WO1996003322A1

WO1996003322A1 - Two-piece moulded plastic pallet

Info

Publication number: WO1996003322A1
Application number: PCT/NZ1995/000064
Authority: WO
Inventors: Robert William Campbell
Original assignee: Pallenz Limited
Priority date: 1994-07-22
Filing date: 1995-07-20
Publication date: 1996-02-08
Also published as: AU2992495A

Abstract

The pallet (1) is comprised of two halves, an upper half (2) and a lower half (3). The halves (2 and 3) have been connected together by using male/female connectors (7/8) respectively. The male connectors (7) are a tapered lug having a rounded top which prevents penetration of the male connector (7) into the pallet (1) if excessive force is loaded onto the pallet (1). The female connector (8) is an aperture which is of a complimentary shape to the male connector (7). The top half of the pallet may have grooves moulded into the upper and lower surfaces so that inside the pallet top half the upper and lower surfaces touch or 'kiss off'. Not only does this add to the overall stiffness and strength of the pallet, but also the top and bottom surface are kept the same distance from each other. The 'kiss offs' can be arranged so as to transfer the static load from the top surface through to the bottom surface and to the ground. Not only does this add strength to the bottom of the pallet, but also provides a path through which the static load can be transferred from the top half of the pallet through to the ground. This obviates the change of the plastic buckling.

Description

TWO-PIECE MOULDED PLASTIC PALLET

TECHNICAL FIELD

This invention relates to a method of manufacturing a pallet.

The term pallet is one which is well known to the transportation and storage industry. In this specification, this term is used to describe a support base which allows for access of fork lift tines inside or under the support base so that a fork lift can lift the support base and any product supported by that base.

BACKGROUND ART

Presently, the most common type of pallet used is a wooden pallet. Unfortunately, there are problems associated with the use of this material in pallets.

Wooden pallets have a short life on account of their lack of durability. Further, many countries will not accept wooden pallets for quarantine reasons as bacteria and other contaminants may reside in the wood. Other problems with wooden pallets is that the nails used tend to puncture bags and spill product placed on the pallet. A further problem is that wooden pallets have a tendency to rot and increase in weight due to water absorption.

One consequence of these problems is that the wooden pallet is often destroyed or otherwise disposed of in the country to which they are exported to. Apart from being wasteful, many countries are now refusing to dispose of the pallets for environmental reasons. This is because the nails used in wooden pallets make them unsuitable for recycling and they are normally only used as land fill.

Plastic pallets are known which overcome a number of the problems associated with wooden pallets. However, plastic pallets presently made have problems of their own.

Typically, plastic pallets are formed by a process known as injection moulding. With injection moulding, there is provided a mould into which molten plastic is injected under pressure. The cost of producing a mould of a size of a pallet is extremely expensive. However, of more importance is that there is only a limited number of injection moulding machines that actually have the capability to apply sufficient force to hold a pallet size mould together when it is being injected with fluid plastics material under pressure.

An alternative method of plastics moulding is rotational moulding which requires less expensive machinery than injection moulding. Pallets are not generally seen as being an ideal candidate for manufacture by rotational moulding, this is because pallets are required to be hollow to allow the insertion of fork lift tines, but are also required to have a certain degree of strength. The problem with rotational moulding is that cores within the mould need to be able to be pulled out from inside the mould if hollows are to be introduced. Because of this, the design of the cores is required to be simple and there are limitations in what you can add in terms of other design features such as strengthening ribs.

It is an object of the present invention to address the above problems, or at least to provide the public with a useful choice. Further objects and advantages of the present invention will become apparent from the following description which is given by way of example only.

DISCLOSURE OF INVENTION

According to one aspect of the present invention there is provided a method of manufacturing a pallet, characterised by the steps of a) manufacturing two pallet halves, and b) joining the pallet halves together to create a complete pallet.

A method of manufacturing a pallet whereby two halves are created and then joined together overcomes a number with problems of the prior art.

Firstly, plastic moulding may be used to create the pallet halves. For example, if a pallet is made with two separate halves, smaller moulds are required. Thus, there is provided a means by which a pallet may be injection moulded with smaller loads and less expensive machines than previously thought possible.

Another advantage of the present invention is that it lends itself to the manufacture of pallets using rotational moulding, which as discussed is less expensive than injection moulding.

