|Title of Invention||
"RECYCLED RUBBER RAIL ROAD CROSSTIES"
|Abstract||A method for the manufacture of a railroad crosstie from recycled rubber 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. A feature of the invention is to produce a crosstie having at least one longitudinal side incorporating a plurality of indentations for more effective frictional engagement upon installation into a gravel bed to avoid slippage.|
|Full Text||RECYCLED RUBBER RAILROAD CRQSSTffiS
1. Field of the Invention
The invention relates to railroad rail support systems, specifically railroad crossties
or ties, and their method of manufacture.
2. Background of the Invention
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.
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. A relatively new approach
has been to produce a tie from cement having an iron center and encased within
recycled rubber and/or recycled plastics.
These alternative products suffer from one or more significant drawbacks. The
railroad industry is seeking an economical alternative to wood. Drawbacks
encountered with cement and reinforced concrete is that although 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.
Another significant drawback to these alternative crossties is the relatively low
force required to withdraw a spike driven into the tie. It is highly 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.
Additionally, almost all alternative tie products have increased noise levels as
trains pass, due to the surface hardness and steel, cement and plastic cross ties also
tend to undesirably shift in the gravel bed.
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 lowcost,
have similar performance characteristics, and have a longer life than a wood
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.
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.
As mentioned earlier, another problem facing the railroad industry is tile 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.
3. Disclosure of Invention
A method to manufacture railroad crossties from discarded rubber has been
developed. The rubber railroad tie can be used as wood tie replacements for new
and re-laid tracks. The rubber railroad tie can be made economically and utilize the
abundant supply of discarded rubber tires stockpiled at waste disposal sites. A
functional new design is disclosed which increases the frictional contact between
the crosstie and a gravel bed to prevent undesired crosstie movement.
4. Summary of Invention
The rubber railroad crosstie made according to the invention ("Tie") is made by a
process which heats granulated recycled rubber (sometimes referred to as crumb
rubber, rubber dust, or rubber fines), preferably not larger than 30 mesh (590
microns). The heated rubber is preferably milled and then extruded to obtain the
desired width and depth and thereafter cut to the desired length.
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
My invention requires two specific types of RCR. The first type is made from
vulcanized rubber. The primary source for vulcanized rubber is from automobile
and truck tires. The primary source for the second type is from tires classified as
natural rubber or rubber which has been de-vulcanized. Natural rubber tires are
mostly off-the-road (OTR) tires, which have less sulfur and zinc content than
vulcanized rubber, and have a lower melting point. 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.
Air pollution is not a concern during the process. The preferred milling and
extrusion temperature is between 290-310 degrees F (143-154 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.
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
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 may be formed using discarded automobile tires provided the
steel has been removed.
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.
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
My railroad tie is 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.
Ties can be manufactured into any length desired and are recyclable.
Creosote, a known carcinogen commonly used in the manufacture of wooden
railroad crossties, is not used in the manufacture of the Tie.
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 f t x 9 i n x 7 i n
(259 cm x 23 cm x 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).
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.
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.
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.
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.
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.
An optional and unique feature is that the Tie can be made 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 factional
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.
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.
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.
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.
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.
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.
The indentations can be formed while the Tie is still hot and receptive to
deformation. Alternatively, a Tie which is compression molded can have ribbed
sides integrated as part of the mold pattern. 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.
