provisional application filed May 15, 2000 bearing
serial No. 60/204,342.
TECHNICAL FIELD
[0002] The invention relates to railroad rail support systems,
specifically railroad crossties or ties, and their method of
manufacture.
BACKGROUND OF THE INVENTION
[0003] The majority of railroad track today is comprised of wooden
crossties, sometimes referred to simply as ties, for alignment and
support of iron rails placed thereupon. However, for a variety of
reasons, such as the use of lower quality pine rather than oak due
to high timber costs, alternatives to wooden crossties have become
available to the railroad industry.
[0004] These alternative products can be either made of new or
recycled materials. Cement, reinforced concrete, metal, recycled
wood, plastic, composites of various recycled materials, and other
products have been made.
[0005] One of these alternative products is described in U.S. Pat.
No. 6,179,215 issued to Shea. Shea describes a composite railroad
crosstie comprising individual pieces assembled to form a crosstie.
These individual pieces include a top and bottom casing section
made from a 50-50 mixture of high density polyethylene and crumb
rubber, tubular reinforcing beams positioned in the inner cavity
formed by the top and bottom sections and then a reinforcing
material such as concrete is pumped into the remaining void space
within the inner cavity. While incorporating some usage of crumb
rubber, the majority of the weight is attributable to the higher
density concrete and tubular components. Assembly of these
components adds to the overall cost of manufacture.
[0006] Another alternative product is the crosstie disclosed in
U.S. Pat. No. 6,247,651 issued to Marinelli. In Marinelli, a
crosstie is formed in the shape of an I Beam comprising 65%
recycled high density polyethylene and polypropylene plastics, 20%
granulated rubber tires and 15% glass fibers. While not made of
heavy materials such as concrete or steel, the rubber composition
of the Marinelli crosstie is only 20%.
[0007] These alternative products have disadvantages. The railroad
industry is seeking an economical alternative to wood. While cement
and reinforced concrete are durable, they weigh substantially more
than ties made from wood. Transportation costs are higher and
handling is more difficult because of the increased weight. Ties
made with a metal core must also be encapsulated with a
non-conductive material for safety and operational concerns.
Encapsulation is an additional step which increases the cost of the
tie.
[0008] Another disadvantage associated with these alternative
crossties is the relatively low force required to withdraw a spike
that was driven into a tie. It is desirable to have a higher
withdrawal force. A higher withdrawal force translates into a more
secured spike and reduces or eliminates the need to reset a
spike.
[0009] Additionally, almost all alternative tie products have
increased noise levels as trains pass due to the surface hardness.
Steel, cement and plastic cross ties also tend to undesirably shift
in the gravel bed.
[0010] As a consequence, demand from the railroad industry for
non-wood ties has been low. It is believed that high demand would
exist if a tie could be made for low-cost, have similar performance
characteristics, and have a longer life than a wood tie.
[0011] In the recycle and rubber tire industries, there has been a
concern for many years regarding what to do with discarded tires. A
problem facing these industries has been how to recycle discarded
rubber products, and especially vehicular tires into useful and
economical end products. More information on the various problems
relating to the disposal and recycling of discarded tires is
provided in the background sections of U.S. Pat. No. 4,726,530
(Miller et. al.) and U.S. Pat. No. 5,094,905 (Murray).
[0012] Technology exists for discarded rubber tires to be recycled.
Tires are generally comprised of rubber, steel belts and beads, and
fiber such as rayon, nylon, and other polyesters. Present
technology can shred and granulate tires and have the metal
separated magnetically, and the fibers removed by vacuum. The
rubber can be shredded or ground into any desired size. This
technology is described in the Miller et. al. patent cited earlier.
Utilizing separation technology, discarded rubber tires are
available as a source for recycled products.
[0013] As mentioned earlier, another problem facing the railroad
industry is the useful life or longevity of a crosstie before it
requires replacement. This concern is even more prevalent today
than in the past. Presently in the United States, crossties are
mostly made from softwoods such as pine rather than hardwoods such
as oak. Softwood crossties do not have the longevity of hardwoods.
As an example, softwood crossties are susceptible to accelerated
deterioration in high moisture environments. A tie in a swamp area
may have an operational life expectancy of only three to four
years. It is believed that the railroad industry would be receptive
to more durable alternatives to wood where cost savings can be
realized.
