Abstract:
A plastic pallet has reinforcing beams which fail during a fire due to the effects of heat, so the pallet prematurely collapses and thus the rate of heat evolution is diminished, sufficient to meet fire standards. In one embodiment metal beams embedded in the plastic of the pallet have lengths which are shorter than the span between the rails of a pallet rack. They drop down and cause pallet collapse, when the surrounding plastic softens or melts. In another embodiment, the beam is a metal, fiberglass or graphite reinforced composite thermoplastic, which loses strength when the matrix softens or otherwise fails. In another embodiment, a metal beam has two parts which are connected by a thermoplastic fitting which softens and the fails during a fire.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     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. 
     
    
     BACKGROUND  
       [0002]     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.  
         [0003]     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.  
         [0004]     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).  
         [0005]     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.  
         [0006]     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.  
       SUMMARY  
       [0007]     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.  
         [0008]     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.  
         [0009]     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.  
         [0010]     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. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     Referring now to the accompanying FIGURES, which are meant to be exemplary and not limiting:  
         [0012]      FIG. 1  shows a bottom side of an exemplary plastic pallet having an array of beams which are embedded in the bottom of the pallet;  
         [0013]      FIG. 2  shows a detail of the top cross section view of an exemplary pallet corner;  
         [0014]      FIG. 3  is a vertical elevation end view of exemplary pallet supported in a warehouse rack along its opposing lengthwise ends;  
         [0015]      FIG. 4  is a front elevation view of an exemplary beam incorporated in a pallet;  
         [0016]      FIG. 5  is a bottom view of a pallet incorporating a plurality of exemplary beams;  
         [0017]      FIG. 6  is a bottom view of a pallet incorporating a plurlity of exemplary beams;  
         [0018]      FIG. 7  is a bottom view of a pallet incorporating a plurlity of exemplary beams;  
         [0019]      FIG. 8  is a cross sectional view of an exemplary tubular beam and connector; and  
         [0020]      FIG. 9  is a cross sectional view of an exemplary tubular beam construction. 
     
    
     DETAILED DESCRIPTION  
       [0021]     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.  
         [0022]     Referring now to  FIG. 1 , a bottom side of an exemplary plastic pallet  20  is illustrated, wherein an array of beams is embedded in the bottom of the pallet. Without being limited, pallet  20  may be constructed in accord with the aforementioned commonly owned U.S. Pat. No. 6,705,237 to Moore et al., the disclosure of which is hereby incorporated by reference. The embedded beams are represented in this and other figures by dashed lines.  
         [0023]     Referring still to  FIG. 1 , the exemplary beam array comprises lengthwise beams  24  and cross beams  26 . (Length and width are arbitrary in this disclosure, except that a pallet is considered to mount in a rack with its length parallel to the rails  30  of the rack.) In one embodiment, the beams are perforated steel box beams. In another exemplary embodiment, the beams run around the rectangular periphery of the pallet. In another exemplary embodiment, the beam ends are close to each other, but the beams are not structurally attached to each other.  
         [0024]     Referring now to  FIG. 2 , a detail of the top cross section view of an exemplary pallet corner is illustrated. The beams cross in the center of the pallet. The beams may be in the base and top frame of the pallet and are generally parallel to the plane of the pallet, that is to the plane of the goods-carrying deck  34  at the top of the pallet.  
         [0025]     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.  
         [0026]     Referring now to  FIG. 3 , a vertical elevation end view of exemplary pallet  20  is illustrated as supported in a warehouse rack along its opposing lengthwise ends  36 . The opposing sides  36  of the pallet rest on opposing side lips of L-shape cross section rails  30  of an exemplary pallet storage rack. Without being limiting, the distance between the inner edges of the racks, RL, is typically about 42 inches, to receive a typical pallet which is 48 inches wide.  
