US 3835792 A
The invention relates to lightweight, reusable, molded plastic pallets used for support and transport of articles stacked thereon. The pallet has top and bottom decks, each having a generally corrugated structure, the transverse cross-sectional contour of the corrugations preferably being trapezoidal in shape, and both being provided with a plurality of feet, the feet on the top deck extending from the bottom face thereof and complementary feet extending from the top face of the bottom deck, the aligned feet of the top and bottom decks being adapted to be fastened together, permanently or disconnectedly, to form a space between the two decks for receiving the tines of a fork-lift loading apparatus, such as a lift truck.
Description (OCR text may contain errors)
United States Patent Wharton Sept. 17, 1974' [5 PALLET CONSTRUCTION 3,680,496 8/1972 Wcstlake 108/58 1 Inventor: Thomasvarker Wharton, 1001 3333385 111333 $132,332: .II'I. 183/22 Pembrook Dr., Neenah, Wis. 54956 I l I l h 1 Filed! 06- 3 1972 Primary ExaminerPaul R. Gilliam App]. No.: 302,340
Related US. Application Data Attorney, Agent, or Firm-Ladas, Parry, Von Gehr, Goldsmith & Deschamps  ABSTRACT The invention relates to lightweight, reusable, molded plastic pallets used for support and transport of articles stacked thereon. The pallet has top and bottom decks, each having a generally corrugated structure, the transverse cross-sectional contour of the corrugations preferably being trapezoidal in shape, and both being provided with a plurality of feet, the feet on the top deck extending from the bottom face thereof and complementary feet extending from the top face of the bottom deck, the aligned feet of the top and bottom decks being adapted to be fastened together, permanently or disconnectedly, to form a space between the two decks for receiving the tines of a fork-lift loading apparatus, such as a lift truck.
3 Claims, 9 Drawing Figures SHEET 1 0F 5 manna sen mu Pmmanswmn 3.835.792
SHEET 3 UF 5 v I IIGEQZQQ] PAIENIEDSEPITIBH 3%5192 sumsnrs 1 PALLETCONSTRUCTION CROSS-REFERENCE TO CO-PENDING APPLICATIONS This application is a continuation-in-part of my copending application Ser. No. 131,087 filed Apr. 5, 1971, now U.S. Pat. No. 3,702,100, issued Nov. 7, 1972, and assigned to the assignee of the present application.
SUMMARY OF THE INVENTION This invention generally relates to relatively lightweight, nestable, reusable pallet constructions made of molded plastic material and is more particularly concerned with a pallet assembly made of two decks, top and bottom, which are spaced with respect to each other. v
In the development of reusable molded plastic pallets, the major objective is to impart to the pallet the greatest stiffness and strength with the use of the least amount of material, least machine production time, and least investment in molds and in molding machinery. These requirements have been met by an invention which utilizes and combines a unique design, an efficient type of material, and a particularly suitable manufacturing process.
From the design standpoint, these requirements are met by the use of unique corrugated decks. Since a corrugated deck is weaker in bending strength and stiffness in the direction perpendicular to the axes of the corrugations, three important structural features are embodied in the corrugated decks according to my invention to overcome this weakness. First, the corrugations are made generally trapezoidal in shape, rather than in the conventional wavy corrugated shape, to provide more material in the flange areas of the crosssection. These flat surfaces act as the flanges of an I- beam. The near-vertical portions of the corrugations act as the web of an I-beam, although they are sloped for easy removal from the mold. This shape also provides the necessary flat surface on the top of the top deck for the pallet load and on the bottom of the top deck for sufficient area of contact with the tines of the mechanical handling equipment such as lift trucks. Secondly, the corrugations in both decks may be positioned in symmetric patterns so as to support each other and minimize distortion and racking. This positioning of the corrugations also provides greatest strength in the areas between the pallet feet which will bear on the tines of the lift truck when handled since the corrugations run transverse to the lift truck tines. Thirdly, in the direction opposite to the corrugations, which is the weaker direction of any conventional corrugated structure, strength and stiffness are increased by the provision of integral ribs between corrugations on the top and bottom faces of the two decks. These ribs are aligned so as to provide continuous spaced beams through the pallet body to provide maximum strength and stiffness in the direction opposite to the corrugations.
