Rackable plastic pallet

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RACKABLE PLASTIC PALLET

Background of the Invention

This invention relates to shipping and storage pallets and more particularly to pallets having a plastic construction.

Pallets have traditionally been formed of wood. Wood pallet however have many disadvantages. For example, they are subject to breakage and thus are not reusable over

<td> an extended</td><td> period</td><td> of</td><td> time.</td><td> They</td><td> also take</td><td> up a</td>

<td> 10 considerable</td><td> amount</td><td> of</td><td colspan="3"> valuable floor space in</td><td> the</td>

<td colspan="2"> warehouse when they</td><td colspan="2"> are not</td><td> in use.</td><td> They are</td><td> also</td>

<td> difficult to</td><td colspan="2"> maintain</td><td> in a</td><td> sanitary</td><td> condition,</td><td> thus</td>

limiting their usability in applications where sanitation is important, such for example as in food handling applications. In an effort to solve some of the problems associated with wood pallets, plastic pallets have been employed with some degree of success. In one generally successful form of plastic pallet design, a twin sheet construction has been used in which upper and lower plastic sheets are formed in separate molding operations and the two sheets are then selectably fused or knitted together in a suitable press to form a reinforced double wall structure. Whereas these twin sheet plastic pallets are generally satisfactory, when they are stored in a rack in a loaded condition, the plastic material of the pallet over a period of time may tend to creep with the result that the platform structure of the pallet may warp to an extent that

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PCT/US91/01223 the pallet becomes disengaged from the rack support members and the pallet, with its load, falls out of the rack. The pallet warpage also creates problems with respect to automatic retrieval systems which depend for their successful operation on the pallet maintaining an essentially unwarped configuration. Attempts have been made to avoid these warpage problems in plastic pallets by arranging some,.., manner of stiffening insert assembly in association with the plastic main body of the pallet ,but these prior art stiffening arrangements have tended to be unduly complicated and unduly expensive.

Summary of the Invention

This invention is directed to the provision of a plastic pallet which is extremely résistent to creepage or warpage.

More specifically, this invention is directed to the provision of a plastic pallet which may be stored on a rack in a loaded condition over extended periods of time without incurring any significant creep or warpage.

The invention is further directed to an improved method for forming a plastic pallet.

The invention pallet is of the type including a plastic planar upper main body structure defining a planar upwardly facing load receiving surface and a plastic planar lower base structure secured to the main body structure in an underlying relation thereto and coacting therewith to define tunnels therebetween for the entry of material handling equipment.

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According to an important feature of the invention, at least one of the structures comprises a twin sheet structure formed of upper and lower plastic sheets individually thermofarmed and fused together to form the structure.

According to a further feature of the invention, the main body structure is fused to the base structure.

According to a further feature of the invention, both of the structures are formed as twin sheet structures each including thermoformed upper and lower sheets fused together.

According to a further feature of the invention, the base structure includes a plurality of beam members extending parallel to the load receiving surface of the main body structure. In one embodiment of the invention, the beam members are constituted by discrete beam member assemblies individually secured to the under side of the main body structure and in another embodiment of the invention, the beam members are encapsulated in a common .20 base structure.

According to a further feature of the invention, the main body plastic structure includes a platform section and a plurality of legs extending downwardly from the platform section, and the base structure is secured to the

- 25 bottoms of the /. legs. ;; ? This arrangement provides an efficient, and / convenient means : of ; mounting the base structure to the main body plastic structure.

According to a further feature of the invention, the base structure includes a plurality of raised portions

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PCT/CS9V01223 extending from a location proximate one side edge of- the base structure to a location proximate another side edge of the base structure and a beam member is coextensive with each raised portion of the base structure. This arrangement provides a convenient and effective means of packaging the beam members relative to the remainder of the pallet.

According to a further feature of the invention, each beam member comprises a metallic tubular beam. This arrangement allows inexpensive and commercially available tubular stock to be employed in the construction of the invention pallet.

