Carrying element such as pallet

Abstract: A carrying element mainly made of synthetic material comprising an upper surface (1), an intermediate section (6) located under the upper surface (1), which is connected to the upper surface (1) by a welded joint, and a base (11) provided under the intermediate section (6) with protrusions (14) which extend via passages (9) in the intermediate section (6) through to the upper surface (1) where these protrusions (14) are welded to the upper surface (1). The welded joint of the upper surface (1) and the intermediate section (6) and the welded joint of the upper surface (1) and the aforementioned protrusions (14) are provided at almost the same level. The various parts (1), (6), (11) of such a carrying element can be joined together into a unit during one and the same welding operation. Furthermore strengthening means, such as a rib structure (5), (8) can be enclosed between the upper surface (1) and the intermediate section (6).

Description: This invention relates to a carrying element mainly made of synthetic material, comprising an upper surface, an intermediate section located under the upper surface which is connected to the upper surface by a welded joint, and a base provided under the intermediate section. This invention more especially relates to a pallet with the characteristics described above. Pallets are principally used for stacking up and/or moving goods. In conditions where hygiene is of great importance, such as for example in the food industry, pallets are used which are mainly made of synthetic material and whose surface area is almost completely closed, in order to limit as far as possible the number of difficultly accessible places where dirt can become lodged. Such pallets can be very easily and very thoroughly cleaned, both in automatic tunnel washers and with high-pressure cleaners. Pallets exist with a hollow carrying plate, on to which a set of legs is welded. The hollow carrying plate and the set of legs are manufactured as separate parts by injection moulding and are subsequently attached to each other by thermal welding. When manufacturing these pallets only one single welding operation is required. A disadvantage of these known pallets is however that the hollow carrying plate provides insufficient rigidity. The fact that the pallet is constructed out of only two parts, furthermore results in a number of restrictions with regard to its design. Hence among others certain roundings-off are not feasible, and certain bevellings can only be achieved with complex moulds. The set of legs comprises legs that are connected to each other at the bottom by connecting strips and at the top by a plate. In order to construct such a form with a closed cut-away (between the legs, the plate, and the connecting strips) the mould must comprise sideways sliding parts. Such moulds are complex and expensive. Because of this it is necessary to inject products, which among others because of the sturdiness of the pallets have to have great differences in thickness. This results in relatively long cycle times, and pieces, whose various parts have a different shrinking behaviour, with the result that these pieces will deform. Pallets also exist which are constructed out of a hollow carrying plate, in which a rib structure is provided, welded to a set of legs. In order to be able to achieve this internal rib structure the carrying plate must be made out of two parts. An upper plate-shaped part with an almost flat upper surface area and with downward directed ribs on the underside (an upper surface), and a lower plate-shaped part with upward directed ribs on the upper side (an intermediate section). These two parts are welded together. In addition each rib of the upper part is welded to a rib of the lower part. Both parts fit so into each other that they form a completely closed hollow carrying plate with an internal rib structure. The pallet thus formed provides sufficient rigidity because of the rib structure in the carrying plate. A disadvantage is however that two welding operations are required for the manufacturing of this pallet: during a first welding operation the upper and the lower part of the carrying plate are welded together. During a second welding operation the set of legs is welded to the carrying plate. This latter welding operation has to be carried out at a difficulty attainable place. The manufacturing operation of this pallet is therefore a time-consuming and difficult technique. Another type of pallet is described in document WO 94 10051, having an upper platform with a smooth top surface, a ribbed bottom surface and spacer bases soldered thereon to create a free space for the forcks of a fork stacker or a lifting truck. The object of this invention is to provide a carrying element with the characteristics indicated in the first paragraph of this description, which can be manufactured according to a method which is simpler and less time-consuming than the method described in the preceding paragraph, that nevertheless provides sufficient rigidity, and that can be produced with a closed surface area. This objective is achieved by providing such a carrying element, with a base which comprises at least one protrusion, which extends via a passage in the intermediate section through to the upper surface, where it is joined to the upper surface by a welded joint, while the welded joint of the upper surface and the intermediate section and the welded joint of the upper surface and the aforementioned protrusion are provided at almost the same level. The upper surface, the intermediate section and the base of the carrying element can be joined together into one unit during one and the same welding operation. The carrying element can therefore be manufactured in a simple and fast manner. Furthermore the carrying plate is produced in two parts (an upper surface and an intermediate section provided thereunder) so that it can be provided with enclosed strengthening means, such as e.g. a rib structure. The carrying element according to the invention can consequently be so produced that on the one hand it provides sufficient rigidity, and on the other hand has a closed surface area. With a preferred embodiment according to this invention the