GB2571062A

GB2571062A - Improvements for cutting and welding of rotationally moulded containers

Info

Publication number: GB2571062A
Application number: GB1720852.1A
Authority: GB
Inventors: Bray David; Finch Jon
Original assignee: Leafield Environmental Ltd
Current assignee: Leafield Environmental Ltd
Priority date: 2017-12-14
Filing date: 2017-12-14
Publication date: 2019-08-21
Anticipated expiration: 2037-12-14
Also published as: GB2571062B; GB201720852D0

Abstract

A method of altering the size of a moulded plastic component (101, figure 1d) having first and second grooves. The method comprises cutting along the first groove to form a first component 92 having a first cut edge, cutting along the second groove to form a second component 93 having a second cut edge, abutting the first cut edge and the second cut edge, and welding the first cut edge and second cut edge together. Alternatively, a plastic component could be created from two components each with a groove that is cut to provide the first and second cut edges. The grooves may be circular, rectangular, U-shaped or V-shaped (11, 12, 13, 14, figure 2). The edges may be joined by a strip weld or dressed off weld (24 or 26, figure 3) and the method may be used with double skin containers (figure 11). The weld may be reinforced with a metal insert 90 comprising a plate with holes (figure 13a) that is heated to a temperature above the melting point of the plastic container and then pressed into position so melted plastic flows around and through the mesh.

Description

This invention relates to a method of altering the size of a moulded plastic component. It also relates to a moulded plastic component, a method of creating a moulded plastic component and a kit of moulded plastic components.

Background

The rotational moulding of plastics is a well-known technique for producing hollow plastic parts whereby a mould is charged with plastic powder and subsequently turned or rotated as the temperature of the mould is increased. As the plastic powder flows over the heated mould surface it becomes tacky and adheres to that surface so that that when all the powder is exhausted, a uniform layer of plastic is formed. The mould is subsequently cooled, the plastic solidifies and the plastic part is then removed from the mould.

The rotational moulding process can be used to create hollow products, such as ruggedized containers (e.g. cases). There is an extensive range of case sizes already available on the market which suit the majority of needs, however there is still a substantial requirement for bespoke cases for specific applications. When the potential manufacturing volumes are high it can be economically viable to design a new case suited to the customers’ specific needs and have new tooling I moulds manufactured. Once these cases have been manufactured and the order requirements fulfilled, the case can become part of a standard range of sizes.

Multi part I modular moulds allowing many features to be incorporated into the case design and, more pertinently, modular sections of tooling I moulds to be removed and replaced with those of different dimensions.

Modular tooling will go some way to satisfying the need for bespoke case sizes by mixing and matching existing stock of modular sections, or manufacturing additional new sections to fit with existing modular sections. This allows the creation of new bespoke case heights/lengths or widths with minimal investment, and shorter lead times, compared with the traditional method of building a complete new tool suited to the bespoke application.

Even though manufacturing only a few new modular tooling I mould sections can significantly reduce costs incurred in making a new size case, compared to those of a complete new tool I mould, there will still need to be a reasonable volume of bespoke products required to justify the necessary tooling I mould and design time investment of new modular sections.

Sometimes a customer will require only a handful of bespoke products, or possibly only one case in a new size. In these instances, even modular tooling will not be economically viable.

To satisfy this small volume requirement, a “cut and weld” technique can be used to manufacture cases to specific customer dimensional requirements. A prior art cut and weld technique is shown in Figs. 1a-c.

The first step of the technique is to select an appropriate standard size case based on dimensional compatibility with the requirements of the new bespoke case size. The selected case is then examined and the most appropriate cutting locations are determined. The case is then cut down to produce sections of the required size.

The cutting process can be done by hand or band saw, or other appropriate cutting machine, but in all cases care must be taken to ensure the cut edges are straight and square to the adjacent case faces. Any burrs on the edges are then trimmed using standard trimming tools. The edge of the plastic moulding is then chamfered on both sides to an angle of approximately 45 degrees. This creates a groove shape either side of the plastic into which the weld will be filled. This is similar to the process of butt welding metal components.

Fig. 1a shows a cross-sectional view of a section of a moulded case wall 1 at this stage of the process. A pair of cuts has been made in the moulded case to produce a pair of sections. These have been pushed together so that the cut edges 2 abut one another. The cut edges 2 have been chamfered at a 45 degree angle as indicated at reference numeral 3.