Since the legs extending upwardly from the bottom deck mate with respective legs extending downwardly from the top deck, it is only necessary to provide structural interconnections between the adjacent legs, open areas being provided between the structural interconnections thereby achieving economy in plastic material consumption. The load supporting framework surrounding each foot of the bottom deck is integral with the bottom deck and comprises at least two parallel runners interconnected through load distribution portions integrally connecting with the upwardly extending walls of the foot. In view of the heavy load supported by the runners, it is preferable to reinforce the runners, in a transverse direction, with a plurality of ribs. The connecting portions of the bottom deck which interconnect the feet are also provided with at least two parallel runners interconnected by load-distributing portions. There runners also may be reinforced with trans verse ribs.
The mating portions of the feet are provided with protuberances and interconnecting passage means which index the mating feet with each other and provide a passage for drainage.
As more fully described in the above-referenced copending application, the pallet assembly is manufactured by using a form of injection molding known as the structural foam process. This results in the production of strong and light-weight top and bottom decks.
Commercial methods of producing thermoplastic structural foams are described in Modern Plastics Encyclopedia 1969-1970, published by McGraw-Hill, New York, pages 243-247. A further discussion can be found in the 1970-1971 issue of this work, at pages 243-247. Also in Foamed Plastics, Vol. 9, Encyclopedia of Chemical Technology, 2nd Ed. 1966, pages 847-884, and U.S. Pat. No. 3,268,636, Aug. 23, 1966.
As is explained more fully in the above-referenced copending application, it is preferable to design the pallet so that all of the structural members of a uniform thickness, preferably on the order of one-fourth inch, so that the efficiency of the molding operation may be optimized. This can be accomplished easily, of course, by spacing the mold members one-fourth inch apart.
It is therefore an object of this invention to provide an improved pallet constructions.
A further object of this invention is to provide an improved foot construction for a molded pallet.
A feature of this invention is to provide a pallet construction with nestable upper and lower decks.
A further feature of this invention is to provide a pallet deck with load distributing portions on its lower face.
DESCRIPTION OF THE DRAWINGS The advantages and novel features of the inventive molded pallet assembly construction will be apparent on the following description of the preferred embodiment of the invention, wherein:
FIG. 1 is a perspective, exploded, view of the pallet assembly having top and bottom decks, with the top faces of the decks being exposed;
FIG. 2 is a perspective, exploded, view of the pallet assembly having top and bottom decks, with the assembly being shown inverted. so thatthe bottom faces of the decks are exposed;
FIG. 3 is a plan view of the top of the top deck; FIG. 4 is a plan view of the bottom of the bottom deck;
FIG. 5 is a fragmental perspective view of a comer of the pallet assembly, as shown in FIG. 1, but showing complementary feet mated together;
FIG. 6 is a sectional view taken through the corner of the pallet assembly along line 6-6 of FIG.
FIG. 7 is the sectional view of a portion of the bottom deck taken along line 77 of FIG. 5;
FIG. 8 is a fragmental perspective top view of a modified construction of a foot having a generally truncated octagonal conformation, extending from the top face of a bottom deck; and
FIG. 9 is a fragmental perspective bottom view of the foot and bottom deck shown in FIG. 8.