According to a further feature of the invention, the base structure includes a plastic housing encapsulating each beam. This arrangement provides a convenient means of incorporating the beams into the base structure.

.. According to a further feature of the invention, the base structure is formed as a twin sheet structure including a first plastic sheet overlying the beams fused to a second plastic sheet underlying the beams. This arrangement allows the known and effective twin sheet technology to be employed in the construction of the base structure of the pallet.

According to a further feature of the invention,

-the base structure is secured.to the main body structure.by . ,(- fusing the. upper faces of the plastic housings of the base structure to lower faces of the main body structure. This

... arrangement provides a simple, effective and inexpensive

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PCT/US91/01223 _s 3076840 “ □ — means of rigidly securing the upper and lower structures of the pallet together to form the final pallet assembly.

According to a further feature of the invention, the base structure includes a generally planar lower portion and the beam members are positioned on the lower portion. This arrangement provides a flat lower foot portion to firmly plant the pallet on its associated support surface while further providing means to mount the beam members to the base structure.

According to a further feature of the invention, the legs of the main body structure are arranged in rows; the beam members are positioned in parallel relation on the upper side of the planar ' lower portion of the base structure with each beam member positioned beneath a respective row of legs; and openings are provided in the planar lower portion between adjacent beam members. This arrangement allows material handling equipment of the type commonly referred to as a lowboy to enter the tunnels between adjacent beams by riding over the planar lower portion and thereafter positioning the wheels of the lowboy in the openings in the lower planar portion to allow the wheels to react against the support surface to allow the _; lowboy to lift the pallet.

Brief Description of the Drawings-&lt;

FIGURE. 1 is a perspective view of a plastic pallet according to the invention;

FIGURE 2 is a bottom view of the invention pallet;

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FIGURE 3 is a cross-sectional view taken on line

3-3 of FIGURE li

FIGURE 4 is an exploded perspective view of the invention pallet;

FIGURE 5 is a perspective view of the base structure of the invention pallet?

FIGURE 6 illustrates steps in the formation of the invention pallet?

FIGURE 7 illustrates the invention pallet 10 employed in a rack structure in a loaded configuration;

FIGURE 8 is a cross-sectional view taken on line 8-8 of FIGURE 1 and illustrating the manner in which the invention pallet may be lifted with a lowboy?

FIGURE 9 is a perspective view of ah alternate 15 form of plastic pallet according to the invention;

FIGURE 10 is a bottom view of the pallet of

Figure 9?

FIGURE 11 is a cross-section view taken on line 11-11 of Figure 9;

FIGURE 12 is a detail, bottom view of the leg construction employed in the pallet of Figure 9?

FIGURE 13 is a perspective fragmentary view of the beam structure employed in the pallet of Figure 9; and

FIGURE 14 is as cross-sectional view taken on 25 line 14-14 of Figure 13;.... ...............

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Detailed Description off the Preferred.. Embodiment

The invention pallet 10, as seen in Figures 1-8, broadly considered, includes a main body plastic structure 12 and a base structure 14.

Main body plastic structure 12 includes a planar platform section 16 and a plurality of legs 18 extending downwardly from the platform section. Platform section 16 defines an upwardly facing planar load receiving surface 20, and legs 18 are hollow and open upwardly in load receiving surface 20 to form a plurality of rectangular openings 22 in the load receiving surface 20. For example, nine legs may be provided with one leg at each corner of the pallet, an intermediate leg along each side of the pallet, and a central leg.

Plastic structure 12 embodies a twin sheet construction and is formed by vacuum forming an upper polyethylene plastic sheet 24, vacuum forming a lower polyethylene plastic sheet 26, and thereafter fusing the two sheets together at selected points to form the final

20. plastic structure. The fusion or knitting points are illustrated in the drawings by dashed lines between the upper sheet 24 and the lower: sheet 26. As shown, the upper and lower sheets may.be fused or knitted at the interface of peripheral flange portions 24a,26a? at the interface of .25 .downwardly, extending; leg portions 24b,26b; and at the .«interface of‘.downwardly extending protrusions -24c on the . upper sheet 24 and upwardly extending protrusions 26c on the lower sheet 26.; Further details of the manner in which a plastic twin sheet pallet of this general construction

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- 8 may be formed are disclosed in United States Patent No. 4879956 assigned to the assignee of the present application.