Fig. 1b shows a section of the moulded case wall 1 of Fig. 1a at a second stage of the process. The cut edges of the moulded case wall have been clamped or held together (clamp not shown). The cut edges 2 have been tacked together to ensure alignment (tacks not shown). The cut edges 2 have then been welded together using a full strip, or continuous fillet, weld 4.

There are a number of different welding techniques, the most common using a strip welding or a Drader (RTM) injection welding gun.

Once the case sections have been welded together the excess weld I polymer needs to be trimmed away or dressed off to produce an aesthetically acceptable finish. Fig. 1c shows a section of welded case wall of Fig. 1b with the weld dressed off as indicated at reference numeral 5. Once all the cut sections are welded and dressed of the assembly of the relevant case furniture can be carried out in the usual manner.

Fig. 1d schematically shows a side view of a prior art cutting and welding technique applied to a case 101. In the top image a rotationally moulded case 101 is shown. The case 101 has a length A. In the middle image the case 101 has been cut to produce a first section 102 having a length B, and a second section 103 having a length C. In the lower image the first section 102 has been welded to the second section 103 using the cut and weld technique shown in Figs. 1a-c to produce a case 104 having a length D, where D = B + C. The length D is less than the length A of the case 101 prior to the cut and weld technique being performed. However, if two cases are used, cuts can be made to produce to sections each having a length that is more than half of the original case length. The welding together of these two sections will produce a case with an overall length greater than that of either of the two original cases.

The above technique can only be carried out by someone with skill and experience of welding. An aim of this patent application is to make the cutting and welding job easier and reduce the degree of skill required, whilst improving the strength of the welded case. This aim is achieved by providing groove features on the moulded case wall that indicate suitable cutting points. Additional technical benefits are achieved by the invention as set out in the description below.

Summary of the invention

In accordance with a first aspect of the present invention there is provided a method of altering the size of a moulded plastic component, the plastic component having first and second grooves, the method comprising the steps of:

cutting along the first groove to form a first component section having a first cut edge;

cutting along the second groove to form a second component section having a second cut edge;

abutting the first cut edge and the second cut edge; and welding the first cut edge and second cut edge together.

At least one of the first groove and second groove may run horizontally around the component.

At least one of the first groove and second groove may run vertically around the component.

The moulded plastic component may comprise a double skin, and at least one of the first groove and second groove is located on an internal surface of the double skin.

At least one of the first and second groove may be located on a perimeter return lip of the moulded plastic component.

The moulded plastic component may comprise a pair of parallel ribs projecting out a surface of the moulded plastic component, the first or second groove being formed by a valley between the pair of ribs.

The first or second groove may be formed by a channel cut into a surface of the moulded plastic component.

The first or second groove may be substantially V shaped.

The first or second groove may be substantially U shaped.

The first or second groove may be substantially rectangular in shape.

The method may further comprise the steps of:

providing an insert comprising a plurality of apertures;

heating the insert;

swaging the insert into the moulded plastic component, such that the insert lies across the abutment between the first and second cut edges.

The insert may comprise a perforated sheet of metal.

The insert may comprise an expanded sheet of metal.

The moulded plastic component may be a case, container, lid, pallet or dolly.

In accordance with a second aspect of the present invention there is provided a method of creating a moulded plastic component, the method comprising:

providing a first plastic component having a first groove;

providing a second plastic component having a second groove;

The first or second groove may be substantially V shaped.

The first or second groove may be substantially U shaped.

The first or second groove may be substantially rectangular in shape.

The method may further comprise the steps of:

providing an insert comprising a plurality of apertures;

heating the insert;

The insert may comprise a perforated sheet of metal.

The insert may comprise an expanded sheet of metal.

The moulded plastic component may be a case, container, lid, pallet or dolly.

In accordance with a third aspect of the present invention there is provided moulded plastic component comprising:

a first groove; and a second groove, wherein the first and second grooves are positioned such that cutting along the first and second grooves produces first and second component sections having respective cut edges which may be abutted and welded together to produce a moulded plastic component of reduced size.

In accordance with a fourth aspect of the present invention there is provided kit of moulded plastic components comprising:

a first plastic component having a first groove;

a second plastic component having a second groove;

wherein the first groove is positioned such that cutting along the first groove produces a first component section having a first cut edge;

wherein the second groove is positioned such that cutting along the second groove produces a second component section having a second cut edge;

wherein the first cut edge and the second cut edge can be abutted and welded together to form a plastic component of greater dimensions than either of the first plastic component and the second plastic component.