DETAILED DESCRIPTION Referring to the drawings, FIG. 1 illustrates a pallet assembly comprising a top deck and a bottom deck 22. The bottom deck 22 has the form of a rectangle with a plurality of hollow feet 24 positioned along the narrow sides of the rectangle and the plurality of hollow feet 26 positioned across the width of the rectangle and interposed centrally between the other feet 24. The feet 24 and 26 possess a truncated rectangular pyramidal form having slanted walls which assist withdrawl of the bottom deck from the mold during molding operation and which further permit nesting of the bottom decks when stacked on each other. The bottom portion of the feet may also be provided with stacking (antijamming) brackets not shown, as is well known in the art. The middle feet 26 may be larger than the feet 24, as is shown in FIGS. 14. The feet 24 along the narrow sides of the bottom deck 22 are interconnected by'connecting portions 28 and the middle feet 26 interconnect with each other by connecting portions 30 and interconnect with feet 24 by means of connecting portions 32. Each of the feet 24 and 26 may be provided with a protuberance 38 extending from the closed end 36 of the foot. The opening 34 passes through a protuberance 38 molded integrally with the supporting face 36. The protuberance 38 is adapted to engage an opening in a complementary foot in the top deck, as will be explained later. These openings permit drainage of the feet in the event that water accumulates therein and furthermore can be used to receive fastening means for coupling the mating feet together. Alternatively, the fastening may be accomplished by various types of joints or fasteners or by an adhesive interposed between the joints or mating faces of two complementary feet.
The connecting portions 28 contain parallel corrugations 40 and the connecting portions 32 contain parallel corrugations 42 while connecting portions 30 contain parallel corrugations 44. The form of the corrugations which have a transverse cross-sectional trapezoidal form, can be best seen in FIG. 7, wherein corrugations 42 comprise a series of parallel top and bottom walls or upper and lower base portions 46 and 48, respectively, interconnected by sloping walls or adjacent pairs of opposed legs 50 and 52, respectively. All of the corrugations are reinforced with transverse ribs 54 which are located intermittently along the longitudinal length of the corrugations 42. Since the entire bottom deck is molded, all portions of the constructions extend throughout the entire width and length of the deck integrally to form a single structural unit. For example, ribs 54 actually form continuous beams which extend from one side of the connecting portion 32 to the other.
The areas bounded by the connecting portions 28, 30 and 32 are devoid of plastic material and are designated as 56. Each of the connecting portions 28, 30 and 32 is longitudinally bounded by sloping portions 58 and 60 having load distributing portions 62 and 64 which, as best viewed in FIG. 7, interconnect a pair of runners 66 and 68. As can be readily seen, the load distributing portion 64 is designed to transmit substantially equal stresses to both of the runners 66 and 68. The runners are interconnected bytransverse ribs 70. The spacing of the transverse ribs 70 can be best viewed in FIGS. 2 and 4 wherein the bottom face of the bottom deck 22 is exposed to view. The reinforcing ribs 54 interconnecting the corrugations 40, 42 and 44 are also visible in these views.
Each of the feet 24 and 26 is bounded by a framework 72 integrally formed with the sloping walls of the feet. As best seen in FIG. 6, the framework 72 comprises a load distribution portion 74 from which a pair of runners 76 and 78 emerge. The load distribution portion 74 is designed to transmit approximately equal stresses to both of the runners 76 and 78. To strengthen h r sad 18.-.!Qi9f9293 29ttihi8" te transversely at intervals, as made manifest in FIGS. 2 and 4.
The sloping portions 58 and 60 which form the inner and outer peripheries of the bottom deck 22 cooperatively unite with the external portions of the frameworks 72 of the feet 24 and 26 to provide a continuous and uninterrupted peripheral loading surface for the bottom deck 22, as viewed in FIGS. 2 and 4. Runner 66 are unitary with runner 78 in the framework of the feet 24 and 26 to provide continuous beams. Similarly, the opposed legs 50 and 52 of the corrugations are unitary with the ribs 80 in the framework 72 of the feet 24 and 26 to provide continuous beams.