By way of example, the mechanical properties of a Tie made according to the
invention are as follows:
Density: 74.8 lbs/ft3 (1200 kg/m3)
Thermal expansion coefficient: 0.005% per deg F (0.003% per deg C)
Modulus of rupture: 26,982 psi (186,041 kPa)
Modulus of elasticity (bending): 6,717,000 psi (46,313,715 kPa)
Modulus of elasticity (compression): 174,144 psi (1,200,723 kPa)
Limit of elasticity: 487,584 psi (3,361,892 kPa)
Hardness: 9241bs/in (165 kg/cm)
Pressure to insert spike: 4,200 psi (28,959 kPa)
Pressure to withdraw spike: 3,360 psi (23,167kPa)
Life expectancy: 30-60 years
Weight load capacity (per Tie): 521,000 Ibs (236,534 kg)
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 either steel, cement or concrete
5. Brief Description of Drawings
The details of the invention will be described in connection with the accompanying
drawings in which Fig. 1 is an overall process flowchart for the manufacture of a
rubber crosstie; Fig. 2 is a perspective view of an installed crosstie, made
according to the invention; 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 and Fig. 4 is a perspective view of a portion of a crosstie, having
an alternative type of indentation, namely a plurality of ribs.
6. Best Mode for Carrying Out the Invention
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
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 is required and are stored
separately and identified in Fig. 1 as 20 and 30 respectively.
The mesh size is vital to the cohesive properties of the tie. A smaller mesh size
enables uniform heating and a stronger bond due to each particle having a larger
surface area. Natural rubber has a lower melting point and is more adhesive than
vulcanized rubber and it is this natural rubber portion which 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 of a larger size than 30 mesh (590 micron). Small
quantities of larger size particles may exhibit acceptable performance
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 Banbury mixer is used.
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 0.25% to
0.50% of the total weight. Appropriate polymer additives can include neoprene,
polyethylene, urethane and ABS.
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. As an example, ingots have been cooled to a surface temperature
of 100 deg F (57 deg C) before the test. If the test obtains a value below 6,800 psi
(46,886 kPa), then additional natural crumb rubber is added to the blend. However,
if the percentage of natural crumb rubber is near 35% and the compression test is
below 6,800 psi (46,886 kPa), then polymer is added. The addition of polymer is
preferably only used as a last resort to obtain the desired compression strength;
mainly due to its high cost.
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.
The actual process for manufacturing crossties according to my invention is as
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 290-310
degrees F (143-154 C).
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.
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
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.
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
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. When the Ties reach a
temperature of below 150 degrees F (66 deg C), they can be moved for storage or
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. Indentations can be formed three sides; namely the side
which will become the bottom side when the crosstie is installed as well as the two
adjacent longitudinal sidewalls.
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.
1. A crosstie made from recycled rubber characterized in that the crosstie
a product made by an extruder containing a blend of no larger than 30 mesh (590 microns) recycled natural crumb rubber and recycled vulcanized crumb rubber in a weight ratio of between 10-35% recycled natural rubber to 65-90% recycled vulcanized rubber and where said product exiting said extruder has a temperature of between 240 -370 degrees F (116-188 degC).
2. The recycled rubber crosstie as claimed in claim 1, wherein said crosstie has at least one longitudinal side which has a plurality of indentations.
3. The recycled rubber crosstie as claimed in claim 1, wherein said crosstie has four longitudinal sides and at least one of the longitudinal sides is provided with a plurality of indentations.
4. The recycled rubber crosstie as claimed in claim 1, wherein the rubber crosstie is an extruded product made from a blend of recycled natural crumb rubber and recycled vulcanized crumb rubber in a weight ratio of between 10-35% recycled natural rubber to 65-90% recycled vulcanized rubber.
5. 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 0.0-0.5% 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.
6. The method of producing a crosstie as claimed in claim 5, wherein said strength enhancing polymer is selected from the group comprising neoprene, polyethylene, urethane and ABS.
7. The method of producing a crosstie as claimed in claim 5, comprising a further step of forming a plurality of indentations in at least one side of said extrusion by an indentation-forming means.
|Indian Patent Application Number||785/DEL/2004|
|PG Journal Number||23/2009|
|Date of Filing||26-Apr-2004|
|Name of Patentee||HANSEN RUBBER PRODUCTS INC.|
|Applicant Address||4218, ENCORE DRIVE, SANTA BARBARA, CA 93110 (US)|
|PCT International Classification Number||E01B 9/00|
|PCT International Application Number||PCT/US01/15296|
|PCT International Filing date||2001-05-11|