For example, the pallets may be moulded in such a way so that the inner halves of the pallets when joined together create an aperture through the pallet which is suitable for the insertion of fork lift tines. This overcomes one of the problems with rotational moulding of pallets as there is no need to design a system whereby cores need to be pulled out from within inside the whole pallet thus limiting the pallet design. Another advantage of the present invention when applied to rotationally moulded pallets is that design features such as strengthening ribs and the like can be readily built into each half of the pallet adding considerable strength to the pallet than if it were to be moulded in a whole.

Reference throughout this specification shall be now made to the manufacture of the pallet being achieved by rotational moulding. It should be appreciated however that the principles of the present invention can apply to other methods of manufacture and that rotational moulding is given by way of example only.

The pallet may be made from any one of a variety of materials, however in preferred embodiments the pallet is made from medium density polyethylene. This material is impact resistant as well as easy and inexpensive to rotationally mould. Further, this material is very compatible to a freezer environment as it does not become brittle.

To give sufficient strength to the pallet it is envisaged that the average wall thickness of the polyethylene will be approximately 5mm, however it should be appreciated that this dimension can change when desired.

The pallet halves may be joined together by a variety of means. In one embodiment of the present invention the pallet halves may have their internal surfaces joined together with low frequency vibration welding. Unfortunately, for articles as large as pallets it is very difficult to input sufficient energy for this method of joining to be successful.

An alternative method of joining the pallets is to use adhesive between the two pallet halves. Unfortunately, if the inner halves of the pallets are smooth, just using adhesive is an ineffective joining method. This is because there is minimal surface area on which the adhesive can act and the shear forces applied to the pallets is usually in the line of the plane in which the adhesive is applied.

According to a preferred aspect of the present invention, the two pallet halves are joined together using male/female connectors

This aspect of the present invention has a number of advantages over other possible means by which the pallet halves can be joined.

Firstly, the use of a male/female connection does not require the application of high energy as with vibrational welding.

Secondly, a male/female connection means that the connection is perpendicular to the shear force plane most commonly encountered by pallets and therefore is more resistive to same. This is obvious when one considers that the male connector is surrounded by material of the female connector which adds considerable more strength to the join than if just adhesive had been used.

A further advantage of male/female connectors is that this method facilitates alignment of the pallet halves which may not be as readily achievable if just pure adhesive was used to line up two smooth pallet halves.

Yet another advantage is that the male/female connectors can in combination be a design feature which gives additional supporting strength to the pallet by forming vertical pillars within the pallet structure.

While the male/female connectors can be the sole method by which the pallet halves can be joined, it is envisaged that in some embodiments of the present invention adhesive is used as well within the male/female connectors and perhaps on other parts of the pallet halves. A suitable adhesive for this purpose as been found by the applicant is a polyurethane sealant and adhesive. This adhesive is moisture cured.

One of the advantages of using adhesive in combination with the male/female connectors is that the adhesive is protected inside the body of the pallet by the walls of the female connector.

In a preferred embodiment of the present invention the halves are plastic welded together.

The material for plastic welding can be colour matched to the pallet and therefore the plastic welded pallet is aesthetically more pleasing than the adhesive described above which presently only comes in three colours. If the plastic welding is the same material as the pallet, for instance polyethylene, then the whole pallet can be recycled. The use of plastic welding instead of steel fasteners has a number of advantages as the addition of post production steel can wear against the plastic material of the pallet causing perforations.

The design of the male/female connectors may come in a variety of forms.

To provide the required strength in the pallet, a number of male/female connectors are required. However, this is not a technique commonly employed in the plastics industry as it can be very difficult to line up male/female connectors and maintain correct alignment. This is because to reach a final product the design has to go through of forming a plug, then a pattern, and then a mould from which the product is made. Shrinkage occurs in these processes and usually the shrinkage is often not uniform. Thus, the applicant has to put careful consideration into the design of the pallet and in the particular male/female connectors.

If the male/female connectors are circular in cross-section, this assists in alignment of the connectors and accommodates shrinkage which will be uniform over a circular cross-section. Further, the applicant has found that by making the male connectors sufficiently long and thin to be flexible, misalignment between the male/female connectors can be accommodated. In one embodiment of the present invention the length of the male connectors is 50mm and the plastic between 4 and 5mm.

