WO1998023489A1

WO1998023489A1 - Paper pallet

Info

Publication number: WO1998023489A1
Application number: PCT/IL1997/000241
Authority: WO
Inventors: Assaf Amir; Ran Klarfeld; Maria Kanyavsky; Victor Shchigal
Original assignee: Kinarot Pallets Ltd.
Priority date: 1996-11-28
Filing date: 1997-07-15
Publication date: 1998-06-04
Also published as: IL119716A; EP1027255A1; AU3457997A; IL119716A0

Abstract

An improved paper pallet (100) includes a generally planar interior construction (102) formed of a cellular paper product and having upper and lower surfaces and transverse sides extending therebetween; and an outer skin (112, 114) formed of a paper product and wrapped around the interior construction (102) so as to define upper and lower planar portions having similar planar dimensions to the upper and lower surfaces of the interior construction and being arranged in touching contact therewith, wherein the outer skin (112, 114) also has transverse portions connecting the upper and lower portions together such that the outer skin has a rectangular cross section.

Description

PAPER PALLET

FIELD OF THE INVENTION The present invention relates to cargo pallets in general and, in particular, to paper pallets

BACKGROUND OF THE INVENTION Cargo pallets made of paper are well known in the art An advantage of paper pallets as opposed to more traditional wooden pallets is that they are much cheaper than wooden pallets, they are much lighter, and they are generally easier to dispose of once discarded A principle aim in the manufacture of paper pallets is forming them so as to bear loads of great magnitude, such that they are capable of replacing wooden pallets regardless of the loading conditions

An indication of the state of the art is provided by the following patent publications

US Patent No 4,319,530, entitled "Pallet Having Runners With Displaceable Sections " relates to a pallet which includes a rectangular deck and also runners and pads which are made of a paper honeycomb material and which are attached to the underside of the deck to support the deck in an elevated position above a floor, a wood pallet, or some other supporting surface The runners extend along the sides of the deck for the full length of the deck The pads, on the other hand, are located between the runners, there being an end pad along each end of the deck and a center pad between the two end pads Entry slots exist between the pads and runners for the full length of the pallet, and these slots are capable of accommodating the tines of a forklift Furthermore, the end pads are separated from the center pad by cross channels, which align with sections of the runners that are easily displaced from the remaining portions of the runners under the application of a laterally directed force The sections that are so displaced are capable of passing through the cross channels, and the voids that are formed will likewise accommodate the tines of a forklift Thus, the pallet is supplied in the two-way entry configuration for maximum strength, yet is easily converted to the four-way configuration to provide greater versatility

US Patents No 5,213,050 and 5,230,291 , both relate to a cargo pallet constructed of paper or functionally equivalent sheetstock The pallet design includes a central platform or deck constructed of a honeycomb filler supported by a number of footblocks supporting a central platform on a floor surface The bottom of the pallet is covered by a combination of sheets patterned in such a way that the legs supporting the central platform are integral with that central platform, that is, the footblocks (or legs) do not have a seam at their juncture to the central platform Desirably the lower portion is formed of two sheets, one sheet ("the bottom cover") is cut and folded in such a way that the legs and the surface adjacent the bottom of the central portion are of the shape in which the pallet is finally used The other sheet ("lower facing sheet") is of the general size and shape of the bottom with cutouts allowing the footblocks (covered by the bottom cover sheet) to protrude through that lower facing sheet It is positioned adjacent the bottom surface of the central platform The upper surface of the central platform is covered with a generally continuous sheet ("the upper facing sheet") The upper facing sheet may be a corrugate or heavy stock paper depending upon its ultimate usage To enhance the torsional and deflective strength of the central platform and thence that of the pallet, a corrugated sheet may be used as the upper facing sheet and positioned so that the corrugations of the upper facing sheet and those of the lower facing sheet are not parallel Additionally, the various corrugated sheets may be folded over the edges of the honeycomb core and fastened to another surface US Patent No 5,269,219 entitled "Pallet Design Using Paper Materials," describes a pallet fabricated from paper products This pallet has a load-supporting deck, a top cover sheet with tuck tabs that provides a fastening and link to the runners, a bottom sheet glued to the deck that provides a solid surface to attach the runners, and runners spaced apart and at the appropriately height to provide access and maneuverability to the forks or a forklift or handjack The pallet is formed from a combination of paper, paperboard, corrugated paper board, honeycomb and adhesive and the fabrication of the pallet reduced to a minimum of parts provides a sufficiently strong yet lightweight support for goods competitive in cost to conventional wood pallets None of the above-described paper pallets presents an alternative to the conventional wooden pallets under very high loading, and for substantially all types of loading, whether concentrated or distributed SUMMARY OF THE INVENTION It is thus an aim of the present invention to provide an improved paper pallet, which is constructed so as to more efficiently utilize the inherent mechanical properties of different paper components formed of different paper products, thereby to provide a pallet which is capable of bearing substantially higher loading than that of prior art paper pallets, without regard to whether the load is a concentrated load, or whether it is a distributed load

