PLASTIC PALLET WITH STIFFENING STRUCTURE

Abstract

A plastic pallet comprising a deck for storing objects to be transported, feet which are formed protruding from a deck underside, and runners which are formed in each case connecting at least two feet to each other on their undersides. The plastic pallet also comprises at least one stiffening structure which comprises lower side rails arranged in the runners, and upper side rails arranged spaced apart therefrom, which are arranged above the lower side rails running parallel thereto. The stiffening structure comprises rungs, each with a predominantly closed surface, which connect the lower side rails in the feet to the upper side rails. The rungs are formed in one piece on the side rails or are connected thereto in each case via contact surfaces in bonded, friction-locking or form-locking manner. As such, the pallet bending stiffness and shear strength in a plane parallel to the deck upper side are increased.

Claims

1. A plastic pallet, comprising: a deck for storing objects to be transported, feet which are formed protruding from a deck underside, and runners which are formed in each case connecting at least two feet to each other on undersides of the feet, at least one stiffening structure, comprising lower side rails arranged in the runners and upper side rails arranged spaced apart therefrom, which are arranged above the lower side rails running parallel thereto wherein the at least one stiffening structure comprises rungs, each rung having a predominantly closed surface, which connect the lower side rails in the feet to the upper side rails, wherein the rungs are formed in one piece on the side rails or are connected thereto in each case via contact surfaces in a bonded, friction-locking or form-locking manner, whereby the bending stiffness of the pallet and the shear strength of the pallet in a plane parallel to the deck upper side are increased.

2. The plastic pallet according to claim 1, wherein the side rails have a predetermined thickness.

3. The plastic pallet according to claim 1, wherein in the case of a connection of the rungs to the side rails via contact surfaces, a size of the contact surfaces is predetermined depending on a predetermined maximum bending and shear load of the plastic pallet.

4. The plastic pallet according to claim 1, wherein the rungs have a predetermined height in the longitudinal direction of the side rails, which corresponds to at least 80% of a width of a respective foot receiving the rung, wherein, in the case of a bonded, friction-locking or form-locking connection, the extent of the contact surfaces in the longitudinal direction of the side rails corresponds to the predetermined height.

5. The plastic pallet according to claim 3, wherein the side rails are formed as hollow structures assembled from various surfaces, as tubes with the cross-section of a rectangle, or as T-beams or double T-beams, wherein in each case at least one of the surfaces of a side rail is aligned perpendicular to a longitudinal direction of the side rails and the rungs.

6. The plastic pallet according to claim 5, wherein in the case of a bonded connection of the rungs to the side rails, the contact surfaces lie in a plane perpendicular to the longitudinal direction of the side rails and rungs and an extent of the contact surfaces in a direction of the thickness of the side rails is at least one-quarter of the thickness.

7. The plastic pallet according claim 1, with rungs formed in one piece on the side rails, wherein the at least one stiffening structure is formed as an extruded aluminium profile with openings made between the rungs.

8. The plastic pallet according to claim 1, wherein at least one lower side rail, one upper side rail and two outer rungs are formed in one piece from a bent tube with a square cross-section.

9. The plastic pallet according to claim 8 with three rungs formed in one piece on the side rails, wherein the tube is bent into a shape of two side rails with rungs lying in between.

10. The plastic pallet according to claim 9, wherein the two tube ends are bent from one of the side rails to the other, opposite side rail and form a middle rung, and are connected to each other and to the other, opposite side rail in a bonded manner over an entire thickness of the opposite side rail.

11. The plastic pallet according to claim 1, wherein the lower side rails and the upper side rails are formed as tubes with a square cross-section and at least inner rungs are formed as plate-shaped connection elements, and the contact surfaces are formed as standing seams on two opposite sides.

12. The plastic pallet according to claim 1 with rungs formed in one piece on the side rails, wherein the at least one stiffening structure is formed as a rolled and bent metal profile with openings made between the rungs.

13. The plastic pallet according to claim 12, wherein the side rails are formed on the profile edges as standing seams, double standing seams, foldovers or combinations thereof.