Base structure 14 includes a plurality of beams

40, an upper plastic sheet 42, and a lower plastic sheet

44. Each beam 40 may comprise, for example, a rolled steel tubular member having a generally rectangular crosssectional configuration.

Plastic sheets 42 and ^44 are preferably formed of 10 polyethylene- Base structuré'-14 is fabricated by forming sheet 42, preferably in a vacuum forming operation, into the convoluted, generally sinusoidal configuration, best seen in Figure 4, including base portions 42a and a plurality of parallel upstanding rib portions 42b; forming sheet 44, preferably in a vacuum forming operation, into a convoluted configuration, best seen in Figure 4, including base portions 44a and parallel pairs of raised rib portions 44b each defining an upwardly opening groove 44c therebetween? placing a beam 40 in each groove 44c; placing upper sheet 42 over lower sheet 44 with each raised rib portion 42b overlying and encapsulating a respective pair of rib portions 44b and with each raised rib portion 42b coacting with a respective groove 44c to encapsulate the .·. j-·:respective beam 40 within, groove 44c.

_/?itr25 - : - ; . .Upper and. lower sheets :42,44 are brought together ·— while . still·in a heated,, fusible condition to selectively fuse portions of the upper sheet to portions of the lower sheet. Specifically, the under sides of base portions 42a of upper sheet 42 are fused to the upper sides of base

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<img file="CA2076040C_D0001.tif" />

portions 44a of lower sheet 44 and the under sides of ribs 42b are secured to the upper sides of ribs 44b to encapsulate beams 40 and form the final base structure, as best seen in Figure 5. The completed base structure comprises a planar lower or foot portion 14a formed of the fused together base portions 42a, 44a of the upper and lower sheets and a plurality of rib portions 14b formed of the fused together rib portions 42b,44b of the upper and lower sheets encapsulating the respective beams 40. Base structure 14 also includes a plurality of generally rectangular openings or apertures 14c in the planar lower or foot portion 14a of the base structure between adjacent rib portions 14b. Preferably, and as shown, four apertures 14c are provided with two apertures between each pair of adjacent rib portions 14b.

As best seen in Figure 5, the ends 50 of the base structure 14 include plastic end portions 42d, vacuum formed as part of the upper sheet 42, which act in the completed base structure to cover the otherwise exposed ends of the beams 40 so as to preclude the entry of contaminants and moisture into the base structure and present an aesthetically pleasing appearance. It will be

-understood that end portions 42d of upper sheet 42 are ,ΐfused, during.the formation of the base structure, to the

- rend edge faces of· the respective rib pairs 44b of the lower . sheet 44.

As best seen in Figures 1 and 4, the legs 18 of main body structure 12 are arranged in three parallel rows

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2076040 _₁₀_ with three legs in each row and the base structure 14 is positioned beneath nain body structure 12 with each rib portion 14b mounted beneath and extending along a row of legs so that each rib portion 14b coacts at its upper face with the lower side of three legs.

The base structure 14 has an overall size and shape generally corresponding to the overall size and shape of the main body section 12 and is positioned beneath the main body structure 12 such that the edges of the base structure are generally coextensive with the corresponding edges of the main body structure.

To secure the base structure 14 to the main body structure 12, and as best seen in Figure 6, the main body structure 12 is positioned above a platen 60 and the base structure 14 is positioned beneath the platen 60 (as seen in Figure 6a) ; the main body structure 12 and the base structure 14 are brought into contacting relation with the upper and lower faces of the platen 60 (as best seen in Figures 6b) with the lower or bottom sides of the legs 16 contacting the upper face of. platen 60 and the upper faces of rib portions 4 2b contacting the lower face of the platen; the platen is suitably heated as by electric means to render the plastic material contacting the platen fusible; and (as seen in Figure 6c) the base structure and main ; body structure are moved away from the platen, the platen is removed, and the: base structure and main body structure are brought together to press the lower or bottom sides of the legs against the upper faces of the rib portions 42b to fuse or knit the plastic material of the

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-_1Χ_ 2076040 main body structure and of the base structure at their interfaces to form the final pallet assembly.