There is thus provided, in accordance with a preferred embodiment of the invention, an improved paper pallet which includes a generally planar interior construction formed of a cellular paper product and having upper and lower surfaces and transverse sides extending therebetween, and an outer skin formed of a paper product and wrapped around the interior construction so as to define upper and lower planar portions having similar planar dimensions to the upper and lower surfaces of the interior construction and being arranged in touching contact therewith, wherein the outer skin also has transverse portions connecting the upper and lower portions together such that the outer skin has a rectangular cross-section

Additionally in accordance with a preferred embodiment of the invention, the outer skin includes a planar bottom sheet arranged in touching contact with the lower surface of the interior construction, and a top sheet having a planar interior portion in touching contact with the upper surface of the inteπor construction, and further having a plurality of flaps each having an inner flap portion folded down about the transverse sides of the interior construction and further having an outer flap portion folded so as to overlap the planar bottom sheet, and fastened thereto, thereby to facilitate stress distribution between the bottom sheet and the top sheet

Further in accordance with a preferred embodiment of the invention the interior construction includes a planar deck member defining the upper surface and also having a downward-facing surface, and a plurality of spacer members fastened to the downward-facing surface of the deck member and arranged thereon and having a height sufficient to define a plurality of channels formed so as to accommodate lifting elements, the spacer members further defining the lower surface

Additionally in accordance with a preferred embodiment of the invention, the bottom sheet is fastened directly to the lower surface and is configured so as to be extend directly across the channels so as to bound the channels at a bottom side thereof, thereby providing maximum tensile resistance to forces applied to the pallet

Further in accordance with a preferred embodiment of the invention each channel has a height which is substantially the same as the height of the spacer members

Additionally in accordance with a preferred embodiment of the invention, the top sheet has formed in each inner flap portions thereof a pair of openings in registration with the channels, and shaped so as to permit entry into the channels of the lifting elements

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more fully understood and appreciated from the following detailed description, taken in conjunction with the drawings, in which

Fig 1A is a top perspective view of a paper pallet constructed in accordance with a preferred embodiment of the present invention, Fig 1 B is a view similar to that of Fig 1A, but showing a partial cross-section thereof,

Fig 2 is a bottom perspective view of the paper pallet of Fig 1A, Fig 3A is an exploded view of the pallet of Figs 1A - 2, Fig 3B is a plan view of the top sheet of the pallet of Figs 1A - 3A in a pre-folded state,

Figs 4A and 4B are top and bottom perspective views of a paper pallet similar to that of Figs 1A-3B, but constructed in accordance with an alternative embodiment of the invention,

Fig 5 is an exploded view of the pallet of Figs 4A and 4B, Fig 6 is a cross-sectional illustration of the pallet of the invention, shown diagrammatically under uniformly distributed loading,

