Abstract:
A hollow molded unitary plastic pallet is provided for use in handling and transporting cargo, particularly with forklift trucks. The pallet comprises upper and lower surfaces with legs disposed on the lower surface. Reinforcement of the pallet is achieved by means of holes through the pallet surfaces and by means of reinforcing grooves disposed on the legs and on the lower surface of the pallet. The grooves on the lower surface extend from the holes to the legs and continue down along the length of the legs to their bases.

Description:
BACKGROUND OF THE INVENTION 
     This invention pertains to pallets useful in material handling, particularly to one-piece plastic pallets designed for use with forklift equipment. 
     For a number of years, wooden pallets have been a mainstay of the material handling business. In the past, wooden pallets have provided advantages of economy, simplicity and durability, principally because of the lack of other suitable materials. With the growth in the plastics industry, a wide variety of plastic materials have been investigated to determine their suitability for use as a pallet material. By comparison with wood, plastics offer the advantage of cleanliness and cleanability. Many plastics, moreover, can also be manufactured into pallets in a single molding operation, thereby avoiding costly hand labor in their fabrication. The molding operation also affords an opportunity to include design features in the pallet for various reasons. Improved stacking of empty pallets, reinforcement and resistance to damage are some of the goals which can be attained through special designs of plastic pallets. 
     Because of the capability of plastic materials to provide certain advantages over conventional wood and metal pallets, standards have been adopted by some organizations which require highly specialized properties. In the food and pharmaceutical processing industries, for example, cleanliness and cleanability are important. A pallet which can be steam-cleaned to provide a surface suitable for direct contact with unpackaged food is a desirable article. Resistance to chemicals such as detergents, acid foodstuffs, fish oils and vegetable oils is also important. Capability to withstand rough treatment without developing splinters or broken edges or corners is desirable in any application, including the food and pharmaceutical business. Light weight and temperature resistance are two more attributes desirable and attainable in plastic pallets. 
     Providing a plastic pallet light in weight, durable, easily cleaned, capable of supporting heavy loads and of being used with forklift equipment constitutes one of the principal objects of this invention. A specific object is to provide a pallet of the above type which is preferred for use within the food and pharmaceutical processing industries. 
     SUMMARY OF THE INVENTION 
     This invention is directed to hollow unitary plastic pallets comprising 
     A. AN UPPER SURFACE; 
     B. A LOWER SURFACE; 
     C. AN EXTERIOR EDGE WALL EXTENDING BETWEEN SAID UPPER SURFACE AND SAID LOWER SURFACE AND CONNECTING THE TWO SURFACES; 
     D. LEGS INTEGRALLY ASSOCIATED WITH SAID LOWER SURFACE AND EXTENDING DOWNWARDLY FROM SAID LOWER SURFACE; 
     E. AN INTERIOR SUPPORT MEMBER EXTENDING BETWEEN AND CONNECTING SAID UPPER AND LOWER SURFACES, SAID MEMBER BEING LOCATED WITHIN THE PERIMETER OF SAID EXTERIOR EDGE WALL; 
     F. REINFORCING GROOVES DISPOSED ON SAID LOWER SURFACE EXTENDING FROM SAID INTERIOR SUPPORT MEMBER TO SAID LEGS, AND 
     G. REINFORCING GROOVES DISPOSED ON SAID LEGS, EXTENDING FROM SAID LOWER SURFACE TO THE BASE OF SAID LEGS. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
    
    
     In the accompanying drawings: 
     FIG. 1 is a perspective view of the top and two sides of a pallet within the scope of this invention; 
     FIG. 2 is a perspective view of the bottom and two sides of the same pallet; and 
     FIG. 3 is a bottom plan view of the pallet. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings, a pallet 1 is shown having an upper surface 21 and a lower surface 9 joined together by an exterior side edge walls 10 and exterior front and back edge walls 23 to form a hollow unitary structure. The legs 5, 6, 7 and 8 of the pallet are designed and proportioned to permit the tines of a forklift truck to pass between the legs and under the lower surface of the pallet when the tines are inserted from at least one direction. Preferably the legs are so arranged that the pallet can be lifted by the forklift tines when inserted from any of a number of directions. In the case of square pallets, the legs are preferably arranged to accommodate the tines of a forklift inserted from any of the four sides of the pallet. The same is true of a rectangular, non-square pallet. To facilitate the description of rectangular non-square pallets, the longer sides of the pallets will be referred to as the front and back while the shorter sides will be referred to simply as the sides of the pallet. It is understood of course that the front, back and sides of a square pallet will be identical. In the accompanying drawings, the rectangular pallet has four corner legs 5, 2 side legs 6, 2 front and back legs 7 and a center leg 8. Positioned