FIELD OF THE INVENTION

This invention relates to pallets that are typically used in the international transport and warehousing industries and in particular, the invention relates to high-performance, light-weight plastic pallets, capable of supporting heavy loads.

BACKGROUND TO THE INVENTION

The international transportation and warehousing industries have historically used wooden pallets for transporting and storing goods. Due to the danger of transporting pathogens with wooden pallets there is now an international drive to replace wooden pallets with plastic pallets, i.e. pallets manufactured from man-made polymers.

Plastic pallets of different sizes, weights and configurations are used to carry loaded goods of various sizes and weights on their upper surfaces or load decks - which are typically contiguous and flat.

Both wooden and plastic pallets have a tendency to deflect when carrying heavy loads across a variety of transportation and weight-bearing scenarios. There are also a large variety of pallets that are designed to meet a spectrum of needs for the transportation industry, ranging from lightly structured light-weight pallets for light loads (often for single use), to heavily structured heavy-weight pallets (sometimes containing metal reinforcements) that are designed for extremely heavy loads.

Most pallets can be placed in a warehouse racking system where each pallet is typically only supported along two opposing edges with the rest of the pallet body being unsupported. Depending on the weight of a payload on such a pallet, the pallet body will deflect downwardly to a lesser or greater extent and while some pallets are considered safe for use in these load scenarios and are “partially or fully rack- compatible”, others are considered to be dangerous when used in these load scenarios and are“not rack-compatible”. Plastic materials used to manufacture pallets cost-effectively are generally not very stiff, yet pallets often carry loads of 1 ,000 kg or more and under such high loads, plastic pallets tend to distort excessively. The pallet body typically tends to deflect downwardly along the centres of the top deck and base or lower extremities of the pallet body. This deflection is especially pronounced when a pallet is placed in a warehouse racking system where the pallet body is not fully supported across the base. This is in contrast to a non-racked load scenario where a loaded pallet is supported on a flat level surface such as a warehouse floor.

Excessive distortion and deflection of pallets often cause loaded goods on the pallets to bear some stress and or to be strained, with the potential for damage to the loaded goods. Further, excessive deflection of a pallet body can cause edges of the pallet to slip from the racking system, resulting in the pallet and its load falling - potentially causing substantial damage - also with the possibility of causing other racked and loaded pallets also to fall. Additionally, there is a risk that such a falling pallet may damage objects below or expose warehouse personnel to danger.

In attempts to stiffen and strengthen pallet bodies to reduce distortion and deflection, pallet manufacturers have increased the quantities of plastic materials used to manufacture pallets. Where extra-heavy loads are to be carried by a pallet, additional reinforcing elements are used - typically in the form of metal elements such as bars, designed to bear bending stresses, which are usually housed within apertures in the pallet body that are designed to accept these metal elements.

The metal elements bear much of the weight and stresses imparted by the load and these are spread across the pallet body in manners intended to reduce distortion and deflection of the pallet body.

Due to the use of additional plastic material and/or metal elements to bear the heavy loads applied to the pallet deck, plastic pallets have become heavier and more expensive to produce to the point that it is now common to find“fully rack-compatible” plastic pallets that are capable of carrying heavy loads, containing in excess of 23kg of plastic within the pallet body structure and with the addition of the metal elements, have a total weight in excess of 26kg.

The addition of metal elements that essentially become part of the pallet body is problematic at the end of the usable life of the pallet when the metal elements need to be removed before the plastic content of the pallet body can be recycled.

Further, corrosion of the metal elements is an additional problem during the life cycle of the pallet and if the pallet is overloaded during use, the metal elements tend to deform permanently with a deflected shape. This deformation creates stress within the pallet body, it potentially alters the shape of the pallet, it potentially damages the plastic in the immediate vicinity of the deformed metal elements and the deformed metal elements often prove difficult to remove for maintenance or pallet scrapping purposes, prior to reclaiming the plastic content of the pallet.

Plastic pallets are typically considerably more expensive than wooden pallets.

