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(11) | EP 0 595 612 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Support structure for a pallet |
| (57) Composite support structures are disclosed comprising slabs of foam (5, 6) substantially
encased in skins (7) of hollow structured sheet. A number of support structures (1,
2, 3, 4) may be combined in a lightweight modular pallet for use in the transportation
or storage of goods. Each support structure of the pallet may have only a single row
of legs (20), the legs being held in place and the pallet being strengthened by internal
bracing members (15). The bracing members alone may be used to join the support structures
(1, 2, 3, 4) to each other, but one method for producing the pallet also includes
a sequence for ultrasonic welding of the skins (7) of the respective support structures
to each other. Ultrasonic welding may also be used to fix other parts of the pallet
together, for example, slide members (25) fixed between the ends of legs (20) of different
rows. A variety of constructions and methods of assembly relating to the bracing members
(15) and slide members (25) is described. |
[0001] This invention relates to support structures and particularly, but not exclusively, to a support pallet for transport and storage of goods, or for use as a platform bearing other loads.
[0002] Traditionally pallets for transportation and storage of goods are constructed of wood as a box-section which is open at both ends to allow entry of the forks of a lifting truck or trolley. The standard size in the United Kingdom is 1000 mm wide and 1200 mm long, and in other parts of Europe 800 mm wide and 1200 long. Typically the weight of a wooden pallet of 800 mm x 1200 mm size is at least 25 kg, whilst that of a similar pallet of plastics is typically in the range 12 to 18 kg. Even a weight of 12 kg makes manhandling difficult, and can significantly reduce payloads that can be carried, particularly in the case of air freight. Moreover, although plastics pallets are typically lighter, they are also more expensive to purchase.
[0003] I have realised that certain constructions using hollow structured sheets and rigid foam would be advantageous, and may be appreciably lighter than 12 kg.
[0004] The term hollow structured sheet is used herein to refer to board material in which the principal tensile and compressive loads in bending are borne by a pair of skins forming the faces of the board, whilst the relatively thick, low density interior of the board serves to maintain the spatial relationship between the skins. The interior could have a cellular or rigid foam structure. However, commercially available forms of hollow structured sheet which have been found suitable for the invention use spaced-apart parallel ribs to serve as the interior, the ribs and the skins being of polypropylene or polyethylene, or either of these materials mixed with a proportion of talc filler. These forms of commercially available hollow structured sheet have been found to be amenable to ultrasonic welding.
[0005] By rigid foam I mean foam capable of bearing a relatively high compressive load compared to its density without appreciable collapse. Suitable forms of rigid foam are grades of expanded polystyrene and polyethylene foam, higher densities being used for greater strength.
[0006] According to a first aspect of the present invention a support structure comprises hollow structured sheet and a layer of rigid foam, the layer of rigid foam being substantially encased in the hollow structured sheet and being relatively thick in relation to the thickness of the hollow structured sheet.
[0007] Preferably the hollow structured sheet is formed with at least one strengthening flap which projects into an intermediate portion of the layer of rigid foam to strengthen the support structure. Desirably the flap projects into the layer of rigid foam substantially to the full thickness of the layer of rigid foam.
[0008] Preferably the hollow structured sheet is secured around the rigid foam by a welding process. The welding process is conveniently an ultrasonic welding process.
[0009] For applications of the support structure requiring greater strength, edge faces of the layer of rigid foam which are encased in hollow structured sheet may be encased with two or more thicknesses of hollow structured sheet which are conveniently attached to each other by ultrasonic welding. Similarly, where strengthening flaps projecting into the foam are provided these may be increased in strength by attaching extra thickness of hollow structured sheet.
[0010] Preferably the layer of rigid foam is at least five and most preferably at least ten times the thickness of the hollow structured sheet.
[0011] According to a second aspect of the present invention a pallet comprises a platform, bracing means and a plurality of spaced-apart legs on which the platform stands, the upper portion of the legs being received in sockets in the platform, each leg being joined to at least one other by the bracing means, and the platform comprising at least one support structure in accordance with the first aspect of the invention.
[0012] Preferably the bracing means comprises at least one bracing member which is substantially contained internally of the platform and which passes through the upper portion of the legs which are thereby joined by the bracing member and which also passes through a portion of the rigid foam which is disposed therebetween.
[0013] Desirably the pallet comprises more than one support structure abutted edge to edge, the abutting edges being faced with respective edge face portions of hollow structured sheet and at least one said bracing member passing from one support structure to another through the respective abutting edges and respective edge face portions of hollow structured sheet therebetween.