Detailed description

The invention will now be described with reference to the accompanying drawings, in which:

Figs. 1a-c schematically show a cross-sectional I perspective views of a prior art cutting and welding technique;

Fig. 1d schematically shows a side view of a prior art cutting and welding technique applied to a case;

Figs. 2a-d schematically show cross-sectional views of parts of rotationally moulded containers in accordance with embodiments of the present invention;

Figs. 3a-c schematically show cross-sectional views of a cutting and welding technique in accordance with an embodiment of the present invention;

Figs. 4a-e schematically show cross-sectional views of parts of rotationally moulded containers in accordance with embodiments of the present invention;

Figs. 5a-c schematically show cross-sectional views of a cutting and welding technique in accordance with an embodiment of the present invention;

Figs. 6 and 7 schematically show cross-sectional views of parts of rotationally moulded containers not according to the present invention;

Fig. 8 schematically shows part of a rotationally moulded container in accordance with a further embodiment of the present invention;

Fig. 9 schematically shows part of a rotationally moulded container in accordance with a further embodiment of the present invention;

Figs. 10a-11b schematically show cross-sectional views of cutting and welding techniques in accordance with further embodiments of the present invention;

Fig. 12 schematically shows side, plan and perspective views of an insert for reinforcing a welded joint;

Figs. 13a and 13b schematically show plan and perspective views of inserts suitable for use with the method of the present invention;

Fig. 14 schematically shows a cross-sectional view of part of a rotationally moulded container in accordance with the present invention;

Fig. 15 schematically shows a perspective view of a completed cut and weld joint, showing the location of the optional insert;

Fig. 16 schematically shows a plan and cross-sectional view of an insert swaged into a surface of a rotationally moulded container;

Fig. 17 schematically shows a detailed view of area Y indicated in Fig. 16; and

Fig. 18 schematically shows a perspective view and a side view of a rotationally moulded container in accordance with the present invention.

Figs. 2a-d schematically show cross-sectional views of rotationally moulded containers in accordance with embodiments of the present invention. Each of the containers 10 comprises a guide means in the form of a groove 11, 12, 13, 14 premoulded into the case wall. In each case, the lower surface of the case corresponds to an outer surface of the container and the upper surface shown corresponds to an inner surface of the container.

The addition of a grooved shape in the container wall negates the need for some of the finishing: if the case is cut so that the finished I required edge is along the centre of a groove, the cut edge facing the outer surface of the container would not need to be chamfered by a finishing operation.

Such grooves may be added at appropriately identified locations in the container to indicate suitable cutting points and so save chamfering time. The grooves will often be on the underside of container, but could equally be on any face of the container body or lid. The groove helps assist the cutting and welding process. It creates a line I edge in which the cutting blade can follow and the groove creates a hollow which is filled by the weld.

Fig. 2a shows a circular groove 11. Fig. 2b shows a rectangular groove 12. Fig. 2c shows a u-shaped groove 13. Fig. 2d shows a v-shaped groove 14.

The groove feature is not fixed in design and can be changed to suit the location on the case and the specification of the case. However, for any shape I location of groove, the technique and method for cutting and welding remains the same.

Figs. 3a-c schematically show cross-sectional views of a cutting and welding technique in accordance with an embodiment of the present invention.

In Fig. 3a a pair of cut container sections 20, 21 have been brought together so that their respective cut lines abut along a line 22. Each container section 20, 21 has been cut along a respective groove formed therein. The cutting process can be done by hand or band saw or other appropriate cutting machine but in all options care must be taken to ensure the cut edges are straight and square to the adjacent case faces. Any burrs on the edges have been trimmed using standard trimming tools.

As each cut position was along a moulded-in groove, the outer edges of the plastic moulding (i.e. the lower edge shown in Fig. 3a) do not need to be chamfered. The inner face of a rotational moulding is not defined by the tool I mould face, and so the comers of the inner surface adjacent the cut edges have been chamfered by conventional means to an angle of approximately 45 degrees as shown at reference numeral 23.

The machined chamfers on the inner faces create a groove shape either side of the plastic into which the weld will be filled. On the outer surface the two halves of a moulded groove come together to form a recess to weld into.

