GB2529532A - Rotationally moulded cases - Google Patents

Abstract

An insert for attaching a latch to a plastics product formed by a rotational moulding process, comprises a metal sheet 23 folded to form a polyhedron shape forming a cavity 24, the metal sheet including holes for attaching the latch (e.g. by means of a rivet). Preferably, the polyhedron comprises a triangular prism, e.g. a tetrahedron. A plastics case comprising an insert is also disclosed.

Description

Rotationally Moulded Cases This invention relates to an insert for attaching a latch to a plastics product formed by a rotational moulding process and a plastics case comprising an insert.

The rotational moulding of plastics materials is a well-known technique for producing hollow plastics material parts. In such a process, a mould is charged with plastics powder and subsequently turned or rotated as the temperature of the mould is increased. As the plastics 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 plastics material is formed. The mould is subsequently cooled, so the plastics material solidifies and the plastics pad is then removed from the mould.

Being hollow products, ruggedized containers and cases have been commonly manufactured using the rotational moulding process. More recently however, some such containers, particularly the smaller flatter ones with high volume sales potential, have been injection moulded.

The advent of injection moulded cases has, to a large extent, detracted manufacturers investment and interest from rotationally-moulded products, resulting in reduced interest and development in rotationally-moulded cases in recent years. As a result, the design of rotationally-moulded cases has not kept pace with recent advances in the design and manufacturing techniques of rotationally-moulded articles.

The development of rotationally-moulded case design has therefore remained fairly static in recent years with minimal innovation.

A fixed design case is ideal for basic/standard applications, but the market for quality ruggedized cases frequently applies to more bespoke applications where the specific needs of the customer, or product to be contained, needs to be taken into account.

Rotationally-moulded cases bodies are, without exception, designed around two-part operating moulds (bottom and top section) and each tool part is aligned to manufacture one product.

Fig. 1 schematically shows standard closed lid 1 and body 2 moulds for a rotationally-moulded container; and Fig. 2 schematically shows the body mould 2 of Fig. 1 in an open configuration.

It is an aim of the present invention to provide an improved container, in particular a ruggedized container, using rotational-moulding manufacture.

This aim is achieved by recognising the benefits of multi-pad I modular moulds, and utilising these to significantly improve rotationally-moulded containers. The container thus produced may possess various novel features, which are described separately below.

The methods in this patent application expands upon the possibilities for articles produced by the rotational moulding process by both innovative use of more recent mould operating techniques, and by utilising the potential of the manufacturing process.

The result is the potential to mould in new features that would otherwise be bolt-on components.

The approach detailed below utilizes both multi-part moulds and modular moulds to increase design flexibility, reduce response time for bespoke designs and reduce investment costs in the long term.

Before turning to the specific features of the present container in more detail, it should be noted that "multi-pad" or modular moulding means that the moulds for lid, body or both are constructed from more than one component part. Figs. 3 and 4 respectively schematically show a modular mould 3 wherein the body part 4 is multi-part, having a base section 5, which is essentially similar to known single part moulds, a lower wall section 11 and an upper wall section 6 pivotably attached to the lower wall section 11 of the body section 4 at an upper extremity thereof. As can be seen in Fig. 4, the wall section 6 may pivot away from the upright position. N.b. for consistency and the purposes of describing the invention below, these reference numerals have been retained as far as possible, e.g. item 6" refers to any upper, pivoting, wall section, regardless of the other aspects of its design.

Multi-part tooling will allow additional features to be rnoulded in, whereas modular moulds will provide the opportunity for range extension without having to build a complete new mould, thus reducing investment and lead time. It can also mean bespoke designs can be more easily justified if investment in only one or two new sections of a mould are required.

In accordance with a first aspect of the present invention there is provided an insert for attaching a latch to a plastics product formed by a rotational moulding process, comprising a metal sheet folded to form a polyhedron, the metal sheet including holes for attaching the latch.

In accordance with a second aspect of the present invention there is provided a plastics case comprising an insert according to the first aspect.