14. The plastic pallet according to claim 5, wherein in the case of a bonded connection of the rungs to the side rails, the contact surfaces lie in a plane perpendicular to the longitudinal direction of the side rails and rungs and an extent of the contact surfaces in a direction of the thickness of the side rails is at least one-half of the thickness.

15. The plastic pallet according to claim 5, wherein in the case of a bonded connection of the rungs to the side rails, the contact surfaces lie in a plane perpendicular to the longitudinal direction of the side rails and rungs and an extent of the contact surfaces in a direction of the thickness of the side rails corresponds to the entire thickness.

16. The plastic pallet according to claim 12, wherein the rungs are formed as plate-shaped rungs.

17. The plastic pallet according to claim 13, wherein the rungs are formed as plate-shaped rungs.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The invention is explained in more detail below, for example with reference to the attached drawings which also disclose features essential to the invention, in which:

[0038] FIG. 1 is a perspective view of a plastic pallet with a ladder-like stiffening structure embedded therein, according to an embodiment;

[0039] FIG. 2 is a perspective view of a plastic pallet without a deck with stiffening structures;

[0040] FIGS. 3A-C depict a first embodiment of a stiffening structure;

[0041] FIGS. 4A-C depict a second embodiment of a stiffening structure;

[0042] FIGS. 5A-B depict a third embodiment of a stiffening structure;

[0043] FIG. 6 depicts a modification of the stiffening structure shown in FIG. 5;

[0044] FIGS. 7A-B depict a fourth embodiment of a stiffening structure;

[0045] FIGS. 8A-C depict a fifth embodiment of a stiffening structure;

[0046] FIGS. 9A-B depict a sixth embodiment of a stiffening structure;

[0047] FIGS. 10A-B depict a seventh embodiment of a stiffening structure; and

[0048] FIGS. 11A-C depict an eighth embodiment of a stiffening structure.

DETAILED DESCRIPTION OF THE DRAWINGS

[0049] FIG. 1 shows a conventional plastic pallet which comprises a deck 1 for storing objects to be transported. In the perspective view shown here, a deck upper side 2 can be seen, opposite which there is a deck underside, not shown; deck upper side 2 and deck underside are spaced apart from each other by the thickness of the deck. Feet 3 are formed protruding downwards from the deck underside. In addition, the plastic pallet also comprises runners 4 which are formed in each case connecting at least two feet 3 to each other on their undersides. The front segment of the plastic palletcomprising three feet and the runners which connect the feetis here shown cut open with the result that a stiffening structure 5 arranged theremarked by hatchingis visible. The stiffening structure 5, of which the pallet here comprises two in the outer runners, is here formed ladder-like and comprises lower side rails 6 arranged in the runners 4 and upper side rails 7 arranged spaced apart therefrom, which are arranged above the lower side rails 6 running parallel thereto. The upper side rails can be arranged in an area between the deck upper side 2 and the deck underside in the deck 1; but they can also be arranged below the deck 1 as shown for example in FIG. 1. In an arrangement of the upper side rails 7 in the area between the deck upper side 2 and the deck underside, the stiffening structure 5 can then be completely enclosed by the plastic of the pallet in the case of a one-piece manufacture.

[0050] The stiffening structure 5 is formed ladder-like and therefore comprises rungs 8 which connect the lower side rails 6 in the feet 3 to the upper side rails 7. The surface of the rungs is predominantly closed, i.e. it comprises no openings or recesses and if it does, then the surface of the openings or recesses is less than 50%, as a rule less than 10%, as a proportion of the entire surface of the rungs 8. Recesses and openings are made only where this is necessary or appropriate for reasons of manufacturing technology.

[0051] The rungs 8 are formed either in one piece on the lower side rails 6 or the upper side rails 7, or they are connected thereto, in each case in bonded manner via contact surfaces. Depending on the embodiment, some of the rungs 8 can also be formed in one piece on one or both side rails and other rungs can be connected to the side rails 6, 7 in bonded manner. The type of adhesive bond is selected depending on the material. In the case of metal stiffening structures 5, welding in particular is a possibility here. Depending on the materialfor example carbon-fiber- and glass-fiber-reinforced plastics can also be used for the stiffening structureother types of connection can also prove appropriate, for example friction- or form-locking connections, wherein all types of form locking can also be combined with each other.