Fig 7 is a bending stresses diagram for the pallet under the loading conditions of Fig 6, Fig 8A is a bending stresses diagram showing both compressive and tensile stresses in the upper deck of the pallet under the loading conditions of Fig 6 at the portion "VIII" therein,

Fig 8B is a cross-section of the pallet portion seen in Fig 8A, taken along line B-B therein,

Fig 9A shows shear stresses σ of the end blocks of the pallet, and tearing stresses τ along the interface between the end blocks and the deck of the pallet of the invention under the loading conditions of Fig 6, at the portion "IX" therein,

Fig 9B is a cross-section of the pallet portion seen in Fig 9A, taken along B-B therein,

Fig 10 shows the tensile resistance of the bottom sheet of the pallet of the invention under the loading conditions of Fig 6, at the portion "X" therein,

Fig 11 is a cross-sectional illustration of the pallet of the invention, shown diagrammatically under a concentrated central loading of 10000 N, and Fig 12 is a graph of bending stresses showing the most concentrated loading in the center of the pallet

DETAILED DESCRIPTION OF THE INVENTION Referring now to Figs 1A, 1 B, 2 and 3A, there is seen a paper pallet, referenced generally 100, constructed in accordance with a preferred embodiment of the present invention As seen particularly in Figs 1 B and 3A, pallet 100 is formed of an interior construction, referenced generally 102, and an outer skin surrounding the interior construction The interior construction 102 is formed of cellular or honeycomb paper products, while the outer skin is formed preferably of corrugated cardboard, heavy paper, Kraft paper, or other similar paper stock Non-paper materials may also be used, as required, for the outer skin, the methods of fastening being selected in accordance therewith As will be appreciated from the following description, all the various components are preferably affixed to each other so as to ensure efficient stress distribution throughout the pallet structure Typically, when paper products are used, the different paper components are affixed to each other by hot glue, but other techniques of adhesion may also be used, provided that sufficient structural continuity is provided Furthermore, due to the fact that the pallet of the present invention is constructed of paper which has much greater strength in tension than in compression, the pallet construction is such that, where possible, loads are resisted in tension, rather than compression The resulting pallet is of higher strength than prior art pallets, as will be appreciated from the description below of Figs 6-12

Interior construction 102 is formed of a deck 104 to which are attached a plurality of spacer members 106, having a height 'h' (Fig 3A) The height of spacer members 106 is sufficient to elevate deck 104, thereby to enable accommodation of forklift or other equivalent lifting elements In the present embodiment, spacer members 106 are blocks As mentioned above, both deck 104 and blocks 106 are made from a suitable honeycomb paper product It will be appreciated that, in order to provide maximum strength when the pallet is aligned horizontally, the individual cells are aligned perpendicular to the overall pallet Blocks 106 are fastened, typically by hot glue, to the underside 108 (Fig 3A) of deck 104, such that they combine to provide an integrated structure, and such that blocks 106 provide a degree of stiffening to the deck 104

Blocks 106 have a generally rectangular configuration, and have a longer dimension to smaller dimension ratio in the range 1 1 - 2 1 , although both the shape and the dimension ratio may be modified, as required Blocks 106 of the filler layer are arranged with respect to deck 104 so as to define a plurality of channels, referenced 110, through which the forks of a forklift, pallet truck or other suitable pallet carrying device can enter the pallet structure and lift the pallet 100, together with a load thereon