The invention will now be described with reference to the accompanying drawings, in which: Fig. 1 schematically shows standard closed lid and body moulds for a rotationally-moulded container; and Fig. 2 schematically shows the body mould of Fig. 1 in an open configuration; Fig. 3 schematically shows a sectional view of a multi-part mould in a closed configuration; Fig. 4 schematically shows a sectional view of the multi-part mould of Fig. 3 in an open configuration; Fig. 5 schematically shows a section through the middle of a handle area of a container mould; Fig. 6 schematically shows a sectional view of a case handle formed by the mould of Fig. 5; Figs. 7a, b schematically show a perspective view, and expanded perspective view, of the case of Fig. 6; Fig. 8a schematically shows a multi-part mould with a replaceable lower wall section; Fig. 8b schematically shows a multi-part mould with the lower wall sections removed; Fig. 9 schematically shows a sectional view of the mould of Fig. 8b; Fig. 10 schematically shows a sectional view of part of the mould of Fig. 5; Figs. ha-c schematically show a handle area of the base mould of Fig. 8a; Figs. 12a, b schematically show sectional views of a handle area of the mould of Fig. 8b; Figs. 1 3a-c schematically show a moulded handle produced by the mould of Fig. 9; Figs. 14a, b schematically show an upper tie-down/strapping point of a case; Fig. 15 schematically shows a perspective view of the case upper strapping down point of Fig. 14; Fig. 16 schematically shows a sectional view through the lower strapping down point of the moulding in a further example; Fig. 17 schematically shows a perspective view of the moulding of Fig. 16; Fig. 18 schematically shows a perspective view of a case where the document tube core is not fitted in the mould but replaced with a blanking plate; Fig. 19 schematically shows a perspective view of the case of Fig. 18, showing the interior of a document tube; Fig. 20 schematically shows a sectional view through a corner of the case of Fig. 18; Figs. 21a-c schematically show an insert in accordance with an embodiment of the present invention; Figs. 22a-c schematically show an insert in accordance with a further embodiment of the present invention; Fig. 23 schematically shows an upper case sitting atop a lower case lid; Figs. 24a, b schematically show details of Fig. 23; Figs. 25a-c schematically show a base pattern in accordance with this example; Fig. 26a-c schematically show an alternative arrangement to Figs. 25a-c; Fig. 27 shows a known sealing arrangement; Fig. 28 schematically shows a seal arrangement; Fig. 29 schematically shows a lid-body fitting arrangement in a further example; Figs. 30a-c schematically show details of the example of Fig. 29; Figs. 31 a, b schematically show an alternative example to that of Fig. 29; Figs. 32a-e schematically show an example with improved lid drainage.

Figs. 33a-d schematically show a case lid in a (catch plate fitting recess) in a further

example;

Fig. 34 schematically shows a catch plate for use with the lid of Fig. 33; Figs. 35a, b schematically show the assembled lid of Fig. 33 with the component of Fig. 34; Figs. 36a, b schematically show a latch with padlock attached to the catch plate of Fig. 34; Fig. 37 schematically shows a standard compression latch; Fig. 38 schematically shows the latch of Fig. 37 connected with the catch plate of Fig. 34; Fig. 39 schematically shows an alternative catch plate attached to a latch to form a hinge; Figs. 40a-d, schematically show an alternative latch-based hinge fitting; Fig. 41 schematically shows a case with the fitting of Fig. 40; Fig. 42 schematically shows a case in accordance with the present invention; and Fig. 43 schematically shows an alternative case in accordance with the present invention.

In all these figures and the below-described features, the container takes the form of a ruggedized case, for example for military applications. Other forms of container are of course possible within the scope of the present invention.

For simplicity, various inventive features are described separately below.

The present invention is predominantly concerned with the increased design potential of multi-part moulding where the case body tooling operates in a plurality (greater than two) of parts instead of the usual two (top and bottom) sections. In preferred embodiments, as described below, ten parts are used (including end wall sections), generally similar to the arrangement shown in Figs. 3 and 4. The lower section of each case (although produced from a base and four lower side walls) operates as a unitary mould section, and this part of the moulding is produced by a traditional "bucket-type" mould, where the moulding is removed vertically. The upper section however pivots away as shown in Fig. 4. All features described below denoted "A rely upon such multi-pad moulds. A key element of the multi-pad tooling in accordance with the present invention is that the lower wall sections can be completely removed and the upper pivoting sections and base still fit together to produce a product with moulded in handles.

