Patent Application
20050196233
The invention is directed to articles for absorbing impact energy, such as offset blocks for mounting between guardrails and guardrail posts; bumpers for use at truck loading docks and marine docks; and other articles which may or will encounter impacts by massive objects, and which should beneficially absorb large amounts of kinetic energy.
Guardrails are commonly installed alongside United States highways in areas where it is desirable to prevent vehicles from leaving the highway, e.g., at elevated portions of highway or between opposing lanes of traffic. Such guardrails can be generally classified into one of two performance categories, rigid and non-rigid. Rigid guardrails are not intended to deflect upon impact, and are instead intended to constrain the vehicle and redirect it onto the roadway. As an example, trapezoidal concrete slabs are commonly used to provide rigid guardrails between adjacent lanes of traffic. Non-rigid guardrails, such as the standard steel w-beam, are intended to deflect upon impact so as to absorb and dissipate kinetic energy from an oncoming vehicle without overly damaging the vehicle and harming its passengers. The w-beam primarily dissipates impact energy via several mechanisms: plastic flexural deformation of the rail; deformation and breakage of support posts; and the “plowing” of support posts through the ground. It is estimated that 600-800 million feet of w-beam guardrail are currently installed in the United States.
There has been interest in improving the impact-absorbing qualities of guardrails (e.g. steel w-beams), as well as other types of barriers and railings. For instance, U.S. Pat. No. 6,149,134 and the patents cited therein describe composite and other guardrails which may be used as substitutes for common steel w-beam guardrails. However, there has thus far been little attention paid to the properties of the structures used to mount/anchor guardrails and other impact-dissipating structures, and the possibility of modifying their properties to achieve beneficial increases in their ability to dissipate energy.
The invention, which is defined by the claims set forth at the end of this document, is directed to bumpers and similar objects which are used to receive and dissipate large amounts of impact energy, and offset blocks and mounting posts for such objects. A basic understanding of some of the preferred features of the invention can be attained from a review of the following brief summary of the invention, with more details being provided elsewhere in this document.
A basic exemplary version of the present invention provides an offset block for the absorption of impact energy, wherein the block includes an inner core which is at least partially formed of elastic material, and an outer shell which is at least partially formed of a rigid material. The core of the block is preferably made from recycled elastomeric materials such as rubber from discarded vehicle tires. The core also preferably has an outer surface configured to promote adequate adhesion to the shell. For instance, the core surface may contain one or more elongated grooves depressed inwardly into the length of the surface of the core. Alternatively or additionally, the core surface may be lightly ground to leave a rough finish to promote the desired adhesion between the shell and the core.
The core of the block is substantially surrounded by the rigid outer shell. The elastic material of the core provides the compressive strength necessary to absorb impact forces. However, without a rigid shell, the core is vulnerable to excessive buckling upon impact. Therefore, the rigid material of the shell is bonded to the elastic core so as to provide the protection necessary to prevent excessive damage to the core. The shell is preferably at least partially made from recycled materials such as polycarbonate, acrylonitrile butadiene styrene (ABS), and polypropylene. In combination, the rigid shell and elastic core absorb energy from impact forces and distribute such energy evenly across the surface of the block. This helps to provide a uniformly smooth collapse of the block under impact.
Additionally, the rigid shell helps to improve the life and performance of the block, allowing the core to absorb multiple impacts before needing replacement. Further, the rigid shell provides improved resistance to freezing temperatures, improved moisture stability, and/or an improved resistance to drastic changes in temperature. Thus, the rigid shell helps to prevent deterioration of the block from exposure to environmental conditions.
The rigid shell can usefully contain a fibrous reinforcing material embedded therein, such as single, bundled or braided continuous fibers, discontinuous fibers, or woven or non-woven fabrics. A particularly preferred reinforcing material includes glass fibers. Alternatively or additionally, a layer of fibrous reinforcing material may be interposed between the shell and the core of the block. In a preferred version, chopped and/or continuous glass fibers are used for reinforcement.
The block may be installed in different settings for applications requiring shock absorption. The block preferably includes a mounting bore which extends through the block, thereby allowing a fastener to be inserted to engage the block to a bumper (such as a guardrail) and/or a mounting structure (such as a mounting post for a guardrail). For instance, the block may be mounted on a bumper to enhance its ability to dissipate impact energy, and/or to better protect the bumper from damage upon impact. The block may also be mounted on a mounting structure that is immovably anchored to its surroundings, such as a guardrail or loading dock. In addition, two or more energy absorbing blocks may be used in combination with each other to provide additional protection from impact forces. For instance, multiple blocks may be stacked together and mounted on a bumper, mounted on a mounting structure, interposed between a bumper and an anchored mounting structure (e.g. a sunken post), or positioned in any other desired configuration. Because the block is easily mounted to other blocks or to mounting structures, it can be used in a variety of configurations.
Further, the block is easy to replace. For instance, a damaged block mounted on a guardrail can be easily replaced with a substitute block without replacing the entire guardrail. By simply removing the fastener, the block can be removed from the mounting structure, reducing labor costs.
The description set out above is merely of exemplary preferred versions of the invention, and it is contemplated that numerous additions and modifications can be made. These examples should not be construed as describing the only possible versions of the invention, and the true scope of the invention will be defined more fully from the following detailed description and claims of the preferred version of the invention made in conjunction with the accompanying drawings.