in back of the four areas between a corner leg 5, side leg 6, front or back leg 7 and center leg 8 is a corner hole 2. Front and back holes 3 are located between front and back legs 7 and center leg 8. Side holes 4 are located between side legs 6 and center leg 8. All of the holes are bounded by interior wall 20 connecting the upper surface 21 and lower surface 9. The interior walls serve as interior support members maintaining suitable spacing between the upper and lower surfaces. Along the lengths of all of the legs 5, 6 and 7 are reinforcing grooves 11 extending from the upper surface 21 of the pallet to the base of the leg. Inasmuch as the legs 5, 6 and 7 are integrally associated with the lower surface 9 and exterior edge wall 10, the reinforcing grooves 11 are also integrally associated with the legs and the exterior edge wall. On the lower surface 9 are a number of additional reinforcing grooves extending from the various holes to the legs and down the lengths of the legs to their bases. Extending from each corner hole 2 to the corner leg immediately adjacent thereto are two reinforcing grooves 12. From the same corner holes 5 one reinforcing groove 13 extends to the front or back leg 7 adjacent to the hole. Another two reinforcing grooves 17 and 22 extend from the hole 5 to the center leg 8. And a reinforcing groove 14 extends from the hole 5 to side leg 6. From each front and back hole 3 there are two reinforcing grooves 18 extending to the center leg 8 and two additional grooves 19 extending to each of the front and back legs 7. The side holes 4 also have four reinforcing grooves extending to adjacent legs, two grooves 15 extending to the side legs 6 and two grooves 16 extending to the center leg 8. As can be seen from the drawings, all of the grooves are integrally molded into the lower surface 9 and the legs, down which legs the grooves extend to the base of the legs. 
     The dimensions and structural details of the pallets can vary within fairly wide limits. The interior support members are readily included in the pallet in the form of interior walls which circumscribe apertures in the pallet surfaces. The apertures or holes can be as few as one, preferably at least about four, and as many as 16 or 20. The apertures will usually number from about 4 to 16, with eight apertures being preferred. The sizes and shapes of the apertures can also vary considerably depending upon load requirements, the total number of apertures, size and shape of the pallet, size and placement of the legs and the placement of the reinforcing grooves on the lower surface of the pallet. For pallets with 9 to 15 square feet of loadbearing surface containing eight circular holes, holes having diameters of 6 inches are satisfactory. Depending upon a variety of other factors, apertures can vary from 2 inches or less up to about 12 inches or more in their smallest dimension. The apertures in the pallet surfaces serve a multiple purpose. First the apertures, together with their interior walls connecting the upper and lower pallet surfaces, provide reinforcement of the pallet by supplying additional support elements between the upper and lower surfaces, thereby transferring loads from the upper pallet surface to the lower surface. Secondly, the apertures provide means for permitting fluids such as water, grease, cooking oil and the like to run off the surface. The apertures also facilitate ventilation and air flow around certain materials transported on the pallets such as cooked food, fresh fruit and vegetables and flowers. Prompt freezing of other foods such as ice cream is also facilitated by the presence of the ventilating apertures. 
     The number of legs on the pallet can vary from a minimum of two up to any reasonable maximum of 15 to 20 or more. Considering both structural design limitations as well as economies in the molding operation, the number of legs is preferably from about 4 to about 12, and most preferably 9. The lengths of the legs from the lower surface of the pallet to the base of the legs should be at least about three inches if the pallet is to be used with forklift equipment to permit the tines of the forklift truck to pass under the pallet easily. Preferably, the legs will be from about 3.5 to about 8 inches long and more preferably about 4 inches. The opening between the legs can also vary substantially from no opening in the case of one continuous leg spanning one entire side of a pallet, up to 36 inches or more. Preferably the openings between the legs are at least 3.5 or 4 inches up to about 18 or 24 inches. 
     Regarding the pallet surfaces, they can be 1/16 inch or less up to one inch or more in thickness, depending upon the maximum load the pallet is designed to sustain. Pallets capable of carrying loads of 4 to 5 pounds per square inch can be designed with upper and lower surfaces of 1/8 inch thicknesses. It is often convenient to make hollow pallets with all wall thicknesses, including the legs and exterior edge wall, identical. For certain applications, however, it may be desirable to manufacture the pallet with some wall thicker than others. As an example, the upper and lower surfaces of a pallet can be molded 1/8 inch thick and the walls of the legs much thicker such as 1/2 inch or more. 
