METHOD OF MANUFACTURING A PALLET, AND A PALLET MANUFACTURED BY THE METHOD

Abstract: A method is described for manufacturing a plastic pallet comprising an upper body (1), a lower body (3), reinforcing material (6) and reinforcing elements (7, 8) placed between the upper body (1) and the lower body (3), which method comprises the following steps: a) casting one of the bodies (1, 3) in a moulding machine having a plurality of injection nozzles; b) casting the reinforcing material (6) separately; c) placing the reinforcing material (6) and reinforcing elements (7, 8) in the cast body (1, 3); and d) casting the second body (3, 1). A plastic pallet manufactured using the method is also described.

Description: Method of manufacturing a pallet and a pallet manufactured by the method The present invention relates to a method for manufacturing a pallet, and a pallet manufactured by the method according to the preamble of the independent claims. Today's pallets which meet the safety requirements (strength requirements) and standard measurements for open return systems have hitherto been made of wood. Wooden pallets are well established on the market and form the basis for the Europallet standard, and thus for the external equipment such as trucks, pallet racks and automatic stores. However, new hygiene requirements have arisen in the food industry, amongst others, which means that the wooden pallets cannot be used in connection with production. This involves re-palletising from a closed system in the production plants to an open system in connection with transport, which results in poor logistics and is extremely costly. Furthermore, the grocery trade has also established new requirements calling for the removal of wooden pallets from the shops in order to meet both hygienic and visual standards. On account of today's rational methods of operation, a system has been established wherein the pallets, ready packed by the suppliers or manufacturers, are driven straight out into the shops, and this has resulted in new requirements from the retail trade as mentioned above. Single use or disposable pallets are used to a great extent today in order to meet the new requirements, but this system is becoming excessively expensive both for the supplier and for the shops because of the need to dispose of the single use packaging, including charges for the delivery of waste to public refuse tips. There is thus a need to provide a plastic pallet that is adapted for multipurpose use and which meets the safety requirements of an open return system by satisfying the requirement with respect to weight load from an applied load that is allowed when using standard Europallets made of wood, thereby becoming compatible and thus capable of being used as a standard for plastic pallets for the food industry. (The strength requirements are given in the ISO standard specifications for plastic pallets.) The pallet must also meet the hygiene requirements which are laid down by the Food Control Authority and other authorities. Attempts have been made to use plastic pallets of various kinds where the pallets have had to run in closed systems, and the pallets have not been stackable in pallet racks since at elevated temperatures, for instance +40°C, the plastic softens and the pallets sag, and may ultimately fall out of the pallet racks and cause an accident if they are subjected to a load weight which is permitted in a compatible system involving the wooden Europallets. Plastic pallets have therefore previously involved re-palletising from or to wooden pallets in order to meet the safety requirements during storage in pallet racks. This has been found to be excessively expensive. It thus imperative that the plastic pallets should be fully compatible with the load requirements and measurements for return wooden pallets according to the Europallet standard. Attempts have been made to increase the amount of plastic in the pallets in order to meet the requirements, but this has resulted in the pallets becoming unmanageably heavy and in addition not meeting the stipulated measurement requirements with respect to height in the Europallet standard. Furthermore, it is known that the pallets are reinforced with, for example, inserts of steel and aluminium on the long side, for example, beams, to meet the strength requirements with respect to sagging. This is in fact known from inter alia Norwegian Patent Application Nos. 960 120 and 860 910 which have been tested. US Patent 4,397,247 makes known the moulding of a pallet with embedded reinforcement. US Patent 3,915,098 makes known a pallet and a method for the manufacture thereof, which pallet consists of expandable polystyrene, in which reinforcing elements are embedded. GB 1168418 and US 3,880,092 make known plastic pallets with embedded reinforcing elements. Norwegian Published Patent Application 1700573 makes known a pallet with cellular structures provided in the pallet load surface. The results of the said solutions have been that sagging has continued to occur on the short side. The problem in the pallet racks may appear to be resolved, but when handled on trucks when supporting a heavy load, for example, brewery crates, the outer edge of the pallet sags and the outermost row of crates falls off on