The present invention seeks to provide plastic pallets that can be produced at low cost and still have a high load bearing ability, while preferably being rack-compatible and preferably without a need to recover parts of the pallet before recycling its polymeric body. The invention also seeks to provide pallets that can be made entirely or largely from recycled material and that can be recycled easily. Lastly, the invention seeks to provide pallets with a low profile or height, to reduce weight and maximise storage space above the pallet’s load deck.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a pallet which comprises:

a pallet body of a plastic material, said pallet body defining a load deck that is convex along at least one direction of curvature when the pallet body is un-loaded; and at least one flexible tensile element having at least a part that extends across an underside of the pallet body along the direction of curvature. The phrase“across an underside of the pallet body” includes embodiments where the tensile element is recessed or embedded in the pallet body, e.g. in close proximity to the periphery of the pallet body.

The tensile element may extend in a continuous loop and may extend generally around the pallet body and/or generally along the load deck.

The phrase“generally around the pallet body” includes embodiments where the tensile element is recessed or embedded in the pallet body, e.g. in close proximity to the periphery of the pallet body and still around the bulk of the pallet body. Similarly, the phrase“generally along the load deck” includes embodiments where the tensile element extends in close proximity to the load deck.

The tensile element may be fixedly attached to the pallet body, e.g. the pallet body may include an insert, e.g. an insert of a material that is different from the pallet body, and the tensile element may be fixedly attached to the insert, e.g. by being welded to the insert.

The pallet body may include a bottom structure that extends between the undersides of at least some of the pillars and the tensile element may be embedded within said bottom structure.

The pallet may include a plurality of said tensile elements and the tensile elements may be parallel to one another, may extend transversely to one another, and/or may extend in any direction. Similarly, the load deck may be convex along multiple directions of curvature when the pallet body is un-loaded and the pallet may include a plurality of the tensile elements, extending along directions of curvature.

Each tensile element may be received in a groove defined in the pallet body and the grooves may be covered, at least in part, with lids. Instead, the covered grooves may be integrally formed in the pallet body or the tensile elements may be moulded in situ in the pallet body.

The tensile elements may be straps and may be of a plastic material such as nylon, or any other material suitably resistant to elongation.

According to another aspect of the present invention there is provided a method of making a pallet, said method comprising:

moulding a pallet body of a plastic material, said pallet body defining a load deck that is convex along at least one direction of curvature when the pallet body is un loaded; and

installing a tensile element on the pallet body, such that said tensile element has at least a part that extends across an underside of the pallet body along the direction of curvature.

The method may include placing the tensile element under tension and the tension may be selected to place the pallet body under a predetermined bending stress or deformation.

The method may include attaching the tensile element to the pallet body, e.g. by welding the tensile element to the pallet body, and the method may include installing one or more anchor formations on the pallet body and welding the tensile element to the anchor formations.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show how it may be put into effect, the invention will now be described by way of non-limiting example, with reference to the accompanying drawings in which:

Figure 1 shows a top plan view of a first embodiment of a pallet according to the present invention;

Figure 2 shows a side view of the pallet of Figure 1 , in an un-loaded condition;

Figure 3 shows an end view of the pallet of Figure 1 in an un-loaded condition; Figure 4 shows a top three-dimensional view of a second embodiment of a pallet according to the present invention;

Figure 5 shows a diagrammatic side view of a pallet according to the present invention, in an un-loaded condition;

Figure 6 shows a diagrammatic side view of the pallet of Figure 5, in a loaded condition; Figure 7 shows a detail top three-dimensional view of part of a load deck of a third embodiment of a pallet according to the present invention, with an insert removed; Figure 8 shoes a detail top three-dimensional view of part of the load deck of Figure 7, with the insert in position;

Figure 9 shows a detail sectional view of part of the load deck of Figure 7 with the insert in position; and

Figure 10 shows a top plan view of the pallet of Figure 7, with nine inserts in position.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to the drawings, a pallet according to the invention is generally identified by reference number 10, with suffixes referring to the three embodiments of the pallet shown in Figures 1 to 3 as 10.1 , in Figure 4 as 10.2, and in Figures 7 to 10 as 10.3, respectively.