[0014] Preferably the adjacent edge face portions are joined to each other, and this may conveniently be achieved by ultrasonic welding.
[0015] However, as an alternative, or in addition, the hollow structured sheet of each support structure is preferably welded to the bracing means so as to connect the support structures together.
[0016] Preferably the legs are arranged in rows running transversely to each support structure the lower ends of the legs in each row being joined by a respective slide member.
[0017] The slide members are principally to spread the weight of the pallet when loaded and stacked on top of another loaded pallet. However on some surfaces the slide members may enable the pallet to be moved by sliding.
[0018] Preferably the slide members in transverse cross-section comprise a substantially rectangular base portion and a rounded head portion joined to the base portion by a neck which is narrower than the respective widths of the base and head portion.
[0019] Conveniently slots are provided through the lower portions of the legs which have a profile corresponding to the head portion and neck and which open at the bottom of the legs thereby enabling the head portion and neck of a respective slide member to be inserted through the lower portions of the legs.
[0020] The head portion and neck thus not only provide a means of strengthening and stiffening the slide member, but also a means of attachment to the legs. Once the slide member has been slotted onto the end of each of the legs in the respective row, it may be prevented from relative longitudinal movement thereto by ultrasonic welding, or by another convenient form of attachment, to one or more of the legs.
[0021] Sufficient clearance is provided between the slide members and the underside of the platform for insertion of the forks of a lifting truck or the forks and wheels of a lifting trolley. The rounded head section of the slide members ensures that the trolley wheels can easily ride over the slide members on insertion.
[0022] However simplified forms of slide member are also proposed without a rounded head, for example a T-section slide member with a flat head. The stem or upright portion of the T may be rectangular in section corresponding to a neck and base of the same width, the head of the T passing through slots in the lower portion of the legs in a similar manner to the rounded head already described.
[0023] For high load applications, the slide members and/or bracing members are preferably formed of hollow section allowing a reinforcing bar to be inserted.
[0025] According to a third aspect of the present invention a method of producing a pallet in accordance with the second aspect of the invention comprises the steps of cutting out a piece of hollow structured sheet for forming a support structure of the pallet, cutting apertures in the piece for receiving legs and bracing means therethrough, forming folds in the piece by pre-folding so as to define face portions of the support structure, forming a support structure sub-assembly from rigid foam and from the piece of hollow structured sheet comprising sockets and channel means in the foam which open at the respective apertures in the piece of hollow structured sheet, inserting pre-formed legs into the respective sockets, inserting bracing means into the channel means and through the legs, and securing the bracing means from coming out of the channel means.
[0026] Preferably the bracing means comprises a plurality of bracing members, and the channel means comprises a plurality of channels, each channel being formed with a single aperture in the outer surface of the support structure sub-assembly for insertion of a respective bracing member, the bracing member being inserted fully inside the pallet and being prevented from coming out of the channel by securing a flap over the aperture. Conveniently the flap is hollow structured sheet formed integrally with the hollow structured sheet surrounding the aperture.
[0027] Where slide members are provided, these are conveniently attached to the legs as the final stage in producing the pallet.
[0028] Preferably, in forming the pallet sub-assembly, the rigid foam of the support structure sub-assembly comprises two elongate slabs of rigid foam each integrally moulded with the respective sockets and channel means and the piece of hollow structured sheet encasing the foam comprising a pair of strengthening flaps, the two slabs being positioned alongside each other and the piece of hollow structured sheet then being secured around the slabs with the strengthening flaps inserted between the slabs.
[0029] According to a fourth aspect of the present invention a method of producing a pallet in accordance with the second aspect of the invention comprises the steps of cutting out pieces of hollow structured sheet for forming the respective support structures of the pallet, cutting apertures in the pieces for receiving the respective legs and bracing means therethrough, forming folds in the pieces by pre-folding so as to define face portions of the respective support structures, joining all the pieces together to form a sub-assembly of the hollow structured sheet, the edge face portions of different support structures which are in abutment in the completed pallet being joined by ultrasonically welding them together, forming a pallet sub-assembly from rigid foam and from the hollow structured sheet sub-assembly, the pallet sub-assembly being formed with sockets and channel means in the foam which open at the respective apertures in the hollow structured sheet, inserting pre-formed legs into the respective sockets, inserting bracing means into the channel means and through the legs, and securing the bracing means from coming out of the channel means.