         [0027]     Referring still to  FIG. 3 , in another exemplary embodiment, the cross beams  26  have a length LB which is less than the spacing RL between the rails, and the beams are centered between the opposing lengthwise sides  36 . Thus, there is a gap G between the vertical extension of the ends of the beams and the vertical extension of the inner edges of the lips of the pallet rack. As used herein, a beam which is shorter than the width between the rack edges is called a “short beam”. Of course, there is some clearance between the vertical sides of the rails of the rack and the outside edges of the pallet. Thus, in another exemplary embodiment, the lengths of beams  26  are sufficiently short to accommodate the resultant play or possible shifting from side to side of a pallet mounted in the rack. Thus, in all cases with regard to this exemplary embodiment, the end of a beam  26  will not be above the vertical extension of the innermost edge of the rail. In other exemplary embodiments, e.g., where one end may extend beyond said vertical extension, and the other does not, the length and/or position of the beams may chosen accordingly to anticipate shifting within the rack.  
         [0028]     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.  
         [0029]     Referring now to  FIG. 6 , in another exemplary embodiment, at least one beam  26 A is offset (although all beams may be) from one lengthwise edge so that one end of the beam is vertically above the rack rail, but the other end is not. In this exemplary embodiment, the cross beams may be short beams, or they may have lengths which are equal or greater than the space between the rail inner edges.  
         [0030]     As illustrated in  FIG. 1 , lengthwise beams  24  run generally parallel to the rails and generally transverse to the cross beams. Lengthwise beams  24  need not have the features of the cross beams. Of course, if the pallet is intended also for mounting in racks which hold the pallet cross-wise, then beams  24  may have the same features as are described for cross beams  26 . In a pallet having the desired cross beam features described herein, beams  24  may be displaced inwardly relative to the edges of the rails of the rack, as for example, shown in  FIG. 4  and  FIG. 7 . Because, in this exemplary embodiment, the lengthwise beams are not structurally attached to the cross beams, the engineered pallet works even when both lengthwise beams lie vertically above the rack rail when the pallet is stored.  
         [0031]     Referring now to  FIGS. 5-7 , exemplary beam configurations are illustrated.  FIG. 5  illustrates an exemplary configuration wherein beams  26  overlie one cross rail  30 , but not another.  
         [0032]      FIG. 6  illustrates an exemplary embodiment wherein cross beams  26  are staggered in their offset. Beams  26 A are offset to the right, and beam  26 B is offset to the left. So, in use two of the beam ends at one side of the pallet have a gap G 3  relative to the rail  30 L, while the other beam end has a gap G 4  relative to rail  30 R.  
         [0033]      FIG. 7  illustrates an exemplary embodiment wherein cross beams  26  are all offset to one side of the pallet. That is, the ends are farther from one side than from the other side. Thus, in use all the beam ends will be farther from the rail  30 L than from rail  30 R. Lengthwise beams  24  are also incorporated into the pallet.  
         [0034]     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.  
         [0035]     Referring now to  FIG. 8 , another exemplary embodiment, incorporates a metal cross beam  26 D made of two pieces joined by a press-fit thermoplastic connector  32 . In another exemplary embodiment, the connector is offset from the center of the beam length, so it is not under a column. In such embodiment, there will be less mass of plastic to provide thermal inertia and inhibit heating and softening during a fire. The plastic of the connector may have the same or different properties, as compared to the plastic of the pallet. When there is a fire, the plastic of the connector  32  melts and fails, under the stresses imposed by the pallet weight and whatever load is on the pallet, and the pallet collapses. In this embodiment and the following two embodiments, the lengths of the cross beams may be short or of regular length.  
         [0036]     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  
         [0037]     In another exemplary embodiment, the beam comprises lamellae, such as strips of sheet metal or strands of wire. For example, the cross section of  FIG. 9  shows tubular beam  26 F, comprising shaped pieces of light metal angles  34 , held together using a thermoplastic or other heat degradable adhesive, or an injected encapsulating layer, as suggested by the dashed line  36  in the Figure. In a fire, the adhesive fails and the beams fails. While softening is the likely intentional failure mode of the plastics and matrixes here, other modes of failure due to heating may ensue.  
         [0038]     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.  
         [0039]     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.  
         [0040]     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.