Each embodiment of the pallet 10 comprises a pallet body 12 which includes a rectangular load deck 14 and feet or pillars 16 extending downwards from the underside of the load deck at each corner of the load deck and midway along each edge of the load deck. The load deck 14 can be of solid construction, have slats, a grid structure, define holes, or any other suitably contiguous structure with sufficient strength to carry a payload. The load deck 14 is typically planar, or flat, but can include protuberances, recesses or other formations, e.g. for carrying particular payloads. Each pallet 10 further includes a central pillar that is not shown in the drawings. Each pallet 10 also includes a base or bottom structure 1 8 that extends between the undersides of the pillars 16 and the bottom structure can be a bottom deck, any number of runners, a part or complete“picture frame”, any number of“skids”, or any other formation.

The load deck 14, pillars 16 and bottom structure 18 together form the pallet body 12 and are all made of a plastic material, e.g. polyethylene terephthalate (PET), high density polyethylene (HDPE) or the like. They may be integrally made, e.g. by being injection moulded, or they may be assembled or attached together and they may be of different materials, but these parts of the pallet 10 can normally be recycled without a need for dismantling or stripping. The plastic material of which the pallet body 12 is made, could be virgin material, could include recycled material and/or could include fillers, reinforcing fibres, or the like. The size of the pallet 10 can vary, but it is typically of a standardised size, e.g. 1200 X 1000mm, 48 X 40 inch, or any other standard size.

The present invention is not limited to pallets as shown in the drawings, but also applies to pallets without bottom structures, pallets with other structures serving to keep the load deck elevated, i.e. pallets with different pillar arrangements and/or that have other structures in lieu of pillars.

Referring to Figures 1 to 3, the first embodiment of a pallet 10.1 is rectangular and its pallet body 12 defines three strap grooves 20 that extend longitudinally, generally parallel to one another, across its load deck 14. Similarly, the pallet body 12 defines two strap grooves 22 that extend transversely across the load deck 14. The strap grooves 20,22 are aligned with the pillars 16 and extend continuously along the outsides of the pillars and along the underside of the bottom structure 1 8. In each of these strap grooves, a tensile element, preferably in the form of a flexible strap 32 is received, and each strap extends around the pallet 10.1 in a loop, along its strap groove. The pallet body 12 is shown with exaggerated curvature (for the sake of explanation), with the result that the strap 32 is visible below the bottom structure 18 in Figure 2, but in practice, the curvature of the pallet body is likely to be less, so that the straps would only extend inside their strap grooves 20,22.

The pallet 10 is shown in Figures 1 to 3 in an un-loaded state, without any load on its load deck 14. This is also the un-loaded form in which the pallet body 12 would be made initially, during manufacture. In a typical preferred embodiment of the invention, the pallet body would be moulded in a single step and would have the un-loaded shape shown in Figures 1 -3, when it exits the mould. In the un-loaded state, the load deck 14 is convex along two directions of curvature. The first direction of curvature is the longitudinal direction of curvature 24 and the convex shape of the load deck 14 along this direction can best be seen in Figure 2. The second direction of curvature is the transverse direction of curvature 26 and the convex shape of the load deck 14 along this direction can best be seen in Figure 3. In other embodiments of the invention, the load deck 14 may be convex only along one direction of curvature, or along other directions of curvature, e.g. diagonally, but at least one of its directions of curvature corresponds generally (at least partly) with the direction of one or more of the straps 32.

The straps 32 are fitted after the pallet body 1 2 has been manufactured and are tensioned and their ends attached together, e.g. by welding or with clips, to form continuous loops around the pallet body - along the load deck 14, down the sides of the pillars 16 and along the bottom structure 18. In other embodiments, the straps only extend partially around the pallet body 12, e.g. the straps could extend only along the underside of the pallet body, between the undersides of the pillars 16, or the like. In embodiments where the straps do not extend in continuous loops around the pallet body 12, they are fixedly attached to the pallet body.