Some features are however not dependent upon such multi-part moulding, and these are clearly highlighted in the following text.

A-i) Moulded-in handles using multi-part moulding One significant benefit of multi-pad tooling is that lifting/carrying handles can now be moulded-in as an integral pad of the product.

Traditional rotationally-moulded cases require bolt-attached, riveted or screw-on handles, with various disadvantages associated with them, including: 1) Additional cost of handle components; 2) Additional finishing/assembly time, reducing the number of handles that can cost-effectively be included; 3) Potential scratching/rusting if metal handles are used; 4) Handles can (in the case of impact damage) be separated from the case wall.

5) On conventional cases, sprung drop handles are often used to ensure that the handle folds back within the outer perimeter of the body when not in use. This is helps prevent the handle from snagging on other objects whilst in transit, but if the spring fails, or becomes dislodged the handle can drop to a vulnerable position outside the case wall. This is particularly a problem if the case is upside down.

6) The conventional method of fixing a handle to a case is to drill and rivet through the case wall. In order to prevent air and water ingress seals are used in the assembly. This introduces an element of uncertainty, or future problems] should a sealing washer be incorrectly fitted or perish.

The described method of moulding on the handle overcomes or significantly reduces these problems.

The undersides of the or each handle may be formed from the lower, fixed pad of the mould, whilst the upper section of the handle is formed from the upper wall sections of the mould (i.e. those which pivot out for opening). In this example, a channel formed within the body of the case acts as a handle cavity.

Fig. 5 schematically shows a section through the middle of the handle area of an exemplary case mould having three wall sections, with the handle cavity shown at 7.

The handle cavity 7 is open at each end to allow plastics material to enter during moulding. The handle cavity is formed by respectively cooperating projections / flanges 8, 8' located on the adjacent mould sections which abut when the mould is in the closed configuration.

This mould construction method produces a case 9 having a moulded handle 10 as schematically shown in Figs. 6 (sectional view), 7a (perspective view) and 7b (enlarged perspective view).

With this method, it is essential to shape the mould sections so that the opening pivot motion remains unrestricted by material proximate the handle.

This method produces a seamless handle which is an integral part of the case body, thereby providing additional strength over conventional non-integral handles. A further benefit is that more handles may be included in the product than would normally be included. The case shown in Fig. 7a for example has a total of eight integrally-formed carry / lifting handles. For comparison, standard cases of this type would usually only have four handles. This makes handling I manoeuvring of the case easier.

This method also totally eliminates the need for drilled holes in the outer skin of the case. This acts to maintain the integrity of the case from an air and water sealing point of view, eliminating workmanship and seal quality issues.

It should be noted that another significant benefit of multi-part tooling is that modular sections can be removed or interchanged. The fixed lower wall section modules, e.g. 11 as shown in Fig. 3, can be replaced with various height alternatives as shown in Fig. 8a, where it has been replaced with a significantly shorter height wall section 11'. Fig. 8b shows an arrangement where the lower wall section has been removed completely, and so the upper wall section 6 is located directly on top of the base 5.

In this example the handle is formed in exactly the same way between the lower side wall 11' and upper pivot out wall sections 6.

A-u) A lower case, with moulded-in handles, by removing lower mould wall sections.

As noted above, a lower (i.e. reduced in height) case may also be created by completely removing the lower walls (11 in Fig. 3). Thus one set of moulds can effectively produce two products with the same footprint but two different heights. As can be seen in Fig. 5, the design of the mating projections I flanges X between the

B

upper pivoting section 6 (flange 8) and the lower side walls 11 (flange 8:) has matching geometry to that between the upper pivoting section 6 (flange 8) and the base section 5 (flange 8"). Fig. 9 schematically shows a sectional view of the mould, similar to Fig. 5, but with the lower wall section 11 removed.