DISCLOSURE OF INVENTION
[0014] A method to manufacture railroad crossties from rubber has
been developed. The rubber crosstie can be used as wood tie
replacements for new and re-laid tracks. The rubber crosstie can be
made economically and preferably utilize the abundant supply of
discarded rubber tires stockpiled at waste disposal sites.
SUMMARY OF THE INVENTION
[0015] The rubber railroad crosstie made according to the invention
("Tie") is made by a process using granulated rubber (sometimes
referred to as crumb rubber, rubber dust, or rubber fines),
preferably not larger than 30 mesh (590 microns). The crumb rubber
is preferably milled and then extruded to obtain the desired width
and depth and thereafter cut to the desired length.
[0016] Recycled crumb rubber (RCR) can be made from discarded tires
commonly available at waste disposal facilities. RCR can be made
available by type and mesh size.
[0017] The preferred embodiment of my invention requires two
specific types of RCR.
[0018] The first type of RCR is made from vulcanized or synthetic
rubber. The primary source for vulcanized rubber is from automobile
and truck tires.
[0019] The second type of RCR is rubber having less sulfur and zinc
content than vulcanized rubber and has a lower melting point;
sometimes referred to as natural or devulcanized rubber. The
primary source for the second type is from tires classified as
mostly off-the-road (OTR) tires. It is to be understood that there
may exist some vulcanized rubber in natural rubber tires. However,
the tire industry recognizes this fact and the "natural rubber
tire" designation is understood to include some small percentage of
vulcanized rubber.
[0020] Air pollution is not a concern during the process. The
milling and extrusion temperature is between 240-370 degrees F.
(116-188 deg C.). At this temperature range, there are no
significant amounts of toxic or hazardous gases escaping into the
production area or environment. Waste tires and rubber crumbs are
not generally classified as hazardous materials; but rather as a
waste management disposal problem.
[0021] Besides discarded rubber, small additions of polymers may be
used in the manufacturing process for strength enhancement. The
amount necessary will be dependent upon the actual rubber
composition used to form a Tie according to my invention and could
account for up to 5% of the overall weight of the Tie.
[0022] It is also possible to produce a rubber railroad crosstie
which, in addition to the rubber mentioned above, utilizes the
fiber also found in vehicular tires. In other words, a crosstie is
preferably formed using discarded automobile tires provided the
steel has been removed. In situations where steel is removed, it is
done to eliminate the possibility of conductivity through the Tie
while also maximizing its useful life.
[0023] However, it is possible, if conductivity is not a concern,
to use steel in the formation process. If this is done, tires can
be ground into the appropriate mesh size not having the steel
removed and then combined with the appropriate amount of strength
enhancing polymer. A drawback to this alternative is that the
overall useful life of the Tie would be reduced but the
manufacturing costs may be less.
[0024] The Tie can be made by either a compression mold or an
extrusion process. The operating pressure for extrusion is
dependent upon several factors including the viscosity, screw speed
and orifice size. In general, an extrusion process operating
between 240-370 degrees F. (116-188 deg C.) should operate in a
pressure range of between 250-2,500 psi (1,724-17,240 kPa). Due to
the logistical problems associated with a high volume compression
mold process, it is more preferable to utilize a continuous
extrusion process.
[0025] Once formed, the color of the Tie is black. Over time, the
surface will oxidize and may turn to an ashen black or gray.
Testing has indicated that the Tie is not subject to the level of
cracking and product degradation under sunlight as occurs for
rubber tires.
[0026] My railroad tie is preferably made completely from
non-conductive materials. Therefore, no special precautions are
necessary as with other ties partially made from metals and which
could conduct electricity.
[0027] Ties can be manufactured into any length desired and are
recyclable.
[0028] Creosote, a known carcinogen commonly used in the
manufacture of wooden railroad crossties, is not used in the
manufacture of the Tie.
[0029] The weight of the Tie made according to the invention is, on
average, between 13% to 50% less per unit when compared to other
railroad tie alternatives to wood. By way of example, for a
standard railroad crosstie measuring 8.5 ft.times.9 in.times.7 in
(259 cm.times.23 cm.times.18 cm), a crosstie made according to the
invention would weigh approximately 278 pounds (126 kg), while one
made from concrete would weigh over 500 pounds (227 kg).