[0052] Through the one-piece formation of the rungs 8 on the side rails 6 and 7, or through the bonded connection via larger contact surfaces on the one hand and through the predominantly closed surface of the rungs 8 on the other hand, the bending stiffness of the plastic pallet and in particular the shear strength of the plastic pallet in a plane parallel to the deck upper side 2 are increased.

[0053] Through the use of stiffening structures 5 formed in such a way, it is possible to reduce the deflection of the plastic pallet when supporting a load in the middle, for example from 22 mm to less than 10 mm in the case of a plastic pallet with the dimensions 1200 mm800 mm and with 3 feet connected to runners. The shear stiffness is increased as shear forces are diverted via or absorbed by the stiffening structures 5 which can in particular be made of metal.

[0054] FIG. 2 shows a plastic pallet without a deck; here only the feet 3 with runners 4 formed thereon are shown. Stiffening structures 5 are inserted in the two outer foot-runner elements. In addition, cross braces 9 are also shown here, which further increase the stability of the plastic pallet. These cross braces 9 can also be made of metal. However, they are purely optional and not strictly necessary for achieving the desired effect. In the interests of the lowest possible mass of the plastic pallet, the cross braces 9 can be dispensed with. They can be inlaid in the pallet independently of the stiffening structures 5, but also connected in bonded, form-locking and/or friction-locking manner thereto, in order to form an even more stable structure. In the present case the two outer cross braces 9 are pushed through openings in the stiffening structures 5 or in the rungs 8 and form a grid therewith. The middle cross brace 9 is only laid on, but could also be integrated into the grid.

[0055] Using the stiffening structures 5 it is possible to reduce the deflection to the degree that is considered permissible in the case of wooden pallets of a comparable size, or to an even lower degree. The thicker the stiffening structuresby thickness is meant the extent perpendicular to the longitudinal direction of the side rails and perpendicular to the longitudinal direction of the rungsthe higher the shear and bending stiffness, which is however associated with a higher mass. Although plastic pallets are per se lighter than wooden pallets of the same size, in the case of correspondingly thick stiffening structures 5 the weight of comparable wooden pallets can be exceeded, thereby losing a substantial advantage of plastic pallets.

[0056] However, if on the other hand the thickness of the lower side rails 6, the upper side rails 7 and the rungs 8 is selected too small, for example as pure sheet with a constant thickness, in the case of too small a thickness, the necessary shear stiffness cannot be realized. For this reason, at least the upper side rails 7 and the lower side rails 6 have a predetermined thickness.

[0057] In the case of a bonded connection of the rungs 8 to the side rails 6, 7 via contact surfaces, and also in the case of a friction- or form-locking connection, the size of the contact surfaces is selected or predetermined depending on a predetermined maximum bending and shear load of the plastic pallet; as a rule the contact surfaces should be selected as large as structurally possible.

[0058] In the longitudinal direction of the side rails 6, 7 the rungs 8 have a predetermined height for increasing the shear stiffness and bending stiffness in the longitudinal direction of the side rails 6, 7, which is based on the width of the feet; it should be at least 80% of the width of the respective foot receiving the rung. Here the term height is used on the basis of a standing ladder, for a lying structure it corresponds to the width. In the case of a connection of the rungs 8 to the side rails 6, 7 via contact surfaces, the extent of the contact surfaces in the longitudinal direction of the side rails 6, 7 preferably corresponds to the predetermined height.

[0059] For the embodiment of the side rails 6 and 7, many design variants are possible, for example the lower side rail 6 and/or the upper side rail 7 can be assembled as hollow structures from various surfaces, for example they can be formed as tubes with the cross-section of a quadrilateral, in particular a trapezium, rectangle or square, which facilitates the connection of the contact surfaces; but an embodiment as a T-beam or as a double T-beam is also conceivable. At least one of the surfaces in each case of one side rail (6, 7) is then preferably aligned perpendicular to the longitudinal direction of the respective side rail 6, 7 and perpendicular to the longitudinal direction of the rungs 8. Contact surfaces can then be formed on these surfaces, in particular for the adhesive bond.