The handle geometry cannot be replicated at the lower end of the lower section 11 of the side wall as this would always form a second handle at the base of the case which could not be removed from the mould. The lower section 12 of the lower side wall 11 therefore has no handle details included, however the upper surface of the base mould 5 must have a handle shape if a handle is to be formed when only the base 5 and upper pivoting sections 6 of the mould mate. Fig. 10, essentially an enlarged view of a portion of Fig. 5, schematically shows a sectional view, with the lower handle details in the base section 5 of the mould but not in the lower wall section 11.

Fig. 11 shows how the lower pad of the handle in the base mould is shut off and not formed when a middle section of tooling is placed above it. In order to form a handle shape along the base of the handle (when the lower base walls are removed), yet prevent plastic powder access (when all mould walls are in place), and the lower surface of a handle forming, a "shut-off" 13 is required at each end of the handle cavity recess provided in the base 5. Each shut-off 13 comprises an upwardly extending projection, i.e. extending toward the side wall lower section 11. The shut-offs ensure that the plastic powder cannot flow into the handle cavity section 7' of the lower of a three-pad mould wall, but still creates a rounded handle underside for the bulk of the handle length in a two-part mould wall. The shut-offs can be seen in Fig. 11, at each end of the handle cavity 7', with Fig. 1 la schematically showing a sectional view through the handle area of a three-pad mould, with the handle extending parallel to the plane of the page, Fig. 11 b schematically showing an enlarged view of pad of Fig. 11 a (the shut off) and Fig. lic schematically showing a sectional view along A-A, i.e. through a shut-off with the handle extending into the page. Here it can be seen that the shut-off also extends inwardly, i.e. towards the interior of the case, in a profiled manner, since it extends for the full width of the handle tube opening in the mould -if it did not extend all the way, powder would still get into the handle cavity. The abutment between each shut-off 13 and the lower surface of the adjacent wall section 11 prevents plastic powder entering the lower handle section of the mould. Mould sections for a fully formed handle can be seen in the upper part of the section in Fig. ha, the handle being formed between the upper wall section 6 and lower wall section 11.

Fig. 12 schematically shows a handle produced when only the upper 6 and lower 5 sections of the mould are used (i.e. with the middle section 11 removed). When using such a two-part mould wall to create a handle at the bottom of the case, the shut-offs 13 (in the base section 5 of the mould) remain but do not come into contact with any part of the mating mould section above. Instead, they create indents at each end of the handle moulding. A rounded form is however created in board of the shut-off profiles creating a comfortable handle grip area. Fig. 12 schematically shows this, with Fig. 12a providing a sectional view of a handle area of the mould and Fig. 12b being an enlarged view of a detail of Fig. 12a. It can be seen that the upper wall section 6 has upturned rounded ends, which do not abut against the shut-offs 13, and so powder entry to the handle cavity 7" is not restricted.

Fig. 13 schematically shows the moulded handle 14 itself, with Fig. 13a being a sectional view with the handle 14 extending into the page, Fig. 13b being a sectional view orthogonal to that of Fig. 13a (viewed from the underside to show the shut-offs), and Fig. 13c being a part-sectional view. The heavy black lines in Figs. 13a-c represent the wall of the moulding. Fig. 13c shows that the handle 14 includes an upwardly extending recess (downward in the view) 15 at each end, created by a corresponding shut-off.

A-ui) Moulded-in lifting I tie-down points -upper section Lifting or tie-down rings are known accessories on ruggedized cases. These rings are conventionally riveted to the case wall with a washer plate on the back to prevent the rivets pulling through the moulding. Generally these rings are only fitted where there is a specific need.

In reality, tying or lashing down cases is a common requirement, even if it is just to secure loads during transit. Moulding in tie-down points that can be included at no additional product manufacturing cost would provide a significant product benefit.

Due to the pivoting element of the upper tool walls shut-through moulding details can be included producing tie down/strapping points at each upper corner of the case body.

The strapping points comprise vertically extending members which are integrally connected at each end to the container bulk, with the vertical members extending within the volume of the case. In effect, they are similar to handles, but extend vertically rather than horizontally, and are located at corners rather than within side walls. Because they extend vertically, they cannot be formed in the same way as the handles described previously. Instead, adjacently positioned side wall mould and end wall mould sections are provided with mutually co-operating male projections, arranged such that when these sections are located together ready for moulding, the two male projections abut (i.e. forming a "shut-through"), forming a channel in the moulding.

