The present disclosure relates to plastic pallets, particularly those used for transporting miscellaneous industrial and commercial goods by means of forklift devices and the like, suitable for use within warehouses.
Plastic pallets have been in use for a long time, but have not gained wide acceptance due to the failure to satisfactorily meet a variety of criteria, including standards of Grocery Manufacturers of America (GMA). Among the criteria in the standard are that pallets have fire resistances, sufficient to not exceed the heat release set by Underwriters Lab Standard 2335 when intentionally set on fire in a test facility, to simulate a warehouse fire. The pallet also must not be too heavy, must be strong enough to carry specified loads, and must be durable in resisting damage during use, as measured by certain tests and field use. So far, no pallet has been able to meet all these criteria. Indeed, the more fire retardant included in the plastics, the more fragile the plastic. Other problems include include excess weight, toxicity of the fire retardants, and cost. Thus, other approaches are sought.
Pallets are stored with and without goods in warehouses, typically in metal racks. Usually, when a fire occurs, many pallets will bum irrespective of the types and distribution of goods stored on the pallets. Where plastic pallets are utilized, and since such pallets may have a great deal of exposed plastic surface area, the heat and rate of combustion of the pallet will be high. A conflagration can result which overwhelms the sprinkler systems of the typical warehouse, particularly one which is designed for wood pallets (which evolve less heat with less rapidity).
U.S. Pat. No. 6,705,237 “Plastic Pallet Design” of Moore et al., the entire contents of which are specifically incorporated herein by reference, discloses a novel thermoplastic pallet comprising rectangular cross section hollow metal beams. The beams may form a structural framework within the spaced apart planes of the bottom and or top parts of the pallet. A pallet using the invention can meet the above-described load standards. Two beam arrays may be used, one near the deck when it is plastic and one near the base. If the deck is strong enough, as may be the case for some pallets, then the beams may be present only at the base.
United States Patent Application Publication No. US 2004/0216648 to Apps et al. discloses a thermoplastic pallet having a continuous metal beam running around the periphery of the pallet for strength; and, the beam is shaped and centered in the pallet so that the outer edges are inboard of the rails which support the pallet on a rack. The construction and performance of the Apps et al. pallet are different from those of the present pallet, which has different beam structure.
The above described and other disadvantages are overcome or alleviated by the present thermoplastic pallet having reinforcing cross beams which preferentially fail. Such pallet may be constructed such that the beams preferentially fail, so that when the pallet heats up in a fire, the pallet collapses and the amount of exposed plastic, and the amount of heat evolution is reduced. In an exemplary embodiment, the reinforcing beams, for example metal beams, are embedded in plastic. The beams run parallel to the plane of a deck of the pallet, and transverse to the length of the pallet and associated storage rack rails which support the opposing sides of a stored pallet.
In one exemplary embodiment, cross beams have lengths which are shorter than the spacing between the interior edges of the rails of a pallet rack. In another exemplary embodiment, one end of a cross beam is above the rail of a rack, while the other end is not, due to choice of length and side-to-side positioning of the beam within the pallet. The beams may be uniformly offset to one side, or they may be staggered in their offsets. Thus, in any embodiment, when the plastic of the pallet softens during a fire, one end of a beam will fall from the proximate edge of the rack as the plastic yields under the load of the beam. When one or more beams fail, the pallet will collapse, as is desired.
In another exemplary embodiment, a pallet has a beam with a composite structure; that is, the beam is reinforced, such as e.g., with metal, glass or graphite fiber, within a matrix, such as a thermoplastic. The plastic matrix is designed to soften during a fire, so that the reinforcement is no longer held therein and so that the pallet collapses. In another exemplary embodiment, the beam comprises fibers of lamellae. In another exemplary embodiment, the beam comprises thin sheet metal pieces. In another exemplary embodiment, a cross beam comprises two pieces that are attached to each other by a thermoplastic connector.
The foregoing and other objects, features and advantages of the present pallet will become more apparent from the following description of exemplary embodiments and accompanying drawings.
Referring now to the accompanying FIGURES, which are meant to be exemplary and not limiting:
The presently disclosed fire collapsible beam pallet recognizes that when there is a warehouse fire involving molded plastic pallets which are stacked one above another in a warehouse rack, the rate of heat output will be mitigated if the surface area of plastic pallet material which is exposed to flames is reduced. Thus, as described by exemplary embodiments herein, a pallet subjected to the heat of a fire desirably fails and falls from the rack. Such pallet may fall onto an underlying pallet and goods, or onto the floor. When multiple pallets sandwich together, the exposed surface area of burnable material will be reduced, and the access of oxygen bearing atmosphere is inhibited.
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In one exemplary embodiment, the pallet has a metal deck. In such embodiment, beams are provided in the rails which comprise the base of the pallet. While the above describes exemplary metal reinforcing beams, beams made of other materials, for example composite plastic materials, such as graphite reinforced plastic, or some strong ceramic, may be used. The beam is, in general terms, a member, partially or fully surrounded by the thermoplastic of the pallet (though not necessarily embedded therein), having substantially different properties, in particular, higher elastic modulus and tensile strength.
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In accordance with the above exemplary embodiments, in the event of a fire, the plastic of the pallet softens and loses strength, and or burns away, and cross beam 26 will no longer be supported at one or both of its ends. As the plastic softens or disappears, the one end of the pallet will fall from the rail, and the pallet will collapse into the space between the rails.
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In the foregoing and following embodiments, at least one cross beam incorporates the features described. If a pallet has a beam which fully spans the space between the opposing sides of the rack, when one or more of the other beams are configured as described above, in a fire, the pallet can be sufficiently weakened by the loss of support of the short or offset beams, such that it will tip around the one or more full length beams.
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As mentioned above, in all cases, the beam need not be a metal material, but may comprise other materials. In another exemplary embodiment, a beam is made of composite plastic material, for instance a strong fiber reinforcement, which beam in incorporated into a less strong matrix or molding compound. The matrix is chosen so that it deteriorates when heated, so that the reinforcing material can no longer serve its purpose and the beam collapses. For example, the beam may comprise long strand glass fibers or graphite fibers contained in a thermoplastic matrix which may or may not be different from the thermoplastic material of the pallet. The matrix softens and yields when there is a fire. Thus, the fibers will be no longer firmly gripped, relative to one another. The beam then loses its structural modulus, its shape, and its load capacity, and it and the pallet collapse. As an example, the reinforcement may be glass or graphite or metal fiber and the matrix may be high density polyethylene HDPE, polypropylene PP, polysufone PSF, polyethersulfone PES, or analogous material
In another exemplary embodiment, the beam comprises lamellae, such as strips of sheet metal or strands of wire. For example, the cross section of
In certain exemplary embodiments, the beam is described as embedded in plastic. It should also be recognized that simply placing the beam near such plastic may be sufficient, as long as melting of the plastic causes the beam to fail or displace. For example, suitable arrangements include placing the beam in a slot, wherein the beam may be partially exposed. Particularly for those embodiments which used a composite structure beam, there may be openings or thinner sections in the plastic around the beam, to speed localized heating and weakening of the beam during a fire.
The principles of the invention may also be applied to other products where there is a static load or dynamic load on the product and the structure desirably loses its strength in event of a fire or other thermal excursion.
While exemplary embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. It is to be understood that the present invention has been described by way of illustration and not limitation.
The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/654,759, filed Feb. 18, 2005, the entire contents of which are specifically incorporated herein by reference.
Number | Date | Country | |
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60654759 | Feb 2005 | US |