     In the accompanying drawings, the placement of the reinforcing grooves is limited to the lower surface of the pallet. It is of course possible and entirely within the scope of this invention to include reinforcing grooves or ridges in or upon the upper surface of the pallet as well as the lower surface. One of the desirable features, however, of a preferred type of pallet is the smooth upper surface of that pallet, free from grooves, protrusions and other surface irregularities. The planar upper surface is particulary desirable for use in the food and pharmaceutical processing industries because the planar surface cleans more easily and also because the surface is less likely to retain dirt, grease, food particles and the like than a surface with a plurality of grooves, recesses and ridges. 
     The thickness of the pallet, that is the distance between the exterior surfaces of the upper and lower pallet surfaces, can also vary widely from a mere fraction of an inch to several inches. For pallets with about 9 to 16 square feet of load-bearing area with wall thicknesses of about 1/16 to 1/4 inch and load-bearing capacities of 6 to 10,000 pounds, a thickness of about one to about four inches has proved satisfactory although thicknesses greater or smaller can be employed. Loadbearing capacities can be increased by using pallet thicknesses of 2 to 6 inches in combination with certain other design details. As a result, there is no practical limit which can be imposed on pallet thicknesses. 
     The dimensions of the reinforcing grooves constitute an important variable of the pallets of this invention. Depending upon the thickness of the pallet and of the legs, the grooves can be either shallow or deep. The grooves can moreover vary in width and depth depending upon their location on the pallet. In a typical 14 square foot pallet with a thickness of three inches, grooves 2 inches deep and 1 inch wide are acceptable. As an alternative, the horizontal grooves in the lower surface of the pallet could be two inches deep and two inches wide with vertical grooves in the legs being as much as one inch or more shallower or deeper or wider or narrower. Another alternative could be to make all the grooves, horizontal and vertical, 2 inches deep and 1 inch wide. It can be appreciated, of course, that if the pallet thickness is 4 or 6 inches instead of 3 inches, the grooves can be made much deeper, thereby reinforcing the pallet even more than is possible with a pallet which is thinner. 
     The material from which the pallet can be made can be any of a large number of plastic materials. Both thermosetting as well as thermoplastic plastics can be used. Examples of suitable polymers include phenolic resins such as phenolformaldehyde, epoxies, melamine-formaldehyde polyesters, polyethylene, polypropylene, nylon, acrylic resins, polystyrene, polyvinyl chloride and a number of other common and specialty plastics including copolymers and terpolymers such as ABS (acrylonitrile-butadiene-styrene polymer). In addition, the foregoing polymers can be modified with innumerable additives such as plasticizers, stabilizers, foaming agents, pigments, fillers and dyes to produce polymer materials with special or improved properties. 
     Depending upon the polymer material used in the pallet, the method of fabricating the pallet can be quite different. Injection molding is one method commonly used in the manufacture of thermoplastic materials. Other possible methods include extrusion followed by hot or cold stamping. In both an injection molding process and in a stamping process, it will be convenient to form the pallet in two halves and then join the halves to form a unitary structure. Many other processes could also employ the above technique. Included are blow molding, casting and thermoforming. Other processes such as blow molding and rotational molding can be used to manufacture a one-piece pallet in one step without the need for joining two or more portions together. Polyethylene, particularly the high-density type with a density of at least 0.93, is a material particularly preferred for use in the above-described pallets because of its combination of low cost, resistance to environmental use, easy moldability and good mechanical properties. When polyethylene is selected as the pallet material, rotational molding is one of the particularly preferred fabrication processes. 
     It should be understood that changes and modifications in the design of the pallet shown herein by rearrangement, elimination or addition to its component parts can be made without departing from the spirit of this invention. For instance, apertures without interior walls could be produced in a pallet and a plastic plug inserted in the pallet structure thereby eliminating the apertures while at the same time providing interior support between the upper and lower surfaces of the finished pallet. Or the apertures could be made very small in the pallet and filled or plugged with plstic material before use. Another obvious modification would be the use of ridges instead of grooves to provide reinforcement in the finished pallet. Ridges used in such a manner should be considered to be inverted grooves and therefore properly included within the scope of the foregoing invention. These and other modifications can be made without departing from the scope of this invention.