When the straps 32 are fitted, they can be placed under tension and/or the pallet body 12 could be bent upwardly or compressed from its ends, temporarily, while the straps are fitted, and released after the straps have been fitted, so that the pallet body 12 returns to its original shape (at least partly) with the straps under tension. The tension in the straps 32 and/or the curvature of the pallet body 12 can thus be adjusted during manufacture of the pallet 10.1 and this will affect the stiffness of the pallet - as described below.

The straps 32 need not be fitted in strap grooves 20,22 and in other embodiments of the invention, the straps extend along the outside of the pallet body 12, are embedded within the pallet body, or are received in recesses such as the strap grooves, which are covered with lids. Providing recesses such as strap grooves 20,22 covering the straps 32, and/or embedding the straps in the pallet body reduces the exposure of the straps to damage. The strap grooves 20,22 cause the straps 32 to be recessed from the load deck 14, the outer peripheries of the pallet’s edges and from the underside of the bottom structure 18, so that the straps are protected against abrasion or similar wear to which these parts of the pallet 10.1 are exposed, from loads, warehouse floors, handling, etc. The strap grooves 20,22 also ensure that the straps 32 remain in their correct positions.

The strap grooves 20,22 are preferably deep enough to ensure that the straps 32 are recessed as described above, with some additional depth for a margin of safety and with sufficient depth to accommodate any attachment means of the straps - e.g. buckles or clips - although the straps do not necessarily need these attachment means and are typically welded end-to-end or are welded to the pallet body 12.

It is also possible to mould the straps 32 into the pallet body 12, however, if this is done, the straps need to be held in place in situ in the mould and it should preferably be taut or under some tension in the mould.

The straps 32 are tensile elements and could be flexible (although flexibility of the straps is not essential) and they are made of any suitable material for bearing substantial tensile loads while resisting elongation. They are preferably made of plastic material such as nylon or PET, which are recyclable plastics, or they can be steel strapping, steel wire, steel wire cable or strapping, or any other strapping that is capable of bearing substantial tensile loads, while resisting elongation. If the straps 32 are made of PET or similar polymeric strapping material, the straps would be light in weight, inexpensive, non-corrosive and generally resistant to damage by water or the elements and it would be easy to remove and replace the straps if any maintenance is required. It would also be easy to remove and reclaim the straps 32 when it is time to scrap the pallet 10.1 and reclaim the plastic materials within the pallet body 12.

The pallet 10.2 shown in Figure 4 is substantially similar to the pallet shown in Figures 1 to 3, except that the pallet 10.2 has a generally square load deck 14 and has three parallel strap grooves 28 that extend across the load deck along each of two orthogonal directions of curvature 30.

Referring to Figure 5, when a pallet 10 according to the present invention is in an un loaded condition, the load deck 14 of the pallet body 12 is convexly curved upward along the direction of curvature 30. The strap 32 includes a top run 34 comprising a length of the strap that extends generally along the load deck 14, two side runs 36 each comprising a length of the strap that extends downwards, and a bottom run 38 comprising a length of the strap that extends across the underside of the pallet 10. The bottom run 38 extends along a strap groove in the underside of the pallet body 12, but due to the convex curvature of the pallet body, the bottom run is separated from the upwardly facing trough 40 of the strap groove. The strap 32 is generally taut and is preferably under light tension, even while the pallet 10 is un-loaded (although the strap could be under substantial tension, if required, thus effectively pre-stressing the pallet body 12).

Owing to the concavely curved trough 40 and the taut bottom run 38, the bottom run is shorter than the length of the trough 40. The bottom run 38 of the strap 32 is taut and straight, whereas the trough 40 is curved. (It is possible that the curvatures of the trough 40 and the underside of the pallet, as shown in Figure 5, may cause the bottom run 38 to appear curved, due to an optical illusion, but the bottom run is taut and straight - and preferably under tension.)

In other embodiments of the invention, in which the strap 32 does not form a loop around the pallet body 12, the pallet 10 still includes a taut bottom run 38. Also, while the use of a strap groove 28 is certainly preferably, for the sake of protecting the strap 32 against damage, it is possible for the bottom run 38 to extend on the underside of the pallet 10, not embedded in a strap groove, but even in such an embodiment, the underside of the pallet body 12 would be concave and would serve the same purpose as that served by the trough 40 in the illustrated embodiment.