[0030] Preferably each of the support structures has a single row of legs, the sockets for the legs being formed in one of the two slabs of rigid foam.
[0031] According to a fifth aspect of the present invention, an alternative method of producing a pallet in accordance with the second aspect of the invention comprises the steps of cutting out a piece of hollow structured sheet for forming a support structure of the pallet, cutting respective apertures in the piece for receiving pre-formed legs and bracing means therethrough, folding the piece so as to form a casing for the support structure, inserting the legs and bracing means into the respective apertures so as to form a pallet sub-assembly, encasing the sub-assembly in a mould and injecting liquid into the mould which sets as rigid foam.
[0032] A suitable material for the foam in this case is polyurethane, which requires the use of corona treated hollow structured sheet and pre-heating of the pallet sub-assembly to 60°C prior to injection.
[0033] By way of example only a specific embodiment of the invention will now be described with reference to the accompanying drawings in which:
Figure 1 is a plan view of a pallet in accordance with the invention,
Figure 2 is a side view of the pallet of Figure 1,
Figure 3 is a view from underneath the pallet of Figure 1, omitting the slide members for clarity,
Figure 4 is an end view of the pallet of Figure 1 from the right hand side,
Figure 5 is a layout plan of a piece of hollow structured sheet for a support structure for the pallet of Figure 1,
Figure 6 is a section A-A of the pallet of Figure 1 taken along the centre line,
Figure 7 is an end view of a slide member for the pallet of Figure 1,
Figure 8 is an end view of one form of bracing member for use in a pallet in accordance with the invention,
Figure 9 is a schematic representation of the arrangement of skins of hollow structured sheet prior to being welded together, and
Figure 10 is an end view of an alternative form of bracing member for use in a pallet in accordance with the invention.
[0034] The present embodiment comprises four support structures designated 1, 2, 3, 4, in the drawings. It would be possible to have a different number of support structures, but an even number as in the embodiment facilitates division into two if half-sized pallets are required. The present embodiment is also of the standard 800 mm x 1200 mm size, but the design is easily adapted for other sizes.
[0035] Each support structure comprises hollow structured sheet and a layer of rigid foam substantially encased in the hollow structured sheet, the layer of rigid foam being relatively thick in relation to the thickness of the hollow structured sheet. The foam layer consists of a pair of elongate expanded polystyrene slabs 5, 6 disposed beside each other, as shown in end view in Figure 6. The dimensions of each slab are approximately 50 x 150 x 800 mm in accordance with the overall pallet width of 800 mm and length 1200 mm.
[0036] Each support structure has an outer skin 7 of hollow structured sheet of 3 mm thickness. Figure 5 shows the layout of a skin 7 and identifies the different face portions namely end face portions 8, edge face portions 9, top face portion 11 and bottom face portions 12. The bottom face portions are provided with flaps 14 which in the completed support structure are disposed between the slabs 5, 6 and serve as additional strengthening means. The end face portions 8 are held in place in the completed structure by flaps 16 which tuck into the ends of the support structure.
[0037] There could be additional flaps (not shown) continuous with the ends of edge face portions 9 which would be folded against the ends of the support structure before the end face portions 8 are secured in position over them.
[0038] The edge face portions 9 and strengthening flaps 14 are each formed with three apertures 21, 22, 23, disposed in three respective rows. The exception is the edge face portion 9 of support structure 4 forming an outer edge of the pallet 6, wherein the apertures are covered by integral flaps 13 (Figure 4) and the edge face portion 9 of support structure 4 forming another outer edge, in which there are no apertures.
[0039] One of the two bottom face portions 12 of the skin 7 of each support structure is provided with a row of three apertures 17 for receiving legs 20.
[0040] The skins 7 are formed by stamping out from hollow structured sheet, and are then pre-folded to form fold lines (shown dashed in Figure 5). In one embodiment of a pallet in accordance with the invention, the skins are next ultrasonically welded to each other by the edge face portions 9 which abut the final assembly of the pallet. It will be appreciated that each skin must be rotated 180° in relation to the adjacent skins prior to welding, since rows of legs on each support structure in the final assembly of the pallet are disposed alternately to the left and to the right.
[0041] Figure 9 is a schematic representation of the way in which skins 7I, 7II, 7III and 7IV for support structures 1, 2, 3, 4 can be laid out on a welding table 18 prior to welding, with the outermost surfaces in contact with the table, and the skins being viewed respectively from the right, left, right and left in relation to Figure 5. The location of the leg apertures are shown on each skin at 10, and the welding sites between the skins is shown at 19. In the arrangement of Figure 9 the welding tool is applied from above to weld between the respective edge face portions 9 but the welding must not penetrate through to the top face portions 11.