[0030] A key feature of the Tie is that it can withstand a 120,000
pound (54,480 kg) compression test upon an area equivalent to a
standard railroad tie plate of approx 96 square inches (619 sq. cm)
Additionally, after the load was removed, no permanent deformation
was visible.
[0031] The Tie is expected to have a useful life of between 30 to
60 years. The longevity of the Tie will reduce the frequency of
crosstie replacement as well as the associated cost for
installation.
[0032] The Tie can be installed side-by-side a wooden railroad tie.
This is in contrast to cement ties and other known alternative
crossties where it is recommended that whole-lines be replaced even
though only some ties require replacement.
[0033] The Tie is designed for attachment in the same way as wood
ties. The preferred method is by use of spikes while clips or
screws could be used alternatively. The type of attachment would
depend on railroad industry preferences for the specific locale in
which the track is laid. No new placement or replacement
technologies or techniques are required.
[0034] Because the Tie is compressed upon formation, further
compressive deformation following installation will be minimal.
This will permit true alignment during installation. Other crosstie
products, including those made from softwoods, have allowances for
compression over time to fit the standard rail attachment plates as
needed and to grip the gravel under-base or bed.
[0035] An optional feature is that the Tie can be made for use with
gravel beds with at least one side having a plurality of
indentations or indented surfaces. As used in this specification,
"indented surface" and "indentation" have the same meaning and are
defined here as a non-flat surface. When a plurality of
indentations are present on at least one longitudinal side of a
crosstie, they collectively are capable of frictionally engaging a
bed of gravel better than if the longitudinal side were a flat
surface. The indentations must be something more than microscopic
deformations which are present on any flat surface; they must be
capable of frictional engagement with a gravel bed to prevent the
crosstie from slipping or sliding as would be the case if the
surface were flat. "Indentation" is also defined to include
configurations such as ribs, serrations, dimples, and other simple
geometric shapes such as diamonds and pyramids which can be
indented into the crosstie.
[0036] In order to function properly, the indentations must be of
sufficient width to permit gravel to enter the concave area. If the
indented width were too small, excessive void spaces would form in
the concave area and therefore not efficiently frictionally engage
the gravel bed.
[0037] The decision of whether to incorporate indented surfaces
would depend upon the use of the Tie. By way of example, if the Tie
were used in high speed rail lines, a gravel bed is not used but
rather the crossties are positioned on a hardened surface such as
cement. A crosstie having indentations is undesirable in this
situation since it would reduce the surface area in contact with
the hardened surface thereby reducing frictional engagement.
[0038] Where gravel beds are to be used, preferably, one side of
the Tie has a plurality of indentations which would face downward
when laid. Most preferably, three longitudinal sides of the Tie
would utilize indented surfaces. The longitudinal side facing
upward when laid need not.
[0039] The purpose of having indentations on the Tie is to allow it
to better frictionally engage the gravel bed into which it is
placed. The depth of each indentation should be limited so as to
not affect the structural properties of the Tie; namely, the
ability to resist compressive loads.
[0040] The indented surfaces will enable the crosstie to resist
sliding in the gravel bed as can be the case when aligning
crossties having harder and smoother surfaces such as those made
from wood, plastic or cement.
[0041] The indentations can be formed while the Tie is still hot
and receptive to deformation. Alternatively, compression molds can
be used and designed to create the desired indentations in the
molded Tie. Still another way for creating the indentations would
be by machining; however this procedure would be expensive in view
of the other methods previously discussed.
[0042] By way of example, the mechanical properties of a Tie made
according to the invention are as follows:
[0043] Density: 74.8 lbs/ft.sup.3 (1200 kg/m.sup.3)
[0044] Thermal expansion coefficient: 0.005% per deg F. (0.003% per
deg C.)