In Fig. 3b the inner chamfered faces have been filled with a fillet or strip weld 24 and the recess formed by the two halves of the moulded groove have been filled with a fillet or strip weld 25.

As in prior art cutting and welding processes, the excess weld I polymer needs to be trimmed away or dressed off to produce an aesthetically acceptable finish. However, having a groove with moulded edges on the outer faces of the case assists in keeping the weld itself straight and neat, and so the degree of weld dressing off for the weld on the outer surface of the container is reduced. In some cases, the depth of the groove may be such that no trimming and dressing of the concealed weld is necessary at all.

Fig. 3c shows the container of Fig. 3b where the weld on the inner chamfered faces has been dressed off as indicated at 26, and the weld in the recess on the outer surface has been trimmed flush with the outer surface of the container as indicated at 27. It may not always be necessary to dress off the welds in the inside of a case, especially if they are neat. In addition, in some applications the case may be filled with foam inserts which would cover any evidence of welding on the inside surfaces of the case.

The grooves shown in Figs. 2a-d and the method shown in Figs 3a-c are particularly useful for producing a container of a different size while having a minimal impact on the external surface of the original, uncut container. As can be seen in Figs. 3a-c, the external weld is trimmed flush to produce a smooth lower surface, and this can be desirable for aesthetic reasons, or reasons of stability, e.g. so that the differently sized container sits on a flat surface without wobbling.

However, as can also be seen in Figs. 3a-c, the grooves of Figs. 2a-d do not produce a differently sized container with a smooth inner surface. Even with the internal weld dressed off, the moulded groove feature and the chamfered edges still project into the interior of the container. In some circumstances, it may be desirable to produce a reduced size container with a smooth I level inner surface. For example, for aesthetic reasons, but also to allow items placed in the case to sit flush against the floor of the case, or to maximise the internal volume of the container.

To achieve this, a twin walled valley groove can be placed in the wall of a container, as shown in Figs. 4a-e.

In each of Figs. 4a-e, a rib or plateau projects out from the case (i.e. from interior to exterior) and a groove is formed in the centre of the rib I plateau.

Fig. 4a shows a projecting rib with a circular groove 31. Fig. 4b shows a projecting rib with a rectangular groove 32. Fig. 4c shows a projecting plateau with a rectangular groove 33. Fig. 4d shows a projecting rib with a u-shaped groove 34. Fig. 4e shows a projecting rib with a v-shaped groove 35.

The grooves shown in Figs. 4a-e are particularly suited to the base of a container where the inner surface is to remain flat and the external projecting ribs have a minimal impact of the aesthetic of the case and do not project beyond the case external dimensions.

Figs. 5a-c schematically show cross-sectional views of a cutting and welding technique in accordance with an embodiment of the present invention using a twin walled valley groove.

In Fig. 5a a pair of cut container sections 40, 41 have been brought together so that their respective cut lines abut along a line 42. Each container section 40, 41 has been cut along a respective groove formed therein. As with the technique described with reference to Figs. 3a-c, this cutting process can be done by hand or band saw or other appropriate cutting machine, and again in all options care must be taken to ensure the cut edges are straight and square to the adjacent case faces. Any burrs on the edges have been trimmed using standard trimming tools.

As the cut positions were along a moulded-in groove in the projecting rib, the outer edge of the plastic moulding (i.e. the lower edge shown in Fig. 5a) does not need to be chamfered.

In Fig. 5b the comers of the inner surface adjacent the cut edges have been chamfered to an angle of approximately 45 degrees to create a groove, and the groove has been filled with a fillet or strip weld 43. On the outer surface the two halves of a moulded groove come together to form a recess to weld into, and the recess has been filled with a fillet or strip weld 44.

Fig. 5c shows the container of Fig. 5b where the weld on the inner chamfered faces has been trimmed flush with the interior wall of the container as indicated at 45, and the weld in the recess on the outer surface has been trimmed flush with the outer surface of the projecting rib as indicated at 46. As mentioned above, it is not always necessary to trim flush the internal surface of the case I container walls. In some instances the welds are hidden from view by protective component foam inserts placed in the case.

Moulded grooves may be found on existing container designs and these may have other distinct purposes.

