Use of recycled plastics for preparing high performance...

Details Use of recycled plastics for preparing high performance... Use of recycled plastics for preparing high performance...

1999-01-27

2001-02-20

Nutter, Nathan M. (Department: 1732)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S241000, C238S084000, C238S085000, C238S106000

Reexamination Certificate

active

06191228

ABSTRACT:

SUMMARY OF THE INVENTION
The present invention relates to use of plastic materials for manufacturing railroad ties. In particular, the invention relates to manufacturing high performance railroad ties from recycled plastics containing polyolefin and polystyrene materials.
Railroad ties serve the function of not only supporting the rails but also maintaining the proper distance between rails under expected loads. Failure to adequately serve either of these roles can lead to a derailment, endangering both lives and property. Yet, railroad ties are subject to extremely harsh conditions, thereby increasing the chance of derailment.
Ties are exposed to large temperature variations, excessive amounts of ultraviolet light, severe weather conditions, attack from microorganisms and insects, and stress imposed by use.
In general, a railroad tie must be able to maintain the desired distance between and under a lateral load of 24,000 lbs., a static vertical load of 39,000 lbs., and a dynamic vertical load of 140,000 lbs. Thus, for a typical railway wherein the distance (gauge) between the rails is 56.5 inches, the ties must be able to maintain this distance without increasing by more than 0.125 inches, under the expected temperature and load variations, so as to prevent derailment.
To effectively withstand such loads, the tie material must possess both stiffness and strength. In this regard, a railroad tie should, in general, exhibit the following physical properties:
compression modulus: at least about 172,000 psi flexural modulus: at least about 172,000 psi compression yield stress: at least about 3,000 psi compression strength: at least about 3,000 psi flexural strength: at least about 3,000 psi
Another factor regarding maintaining the proper distance between rails is thermal expansion. To be suitable as a railroad tie, the material must exhibit a low thermal expansion. Preferably, the material has a coefficient of thermal expansion of less than 6×10
−5
in/in ·° F.
To prevent the occurrence of accidents, the materials used for manufacturing railroad ties need to be stiff, strong and resistant to ultraviolet light, temperature fluctuations, and microbe/insect attack. Also, the material should be nonconductive to preclude electrical flow between the rails. For example, for freight railways, electrical signals are sent through the rails for purposes of communication between the front and back of the train. For passenger railways, electrical power is often sent through the rails themselves. Therefore, to prevent electrical shorts between the rails, the ties supporting the rails should be made from nonconductive materials.
The tie material should also be durable to avoid deterioration due to abrasion during use. For example, one form of abrasion associated with railroad ties is tie seat abrasion. This occurs when the tie plates cut into the ties. Ties that are made from materials that are stiffer and stronger than wood in the direction perpendicular to the tie axis are better at alleviating tie seat abrasion.
Since the rails are to be attached to the ties, the tie material also has to be suitable for use with typical types of fasteners, such as those used for wood materials, e.g., nails, screws, spikes, bolts, etc.
Typically, railroad ties are manufactured from wood, and to some extent steel-reinforced concrete. While wood is a relatively inexpensive material, it is very susceptible to attack from microorganisms such as fungi and insects, which will weaken and deteriorate the tie. To compensate for this, wooden railroad ties are chemically treated to resist such attacks. Examples of such chemical treatments are creosote treatment and chromate/copper/arsenic treatment. These treatments greatly increase costs. Further, chemical treatments only delay attack, not prevent it. Wooden ties are also quite susceptible to damage from harsh weather conditions and excessive sunlight. As a result of these drawbacks, wooden ties require frequent replacement or regauging, again increasing costs, in materials, labor, and disposal. Replacement and/or regauging costs can be quite substantial as ties are being utilized in numbers of about 3000 ties per mile.
Similarly, steel-reinforced concrete railroad ties are also susceptible to degrading forces, for example, abrasion, stress and strain. In fact, concrete ties have been found to cause premature failure of rails. This is because concrete ties are generally very stiff. As a result, when placed at the standard distance, the ties do not aid in absorbing the stress imposed on the rails thereby forcing the rails to flex more between the ties under load. To address this problem, concrete ties are often spaced closer together than wooden ties. This, of course, leads to increased costs.
Damp and freezing weather conditions cause damage to both wooden and concrete railroad ties alike. Water from rain or snow can penetrate into the surface of a wooden or concrete railroad tie. If the tie is then exposed to freezing conditions, the water will expand as it freezes, causing the formation of cracks thereby weakening the tie. In the case of reinforced concrete ties, such cracks can also lead to oxidation of the reinforcement bars.
Attempts have been made to manufacture railroad ties from other materials. For example, Murray, U.S. Pat. Nos. 5,094,905 and 5,238,734, discloses making railroad ties from recycled tires. The costs, however, associated with recycling tires is high. Also, Murray uses adhesives such as epoxies to bind together the granulates of recycled tires. Such adhesives further contribute to high manufacturing costs. In addition, the expected modulus, that is the stiffness, of such a material would be quite low. It is unlikely that a tie made from such material would be able to maintain the proper distance between the rails at the expected load levels. To date, railroad ties manufactured from recycled tires have not found broad commercial application.
On the other hand, plastic polymers and plastic composite materials offer a viable alternative to wood and concrete. Manufactured plastics composites can exhibit the necessary stiffness strength, resistance to heat expansion and deformation, as well as increased resistance to degradation from moisture, excessive sunlight and attacks by microorganisms and insects. Plastic ties would also have a longer expected service life thereby reducing the labor and material costs associated with replacement.
Due to the inherent resistance to microorganisms, insects, and moisture, plastic ties obviate the need for chemical treatments used for wooden ties. This represents not only a cost savings, but will also eliminate waste disposal problems for chemically treated wooden ties.
However, the cost of raw materials is a disadvantage of plastic polymers and plastic composites. Virgin polymer resins can be quite expensive thereby making their use economically unfeasible.
Still attempts have been made to manufacture general replacement lumber from plastics and plastic composites. Trimax of Long Island Inc. manufactures a lumber substitute made from a stiff plastic composite material made of fiberglass and high density polyethylene (HDPE). A typical lumber product made solely of HDPE has a relatively high compression strength of about 3,000 psi, but has a low stiffness, i.e., compression modulus, of only about 100,000 psi. In comparison to HDPE alone, the Trimax material has a higher stiffness (i.e., compression modulus of about 200,000 psi) but a lower strength (compression strength of about 2,000 psi). Due to its low strength, the material is unsuitable for use as a railroad tie.
Eaglebrook Products Inc. also manufactures a synthetic lumber substitute. The material is made from relatively pure HDPE and, therefore, exhibits a comparatively low compression modulus and relatively high coefficient of thermal expansion. For plastic lumber HDPE the coefficient thermal expansion is greater than about 7×10
−5
in/in ·° F. To date, neither of the products manufactured by Trimax and Eaglebrook have found any signif

Affiliated with

Also associated with

Rating

Use of recycled plastics for preparing high performance... does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Use of recycled plastics for preparing high performance..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Use of recycled plastics for preparing high performance... will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2613975