Referring to Figure 6, the pallet from Figure 5 is shown under a load, which is represented by a single arrow 42, but the load could have any distribution along the load deck 14. The pallet 10 is shown supported only at its two opposing edges - as the case would be if the pallet were in a conventional rack. The load 42 causes bending stress in the pallet body 12, which causes the pallet body to bend or deflect downward, but owing to the upwardly convex shape of the pallet body, the load will cause it to straighten, as shown in Figure 6. It is somewhat idealised, for the purpose of illustration, that the pallet body 12 would straighten completely. The pallet 10 is designed so that the stiffness of the body 12, combined with the additional stiffness provided by the strap (see below), allows a maximum bending of the pallet body, under a maximum design load, to the condition in which the pallet body is straight as shown in Figure 6, or preferably still slightly upwardly convex. In other scenarios, where the pallet 10 carries less that its maximum design load, the pallet body 12 would still be curved with a convex load deck 14, albeit less curved than shown in Figure 5. It would be undesirable for the pallet body 12 to deflect so that the load deck 14 becomes concave.

When the pallet body 12 straightens under the bending stress caused by the load 42, the lengths of the strap grooves 28 do not change significantly. This also applies to the trough 40, which generally holds its length as the pallet body 12 straightens. Flowever, the bottom run 38 did not follow the concave trough 40 on the underside of the pallet body 12 and was shorter than the trough 40, while the pallet 10 was un-loaded, as shown in Figure 5, but as the pallet body straightens, as shown in Figure 6, the bottom run 38 moves deeper into the strap groove at the underside of the pallet body until the pallet body is straight and the bottom run 38 extends along the trough 40. The straightening of the pallet body 12 thus causes the bottom run 38 to lengthen and places the bottom run under tension. Flowever, the strap 32 is selected to resist elongation, when under tension and accordingly, the bottom run 38 is brought under tension when the pallet body 12 straightens under the load 42 and accordingly, the bottom run 38 resists straightening of the pallet body and thus adds substantial stiffness to the pallet body 12.

In embodiments where the tensile stress of the bottom run 38 can be transferred to the rest of the strap 32, e.g. when the strap forms a loop as shown in Figures 5 and 6, the tensile stress in the strap is distributed more evenly, but the lengthening of the bottom run 38 as the pallet body 12 is straightened under load 42 still causes the strap 32 to lengthen and thus causes tensile stress in the strap, which resits straightening of the pallet body.

When the strap 32 resists deflection of the pallet body 12, it effectively absorbs a substantial portion of the stresses caused by the load 42 and bears the stress as a tensile stress in the strap. The result is that the pallet 10 deflects substantially less than it would have deflected, if it did not have the strap 32, or put differently, the pallet 10 is capable of carrying a substantially higher load, without deflecting unacceptably and accordingly, by adding the strap to the pallet 10, its load carrying capacity has been increased markedly.