Some prior art containers have a groove running horizontally along the side walls of the case. This groove is adjacent to a tooling split line and its purpose is to aid the trimming of moulding flash. Trimming flash from a flat surface is difficult as the trimming blade will inevitably scratch the plastic either side of the trimming line. Trimming on a corner, or change in surface angle, allows the trimming blade to be angled away from the surface, preventing unwanted surface scratching. However, these grooves are not of sufficient depth for use as cutting and welding grooves.

Grooves for this purpose can be identified, and discerned from cutting and welding grooves, due to their proximity to the moulding split line.

Grooves, or raised ribs, can also be found in existing container designs, their purpose being to add strength. These are known as structural grooves I ribs, but to be effective they must be much deeper than those used in the method of the present invention. They are also generally much wider. The recommended depth of a structural rib, if it is to be effective, is 5 times the polymer wall thickness. The minimum practical thickness of a rotationally moulded case is 2mm. Any less than this and there may be areas where the interior surface of the mould is not coated in plastic powder during moulding, and the resulting case would not have sufficient strength to prevent collapse. This gives a minimum depth of structural rib of 10mm or more. The depth of a cutting and welding rib will typically be in the region of 2 - 5 mm.

Figs. 6 and 7 schematically show cross-sectional views of rotationally moulded containers not according to the present invention.

Figs. 6 and 7 show three examples of deep grooves. These are generally unsuitable for use in the present invention, as even if a cut is performed along a deep groove it will not be possible to weld the two sections together along the cut. Welding guns have a nozzle. For deep grooves, this nozzle will either melt the sides of the groove on entry, or the nozzle will simply not fit at all.

Fig. 8 schematically shows part of a rotationally moulded container in accordance with a further embodiment of the present invention. The rotationally moulded container comprises a cut and weld groove in a surface thereof, generally indicated at 60. The surface of the container comprises a pair of raised ribs, 62, 63 having a grove 61 located therebetween.

Fig. 9 schematically shows a rotationally moulded container in accordance with a further embodiment of the present invention. The cut and weld groove in Fig. 9 is similar to that shown in Fig. 8, however the pair of ribs 65, 66 have been narrowed such that the skin of the container contacts itself on each side of the rib and fills the moulding tool during the moulding process. This forms a pair of solid ribs, compared to the hollow ribs shown in Fig. 8. During this process it is normal for voids / air pockets 67a, 67b to form within the ribs. A groove 64 is located between the ribs 65, 66.

Each of the containers and techniques described with reference to Figs. 2-9 have been related to single skin container bodies and lids. However, some containers are of double skin design. These are typically much stronger than single skins, as the inner and outer skins can be brought together to form kiss points, which create a structural feature adding strength to the container. However, these kiss points may also form grooves for use with techniques in accordance with the present invention.

Figs. 10a-11b schematically show cross-sectional views of cutting and welding techniques in accordance with further embodiments of the present invention.

Fig. 10a shows a double skin container comprising an inner wall 71 and an outer wall 72. The two moulding walls come together at a kiss point 75, which forms an inner groove 73 and an outer groove 74.

Fig. 10b shows a differently dimensioned double skin container comprising an inner wall 76 and an outer wall 77. The moulded walls come together at a kiss point 80, which forms an inner groove 78 and an outer groove 79.

Fig. 11a shows the container of Fig. 10a after two cut sections have been brought together, with their cut edges pushed together to abut down a centre line. A fillet or strip weld 81 has been inserted along an inner groove formed by the inner parts of the two cut sections, and a fillet or strip weld 82 has been inserted along an outer groove formed by the outer parts of the two cut sections.

Fig. 11 b shows the container of Fig. 11 a after the weld in the inner groove has been trimmed flush with the inner surface of the container as shown at 83. The weld in the outer groove has not been trimmed or dressed off as it is concealed by the depth of the outer groove. This saves on labour compared with prior art cut and weld techniques.

Fig. 12 schematically shows side, plan and perspective views of an insert 85 suitable for use in a thread plate welding process. The insert 85 comprises a stem 86 attached to a perforated metal plate 87. The perforated metal plate has a plurality of apertures 88, through which molten plastic can enter when an insert is heated and pressed into the moulded plastic walls of a moulded container.

Welded joints according to the present invention can themselves be very strong but impact damage can cause a split or crack to develop either side of a weld. To help overcome this potential problem an insert can be incorporated into the inner surface of the welded case wall.