The invention pallet will be seen to retain all of the advantages of a plastic pallet while overcoming the disadvantages of prior art plastic pallets. Specifically, the invention pallet is especially effective in situations, as seen in Figure 7, where the pallet is loaded and placed in a loaded condition on a storage rack with the pallet supported by the ends of the base structure. When thus racked, the base structures acts to preclude creepage or warpage of the pallet even over extended periods of storage, thus avoiding the problem with prior art plastic pallets which, when utilised in the loaded, racked situation shown in Figure 7, have tended to creep and warp over a period of time with the result that the pallets have become disengaged from the mounting brackets 52 and the pallets, with their loads, have fallen out of the rack. The invention pallet, by avoiding pallet warpage, also overcomes the problem with prior art pallets wherein the pallets, after extended periods of use, assume a warpage that complicates their handling by standardised automatic retrieval equipment. The foot or lower portion of the base structure of the invention pallet also provides a flat, extensive, footprint , for the pallet to provide a firm

25-, footing_: - for the pallet -.and facilitate movement'*'of the pallet even over irregular transfer surfaces;.·

The... invention pallet also facilitates handling either by the forks of a forklift truck or by lowboys. Specifically, the forks of a forklift truck may enter the

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- 12 pallet from any of the four sides of the pallet with the forks entering into the tunnels formed both crosswise and lengthwise between the legs. As best seen in Figure 8, the pallet also provides access from two sides of the pallet by a lowboy 70 of the type including wheels 72 supporting a lift structure 74 which may be raised in known manner by jacking movement of a handle 76. Although the lowboy may not enter the pallet from the sides parallel to the rib portions 14b, the lowboy may readily enter the pallet from either of the other two sides with the wheels 72 of the lowboy riding readily over the relatively thin obstruction provided by the planar lower or foot portion 14a of the base structure for movement into the apertures 14c to allow the wheels 72 of the lowboy to be positioned on the pallet support surface 78 and provide a reaction surface to allow the pallet to be raised above the support surface in response to jacking movement of the handle 76.

The alternate invention pallet 110, seen in Figures 9-14, broadly considered, includes a plastic main body structure 112 and a base structure assembly comprising ? a; plurality of beam structures 114.

Plastic main body structure 112 includes a planar platform section 16 and a plurality of legs 118 extending downwardly from the platform section.; Platform section 116 •r 25 defines an upwardly-facing planar load receiving surface 120, and legs ^118 are : hollow and open upwardly in load receiving surface 120 to form a plurality of rectangular openings 122 in the load receiving surface 120. For example, nine legs may be provided with one leg at each

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- 13 corner of the pallet, an intermediate leg along each side of the pallet, and a central leg.

Main body plastic structure 112 embodies a twin sheet construction and is formed by vacuum forming an upper polyethylene plastic sheet 124, vacuum forming a lower polyethylene plastic sheet 126, and thereafter fusing the two sheets together at selected points to form the final plastic structure. The fusion or knitting points are illustrated in the drawings by dashed lines between the upper sheet 124 and the lower sheet 126. As shown, the upper and lower sheets may be fused or knitted at the interface of peripheral flange portions 124a,126a; at the interface of downwardly extending leg portions 124b,126b,; and at the interface of downwardly extending protrusions

124c on the upper sheet 124 and upwardly extending protrusions 126c on the lower sheet 126. Further details of the manner in which a plastic twin sheet pallet of this general construction may be formed are disclosed in United States Patent 4879956 assigned to the assignee of the present application.