The pallet body 12 is shown in Figures 1 to 4 with a convex load deck 14 and with a bottom structure 18, in the un-loaded condition. In Figures 5 and 6, the pallet body 12 is shown (by way of diagrammatic representation) as a solid body with a load deck 14 that is convex, when un-loaded and which straightens under loading, and with an underside that is concave (concave when viewed from below, i.e. curved upwards) when un-loaded and straightens along with the load deck, when loaded. Flowever, the pallet body 12 need not have a bottom structure or an underside that follows the curvature of the load deck. In particular, the underside of the pallet body 12, along which the bottom run 38 of the strap extends, could extend a short distance below the load deck or lower down in the pallet body (with space for lifting fork tines above or below the bottom run 38). Also, the shape of the pallet body 12 along its underside, where the bottom run 38 extends, need not be concave when the pallet 10 is un-loaded, e.g. it can be straight or convex when the pallet is un-loaded, so that it will become convex, or more convex when the pallet is loaded. Even further permutations are possible for the shape of the underside of the pallet body 12, along which the bottom run 38 extends and the common essential requirement is that the shape and configuration of the pallet body 12 is such that loading of the convex load deck 14 causes tensile loading of the bottom run 38. Referring to Figures 7 to 10, in some embodiments of the invention, a strap needs to be attached to a pallet body 12, but the materials of the strap and the pallet body are not compatible, e.g. the strap and pallet body could be made of different plastic materials that cannot be welded together with sufficient strength. So, for example, a tool (mould) designed for moulding pallet bodies 12 in PET, could be used to mould pallet bodies in HDPE or polypropylene (PP), but if PET straps 32 will be used, the straps could not be welded to the pallet body with sufficient strength. In such events, ends of the straps 32 can be attached, e.g. by welding, to anchor formations in the form of inserts 44 that can be fixedly attached to the pallet body 12. The inserts 44 preferably include complementary formations that can locate them relative to the pallet body 12, e.g. in the illustrated example, the insert 44 includes a central protuberance 46 that is receivable in an aperture 48 defined in the groove 20 and the insert has two tabs 50 at opposing ends, which fit on opposing sides of webs 52 of the pallet body. Once the inserts 44 have been positioned on the pallet body 12, a strap 32 is fitted in the groove 20 and is welded (preferably under tension, as described above) to the inserts. The tension of the straps 32 holds the inserts in position with the protuberance 46 and tabs 50 engaged with the aperture 48 and webs 52.

Referring to all the drawings, further to some of the advantages of the present invention mentioned above, the invention holds the advantages that it greatly enhances the performance of plastic pallets. A pallet 10 according to the invention requires less plastic material by volume for a given load carrying ability and is lighter, or can carry more load than other plastic pallets containing a similar volume of plastic material, it distorts less, including less outward splaying of the lower extremities of the pallet body 12 and less downward deflection of the load deck 1 4 and bottom structure 18, it does not require metal elements to achieve“fully rack compatible” status, it is less expensive to produce and its plastic contents is fully recyclable.

Of particular importance, is the fact that the convex shape of the load deck 14, combined with the straps 32, provide stiffness to the pallet 10 that is not dependent on the height of the pallet and is not dependent on reinforcing bars or the like. The pallet 10 still needs some height to allow the tines of a lifting fork to enter below the load deck 14, but it does not rely on a high profile to provide stiffness to the pallet body 12. As a result, the pallet 10 can have a lower height, which allows it to have a lower weight and to occupy less space, thus making more space available above the load deck 14, for the pallet’s payload.

In one embodiment, the pallet body 12 is a unitary body, moulded from PET with standard length and width of 1200 X 1000 mm. The centre of its load deck 14 protrudes about 5mm upwards, compared to the periphery of the load deck, upon exiting the mould. However, when PET straps 32 are fitted, they are placed under tension, which places the pallet body 12 under bending stress and causes the load deck to bulge upwards further, when in the unloaded condition and the degree of tension in the straps, as well as the bending stress and deformation (upward curvature) of the body, is set at predetermined quantities to provide the desired stiffness for the pallet 10. The present invention thus allows for the performance of the pallet 10 to be“tuned” by applying more or less tension via the straps 32, causing the load deck 14 to be more or less convex and causing the pallet 10 to be more or less stiff.

Both the body 12 and straps 32 in this example are made predominantly, or entirely from reground (thus recycled) PET. The pallet 10 has a height of 140 mm, which is relatively low and has a total weight of 19.2 kg. The pallet 10 can safely carry a payload of 1400 kg on its load deck 14, when the pallet is supported along two opposing edges, as would typically be the case in a racking or warehousing system, without undue deflection under the payload. (In theoretical modelling, using finite element analysis, the pallet 10 has actually been found to be capable of carrying payloads of twice as much.) For conventional plastic pallets to be capable of carrying loads of 1400 kg safely in a racking environment, the pallets would typically have heights of 160 mm or more, include steel reinforcing bars or tubes and weigh 30kg or more.