[0045] Modulus of rupture: 26,982 psi (186,041 kPa)
[0046] Modulus of elasticity (bending): 6,717,000 psi (46,313,715
kPa)
[0047] Modulus of elasticity (compression): 174,144 psi (1,200,723
kPa)
[0048] Limit of elasticity: 487,584 psi (3,361,892 kPa)
[0049] Hardness: 924 lbs/in (165 kg/cm)
[0050] Pressure to insert spike: 4,200 psi (28,959 kPa)
[0051] Pressure to withdraw spike: 3,360 psi (23,167 kPa)
[0052] Life expectancy: 30-60 years
[0053] Weight load capacity (per Tie): 521,000 lbs (236,534 kg)
[0054] Given that extrusion will yield a crosstie with the above
mechanical properties, other applications are possible for this
sort of extruded rubber product. By way of example, a crosstie pad,
made according to the process described herein, could be positioned
between a crosstie and its underbed for train travel noise
reduction, and shock absorbency when used in conjunction with
steel, cement or concrete crosstie.
[0055] As mentioned earlier, indentations can be used for
frictional engagement with a gravel bed and no indentations are
necessary for the top surface. However, in situations where gravel
beds are not used, there is no reason for a Tie to be produced with
indentations for frictional engagement.
[0056] However, a plurality of spike pre-holes or guide holes can
be formed from the top surface inward into the crosstie for a
pre-determined length. The top surface position of these pre-holes
would be in the Tie at the specific areas where spikes would be
driven into the crosstie. Accordingly, the pre-hole diameter can be
sufficiently wide to permit a spike to be partially inserted a
distance without substantially causing the loss of performance of
the spike in securing the rail to the Tie.
[0057] Precise alignment of the crosstie to the rail would be
necessary and a possible application would be in the construction
of a high speed rail line laid upon a cement or concrete
foundation; something other than a gravel bed which has a tendency
to shift crosstie position.
[0058] The pre-holes are preferably formed one of two ways. If the
ties are formed via an extrusion process, then some sort of
compressing equipment would be used to make the pre-holes,
preferably after each tie is cut. If the ties are formed via a
compression mold process, the molds themselves can be designed to
create the pre-holes.
BRIEF DESCRIPTION OF THE DRAWINGS
[0059] FIG. 1 is an overall process flowchart for the manufacture
of a rubber crosstie.
[0060] FIG. 2 is a perspective view of an installed crosstie, made
according to the invention.
[0061] FIG. 3 is a perspective view of a portion of a crosstie made
according to the invention having pyramid indentations along at
least one longitudinal side.
[0062] FIG. 4 is a perspective view of a portion of a crosstie,
having an alternative type of indentation, namely a plurality of
ribs.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0063] FIG. 1 is a flowchart representing the preferred process for
manufacturing a rubber railroad crosstie. The preferred method of
producing a rubber crosstie is by extrusion. RCR is either made
on-site from readily available tire stockpiles or is provided from
an off-site source. The technology for reducing tires to rubber
crumb is described, as previously mentioned, in the US Patents
issued to Murray and Miller et al. The required RCR size should be
no larger than 30 mesh (590 micron). RCR made from both natural
rubber and vulcanized rubber are stored separately and identified
in FIG. 1 as 20 and 30 respectively.
[0064] The mesh size is vital to the cohesive properties of the
tie. A smaller mesh size, preferably 30 mesh or less, enables
uniform heating and a stronger bond due to each particle having a
larger surface area.
[0065] Natural rubber has a lower melting point and a more adhesive
characteristic than vulcanized rubber. It is the natural rubber
component that provides the adhesive quality necessary to mill and
extrude the Tie. It is however possible to have a small portion of
the overall blend be larger than 30 mesh (590 micron). Small
quantities of larger size particles may exhibit acceptable
performance characteristics.
[0066] Referring to FIG. 1, the RCR made from natural rubber and
vulcanized rubber is blended together in a mixer 50 at a weight
ratio of about between 10-35% natural rubber to 65-90% vulcanized
rubber. Mixer 50 can be a batch mixer or a continuous flow mixer.
Preferably, a continuous flow mixer, such as a Banbury mixer, is
used.
[0067] An appropriate amount of polymer is added to mixer 50 from
polymer tank 40, if necessary, to achieve a desired adhesive
consistency. Polymer is preferably added by spray and the amount to
add to the rubber blend should not exceed 5.0% of the total weight.
Appropriate polymer additives can include neoprene, polyethylene,
urethane and ABS.