An exemplary de-moulding sequence of a rectangular case body is as follows: 1) Lift off the upper section on a hoist; 2) Pivot away the two upper end sections (and remove the end handle undercuts if an end handle is provided); 3) Pivot away the two upper side sections (and remove the side handle undercuts if a side handle is provided); and 4) Lift the moulding out from the base and lower sections of tooling (which are bolted together to form a single operating mould section).

Once the end wall has been pivoted away the side wall can be pivoted away. Both undercut cores used to create the shut-through are removed as the upper side walls are pivoted away.

Fig. 14 schematically shows a upper tie-down strapping point, with Fig. 14a providing a sectional view through a case corner from above, i.e. with the tie-down vertical member 16 extending into the page, and Fig. 14b providing a sectional view through a case corner in a direction orthogonal to that of Fig. 14a, showing the vertical member 16 and shut-through channel 17.

Fig. 15 schematically shows a perspective view of the case corner, detailing the tie-down arrangement. :10

A-iv) Moulded-in tie-down points -lower section The location of the lifting / tie-down points described in A-ui) above is limited to the upper section of the moulding, as that is the area formed by the pivoting cores.

However, there is also a benefit to having tie-down points located proximate the base of the case body.

In this example, one protruding core (in each corner) is provided in the base and in the line of draw when the case body is removed. A mating loose or separate side core is provided in a lower section side wall, and which creates the shut-through. This side core is an undercut which must be removed before the body can be demoulded. It will be apparent that this feature cannot be created if the lower section walls are removed, however the upper tie down points are then quite close to the base of the case).

Fig. 16 schematically shows a sectional view through the moulding produced by the base and removable core, with the member 18 extending up into the case body from the base. Fig. 17 schematically shows an equivalent perspective view.

A-v) Integral moulded documents tube A document holder provides a convenient, safe and externally accessible place to store inspection records and instructions. Conventionally, these are generally provided as metal fabricated flanged tubes with sealed lids. The tube is fitted by cutting a hole into the case wall and clamping it in place by means of screws or rivets and an 0-ring or silicon seal. Such tubes are generally very expensive.

An alternative, known, method is to rotationally mould a separate document tube, to which is fitted an off the shelf screw cap or plug. A flange is integrally moulded at the neck of the tube and this flange is used to bolt the tube to the case wall. Again, an o-ring or silicone seal is used to seal between the case wall and the document tube.

Depending upon available case recess depths, the cap of the document tube can protrude beyond the outer walls of the case making it vulnerable to impact damage and creating breaks in the seal. It also can prevent cases from being stacked closely to each other.

A document tube can be moulded as an integral pad of the case body, maintaining the integrity of the case wall and eliminating any potential leaks.

Preferably, each applicable case mould is produced with a removable blanking plate in one mould wall. This blanking plate can be replaced with document tube core. Fig. 18 schematically shows a perspective view of the case 9 with a removable blanking plate 19.

The core has a threaded section at the end closest to the side wall, which is dimensioned to accept a threaded plug (not shown). The plug can either be a rotationally moulded article or an off the shelf part. Fig. 19 schematically shows a perspective view including the interior of the tube 20.

Deep cores generally cause problems in rotational moulding as material distribution is related to heat distribution within the mould. The document tube is effectively a deep core in the mould which, under normal circumstances, would be difficult to heat, resulting in a very thin plastic material wall. There are conventional techniques available to overcome this such as the use of air movers which force hot air into the restricted areas, however the use of these is limited to ovens or machines with an air supply.

This problem may be solved by including a heat transfer member in the mould. This heat transfer member may for example comprise a separate metal pin (not shown) connecting the base of the tool to the inner end of the large core. This provides an additional route for heat transferred by conduction from the outside surface of the mould to the core to get heat to the end of the core, which is normally not as hot as the outer body. Fig. 20 schematically shows a sectional view through a corner of the case and document tube.

This second small core 22 provided in the base to abut with the document tube core when the mould is in the closed configuration, creates a second opening 21 in the document tube 20, creating an open-ended channel within the body of the case. This must be closed off to create a sealed document tube. This may be closed off by moulding a thread at top of the core and, following moulding, sealing the opening off with an off-the-shelf threaded plug (not shown).