The upper and lower sheets 124,126 are also configured in the region of the bottoms of the legs to fuse together to form a downwardly opening groove 130 in the bottom wall of each leg. Groove . 130 is . defined by a

2.5 groove top wall portion 134 and by outwardly tapering and : ? f downwardly extending groove-side wall portions 136 with top wall 134 and side walls 136 coacting to define a generally trapezoidal cross-sectional configuration for the groove

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2Q7604Q - i4 130. Apertures 138 are also provided in groove top wall portion 134 in a punching operation.

Each beam structure 114 of the base structure assembly has an inverted T configuration in cross section and includes a beam 140, an upper plastic sheet 142, and a lower plastic sheet 144.

Beam 140 may comprise, for example, a rolled steel tubular member and has a generally rectangular crosssectional configuratioh.

λ

Plastic sheets 142 and 144 are preferably formed of polyethylene. The beam structure 114 is fabricated by forming sheet 142, preferably in a vacuum forming operation, into a convoluted configuration (best seen in Figure 14) including base portions 142a and- a central upstanding spine or stem portion 142b; placing beam 140 centrally along lower sheet 144; placing upper sheet 142 over beam 140 in covering relation; and fusing the outboard or base portions 142a of sheet 142 to lower sheet 144 to totally encapsulate beam 140 within the plastic housing formed by the knitted sheets 142,144.

Spine portion 142b of sheet 142 is further „ provided with a series of longitudinally spaced apertures 142c corresponding in number and spacing to a series of

-: longitudinally spaced apertures 142a provided in the upper .-25 .-wall of the beam 140 with the beam apertures 140a aligning

...respectively with. the^: spine'apertures 142c in the completed beam structure. Also, as seen in Figure 13, the ends 150 of the beam structure each include a plastic end portion 142d, vacuum formed as a part of the upper sheet 142, which

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PCT/US91/01223 act in the completed beam assembly to cover the otherwise exposed ends of the beam 140 so as to preclude the entry of contaminants and moisture into the beam structure and present an aesthetically pleasing appearance.

As best seen in Figures 9 and 10, the legs 118 are arranged in three parallel rows with three legs in each row and three beam structures 114 are provided for respective mounting along each row of legs. Thus, the three legs in any given row engage successive portions of a respective beam assembly at longitudinally spaced locations along the beam assembly.

The beam structures 114 have an overall length generally corresponding to the overall length of the platform section 116 and are mounted on the legs such that the beam structures are parallel- and the respective ends of the beam structures are aligned, with the respective end edges of the platform section in the final pallet assembly.

In the final pallet assembly, the spine or stem portion of each beam assembly, as constituted by the spine portion 142b of the first plastic - sheet 142 and the beam 140, assumes a generally trapezoidal-configuration and is received snugly in the trapezoidal grooves 130 in the bottoms of the legs, and the lower sheets 142,144 coact to define a base extending outwardly from the central spine portion in contiguous underlying relation to the legs to form a base for the pallet. As shown, the base portions of the several beam structures coact to provide a wide area, firm footing for the pallet.

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- 16 The beam structures are fixedly secured to the plastic structure 112 by the use of fastener devices such as pop rivets 152 positioned in aligned apertures 138, 142c, and 140a so as to firmly and positively secure the beam structures to the plastic structure. Alternatively, the beam structures may be secured to the plastic structure by knitting or fusing the upper sheet 14 2 of each beam structure to the confronting plastic material of the associated legs. ../*

As with .the pallet of Figures 1-9, the pallet of Figures 1-14 will be seen to retain all of the advantages of a plastic pallet while overcoming the disadvantages of prior art plastic pallets and, specifically, will be seen to be especially effective in situations, as seen in Figure 7, where the pallet is loaded and placed in a loaded condition on a storage rack with the pallet supported by the ends of the beam structures.

Whereas preferred embodiments of the invention have been illustrated and described in detail, it will be apparent that various changes may be made in the disclosed embodiment without departing from the scope. or spirit of the invention.