[0060] In the case of a bonded connection of the rungs 8 to the side rails 6, 7, the contact surface therefore preferably lies in a plane perpendicular to the longitudinal direction of the rungs 8 and the side rails 6, 7. The extent of the contact surface in the direction of the thickness should then as a rule be more than half the thickness. Depending on the embodiment, the rungs 8 can also have a smaller thickness, in the case of formation from a sheet, for example, a thickness corresponding to the sheet thickness.

[0061] Various embodiments of stiffening structures 5 are explained below with reference to FIGS. 3-11.

[0062] FIGS. 3A-C show a first embodiment of a stiffening structure, as this can be used to increase the bending stiffness and the shear strength of the plastic pallet. FIG. 3A shows a view of the stiffening structure from the front, FIG. 3B a cross-section through the stiffening structure in the area of a rung 8 and FIG. 3C a perspective view of the stiffening structure, which here is formed as an extruded aluminium profile 10. The lower side rail 6 and the upper side rail 7 are in each case formed as a T-beam; the thickness of the side rails 6, 7 can for example be 20 mm in the area of the crossbeam of the T. As aluminium is a corrosion-resistant material, separate protection against corrosion can be dispensed with. Between the rungs 8, openings 11 are made, which in the assembled state are situated between the feet of the plastic pallet and allow the entry of the fork of a forklift truck. The rungs 8 are here formed in one piece on the side rails 6, 7 and plate-shaped. In the area below the upper side rail 7, through-holes 12 are optionally arranged, through which, during manufacture in the case of a one-piece pallet, plastic can pass, in order to ensure a firm connection between the stiffening structure and the plastic pallet. The through-holes 12 can also be used for another type of attachment, for example a mechanical one, should clamping into the framework structure of the plastic pallet not be possible; in this case no through-holes 12 are required. In particular, the through-holes 12 are however also suitable for receiving optional cross braces 9, in order to fix these better and produce a stiffening grid structure in the plane of the deck 1, as shown in FIG. 2. An advantage of using an extruded aluminium profile is also the reduced mass. Whereas a wooden pallet with the dimensions 800 mm1200 mm weighs 20-25 kg, the mass of a pallet with the profiles shown in FIGS. 3A-C is approximately 15-20 kg.

[0063] FIGS. 4A-C show a second embodiment of a stiffening structure, which here is formed as a further extruded aluminium profile 13. FIG. 4A shows a view of the extruded aluminium profile 13 from the side, FIG. 4B a cross-section through the profile in the area of a rung 8 and FIG. 4C a perspective view of the extruded aluminium profile 13. Here too, openings 11 are made between the rungs 8. This can be effected for example by punching, cutting or milling. The further extruded aluminium profile 13 shown in FIG. 4 also comprises through-holes 12. However, unlike the extruded profile shown in FIG. 3, here the lower side rail 6 is formed as a tube with a square cross-section and the upper side rail as a double T-beam. Here too, it is of course possible to design one of the side rails as a T-beam, likewise one of the side rails of the extruded aluminium profile 10, which is shown in FIGS. 3A-C, can be designed as a double T-beam or as a tube with a square or rectangular cross-section.

[0064] A third embodiment is shown in FIGS. 5A-B. This is a stiffening structure which is formed as a tube with a square cross-section 14. The tube 14 is bent into the shape of two side rails 6, 7, with rungs 8 lying in between. This is a one-piece design with a maximum of three rungs 8 which is suitable for smaller pallets in particular. All the rungs 8 are formed from the square tube 14. In the example shown in FIG. 5, the outer rungs 8 of the stiffening structure are formed by bending the tube 14 twice, in each case by 90. By contrast, the middle or inner rung 8 is formed in that the two tube ends 15 of one of the side railshere without limiting the generality, the upper side rail 7, are bent 90; the middle rung 8 is therefore formed through the bending. The tube ends 15 are connected to the opposite side railhere the lower side rail 6in bonded manner, for example by welding, here over the entire thickness of the lower side rail 6. To increase the bending and shear stiffness and the stability of the stiffening structure, the tube ends 15 can also be connected to each other in bonded manner; however, in the case of a corresponding fixing in the middle foot in the plastic pallet, this can also be dispensed with.