A further advantage to the heat transfer pin is that it creates a moulded plastic column attaching the document tube to the base of the case mould. This adds to the strength and structural stability of the moulded tube.

A-vi) Desiccant tube I basket Desiccant baskets or tubes are conventionally fitted to cases to reduce moisture build up inside the case and protect sensitive equipment. These are typically metal fabrications fitted to the case wall in the same way as metal document tubes are fitted.

The moulded-in document tube described above can be converted into a desiccant tube / basket by drilling holes into the moulded tube wall.

B) Mould-in cavity plate insert -not reliant on multi-part moulding Ruggedized cases require draw latches to secure the lid and compress the lid to body seal. These can be fitted by simply drilling holes in the case wall and then riveting the latches in place with washers to spread the load, and seals to retain the water and dust seal rating of the case.

As described in the method for moulding in handles, there could be potential problems with this method should a sealing washer be incorrectly fitted or later perish. In addition there are further problems when a latch needs to be replaces and rivets drilled out. The drilling out of the rivet can melt the plastics material locally, enlarging the hole making sealing more difficult a second time round.

An improvement to this would be to mould in a plate with pre-drilled rivet holes for the latch. This would prevent the enlarging of holes when the rivets are drilled out and eliminate the need for load spreading washers but sealing washers would still be needed.

A plate insert including pre-drilled holes is known from US 4,741,972. This describes a "Rotomold insert", which uses an insert comprising two metal plates, one of which is pre-drilled, and secured together to form a cavity therebetween by virtue of the plates being pressed into domed profiles. When the plastics layer forms over the insert during moulding, an air I water-tight chamber is created. This removes the requirement for sealing washers. A problem exists however that forming the dome shape by pressing is expensive and requires special tooling.

The process of moulding in a component involves the following steps: 1) Place the component to be moulded-in into the mould with its locating features lined up with the corresponding features in the mould (e.g. magnets or 0-rings may be used to secure the component); 2) Place the plastics powder in the mould and close the mould; 3) Begin the heating cycle; 4) Once the mould has reached the melting point temperature of the plastics powder the plastics material will begin to coat the mould surface and cover the mould-in component mounting areas; 5) As the mould-in component mounting points reach the melting point temperature of the plastics material, the plastics material will begin to adhere to the component; 6) Once all the powder has been exhausted, the moulded-in component will be completely embedded in the wall of the plastics part; 7) Once the heating cycle is complete a cooling cycle begins; 8) The solidified plastics part is removed from the tool mould and cooled.

According to an embodiment of the present invention, the need for pressing a domed profile is removed by instead using a pre-cut single flat piece of metal 23, which is schematically shown in Fig. 21a, which is folded to create a cavity 24. Figs. 21b, c schematically show such a folded plate in perspective view from two opposing angles.

It can be seen that when folded, a polyhedron, actually a triangular-sectioned prism, is formed, with three side walls and an end wall at each axial end. This requires four fold lines. In more detail: 1) The improved mould-in insert is manufactured as a single flat piece of metal.

This can easily manufactured by laser cutting with no tooling required.

2) No pressed form is required to produce the cavity. Instead the cavity is produced by folding the flat metal plate.

3) No tooling is required to produce the folded form. Instead, what are known in the trade as "Easy bends", may preferably be included so the folded form can be produced simply by hand.

4) As can be seen from Figs. 21b, 21c the folded plate does not, itself, create a totally enclosed cavity. There are gaps created by the "easy bends" and the folding faces do not meet or close the gaps exactly. However, these gaps will naturally fill with plastics material during the moulding process, creating an airtight seal. They also perform an additional function, of acting as keying-in or anchoring-in points for the insert into the plastics material. In the Rotomold process, described additional, outboard anchors are required for this purpose.

As mentioned above, the insert shown in Figs. 21 a-c requires four fold lines. Figs. 22a-c schematically show an alternative embodiment, requiring only three fold lines, with Fig. 22a showing a pre-folded metal blank 25, and Figs. 22b, c showing perspective views of the folded insert 26 from opposing angles. Here, it can be seen that the insert, when folded, forms a polyhedron, in this case a tetrahedron.