[0042] A pair of slabs 5, 6 is then placed in each skin 7 which is then folded around the slabs with flaps 14 and 16 being tucked into their respective positions. Flaps 14 are then ultrasonically attached to the inner surface of bottom face portions 12 by welding through the bottom face portions, and the bottom face portions themselves are joined in each support structure by welding where they come together along the crevice formed by projection of the flaps 16 into the support structure.
[0043] Each of the expanded polystyrene slabs 5, 6 is pre-formed by moulding and is provided with three parallel channels passing transversely across the lower surface. The channels of the slabs are aligned with the three sets of apertures 21, 22, 23 on assembly so as to form three passageways in the pallet which are closed at one end by the outermost edge face portion 9 of support structure 4, but accessible at the other end through respective flaps 13.
[0044] Slabs 5 are provided with three sockets located in alignment with the three apertures 17 on respective skins 7 which are shaped to receive the upper portion of respective legs 20. The legs are formed from lengths of extruded polyethylene tubing which are of square section approximately 50 mm wide and with a wall thickness of approximately 3 mm. In another version, where greater strength is required, the legs could be wider: say 100 mm wide.
[0045] The upper portions of the legs are formed with slots therethrough of the same section as the three passageways, the passageways passing through the slots on assembly and receiving respective bracing members 15 which not only serve to strengthen the pallet and hold it together, but also to hold in the legs.
[0046] In a preferred embodiment of a pallet in accordance with the invention, each bracing member 15 is ultrasonically welded to each bottom face portion 12 of the pallet. The welding process is facilitated by forming the bracing members and the hollow structured sheet from similar polypropylene material.
[0047] One form of bracing member 15 is an extruded plastics bar of T-section as illustrated in Figure 8, which is inverted on assembly. The internal angles of the bar are radiused for greater strength and for ease of insertion into a respective passageway, which is formed with corresponding T-section.
[0048] However each passageway may alternatively be of rectangular section corresponding to a bracing member 15, as illustrated in Figure 10, or to a fabricated bracing member consisting of a number of strips of hollow structured sheet.
[0049] Bracing member 15 as illustrated in Figure 10 comprises an extruded plastics bar, the hollow interior of which is separated into three separate channels by a pair of dividing walls 30. The outer channels 35 are typically 5 mm wide, whilst the central channel 33 is typically 3 mm wide. Metal reinforcing bars may optionally be inserted into the channels 33, 35. When inserting the extruded plastics bar itself, a tapering cover piece or 'nose cone' may be temporarily fitted onto the leading end, the taper serving to reduce resistance to insertion caused by slight misalignment between the strengthening flap 14, edge face portions 9, legs 20 and slabs 5, 6 as the bar is pushed through.
[0050] Typically the fabricated bracing member consists of three strips of hollow structured sheet, each 10 mm thick and 30 mm wide disposed horizontally one above another. For ease of assembly they might be inserted one strip at a time and the lowest strips, being in contact with the inner surface of a bottom face portion 12, could be attached to it by ultrasonic welding after insertion of all the strips.
[0051] For each form of bracing member, flap 13 would normally be sealed over the respective passage by ultrasonic welding after insertion to obviate any tendency of the bracing member or reinforcing bars coming out.
[0052] The ends of the legs in each row of legs running parallel to the bracing members 15 are joined by slide members 25 which are typically extruded polythene bars. Polythene used for the slide members 25 and T-section bracing members 15 and legs 20 may be increased in strength by mixing with glass filler, typically 30% by weight.
[0053] The slide members in section are as shown in Figure 7 with a flat base 26 of width corresponding to the width of the legs, a neck portion 27 perpendicular to the base, and a rounded head 28 on the neck which is appreciably broader than the base, and which curves downwardly on each side towards the base so as to minimise the difficulty of passing the wheels of a lifting trolley over the slide member.
[0054] The lower ends of the legs 20 are provided with downwardly open slots for receiving the head 28 and neck portion 27, the slide members 25 being prevented from sliding out of engagement with the legs after being inserted through the slots in each respective leg by ultrasonic welding thereto in a few places.
1. A support structure comprising hollow structured sheet and a layer of rigid foam,
the layer of rigid foam being substantially encased in the hollow structured sheet
and being relatively thick in relation to the thickness of the hollow structured sheet.