movement. The problem arises also in connection with some automatic packing equipment which carries the pallets under cover, in the same way as a truck. It has also been found that if the pallets are placed on an elevation on the floor or a foreign member on the floor comes under the middle runner (the pallet foot), the pallet will bend upwards in the middle, which results in the load falling off if it is not secured in another way. There is thus a need to provide a pallet wherein side sagging of the outermost portion (area), or bending upwards in the middle portion does not occur when the outer sides of the pallet are loaded during transport on a truck or when using other equipment, and also when the pallet loaded with an unsecured load is placed on substantially uneven surfaces. The aforementioned weaknesses and problems of present plastic pallets for return in an open standardised system for the grocery trade and the food industry, are overcome by the device according to the present invention, as defined in the accompanying claims. Furthermore, because of today's system of transport of goods on pallets to the shops there has arisen a need to be able to lift the goods, for example, crates, in whole stacks (section by section) to obtain a more rational handling and fewer manual lifts, as the crates may often exceed the recommended weight for manual lifts. Present plastic pallets have a smooth cover (top) and so lifting off section by section from the underside of the load resting thereon has not been possible. Another difficulty with today's smooth surfaces is that condensation occurs on the pallet when the load is secured with plastic film and transported in and out of cold storage. Another problem encountered with the known plastic pallets which are produced in several sections that are welded together, is that if the pallet is subjected to substantial loads, for example, by pushing a loaded pallet with the forks on a truck, there is a great risk of the pallet splitting in the joint area. This will mean that the pallet is no longer hermetically sealed, thus allowing moisture to penetrate into the interior of the pallet. Over time this may result in the growth of bacteria, which will mean that the hygiene requirements are no longer met. The object of the present invention is to provide a method for manufacturing a plastic pallet , and a pallet made by means of the method, which are not burdened by the disadvantages described above. The object of the present invention is to provide a method for manufacturing a plastic pallet comprising an upper body, a lower body, reinforcing material and reinforcing elements provided between the upper body and the lower body, characterised in that the method comprises the following steps: a) casting one of the bodies in a moulding machine having one or more injection nozzles; b) casting the reinforcing material separately; c) placing the reinforcing material and reinforcing elements in the cast body; and d) casting the second body together with the already cast body, reinforcing material and reinforcing elements. It is preferable that the lower body should be cast in step a). According to one embodiment the reinforcing material and reinforcing elements are placed in the cast body without taking the cast body out of the mould. According to an alternative embodiment of the method, step b) comprises casting the reinforcing material directly into the cast body. The invention also relates to a pallet consisting of a lower body and an upper body, reinforcing material and reinforcing elements provided between the upper body and the lower body, which pallet is characterised in that the reinforcing material is a foamed polymeric material. The reinforcing elements are preferably made of steel, aluminium, fibre-reinforced plastic or composites thereof or wood. According to one embodiment, the upper body and the lower body are made of two different plastic materials. According to yet another preferred embodiment one of the bodies contains portions of an elastomeric material and/or the second body contains a plastic material containing talc or glass fibre. The invention will be described in more detail below with the aid of exemplary embodiments and with reference to the attached drawings. Figures 1 a-d show a pallet according to the present invention, seen from below, from the side, from above and from the end, respectively. Figure 2 is a cross-sectional view along the line A- A in Figure 1. Figure 3 is a sectional view of the pallet along the line B-B in Figure 1. Figures 1 a-d show a pallet according to the present invention. The pallet consists of an upper sheet-like body which functions as load-bearing surface 1. This upper, sheet-like body may, e.g., be designed to have longitudinal or lateral furrows or grooves 2. The pallet further consists of a lower body 3, designed to have legs 4. In the illustrated embodiment there are three rows of three legs. However, the number of legs may be varied depending upon the size of the pallet and the load the pallet is designed to withstand. In the exemplary embodiment shown in Figure 1 each of the rows of legs are interconnected by means of transverse bodies 5. Figure 2 is a sectional view of the pallet along the line A- A in Figure 1 and in Figure 3 there