C) Stacking centralizing features -accommodating large tolerance variations when cases are stacked -not dependent on multi-part moulding Virtually all rotationally-moulded cases are designed to be stacked on top of each other but it is less frequent that manufacturers design a range of cases where different sizes of case can inter-stack or cross stack. Where this has been attempted, the reliability and the secureness of the stack has been limited.

The main reason for the limited success is that articles manufactured by the rotational moulding process will have large variations in size. A commercial tolerance is typically +1-1% of any particular dimension. With care, and the use of cooling jigs, some features I components can be controlled to within +1-0.75% or even down as low as +1- 0.5% with extreme care. On large articles such as cases, the size variation can therefore be excessive. On a 1 m long case for example the overall length could vary by up to 20mm.

If a traditional stacking pattern was designed to accommodate this tolerance range, the stacking detail would be a very loose fit with the next case in the stack. Such a loose fit would result in an unstable stack and would likely be considered unacceptable by customers. As a result case manufacturers do not attempt to cover a wide range of tolerances and the stacking pattern is designed as a close, neat fit. The result is that small cases will generally stack well whereas the larger the case, the less likely the two case sizes will match, and the less likely the male and female stacking patterns will fit and interlock. In effect, cases must be swapped and selected in order to get a good mating fit I stack with the next case.

A wide tolerance variation can be accommodated whilst maintaining a reliable and snug fit in the stacking features. :10

This is achieved firstly by accommodating all the tolerance movement within the general stacking pattern. This leaves wide gaps between the male up stand on the lid and the receiving recess on the base of the case. However, this alone is not sufficient, since if all the stacking pattern recesses were the same, the case would be able to slide and twist in the tolerance gap.

In a preferred example, case lids are provided with a two-dimensional array of circular male projections, projecting upwardly from the lid. The case bases meanwhile are provided with corresponding female circular recesses.

Secondly, to prevent such sliding, the tolerance gap is removed from a central feature on the base stacking pattern, i.e. so that the central recess is of lower internal dimension I diameter than the surrounding recesses. Each locating feature is relatively small (under 100mm) and the size variation, in this small area, similarly small. The male and female features of the central stacking element can therefore be a snug fit preventing side to side and back to front movement of the case. Fig. 23 schematically illustrates this, showing a sectional view of an upper case 27 sitting atop a lower case lid 28. Fig. 24a schematically shows detail B of Fig. 23, highlighting the central feature 29 with its low tolerance small gap (as dimensional variation is small over a small area).

Elsewhere gaps 30 are maintained to accommodate moulding size variation as schematically shown in Fig. 24b, highlighting detail 0 of Fig. 23.

The stacked cases will however still be able to twist. The stacking pattern shown in Figs. 23-24 is round and therefore allows free rotation within the confines of the tolerance gap. If the central locating feature were square this could potentially reduce twisting, however the length of the case and any small clearance gaps would still allow for significant twisting movement.

To overcome this problem, additional features are included to close the tolerance gap along both the side to side and back to front central axes. Excessive side to side movement is prevented by closing the tolerance gap on the front to back central axis and excessive front to back movement is prevented by closing the tolerance gap on the side to side central axis. Fig. 25 schematically shows a base pattern with the tolerance gap adjusted in this way. Fig. 25a is a plan view of the base stacking pattern, while Figs. 25b and care, respectively, enlarged views of Details C and D from Fig. 25a. As can be seen in Fig. 25, the central recess 31 on each side of the array is narrowed along the axis parallel to the adjacent edge, by partially "squaring off' the circle.

Fig. 26 schematically shows, in similar views to Fig. 25, an alternative example, in which protruding ribs 32 are provided in the corresponding recesses. This also acts to narrow the recesses' effective diameter in corresponding directions. This example allows solid ribs of plastics material to form in the narrow hollows, whereas the larger recesses of Fig. 25 would create hollowed troughs in the case's bottom surface.

In summary, the centre recess detail stops excessive side to side movements but not rotation, whereas the outer or edge details prevent rotation and sideways movement in their respective directions.