The outer skin of the pallet of the invention is formed from two flat paper components, namely, a bottom sheet 112 and a top sheet 114 As seen in Fig 3A, bottom sheet 112 has a generally rectangular configuration, similar to that of deck 104 As seen in Fig 1 B, bottom sheet 112 is arranged in touching contact with the underside of blocks 106 Preferably, bottom sheet 112 is fastened to blocks 106, as by hot gluing Referring now to Figs 3A and 3B, top sheet 114 is formed of a rectangular inner portion 116 from which extend four similar flaps 118 Each flap 118 is connected to inner portion 116 along an upper fold line 120, and is further folded along a lower fold line 122 parallel to upper fold line 120, thereby to define an inner flap portion 124 and an outer flap portion 126 Inner portion 116 of top sheet 114 is arranged in touching contact with an upper surface 126 of deck 104, and is preferably attached thereto as by hot gluing Flaps 118 are folded about upper fold lines 120 which, when pallet 100 is assembled, are in registration with upper edges 128 of deck 104, such that inner flap portions 124 are oriented at substantially 90° with respect to inner portion 116 of the top sheet 114 Outer flap portions 126 are folded about lower fold lines 122 which, when pallet 100 is assembled, are in registration with lower edges 130 of deck 104 Outer flap portions 126 are furthermore, folded down onto a downward facing surface 132 of bottom sheet 112, and are fastened thereto, preferably by hot gluing Side edges 134 of outer flap portions 126 are cut diagonally at approximately 45° or less, so as not to overlap when folded down onto bottom sheet 112, as seen in Fig 2

It is furthermore seen that each inner flap portion 124 has formed therein a rectangular opening 136 These openings are positioned and proportioned so as to be in registration with the channels 110, and so as to be of a similar dimensions to the cross-section thereof Accordingly, when the pallet is engaged by a forklift, its forks enter channels 110 through openings 136 In the present embodiment, pallet 100 is formed with four channels 110, and thus has forklift openings on all four sides

Referring now to Figs 4A, 4B and 5, there is seen a paper pallet, referenced generally 100', constructed in accordance with an alternative embodiment of the present invention Pallet 100' is generally similar to pallet 100 (Figs 1A-3B), and is thus described herein only with regard to differences between the two pallets All components and portions of pallet 100' having counterparts in Figs 1A-3B are denoted in Figs 4A, 4B and 5 by reference numerals similar to those used to denote their counterparts, but with the addition of a prime (') notation Pallets 100' are distinguished from pallets 100 (Figs 1A-3B) by the number of channels 110' and openings 136 In the present embodiment, in place of blocks 106 having a generally square configuration as shown and described above, four elongate spacer members or stringers 106' are provided Stringers 106' serve a similar purpose to that of blocks 106, but define therebetween only two channels 110', such that pallet 100' may be lifted by engagement from a pair of opposite sides only, as opposed to pallet 100 which may be engaged from any side It will be appreciated that, in the present embodiment, it is necessary to provide rectangular openings 136' in two inner flap portions 124' only It will be appreciated by persons skilled in the art that the pallet of the present invention is characterized by particularly high strength due to the provision of the outer skin, formed of bottom sheet 112 and top sheet 114 as a substantially continuous closed, rectangular shape, and wherein applied loads are transferred to bottom sheet 112 in tension, thereby taking advantage of the above-mentioned high strength of paper in tension This is seen particularly in Figs 6 and 11 , in which the pallet of the present invention is shown in diagrammatic cross-section, under uniformly distributed lading and concentrated loading, respectively

In the following description of Figs 6-12, while the pallet is referenced 100, it is to be noted that the illustrated stress and loading characteristics apply both to pallet 100 and to pallet 100'

Referring now briefly to Fig 6, there is seen a cross-sectional illustration of the pallet 100 of the invention, shown diagrammatically under a uniformly distributed typical loading of 83 33 N/mm The following exemplary loading and stress data relate to a pallet of area 1 00 x 1 20 m and overall height 11 cm, of which the deck is 3 cm thick and the blocks or stringers are 7 cm in height and 20 cm wide, and wherein the openings between the blocks or stringers are also 20 cm across

The bending stresses in pallet 100, when loaded as per Fig 6, are seen in the bending stresses diagram of Fig 7 It is seen that under uniform loading, for the structure as a whole, the maximum stresses occur along the interior edge 140 of end block 106a with the deck 104, whereat there is a tensile stress of 1 86 N/mm², and a compressive stress of 0 752 N/mm²

Fig 8A is a bending stresses diagram showing both compressive and tensile stresses in the deck 104 of a portion of the pallet 100, shown also in Fig 8B Fig 9A shows shear stresses σ of the end blocks of the pallet, and tearing stresses τ along the interface between the end blocks 106a and the deck 104 of the pallet 100, shown also in Fig 9B