In some embodiments of the present invention the male connector is in the form of a tapered lug and the female connector is complimentarily shaped. The use of tapered lugs makes the male and female connectors easy to produce using the rotational moulding method as this enables easy removal of the mould. Another advantage of using a taper is that the halves are more easily located with respect to each other as the narrow end of the taper can be guided gently into the wider base of the female connector. Yet another advantage of the taper is that it is a way of distributing the forces on the pallet transmitted to the male connector.

Preferably the tops of the male connectors are rounded. This is because under extreme loads, there will be less chance of the male connectors perforating the pallet.

In preferred embodiments, all of the female connectors are on the lower half of the pallet so that they can absorb the forces being placed on them by the male connectors connected to the top half of the pallet which carries the load. This is not necessarily possible with all rotationally moulded designs. This is because to make a pallet of a certain size, the mould used has a certain volumetric capacity and the mould insets which create the female connectors take up room within the mould. This means that less plastics powder can be introduced which can lead to less strength in the pallet half.

In preferred embodiments the male connectors are comparatively small integers with respect to the overall size of the pallet as rotational moulding lends itself to be more accurate with such smaller integers. This is because undulations can occur over integers having a larger span. Unfortunately, this means that the male connectors could be more easily broken away from the pallet half.

To address the above problem, in some embodiments of the present invention there is provided a number of localised groupings of connectors. It has been found by the applicant that this provides greater strength than scattering a number of individual connector pairs over the inner halves of the pallet.

In some embodiments the localised groupings may be associated with platforms on the internal surfaces of the pallet halves. For example, the platforms may take the form of legs and provide the spacing between the pallet halves required to achieve the apertures through which the fork lift tines can be passed.

The platforms referred to above may take a number of forms. In preferred embodiments, the platforms themselves may provide a separate means by which the pallet halves can be connected. For example, the platforms may themselves act as male/female connectors. In one embodiments the connectors may have a peripheral sleeve which forms a tongue and groove effect with the corresponding platform on the other half of the pallet. As well as the obvious strength benefits of having additional male/female connectors provided by the platforms, there are further advantages as well. One such advantage is hygiene. If there is provided an overlap between two platforms on opposing halves then this provides an additional barrier to the ingress to micro-organisms. This is important as pallets are often used to transport food and medical supplies and thus a high standard of hygiene is required.

Another advantage is that the broader expanse of plastic which forms the interconnecting platforms can add to the aesthetics of the pallet.

It is important that the pallet has sufficient strength to carry the loads placed on it. The applicant has found that one method of transferring the static load to ground is to have a number of "kiss offs" in the pallet. For example, the top half of the pallet may have grooves moulded into the upper and lower surfaces so that inside the pallet top half the upper and lower surfaces touch or kiss off. Not only does this add to the overall stiffness and strength of the pallet, but also the top and bottom surface are kept the same distance from each other.

It is not preferable to have grooves in the bottom half as the grooves can harbour moisture. However, kiss offs can be arranged so as to transfer the static load from the top surface through to the bottom surface and to the ground. For example, moulding for the male/female connectors may extend from the bottom surface of the bottom half of the pallet to the top surface of the bottom half. Not only does this add strength to the bottom of the pallet, but also provides a path through which the static load can be transferred from the top half of the pallet through to the ground. This obviates the chance of the plastic buckling. It is relatively common for pallets to be stored in racks which leave the pallet unsupported in the middle. Rectangular pallets are usually racked with the short sides supported. To ensure that the pallet does not sag when racked, the applicant in preferred designs have configured the pallet to have maximum strength in the direction of the longer length of the pallet. This strength may be enhanced by suitable selection of male/female connector combinations.

In some embodiments, the pallet may have additional slots moulded into it which in rotational moulding means that there is provided additional vertical walls within the halves of the pallet. These walls can stop flexing and the slots can provide a handle for carrying the pallet. The slots can also act as shock absorber flexing within itself so that the load is not transferred across the pallet. This avoids cracking of the plastics material making up the pallet.

BRIEF DESCRIPTION OF DRAWINGS

Aspects of the present invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic perspective view of a complete pallet in accordance with one embodiment of the present invention, and

Figure 2 is a diagrammatic cross-sectional view of a group of male/female connectors in accordance with one embodiment of the present invention, and

Figure 3 is a diagrammatic plan view of a pallet half in accordance with one embodiment of the present invention, and Figure 4 is a cross-sectional view of a pallet in accordance with the present invention

BEST MODES FOR CARRYING OUT THE INVENTION

Figure 1 is a diagrammatic perspective view of a full pallet generally indicated by arrow 1 which has been manufactured in accordance with one embodiment of the present invention.