is a sectional view of the pallet along the line B-B in Figure 1. The pallet consists of a lower body 3 and an upper body 1, each of which is produced in a single piece. Reinforcing material 6 in the form of a foamed polymeric material is provided in the cavities between these two bodies 1 and 3. Beneath and partly in the upper, sheet-like body 1 there are also provided transverse and longitudinal reinforcing elements 7, 8 in the form of rails. These reinforcing elements 7 and 8 are shown in section in Figures 4 and 5 respectively. The reinforcing elements may be of steel, aluminium, glass fibre reinforced plastic composites, wood etc. The manufacture of the pallet will now be explained in more detail with reference to Figures 2 and 3. First the lower body 3 is cast in a plastics moulding machine. Independent thereof, the reinforcing material 6 is cast in a moulding machine. The reinforcing material 6 is subsequently placed in the lower body 3, the reinforcing elements 7 and 8 are placed on top of this combination without the lower body 3 leaving the mould. It will also be possible to first transfer the lower body 3 into a new mould before the reinforcing material 6 and the reinforcing elements 7, 8 are placed in the lower body. The plastic material is introduced into the mould at a low pressure to prevent the reinforcing material from breaking down. To obtain sufficiently low pressure, a plurality of injection nozzles, for instance, 10 nozzles are used. These injection nozzles can be controlled independent of one another and enable the reinforcing material 6 in the form of a foamed polymeric material to be cast in without breaking down because of the pressure that arises when injecting the plastic material into the mould. By using a low pressure and many injection nozzles it is also possible to bind the reinforcing material in the form of foamed polymeric material, which has been placed in the mould, to the plastic materials which are then injected into the mould. This procedure results in the upper body 1 being firmly cast together with the lower body 3 without any joint or seam being formed. This will give the finished pallet strength properties which were unobtainable previously. Optionally, it would be possible to cast the upper body first and the lower body last. There is also the option of casting the reinforcements into the foamed element. In accordance with an especially preferred embodiment, the reinforcing material 6, instead of being cast separately, may be cast directly into the lower or upper body 3, 1 whilst the body is located in the mould. This can be done in that some of the injection nozzles described above supply foamed polymeric material. This will give great advantages as regards production efficiency. By using a plurality of separately adjustable injection nozzles it will be possible to provide plastic materials of different qualities in different parts of the pallet. In one part of the pallet there be, e.g., be an elastomeric material which generates friction and in another part of the pallet a material containing talc or glass fibre for extra reinforcement may be used.

Claims: P a t e n t c l a i m s 1. A method for manufacturing a plastic pallet comprising an upper body (1), a lower body (3), reinforcing material (6) and reinforcing elements (7, 8) placed between the upper body (1) and the lower body (3), characterised in that the method comprises the following steps: a) casting one of the bodies (1, 3) in a moulding machine having one or more injection nozzles; b) casting the reinforcing material (6) separately; c) placing the reinforcing material (6) and reinforcing elements (7, 8) in the cast body (1, 3); and d) casting the second body (3, 1) together with the already cast body (1, 3), the reinforcing material (6) and the reinforcing elements (7, 8). 2. The method of claim 1, characterised by casting the lower body (3) in step a). 3. The method of claims 1-2, characterised by placing the reinforcing material (6) and the reinforcing elements (7, 8) in the cast body (1, 3) without taking the cast body (1, 3) out of the mould. 4. The method of claims 1-4, characterised in that step b) alternatively includes casting the reinforcing material (6) directly into the cast body (1, 3). 5. A pallet consisting of a lower body (3), an upper body (1), reinforcing material (6) and reinforcing elements (7, 8) placed between the upper body (1) and the lower body (3), characterised in that the reinforcing material (6) is a foamed polymeric material. 6. The pallet of claim 5, characterised in that the reinforcing elements (7, 8) are made of steel, aluminium, fibre-reinforced plastic or composites thereof or wood. 7. The pallet of claims 5-6, characterised in that the upper body (1) and the lower body (3) are made of two different plastic materials. 8. The pallet of one or more of claims 5-7, characterised in that one of the bodies (1, 3) contains portions of an elastomeric material and/or the other body (3, 1) contains a plastic material containing talc or glass fibre.

Inventors: MOLANDER DAN, OSBAKK GEORG, MOLANDER, DAN, OSBAKK, GEORG
Applicants: MOLANDER DAN, MOULDEX PLAST AB, OSBAKK GEORG, PETCON AS, MOLANDER, DAN, OSBAKK, GEORG
Application year: 1999
Main classification: B65D19
IPC codes: B65D19