base comprises at least one pair of two wings provided opposite each other with an interval between, while each passage in the intermediate section is provided between two walls of this intermediate section provided opposite each other with an interval between, and while the aforementioned wings of each pair, next to a respective wall of the intermediate section, extend via a passage through to the upper surface, and are connected to the upper surface by a welded joint. Because of this double-walled parts are obtained, through which the rigidity and the sturdiness (among others the resistance to jolts and shocks) of the carrying element are still increased. Ribs are preferably provided on the underside of the upper surface, while each wing of the base is welded to a respective rib. With a very preferred embodiment each wing of the base is welded together with a neighbouring wall of the intermediate section to a rib of the upper surface. A very solid carrying element is obtained with a particularly great rigidity when the upper surface and the intermediate section enclose at least one hollow space, while both the upper surface and the intermediate section are provided with ribs extending in the hollow space, and while ribs of the intermediate section are welded to a respective rib of the upper surface. With a particularly preferred embodiment the carrying element comprises at least one hollow leg, while each pair of wings of the base and the respective walls of the intermediate section extending next to these wings form the double side walls of a leg. Because of this legs are obtained with a very great resistance to jolts and shocks. Preferably several hollow legs are provided, and the hollow space of each leg is closed off on top and underneath by a part of the upper surface, respectively by a part of the base, while neighbouring legs are connected to each other underneath by a connecting strip which is a part of the base. In its most preferred embodiment the carrying element according to this invention is produced as a pallet with an almost completely closed surface area. Such a pallet is very easily and thoroughly cleanable and therefore especially suitable for use in conditions where hygiene is of importance. This invention will be further clarified in the following nonrestrictive description of a possible embodiment of a pallet manufactured out of synthetic material according to the invention. In this description reference is made to the drawings attached hereto, of which figure 1 represents a vertical cross-section of the separate parts of the pallet figure 2 represents a vertical cross-section of the pallet, which is obtained by the assembly of the parts from figure 1. In a particularly preferred embodiment the pallet according to this invention is constructed out of three different parts (see figure 1), each of which is separately manufactured out of a thermoplastic synthetic material, such as for example polyolefins (HDPE, PP, both homo and copolymers), polycarbonates or polyesters, which can be processed into moulded pieces by injection moulding, both with low and high-pressure methods, by compression moulding or by compression-injection moulding. The raw materials used can be of primary or recycled origin. These three parts are: An upper surface (1), which comprises a completely closed, rectangular plate (2) made almost flat, whose upper side is made smooth, or is provided with relief in order to ensure a stable stacking-up and/or a good positioning of the goods on this upper side, while ribs (3), (4), (5) are provided perpendicular on the underside of the plate (2). On each of the four edges of the plate (2) a downward direct rib (3) is provided. These ribs (3) connect to each other at the corners of the plate (2). On the underside of the plate (2) there are zones where a number of adjacent ribs (4), (5) are provided parallel to the ribs of two opposite edges of the plate (2). All ribs (3), (4), (5) extend to the same level (indicated by dashed line in fig. 1) under the underside of the plate (2). There are ribs (4) with the same thickness as the ribs (3) which are on the edge of the plate (2) (called "thick ribs" (3), (4) in that which follows), and there are ribs (5) with a lesser thickness (called "thin ribs" (5) in that which follows). A rectangular intermediate section (6), consisting of a completely closed flat plate (7) with on the upper side upright ribs (8) of the same thickness as the thin ribs (5) of the upper surface (1), and with vertical passages (9) which are delimited sideways by parallel vertical walls (10). The vertical walls (10) and the ribs (8) extend through to the same level (indicated by dashed line in fig. 1) above the upper side of the plate (7) of the intermediate section (6) and have the same thickness. A rectangular set of legs (11), consisting of several leg structures (12) which are connected to each other underneath by connecting strips (13). Each leg structure (12) comprises two parallel vertical walls (14) which are connected to each other underneath by a closed horizontal bottom surface (15). The upper surface (1) and the intermediate section (6) are further so produced that these parts (1), (6) can be placed on each other in a position whereby each wall (10) of the intermediate section (6) lies in the extension of a thick rib (3), (4) of the upper surface (1), and whereby each rib (8) of the intermediate section (6) lies in the extension of a thin rib (5) of the upper surface (1) (see figure 2). The set of legs (11) is also further so produced that each pair of parallel walls (14) of the leg structure fits with very little play into a passage (9) between parallel walls (10) of the intermediate section (6), and that the upper edges of the walls (10) of the intermediate section (6) and the upper edges of the walls (14) of the leg structure (11) come to lie at almost the same level when the leg structure (11) and the intermediate section (6) are joined together (see figure 2). The separately formed parts (1), (6), (11) are joined together into one unit by first sliding each leg structure (12) of the set of legs (11) into a respective passage (9) of the intermediate section (6), and by subsequently welding the upper surface (1) on top of this