2. A support structure as claimed in claim 1 in which the layer of rigid foam is at least
ten times the thickness of the hollow structured sheet.
3. A support structure as claimed in claim 1 or claim 2 in which the hollow structured
sheet is secured around the rigid foam by a welding process.
4. A support structure as claimed in any one of the preceding claims in which the hollow
structured sheet is formed with at least one strengthening flap which projects into
an intermediate portion of the layer of rigid foam to strengthen the support structure.
5. A support structure as claimed in any one of the preceding claims in which edge faces
of the layer of rigid foam encased in hollow structured sheet are encased in a plurality
of thicknesses of hollow structured sheet which are attached to each other.
6. A pallet comprising a platform, bracing means and a plurality of spaced-apart legs
on which the platform stands, the upper portion of the legs being received in sockets
in the platform, each leg being joined to at least one other by the bracing means,
and the platform comprising at least one support structure as claimed in any one of
the preceding claims.
7. A pallet as claimed in claim 6 comprising more than one said support structure, in
which the bracing means is welded to the hollow structured sheet of each support structure
so as to connect the support structures together.
8. A pallet as claimed in claim 6 or claim 7 in which the legs are arranged in rows running
transversely to each support structure the lower ends of the legs in each row being
joined by a respective slide member.
9. A pallet as claimed in claim 8 in which the slide members in transverse cross-section
comprise a head portion and a neck which is narrower than the head portion, and in
which slots are provided through the lower portions of the legs, the slots having
a profile corresponding to the head portion and neck of the cross-section and opening
at the bottom of the legs thereby enabling the head portion and neck of a respective
slide member to be inserted through the lower portions of the legs.
10. A pallet as claimed in claim 8 or claim 9 in which the slide members or bracing means
is formed of hollow section to allow insertion of a reinforcing bar.
11. A method of producing a pallet comprising the steps of cutting out a piece of hollow
structured sheet for forming a support structure of the pallet, cutting apertures
in the piece for receiving legs and bracing means therethrough, forming folds in the
piece by pre-folding so as to define face portions of the support structure, forming
a support structure sub-assembly from rigid foam and from the piece of hollow structured
sheet comprising sockets and channel means in the foam which open at the respective
apertures in the piece of hollow structured sheet, inserting pre-formed legs into
the respective sockets, inserting bracing means into the channel means and through
the legs, and securing the bracing means from coming out of the channel means.
12. A method as claimed in claim 11 in which, in forming the pallet sub-assembly, the
rigid foam of the support structure sub-assembly comprises two elongate slabs of rigid
foam each integrally moulded with the respective sockets and channel means and the
piece of hollow structured sheet encasing the foam comprising a pair of strengthening
flaps, the two slabs being positioned alongside each other and the piece of hollow
structured sheet then being secured around the slabs with the strengthening flaps
inserted between the slabs.
13. A method of producing a pallet comprising the steps of cutting out pieces of hollow
structured sheet for forming a plurality of respective support structures of the pallet,
cutting apertures in the pieces for receiving respective legs and bracing means therethrough,
forming folds in the pieces by pre-folding so as to define face portions of the respective
support members joining all the pieces together to form a sub-assembly of the hollow
structured sheet, the edge face portions of different support structures which are
in abutment in the completed pallet being joined by ultrasonically welding them together,
forming a pallet sub-assembly from rigid foam and from the hollow structured sheet
sub-assembly, the pallet sub-assembly being formed with sockets and channel means
in the foam which open at the respective apertures in the hollow structured sheet,
inserting pre-formed legs into the respective sockets, inserting bracing means into
the channel means and through the legs, and securing the bracing means from coming
out of the channel means.
14. A method as claimed in claim 13 in which each of the support structures comprises
two slabs of rigid foam and has a single row of legs, the sockets for the legs being
formed in one of the two slabs of rigid foam.
15. A method as claimed in any one of claims 11 to 14 in which the bracing means comprises
a bracing member to the leading end of which during insertion a tapering cover piece
is fitted to reduce resistance to insertion.
16. A tapering cover piece for use in the method of claim 15.
17. A method of producing a pallet comprising the step of cutting out a piece of hollow
structured sheet for forming a support structure of the pallet, cutting apertures
in the piece for receiving pre-formed legs and bracing means therethrough, folding
the piece so as to form a casing for the support structure, inserting the legs and
bracing means into the respective apertures so as to form a pallet sub-assembly, encasing
the sub-assembly in a mould and injecting liquid into the mould which sets as rigid
foam.