The pallet 1 is comprised of two halves, an upper half 2 and a lower half 3. The halves 2 and 3 have been connected together by using male/female connectors as illustrated in Figures 2 and 3.

It can be seen that the structure of the pallet 1 is such that there are a number of apertures 4 through which the tines of a fork lift can pass enabling the pallet 1 to be readily lifted.

In addition to the apertures 4, there are a number of pillars 5 which space apart the halves 2 and 3 of the pallet enabling the apertures 4 to be formed.

Between the pillars 5 are a number of slots 20 which contribute to the strength, shock absorption and the handling ease of the pallet.

Figure 2 is a perspective view of a pillar 5. The pillar 5 is slightly tapered and has a platform 6 on which other male connectors 7 and female connectors 8. Around the peripheral edge of the platform 6 is a sleeve 9.

The male connectors 7 are a tapered lug having a rounded top which as described earlier in the specification prevents penetration of the male connector 7 into the pallet 1 if excessive force is loaded onto the pallet 1.

The female connector 8 is an aperture (not clearly shown) which is of a complimentary shape to the male connector 7.

A number of the pillars 5 are situated on the inside of each of the halves 2 and 3. Figure 3 is a plan view of the bottom half 3 of the pallet 1 showing possible placement of the pillars 5.

The top half 2 of the pallet 1 may have complimentary pillars 5 with the associated groupings of male connectors 7 and female connectors 8 so that it can be fitted directly onto the bottom half 3 to make a secure fit. The sleeve 9 on the pillars 5 may also complimentarily fit forming an overlap which is both aesthetic and hygienic in addition to adding strength to the pallet structure. In preferred embodiments, the female connectors 8 are filled with adhesive which helps in holding the pallet 1 together.

To ensure secure fit of the two pallet halves 2 and 3, weight may be placed on top of the pallet 7 until the adhesive is cured.

Figure 4 is a cross-sectional view of a pallet in accordance with one embodiment of the present invention. Construction of the pillars 5, male connectors 7 and female connectors 8 can be clearly seen. What can also be seen is the "kiss offs" between the top surface 10 of the top half 2 and the bottom surface 11 of the top half 2. Also the kiss offs between the mail connector 7 and the female connectors 8 can also be clearly seen. These kiss offs enables the static load on top of the top pallet half 2 to be transferred through the hollow of the pallet 1 down to the bottom surface 12 of the bottom half 3. Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope of the appended claims.

Claims

CLAIMS:

1. A method of manufacturing a pallet characterised by the steps of

a) manufacturing two pallet halves, and

b) joining the pallet halves together to create a complete pallet

2. A method as claimed in claim 1 wherein the method of manufacturing the pallet is by rotational moulding.

3. A pallet made by the method claimed in either claim 1 or claim 2.

4. A pallet as claimed in claim 3 which incorporates strengthening ribs.

5. A pallet as claimed in either claim 3 or claim 4 wherein the pallet halves are connected together with male/female connectors.

6. A pallet as claimed in claim 5 wherein the male/female connectors are substantially circular in cross-section.

7. A pallet as claimed in either claim 5 or claim 6 wherein the male connectors have a degree of flexibility.

8. A pallet as claimed in any one of claims 5 to 7 wherein the male/female connectors are tapered.

9. A pallet as claimed in any one of claims. 5 to 8 wherein the male connectors have a rounded top.

10. A pallet as^* claimed in any one of claims 5 to 9 wherein the male/female connectors are positioned in localised groupings on the pallet.

11. A pallet as claimed in claim 10 wherein the localised groupings of male/female connectors are on platforms on a pallet half.

12. A pallet as claimed in any one of claims 5 to 10 wherein the male/female connectors are in the form of platforms.

13. A pallet as claimed in any one of claims 11 to 12 wherein the platforms include a sleeve around the upper periphery of the platform.

14. A pallet as claimed in any one of claims 3 to 13 wherein there is provided a means to transfer the static load on the top of the pallet through to the base of the pallet.

15. A pallet as claimed in claim 14 wherein the means of transferring the static load is in the form of kiss offs.

16. A method substantially as herein described with reference to and as illustrated by the accompanying drawings.

17. A pallet substantially as herein described with reference to and as illustrated by the accompanying drawings.