combination of set of legs (11) and intermediate section (6). The hollow space (18) of each leg (17) is closed off on top by the upper surface (1) and underneath by a bottom surface (15). Because of the fact that the parallel walls (14) of each set of legs (12) are between two walls (10) of the intermediate section (6) particularly solid double-walled legs (17),are obtained with a very great resistance to jolts and shocks. Because of the fact that the upper edges of the walls (10) of the intermediate section (6) and of the walls (14) of the set of legs (11) are almost at the same level, the pallet can be joined together during one welding operation at the level indicated in figure 2 by means of a dashed line. Each wall (10) of the intermediate section (6) is moreover together with an adjoining wall (14) of the set of legs (11) welded to a thick rib (4) of the upper surface (1). Each rib (8) of the intermediate section (6) is welded to a thin rib (5) of the upper surface during that same welding operation. The upper surface (1) and the intermediate section (6) in that manner enclose hollow spaces (16) with an internal rib structure (5), (8). The thickness of the thick rib (4) almost corresponds to the thickness of the two adjoining walls (10), (14) which are welded to that rib (4) (in the extension thereof). The welded joints can be achieved by hotplate welding, vibration welding or ultrasound welding. If desired a seal can be provided between adjoining parts of the intermediate section (5) and the set of legs (11). A pallet is obtained which has sufficient rigidity because of the rib structure in the hollow space (16) enclosed by the upper surface (1) and the intermediate section (6), which is suitable for use in conditions where hygiene is of importance because of the fact that it has a completely closed surface area, which has a great resistance to shocks and jolts because of the double-walled legs, and which can be manufactured according to a particularly simple and fast production process. A nonetheless complicated design can be obtained by making use of simple moulds (of the open/shut type, without sideways sliding parts). Because of this the mould costs can be kept down, and short cycle times can be used. Due to the three-part operation it is possible to select the optimum wall thicknesses and roundings-off in the various parts. On machines with sufficiently great plate surface areas, and shot weight, the various parts can be achieved in 1 shot. This is e.g. extremely suitable for processing on low-pressure injection moulding machines with structural foam. Hereby complicated hot-runner systems in the moulds are also avoided. Special attention can be given to the design of the connecting strips between the legs, in function of hygiene, strength, behaviour on roller conveyors, etc... A different compound of the synthetic material can possibly be chosen for the various parts in function of the characteristics selected. For pallets, which have to satisfy the highest demands with regard to hygiene, additional sealing rings can be provided.

Claims: A carrying element mainly made of synthetic material comprising an upper surface (1), an intermediate section (6) located under the upper surface, which is connected to the upper surface (1) by a welded joint, and a base (11) provided under the intermediate section (6), characterised in that the base (11) comprises at least one protrusion (14) which extends via a passage (9) in the intermediate section (6) through to the upper surface (1), where it is joined to the upper surface (1) by a welded joint, and that the welded joint of the upper surface (1) and the intermediate section (6) and the welded joint of the upper surface (1) and the aforementioned protrusion (14) are provided at almost the same level. A carrying element according to claim 1, characterised in that the base (11) comprises at least one pair of two wings (14) provided opposite each other with an interval between, that each passage (9) in the intermediate section (6) is provided between two walls (10) of this intermediate section (6) provided opposite each other with an interval between, and that the aforementioned wings (14) of each pair, next to a respective wall (10) of the intermediate section (6), extend via a passage (9) through to the upper surface (1), and are connected to the upper surface (1) by a welded joint. A carrying element according to claim 2, characterised in that ribs (3), (4), (5) are provided on the underside of the upper surface (1), and that each wing (14) of the base (11) is welded to a respective rib (3), (4). A carrying element according to claim 3, characterised in that each wing (14) of the base (11) is welded together with a neighbouring wall (10) of the intermediate section (6) to a rib (3), (4), of the upper surface (1). A carrying element according to any of the preceding claims, characterised in that the upper surface (1) and the intermediate section (6) enclose at least one hollow space (16), that both the upper surface (1) and the intermediate section (6) are provided with ribs (5), (8) extending in the hollow space (16), and that ribs (8) of the intermediate section (6) are welded to a respective rib (5) of the upper surface (1). A carrying element according to any of the preceding claims, characterised in that it comprises at least one hollow leg (17) and that each pair of wings (14) of the base (11) and the respective walls (10) of the intermediate section (6) extending next to these wings form the double side walls of a leg (17). A carrying element according to claim 6, characterised in that it comprises several hollow legs (17); that the hollow space (18) of each leg (17) is closed off on top and underneath by a part of the upper surface (1), respectively by a part (15) of the base (11); and that neighbouring legs (17) are connected to each other underneath by a connecting strip (13) which is a part of the base (11). A carrying element according to any of the preceding claims, characterised in that it is a pallet with an almost completely closed surface area.

Inventors: FORMENT BERNARD, VANDEVELDE MICHEL, FORMENT, BERNARD, VANDEVELDE, MICHEL
Applicants: I P S N V, I.P.S. N.V.
Application year: 1997
Main classification: B65D19
IPC codes: B65D19