[0065] A modification of this embodiment is shown in FIG. 6. The tube ends 15 which form the middle rung 8 are here spread apart from each other in their end areas, with the result that the middle rung 8 takes on the shape of a Y. With one edge, the tube ends 15 are in each case connected in bonded manner to the opposite side rail, here the lower side rail 6, over the entire thickness of the side rail. The edges in question are preferably provided with larger chamfers in order to provide a contact surface for the bonded connection, which is more stable than a linear, one-dimensional connection. Here too, the rungs 8 are formed in one piece on the lower side rail 6 or on the upper side rail 7, even if, to increase the stiffness, the tube ends are connected in bonded manner to the opposite side rail. Through the spreading of the tube ends 15 into the shape of a Y, the shear stiffness in a plane parallel to the deck 1, or the bending stiffness perpendicular to the deck plane is further increased compared with the design shown in FIGS. 5A-B.

[0066] A further design for a stiffening structure is shown in FIG. 7. FIG. 7A shows a projection view of the stiffening structure from the front, and FIG. 7B a perspective view. In this fourth embodiment the side rails are also formed as tubes with a square cross-section; the lower side rail 6 and the upper side rail 7 as well as the two outer rungs 8 are here likewise formed in one piece from a bent tube 14. The two tube ends 15 are connected to each other in bonded manner in the area of one of the outer rungs 8. The tube ends 15 can however also come together at another point of one of the side rails, for example in the area of the middle rung 8. The middle rung 8 is here formed as a plate-shaped connection element 16, in which on two opposite sides, namely the sides facing the side rails 6 and 7, contact surfaces are formed as standing seams. The plate-shaped connection element 16 is here placed centrallywith respect to the thickness of the lower side rail 6 and the upper side rail 7. The extent of the contact surfaces formed by the standing seams in the direction of the thickness is half the thickness here.

[0067] This fourth embodiment of a stiffening structure has a particularly good cost-benefit ratio, for one thing as the square tube 14 has to be cut to length only once and bent only four times. However, due to the plate-shaped connection element which can have a C- or S-shape in cross-section, the shear strength and bending stiffness are further increased compared with the designs shown in FIG. 5 and FIG. 6, as the plate-shaped connection element 16 can have the maximum height in the longitudinal direction of the side railscorresponding to the width in the viewwhich just makes it possible to completely integrate it into the corresponding foot 3, whereas, in the case of the formation of the middle rung 8 from the bent tube ends 15, the width is predetermined by the thickness of the square tube 14 and cannot be increased. In addition, the stiffening structure shown in FIGS. 7A-B can also be used for pallets with more feet in one direction, as several of the plate-shaped connection elements 16 can readily be placed as inner rungs between the outer rungs formed in one piece.

[0068] A furtherparticularly stablefifth embodiment of a stiffening structure for a plastic pallet is shown in FIG. 8. FIG. 8A shows a side view of a stiffening structure lying on the outer edge of a side rail, FIG. 8B the cross-section in the area of a rung 8 and FIG. 8C a perspective view. Unlike the embodiment shown in FIG. 7, here too the outer rungs 8 are formed as plate-shaped connection elements 16 with standing seams 17 formed thereon for forming the contact surfaces. The plate-shaped connection elements 16 have a C-shape in cross-sectionas shown in FIG. 8C. In this design, the lower side rail 6 and the upper side rail 7 are also formed as a tube 14 with a square cross-section. They can be produced from a tube by sawing. In each case three plate-shaped connection elements 16here of the same kindconnect the upper side rail 7 to the lower side rail 6; the standing seams 17, which are formed on the plate-shaped elements 16 by bending, form the contact surfaces. Their extent in the direction of the thickness of the side rails 6, 7 here corresponds to the entire thickness of the side rails 6 and 7. By means of the contact surfaces, the plate-shaped connection elements are connected to the side rails 6 and 7 in bonded manner. After production of the bonded connection, the stiffening structure still has to be galvanized for protection against corrosion.