[0068] The amount of polymer to be added is dependent upon periodic
testing. Specifically, representative samples of natural rubber
crumbs and vulcanized rubber crumbs which are to be made into
crossties are periodically mixed at between 240-370 degrees F.
(116-188 deg C.) and formed into an ingot by using a compression
mold. Once sufficiently cooled, the ingot is subjected to a
compression test.
[0069] As an example, ingots have been cooled to a surface
temperature of 100 deg F. (57 deg C.) before the test. If the
result is below 6,800 psi (46,886 kPa), additional natural crumb
rubber is added to the blend. However, if the amount of natural
crumb rubber is near 35% and the compression test is below 6,800
psi (46,886 kPa), polymer is added. The addition of polymer is
preferably used to obtain the desired compression strength; mainly
due to its high cost.
[0070] Since this process is utilizing recycled rubber, it is not
feasible to obtain an accurate chemical composition of the
feedstock. In other words, a facility which processes discarded
tires into RCR will be shredding thousands of tires made in
different years by dozens of tire manufacturers. A practical way to
ensure that the proper RCR blend for extruding my Tie is to perform
the periodic compression testing mentioned above.
[0071] The actual process for manufacturing crossties according to
my invention is as follows:
[0072] Subsequent to the blending in mixer 50, the rubber crumb
blend, including polymer if necessary, undergoes a milling process
60 using preferably a roller mill which heats the rubber blend to
between 240-370 degrees F. (116-188 deg C.) and compresses the
heated mixture into strips to form feedstock for the extrusion step
to be discussed shortly. Most preferably, the temperature is held
between 290-315 degrees F. (143-156 C.).
[0073] Milling process 60 is followed by extrusion 70. Depending
upon the relative outputs between milling 60 and extrusion 70, the
milled product may be placed in storage 65 for a short period of
time before extrusion.
[0074] During extrusion 70, the temperature is preferably
maintained within the same range mentioned above for the milling
process. The desired pressure range for extrusion is between 250 to
750 psi (1,724-5,171 kPa). Screw type extruders are preferred.
[0075] A die is selected which will provide an extrudate having the
desired width and height for the Tie product. As the product exits
the extrusion process, 70, it has the desired height and width and
is cut to the desired length of crosstie.
[0076] No special quenching is required and the rubber crosstie can
be cooled/cured 80 by ambient temperature. After the Ties have been
cooled, they are ready for storage and shipping. A problem may
occur if the rubber crossties are immediately exposed to ambient
conditions which are at or below 32 degrees F. (0 deg C.). The
physical properties, specifically compression strength, may be
jeopardized if the Tie is cooled too quickly. Therefore, gradual
cooling may be required if outside conditions are excessively cold
and this cooling may require the use of a heated room.
[0077] A recommended approach is to place extruded Ties into a
curing room 80 or area for a period of time such as between one to
four hours. This will permit the Ties to cool at a slow rate and
the heat dissipated by the Ties will actually heat the room;
particularly when cold conditions are present outside. As the Ties
cool to a temperature of 150 degrees F. (66 deg C.) or less, they
can be moved for storage or transport.
[0078] The extrusion process can be adapted to indent or deform the
longitudinal sides of the product so as to produce a crosstie 90
having a plurality of indentations such as the ribbed sides 97
illustrated in FIG. 4. Alternatively, FIG. 3 is a partial view of
crosstie 90 having pyramid indentations 95. The indented surfaces
can be made by machine cut. However, the indentations can be formed
into crosstie 90 while it is still deformable. Preferably, as part
of the extrusion step, at least one offset roller (not shown) can
be used to form the plurality of indentations such as serrations or
dimples into the crosstie. Where the intended use of the crossties
is on gravel beds, indentations can be formed on up to three sides;
namely the side which will become the bottom side when the crosstie
is installed as well as the two adjacent longitudinal
sidewalls.
[0079] The plurality of indented surfaces provide improved
frictional engagement with a gravel bed during crosstie
installation thereby avoiding the inherent difficulties of slipping
or sliding upon the gravel bed which occur with other crossties
during positioning and alignment. Frictional engagement is not
necessary for the topside and may hamper proper attachment of the
plate to the tie. Therefore, indentations are not recommended for
the topside. FIG. 2 illustrates a final installed position for a
crosstie 90.
* * * * *