Referring to FIGS. 1-3, the top deck 20 has a rectangular lower face 82 from which a plurality of hollow feet 84 extend outwardly, along each narrow side of the rectangular face, and a plurality of hollow feet 86 extending transversly through the middle portion of the lower face. A rectangular upper face 83 is peripherally bounded by a L-shaped channel 85 having a downwardly extending side 85a and a horizontal side 85b forming a narrow flat margin which is coplanar with the upper face 83. The channel 85 is internally reinforced with spaced transverse ribs 850 as best viewed in FIG. 2. The feet 84 and 86 are provided with passage means such as a drainage outlet 88 which prevents fluid accumulation, and at the same time forms a means for interconnecting with a respective complementary foot extending from the bottom deck 22. As best viewed in FIG. 3, the feet 84 extending along the narrow side of the rectangular top deck 20 are interconnected by connecting portions 90 and are further interconnected with the centrally located feet 86 by means of connecting portions 92, the centrally located feet 86 being interconnected by connecting portions 94. The area bounded by the connecting portions 90, 92 and 94 in each quadrant of the top deck 20 defines a support panel 96. The connecting portions 90 are made up of a series of corrugations 98, similar to the corrugations 42 shown in FIG. 7, which are transversely reinforced with ribs 100. Similarly, connecting portions 92 are made up of a series of corrugations 102 which are, at spaced intervals, reinforced with ribs 104. Also, the connecting portions 94 are made up of a series of corrugations 106 reinforced with transverse ribs 108.
Each support panel 96 is formed of corrugations 110 reinforced by longitudinally extending ribs 112, transversely extending ribs 114 and diagonally extending ribs 116. Strength is imparted to the top deck 20 by molding it as a unitary construction, wherein the reinforcing ribs aligned with each other, constitute a single beam which extends from one side to the other of the top deck. For example, as shown in FIGS. 2 and 3, ribs 104 in the connecting portions 92 run continuously across the width of the top deck by uniting with ribs 114 contained in the support panels 96. Similarly, ribs 100 which run longitudinally of the top deck 20 combine with longitudinally extending ribs 112 in the support panels 96 to extend completely across the length of the top deck.
If additional strength is to be imparted to the feet extending from the top deck 20 and the bottom deck 22, reinforcing rib work may be molded into the feet, for example, as shown by rib work 118 in foot 84 in FIG. 3 and rib work 120 shown in foot 24 in FIG. 4.
In view of the corrugated construction of the top deck 20 and the bottom deck 22, it is desirable that the corrugations be provided with drainage openings, for example as shown by drainage opening 122 interposed between transverse ribs 104 as shown in FIG. 3.
FIG. 5 shows one corner of the pallet assembly and the structural mating of the two feet 24 and 84 as shown in enlarged view in FIG. 6, the opening 88 being dimensioned with respect to the dimensions of the pro tuberance 38 such that a snug-fit is obtained, thereby providing a disconnectable engagement in the event that it is necessary to take the top deck 20 and the bottom deck 22 apart for re-shipment purposes. On the other hand, it is apparent that the mating of the complementary feet of the two decks can be achieved permanently by use of cement or by the introduction of a connecting member, such as a bolt and nut through the passage means 34 and 88.
Although the form of the feet has been described as being a truncated rectangular pyramid it is apparent that octagonal, cylindrical, or other forms for the foot can be utilized so long as molding can be readily accomplished.
Referring to FIGS. 8 and 9, there is shown a modified form of a foot 124 having generally a truncated octagonal form having a series of small walls 126 interconnected by large walls 128 all interconnected by a common base 130 which is provided with a passage means such as an opening 132 which, in this particular embodiment, passes through a protuberance 134. The foot 124 extends upwardly from the top face of a bottom deck 22a. The foot 124 is interconnectedwith other identical feet by means of connecting portions as described in connection with the first embodiment of the disclosed pallet assembly. In this second embodiment, the foot 124, because of the additional wall area it possesses, is stronger than a foot of the same length and width, but of the truncated rectangular pyramid type described previously. Each of the small walls 126 extends from the base 130 through web members 138, shown on FIG. 9, which is angularly disposed between innermost runners 78a. The web members 138, the inner runner 78a and the outer runner 76a comprise a load support framework integrally connected with the small and large walls 126 and 128, respectively. The runners 76a and 780 are reinforced by spaced transverse ribs 80 a. Ribs 80a serve to absorb lateral impacts which may be imparted to the runners 76a, for example, by the tines of a fork-lift truck web members 138 serve to dissipate stresses in the runners 78a, and ribs 80a, as well as stresses in ribs 80b, integral therewith, which latter-mentioned ribs transmit stresses carried by the side walls 50 and 52 of adjacent corrugations. In this manner, the stresses in any part of the deck can be dissipated to other portion, rather than being abruptly terminated as with a generally perpendicular abuttment.