[0069] Although the designs described in FIGS. 5-8 are more expensive to produce compared with the above-described variants made of extruded aluminium profile, they are more sparing with material resources as practically no waste is produced, whereas when the opening 11 is made in the extruded aluminium profiles 10 and 13 described in connection with FIG. 3 and FIG. 4, a substantial proportion of material waste is produced.

[0070] FIGS. 9-11 show further embodiments for stiffening structures which are all formed in one piece from rolled and bent metal profile, for example (steel) sheet or strip steel, wherein openings 11 are again made between the rungs 8. In addition, these stiffening structures also comprise optional through-holes 12. The embodiments differ here only in the formation of the lower side rail 6 and of the upper side rail 7, which are formed on the profile edges by bending, and are formed as standing seams, double standing seams, foldovers or combinations thereof. The metal profile shown in perspective view in FIG. 9A and in cross-section in FIG. 9B in the area of a rung 8 as sixth embodiment of a stiffening structure comprises an upper side rail 7 formed identically to the lower side rail 6. The side rails are formed by a 90 standing seam and two foldovers, i.e. 180 bends, in the opposite orientation. The bends are arranged mirror-symmetrically with respect to a horizontal plane in the sheet, with the result that the profile with the two standing seams forms a C-shape which offers a somewhat higher degree of stability compared with an S-shape which is also possible. All the rungs 8 are formed plate-shaped and in one piece on the side rails 6 and 7.

[0071] The metal profile shown in perspective in FIG. 10A and in cross-section in FIG. 10B in the area of a rung 8 as seventh embodiment of a stiffening structure comprises side rails 6, 7 formed by other bend combinations. The plate-shaped rungs 8 are here also formed in one piece on the side rails 6, 7, and arranged centrally with respect to the thickness of the side rails 6 and 7in FIG. 10B corresponding to the horizontal direction in the sheet plane. However, the upper side rail 7 has a greater widthcorresponding to the vertical direction in the sheet planethan the lower side rail 6. Here the fact can be utilized that on the one hand the runners 4 should be kept flat, however on the other hand for the upper side rail 7in the case of complete enclosure by the plasticalmost the entire deck height can be used. This additionally increases the stability. The side rails 6, 7 are here formed by the combination of several 90 bends (standing seams) and one 180 bend (foldover).

[0072] An eighth design of a stiffening structure is finally shown in FIG. 11. FIG. 11A and FIG. 11B show the stiffening structure formed as a metal profile in perspective, from two opposite sides, FIG. 11C shows the profile in cross-section in the area of a rung 8. Here too, the upper side rail 7 is designed wider than the lower side rail 6. Both side rails 6, 7 are formed as double standing seams. For each side rail, only two bends are required here; the stiffening structure is thus comparatively simple to produce, but also offers a very high bending and shear strength.

[0073] All the profiles are characterized by the fact that, with relatively low mass, they are capable of giving a plastic pallet the required bending and shear stiffness, with the result that the deflection in the middle is no greater than in the case of wooden pallets; on the other hand however, the mass of the plastic pallet with stiffening structures is even lower than in the case of conventional wooden pallets of the same size. Whereas the latter, with dimensions of 1200800 mm, have a weight of 20-25 kg, it is possible with the invention presented here, to keep the weight of the plastic pallets significantly below this, at approximately 15-20 kg.

LIST OF REFERENCE NUMBERS

[0074] 1 deck [0075] 2 deck upper side [0076] 3 foot [0077] 4 runner [0078] 5 stiffening structure [0079] 6 lower side rail [0080] 7 upper side rail [0081] 8 rung [0082] 9 cross brace [0083] 10 extruded aluminium profile [0084] 11 opening [0085] 12 through-hole [0086] 13 extruded aluminium profile [0087] 14 tube with square cross-section [0088] 15 tube end [0089] 16 plate-shaped connection element [0090] 17 standing seam