Fig 10 illustrates the very high tensile stresses that the bottom sheet 112 of the present invention is capable of resisting In particular, the distributed load q = 83 33 N/mm, shown in Fig 6, is equivalent to a tension load of 6423 N The critical equivalent Euler load is 38300 N

Fig 11 is a cross-sectional illustration of the pallet 100, shown diagrammatically under a concentrated central loading of 10000 N By referring to Fig 12 it is seen that, in this case, most of the load is resisted in tension, and that the tension stress immediately beneath the point load is as much as 9 65 N/mm², while the maximum compressive stress is limited to a relatively low 1 52 N/mm²

It is thus seen that, for the pallet of present invention, of which typical dimensions are as follows, typical maximum stresses are as brought below Dimensions of deck 104 1 00 m x 1 20 m Dimensions of blocks 106 20 cm x 20 cm Dimensions of bottom sheet 112 1 00 m x 1 20 m x 0 5 cm thick Top sheet 114

Inner portion 116 1 00 m x 1 20 m x 0 5 cm thick Inner flap portion 124 1 00 m x 11 cm x 0 5 cm thick and

1 20 m x 11 cm x 0 5 cm thick Outer flap portion 126 1 00 m x 7 5 cm (approx ) x 0 5 cm thick and

1 20 m x 7 5 cm (approx ) x 0 5 cm thick Maximum stresses 1 Combined maximum bending stresses for the deck 104 and blocks 106, in the center of the pallet σ_tens = 9 65 N/mm²

2 Bending stress at the deck - central block interface adjacent to the forklift passageway σ_tens = 6 41 N/mm²

3 Tearing stresses along the interface between the end blocks and the deck of the pallet σ,e_ns = 0 280 N/mm²

4 Shear stresses along the interface between the end blocks and the deck of the pallet τ = 0 138 N/mm²

It will be appreciated by persons skilled in the art that the present invention is not limited by what has been shown and described hereinabove, merely by way of illustrative example Rather, the scope of the present invention is limited solely by the claims, which follow

Claims

1 A paper pallet which comprises a generally planar interior construction formed of a cellular paper product and having upper and lower surfaces and transverse sides extending therebetween, and an outer skin formed of a paper product and wrapped around said interior construction so as to define upper and lower planar portions having similar planar dimensions to said upper and lower surfaces of said interior construction and being arranged in touching contact therewith, wherein said outer skin also has transverse portions connecting said upper and lower portions together such that said outer skin has a rectangular cross-section

2 A paper pallet according to claim 1 , wherein said outer skin comprises a planar bottom sheet arranged in touching contact with said lower surface of said inteπor construction, and a top sheet having a planar interior portion in touching contact with said upper surface of said interior construction, and further having a plurality of flaps each having an inner flap portion folded down about said transverse sides of said interior construction and further having an outer flap portion folded so as to overlap said planar bottom sheet, and fastened thereto, thereby to facilitate stress distribution between said bottom sheet and said top sheet

3 A pallet according to claim 2, wherein said interior construction comprises a planar deck member defining said upper surface and also having a downward-facing surface, and a plurality of spacer members fastened to said downward-facing surface of said deck member and arranged thereon and having a height sufficient to define a plurality of channels formed so as to accommodate lifting elements, said spacer members further defining said lower surface

4 A pallet according to claim 3, wherein said bottom sheet is fastened directly to said lower surface and is configured so as to be extend directly across said channels so as to bound said channels at a bottom side thereof, thereby providing maximum tensile resistance to forces applied to said pallet

5. A pallet according to claim 4, wherein each said channel has a height which is substantially the same as the height of said spacer members.

6. A pallet according to claim 3, wherein said top sheet has formed in each said inner flap portion thereof a pair of openings in registration with said channels, and shaped so as to permit entry into said channels of the lifting elements.