Other forms of legs may be desirable, of course, depending upon the desires and needs of the ultimate consumer. For example,a truncated cone-shaped leg might be employed. In fact, it may be desirable not to employ any leg at all on the bottom deck, and to merely affix the bottom deck to the underside of the legs of the upper deck.
The form of the top deck foot selected will dictate the dimensions of the corrugations to be selected. In the present embodiment, corrugations 98 and 102 terminate in end walls 98a and 102a integral with a pair of sloping walls 84a and 84b of the foot 84, as shown in FIG. 5. The recessed corrugations 102b have end walls 102:: integral with a part of the sloping wall 84a and 8411. End walls 102a and 1020 form a continuous beam across the top part of the walls 84a and 84b to effectively reduce the unsupported column height of the leg. Thus, the walls in each foot are strengthened at least on two sides by the series of longitudinal and transverse corrugations, as seen in FIG. 3.
The present molded structural foam plastic pallet offers many advantages over prior molded plastic and thermoformed plastic pallet constructions. Heretofore, plastic pallets have not been economicallyfeasible because they have been either too weak and flexible or too costly. The combination of the unique design of this pallet and the structural foam plastic process of injection molding results in a pallet with the required strength and stiffness and a pallet which is competitively priced. I
Although the present pallet is generally of a corrugated structure, its unique design has remarkable omnidirectional strength and resistance to bending under load stresses through the full width and length of the pallet deck. The pattern of the corrugations reinforced by transverse ribs, as previously described, provides a deck with omni-directional strength since it has no continuous lines of corrugations which would result in a weak axis, and has no intersections of corrugations, which would result in a point of stress concentration.
The dimensions and configuration of all the structural elements of the top and bottom decks of the pallet are proportioned so that the like or unlike (top or bottom) decks can be nested for shipment or storage. The undersurfaces of the top deck have a taper that is the same as in the upper surface of the bottom deck so that the pallets are nestable. In my preferred pallet construction, each deck occupies only about one and one quarter inch of stacking height even though each assembled double-deck pallet when supported on a floor is five and three-quarters inches high.
The top and bottom faces of the pallet are planar. The loaded pallets can therefore be readily moved over a floor or may be carried on various conveying devices including those having a series of rollers.
The corrugated structure of the top and bottom decks provides approximately equal exposed horizontal areas on the top and bottom surfaces of the pallet inasmuch as all the corrugations are of the same trapezoidal cross-section. These horizontal surfaces also function as the flanges of an I-beam when subjected to either downward or upward bending loads encountered by pallets.
The hollow feet of the decks which are molded in the form of rectangular truncated pyramids or octahedrons have sloping sides at an angle which permit almost complete nesting. The reinforcing ribs in the bottom wall of the feet provide additional strength. The openings in the recessed corrugations and in the closed ends of the feet permit drainage of accumulated fluids. Also as explained previously, the top deck feet are reinforced at their sides by the spaced corrugations which terminate and are integrally molded with the sides of the feet and the bottom deck feet are reinforced by the peripheral framework integrally formed with the feet.
The construction of the pallet feet provides strength against buckling, breaking or overturning which is a common weakness in prior pallets. As previously described, the side walls of the feet which are integrally molded and merged with the adjacent ends of the corrugations at the open end of the feet are reinforced and supported at the merged positions so that stresses imposed on both the top and the bottom decks are more evenly distributed and thus the foot stability is greatly increased. Also the cross-ribs integrally molded with the inner bottom surface and adjacent side walls act as braces or supports to the upwardly extending walls of the feet, and also they provide added strength by reducing the unsupported height of the foot walls thus making the upwardly extending walls of the feet considerably more resistant to buckling or breaking.