The process is derived from thread plate welding. This is a process where an insert comprising a perforated metal plate with a welded, threaded stud or nut attached (for example, the insert shown in Fig. 12) is heated and pressed I swaged into the wall of a plastic part. The resultant molten plastic is forced through the holes in the plate and forms multiple plastic rivet heads over the metal plate. The result is a threaded stud or nut firmly attached to the plastic part.

Figs. 13a and 13b schematically show plan and perspective views of inserts for use with the present invention. The inserts comprise reinforcement plates that have no additional threads or nuts attached, and their only purpose is to reinforce the joint between two adjacent cut and weld panels. The plates can be designed in various shapes and sizes to fit in suitable moulding recesses or raised surfaces in the container walls.

The inserts are swaged in place on the inside surface of the moulding so that they are not visible on the outer surface of the case.

The local heat generated, and transferred to the plastic, during this process can distort the surface of the moulding. The plates are therefore preferably located on the underside, or inner facing walls of a case.

If reinforcing plates are required in more visible surfaces of a case they can be located within, or between, moulding features where the strength of the moulded form will help reduce the distortion. Alternatively, placing the reinforcing plates in or around moulding features, will visually distract the eye from any potential distortion.

The reinforcing plates will need to be made from a good heat conducting material (e.g. metals). They may be perforated plates or expanded metal plates, or manufactured by any other method of creating a ridged metal mesh component. The plates can vary in gauge, depending how much additional reinforcing strength is required.

Fig. 14 schematically shows a cross-sectional view of a base of a case in accordance with the present invention. In rotational moulding, moulded features become more dimensionally imprecise the further they are from each other. This means that if welding grooves are positioned between stacking features (for example, the stacking features shown in patent application GB2529532), their inclusion will be limited to locations where the gap between the stacking features is wide enough. Where the tolerances dictate a greater clearance in the stacking feature (further away from the centre of the case) the gap between the stacking features becomes narrower and the space for welding groove becomes progressively smaller. There will come a point where there is insufficient space to accommodate a welding groove and the cut and weld technique can no longer be used in accordance with the present invention. In Fig. 15, the rib indicated at 151 has a width of 23mm, which is sufficient to allow a groove to be placed along it. However, the rib indicated at 152 has a width of 13mm, which is not sufficient to allow a groove to be placed along it. The ribs narrow as they move away from the centre of the case as follows: E = 23mm, F = 20mm, G = 16mm, H = 13mm. However, these dimensions are exemplary only and the exact measurements may depend on factors such as the design and size of the stacking pattern, and the material and processing methods. In all cases the dimensions of the features will always progressively reduce in size as the features get further away from the centre.

Fig. 15 schematically shows a perspective view of a completed cut and weld joint in the bottom of a case (only partially illustrated), showing the location of an optional insert 90. The insert 90 lies across the cut 91, extending into both a first section of the case 92 and a second section of the case 93.

The plate is heated up to a temperature higher than that of the melting point of the plastic used to manufacture the container moulding. The plastic part may also be pre-heated too. The plate is then placed in position and firmly squeezed over the joint line to be reinforced and bridge the two panels. The temperature of the metal melts the polyethylene material in the vicinity of the insert. The melted polyethylene flows around and through the mesh. Once the polymer temperatures drops the polyethylene becomes hard leaving the plates firmly held in place and the panels reinforced.

Fig. 16 schematically shows a cut and weld joint being reinforced with the insert shown in Fig. 13b. A surface of a container 160 has been formed using a cut and weld method according to the invention. An insert 161 has then been heated and swaged into the surface 160 across the cut line. Plastic softened by the heat of the insert 161 has entered the plurality of apertures 162 of the insert 161, holding it in place. The lower part of Fig. 16 shows a cross-sectional view taken across the line X-X indicated in the upper part of Fig. 16.

Fig. 17 shows a detailed view of area Y indicated in the lower part of Fig. 16. As can be seen the plastic of the case extends over the insert 161 to form a rivet 163. This holds the insert 161 in place, and prevents the insert 161 from being withdrawn from the container 160.

Fig. 18 schematically shows a perspective view of a case body 180 in accordance with the present invention. A detailed view of the area indicated at Z is shown on the left hand side, and a cut and weld groove 161 is indicated. A side view of the case 160 is shown in a lower part of Fig. 16, on which a further cut and weld groove 182 is indicated. A pair of handles 183, 184 are positioned on the front of the case. Each handle 183, 184 has a pair of cut and weld grooves 185, 186 and 187, 188 positioned adjacent their lateral sides and running vertically up and down the case. A further pair of grooves 189, 190 are positioned near the edges of the case as shown.