In a preferred version, the block 100 is made by compression molding recycled thermoplastic pellets about the core 102 to form a rigid outer shell 104. While compression molding is a preferred method for forming the outer shell 104 about the core 102, other molding techniques (e.g., injection molding) could be used instead. While thermoplastics are preferred owing to their cost and ease of use, it is also possible that thermosets might be used for the outer shell 104. Testing has revealed that without the outer shell 104, the elastomeric core 102 is vulnerable to excessive damage at the immediate point of impact, and it will rapidly lose elasticity. By adding the outer shell 104, impact forces are distributed more evenly across the area of the block 100, increasing the energy dissipation performance and lifetime of the block 100.
The inner core 102 is preferably prepared by using a saw or other cutting tool to cut discarded vehicle tires into the desired shape and size. The size and shape of the core pieces can vary as the user desires. It is notable that recycled tires are useful materials for the core 102 not only owing to their cost and availability, but also because the treads/grooves and other discontinuities in their surfaces readily allow the shell 104 to complementarily flow about and bond with the core 102 during molding. However, while the elastic inner core 102 is preferably made of portions of discarded tires, other or additional elastomeric materials may be used. If other sources of elastomeric materials are used, the surface of the core 102 may need to be altered, such as by adding grooves 106 or other discontinuities to provide the desired surface for molding. A simple option is to simply sand or otherwise scuff the surface of the core 102 to present a roughened surface for molding.
The thermoplastic used for the shell 104 is preferably at least 90% pure for superior compression, tension and bending properties, though other purity levels may be acceptable if properties are not unduly degraded. Recycled 90% pure ABS pellets have proven to result in a durable shell 104 which retains at least 70% of its tensile, bending and compressive strength after 18 months of aging under harsh conditions (approximately equal to 60 years of standard environmental use).
Once the piece(s) of the core 102 are configured as desired, the core 102 may be placed in a compression or other mold having the desired shape, and the shell 104 may be molded about the core 102. While the mold could present virtually any shape for the exterior of the shell 104, it is preferable that the mold define the shell 104 with an outer surface evenly spaced from, and complementarily shaped with respect to, the core 102 (i.e., that the shell 104 be defined with generally uniform thickness about the core 102). If a reinforcing layer 108 is desired between the core 102 and the shell 104 to further protect the core 102 and distribute loads, the core 102 may be wrapped with fabric or reinforcing strands. A preferred material for the reinforcing layer 108 is glass fiber or cloth, but fiber or cloth of other materials, such as carbon, aramid (KEVLAR), metal, etc. can be used. Alternatively or additionally, rather than situating the reinforcing layer 108 as a boundary between the core 102 and shell 104, it may be embedded in the shell 104, as by interspersing the fibrous reinforcing material among the pellets of the outer shell 104 (e.g., as chopped strands).
The shell 104 is preferably molded about the core 102 by simply pouring thermoplastic particles (beads/pellets, powder, or flakes) into the lower section of a compression mold, inserting the core 102 therein, and then further filling the mold with additional particles prior to closing it with the upper section of the mold. The mold sections are then forced together under heat to compression mold the shell 104 about the core 102. In tests, a SO-230H compression molding machine (PHI-Tulip Corp., City of Industry, Calif.) with a maximum force of 5 tons was used. The two top and bottom pressure plates, used to close the mold sections and apply pressure thereon, are first wrapped with aluminum foil or a similar material for easy cleaning after molding. As the polymer melts about the core 102, they flow about the core 102 (and any reinforcing layer 108), and fill the voids, grooves, and other discontinuities of the inner core 102 to form a complementary interlock between the shell 102 and core 104.
When molding is complete, the pressure is released and the mold is removed from the machine for cooling. Forced air or liquid cooling may be used to speed the cooling process if desired. When cool, the mold sections are removed from the molded block 100, and any finishing modifications (such as a mounting bore 110) may be added. Such a mounting bore 110 could be formed by simply drilling a hole through the block 100, and a liner (such as a length of pipe/tubing) could be fit therein if desired. Alternatively, a mounting bore 110 might be formed upon initial molding of the block 100: the mold sections could include a protrusion which defines a bore 110, and the thermoplastic beads (or other matter to be molded into the shell 104) and tire sections (or other elastic materials defining the core 102) can be fit about the protrusion such that when the compression molding of the block 100 is complete, the mounting bore 110 is defined in the block 100.
Once prepared, the block 100 of the present invention is ready for use in settings where it will be subjected to impact forces. As an example, in
The invention is not intended to be limited to the preferred versions described above, but rather is intended to be limited only by the claims set out below. Thus, the invention encompasses all different versions that fall literally or equivalently within the scope of these claims.
This application is a continuation under 35 U.S.C. §120 of U.S. Utility patent application Ser. No. 10/937,620 filed 9 Sep. 2004, which in turn claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application 60/501,793 filed 10 Sep. 2003, the entirety of both of these prior applications being incorporated by reference herein.
This invention was made with United States government support awarded by the following agencies: DOE (Dept. of Energy) Grant No. DE-FC26-00FT40598 The United States has certain rights in this invention.
| Number | Date | Country | |
|---|---|---|---|
| 60501793 | Sep 2003 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10937620 | Sep 2004 | US |
| Child | 11031772 | Jan 2005 | US |