The novel construction of the bottom deck utilizes extensively in the construction of the connecting portions interconnecting the plurality of the feet and in the framework construction surrounding the openings of the hollow feet permit better load distribution through the use of load-distributing portions from which extend parallel runners additionally reinforced by interconnecting transverse ribs. Since most of the load placed on the pallet assembly is centrally located the pallet assembly has centrally located feet which are designed to support a larger portion of the load than the feet which are located along the sides of the decks.
Other advantages of the molded plastic pallet besides its lightweight include low cubage, durability, capability of being pigmented for color coding, capability of being washed, resistance to mold, mildew, fungus, or rotting, and suitability for embossed markings for identification purposes. A rectangular top deck of size 40" by 48" having a uniform wall thickness of one-quarter inch made of molded structural plastic foam weights approximate 22 pounds. The bottom decks, due to the open portions are even lighter, weigh about 16 pounds each. Thus, empty pallet assemblies of this invention weigh only about 38 pounds, in total, as compared with conventional single-deck wooden pallets which weigh from 70 to over 100 pounds each. The plastic pallets therefore, can be handled by laborers (male and female) as compared with wooden pallets which must be handled by lift trucks. Forty unassembled decks can be nested in a stack only about 102 inches high, as compared with wooden pallets which require about two to three times this amount of space. This means that about two to three times as many plastic decks can be shipped in a truck or rail car for about the same costs as the shipment of wooden pallets.
It is to be understood that the specific embodiments of the invention herein described are illustrative of the novel features of this invention and that changes and modifications of the specific details of construction may be made which are intended to be included within the scope of the appended claims.
1. A pallet assembly comprising top and bottom decks.defining a space therebetween for the insertion of lifting members of a loading apparatus, each deck having a plurality of support panels bounded by connecting portions and defining a body formed in a series of spaced parallel corrugations, the transverse crosssectional contour of the corrugations being in form of regular trapezoids having inclined opposed legs and horizontally disposed upper and lower base portions interconnecting adjacent pairs of opposed legs, with each of said base portions having an inner face, the successive corrugations being reinforced by a plurality of spaced beams integral with said inner faces of said base portions and at least a portion of each leg and extending transversely between pairs of said opposed legs and substantially perpendicularly from said inner face of the base portions, said beams being positioned in the successive corrugations in longitudinal alignment constituting continuous beams for resisting bending stresses exerted on the pallet, the said horizontally disposed exposed upper base portions of said corrugations of said top deck constituting a top planar loadsupporting face, and the oppositely disposed exposed lower base portions of the said top deck being adapted for engagement by fork-lift tines or tying means for securing loads to the pallet, and the said horizontally dis posed exposed lower base portions of said corrugations of said bottom deck constituting a bottom planar loadsupporting face, a plurality of hollow feet integrally formed and extending downwardly from the bottom face of the upper deck and mating with a plurality of complementary integrally formed hollow feet extending upwardly from the upper face of said bottom deck for spacing said top andbottom decks with respect to each other, each of said feet having an open base end and a closed outer end, means for coupling together said spaced top and bottom decks by securing together said closed ends of said complementary feet on said respective top and bottom decks, said bottom deck including an integral reinforced double wall framework defining said open base end of each hollow foot thereon, each framework comprising pairs of closely spaced parallel runners surrounding and integral with said base end of each foot, and a plurality of short transverse ribs extending between and integral with said parallel runners, said framework for each foot further being integral with said corrugations in said bottom deck.
2. A pallet assembly as defined in claim 1, including additional reinforced double wall frameworks having elongated pairs of closely spaced parallel runners and a plurality of short transverse ribs extending between and integral with said parallel runners, said additional frameworks being integral with and interconnecting each of said first mentioned frameworks defining the base of said feet, said additional frameworks further being integral with and parallel to said series of corrugations in said bottom deck.
3. A pallet assembly as defined in claim 1, wherein said frameworks for each of said feet have planar bottom load-supporting surfaces co-planar with said bottom planar load-supporting face of said bottom deck. 1