Alternative arrangements

The invention is not limited to the specific embodiments disclosed above, and other possibilities will be apparent to those skilled in the art.

For example, the reinforcing inserts are not limited to those shown in Figs. 13 and 14-17, and any suitable shape or material may be used in practice. For example, an expanded metal plate may be used to reinforce the cut and weld joint, using the same technique described with respect to Figs. 14-17.

For example, while most embodiments have been explained with respect to cases, the skilled person will appreciate that the technique can easily be applied to any rotationally moulded product. For example, where a case has cut and weld grooves according to the invention, corresponding cut and weld grooves could be provided in the lid of the case, so that the lid may be resized according to the size of the new case by cutting and welding the lid along the appropriate cut and weld grooves. Other examples of rotationally moulded products to which the present invention may be applied include pallets, dollies, containers, and materials handling products in general.

Claims

1. A method of altering the size of a moulded plastic component, the plastic component having first and second grooves, the method comprising the steps of:

2. A method according to claim 1, wherein at least one of the first groove and second groove run horizontally around the component.

3. A method according to claim 1, wherein at least one of the first groove and second groove run vertically around the component.

4. A method according to any preceding claim, wherein the moulded plastic component comprises a double skin, and at least one of the first groove and second groove is located on an internal surface of the double skin.

5. A method according to any preceding claim, wherein at least one of the first and second groove is located on a perimeter return lip of the moulded plastic component.

6. A method according to any preceding claim, wherein the moulded plastic component comprises a pair of parallel ribs projecting out a surface of the moulded plastic component, the first or second groove being formed by a valley between the pair of ribs.

7. A method according to any preceding claim, wherein the first or second groove is formed by a channel cut into a surface of the moulded plastic component.

8. A method according to any preceding claim, wherein the first or second groove is substantially V shaped.

9. A method according to any preceding claim, wherein the first or second groove is substantially U shaped.

10. A method according to any preceding claim, wherein the first or second groove is substantially rectangular in shape.

11. A method according to any preceding claim, the method further comprising the steps of:

providing an insert comprising a plurality of apertures;

heating the insert;

12. A method according to claim 11, wherein the insert comprises a perforated sheet of metal.

13. A method according to claim 11, wherein the insert comprises an expanded sheet of metal.

14. A method according to any preceding claim, wherein the moulded plastic component is a case, container, lid, pallet or dolly.

15. A method of creating a moulded plastic component, the method comprising: providing a first plastic component having a first groove;

providing a second plastic component having a second groove;

16. A method according to claim 15, wherein at least one of the first groove and second groove run horizontally around their respective component.

17. A method according to claim 15, wherein at least one of the first groove and second groove run vertically around their respective component.

18. A method according to any of claims 15 to 17, wherein the first and second plastic components comprise a double skin, and at least one of the first groove and second groove is located on an internal surface of the double skin.

19. A method according to any of claims 15 to 18, wherein at least one of the first and second groove is located on an internal surface of their respective component.

20. A method according to any of claims 15 to 19, wherein the first and second plastic components comprise a pair of parallel ribs projecting out a surface of the moulded plastic component, the first or second groove being formed by a valley between the pair of ribs.

21.

A method according to any of claims 15 to 20, wherein the first or second groove is formed by a channel cut into a surface of their respective plastic component.

22. A method according to any of claims to

21, wherein the first or second groove is substantially V shaped.

23.

A method according to any of claims

15 to 22, wherein the first or second groove is substantially U shaped.

24.

A method according to any of claims

15 to 23, wherein the first or second groove is substantially rectangular in shape.

25. A method according to any of claims 15 to 24, the method further comprising the steps of:

providing an insert comprising a plurality of apertures;

heating the insert;

26. A method according to claim 25, wherein the insert comprises a perforated sheet of metal.

27. A method according to claim 25, wherein the insert comprises an expanded sheet of metal.

28. A method according to any of claims 15 to 27, wherein the moulded plastic component is a case, container, lid, pallet or dolly.

29. A moulded plastic component comprising:

30. A kit of moulded plastic components comprising:

a first plastic component having a first groove;

a second plastic component having a second groove;