If cases are stacked such that the centre recess 29 on the underside of the top case does not come into contact with a corresponding male feature on the lid of the case below (e.g. if it sits on top of a card holder or label recess), then the outer details are responsible for all unwanted movement prevention.

While the central features (i.e. that at the centre of the array and those at the centre of each edge) are preferred as they are optimally placed, some benefit can be obtained by reducing tolerance in other features (e.g. along the central x or y axis shown in Fig. 25a).

D) Lid to body fit -lid centralising features -methods of accommodating body & lid size variations -not dependent on multi-part moulding Fig. 27 shows a conventional method of creating a seal between a case body 33 and lid 34, by mating a recess (filled with a seal 35) of a lid with a corresponding protrusion 36 on the side wall of a case body.

The lid fit between the body and lid must be accurate in order for such sealing features to align and compress the seal. As mentioned above, articles manufactured by the rotational moulding process can have a large variation in size and if the two mating features do not meet up there will be no seal.

Such existing designs only allow for a very small amount of size variation (probably 1- 3mm-max 1.5mm in each side) before the lid and body features fail to line up and the seal becomes ineffective.

Manufacturers will therefore try to mould bodies and lids together on the same machine, at the same time and under the same moulding conditions and machine settings.

Provided both the body and lid have the same degree of grip in the tool (features that will prevent shrinkage during the cooling cycle) both components should end up a similar size.

If a case body and its corresponding removable lid are always kept as a pair there is never a problem. If however a number of cases are used in the same location and the lid I bodies become mixed, there is a high probability that the newly paired lids and bodies will not produce a good airtight seal.

Fig. 28 schematically shows a sectional view of an improved sealing arrangement. The figure shows a side wall 37 of a case body with a depending rim 38 of a lid positioned on top. A seal 39, for example a rubber or silicon seal, is located within a recess formed in the depending rim. A nominal gap on each outer edge of the case (as shown to right of the seal in Fig. 28) can double if the lid is allowed to slide from side to side or front to back. While the seal in this design may remain effective, the latches and catches may no longer line up.

It is common for cases to include lid locating details in the corners. However, in this position they do nothing to arrest the movement between the body and lid unless the body and lid are a neat fit and no, or little, tolerance variation is accommodated.

This aspect, not in accordance with the present invention, aims to alleviate this problem and provides double the degree of movement whilst maintaining an effective seal. This is achieved, stopping much of the side to side and front to back movement without compromising on the larger allowance for size variation, by having corresponding locating features provided between the body and lid, positioned centrally on all sides of each component. This is schematically shown in Fig. 29, which is a sectional view of a horizontal slice of a case in a plane where the lid 40 and case body 41 engage. It can be seen that each side of the depending rim of the lid is provided with a downwardly extending tab 42. The inner surfaces of each case body side wall meanwhile are provided with a pair of inwardly-directed abutments 43, spaced narrowly apart, approximately centrally located along each side, dimensioned to receive corresponding lid tabs therebetween.

Fig. 30a schematically shows, in perspective view, details of the actual case body 9 and lid centralisation features, with Figs. 30b and c providing enlarged detail views of an abutment 43 pair and a tab 42 respectively.

A small locating feature (say 50mm long) will have very little size variation (+1-0.5mm at a tolerance of +1-1%) between the mating pads producing little side to side movement.

The result is a lid that will always sit centrally, and any size variation between body and lid is divided evenly at each side. For example, a 6mm size variation will be 3mm per side as opposed to a potential 6mm on one side and 0mm on the other if no centralisation features are included.

Fig. 31a schematically shows, in a sectional view similar to Fig. 29, a further embodiment, in which these centralisation features are dove-tailed. This profiling further helps prevent dislodging of the features if the case is subject to an impact. Fig. 31b is an expanded view.

E) Lid drainage -compensating for moulding distortion -not dependent on multi-part moulding Rotational moulding is a hollow moulding process and there is no support for the moulding as it cools in the mould. As a result, flat surfaces will generally end up being concave instead of flat.

Ribs across the lid would help support the flat surface and reduce distortion, however there is still likely be some degree of distortion between the ribs. These concave surfaces can collect water if left out in the rain which can then inconvenience a person removing the lid.

Furthermore, since cases need to be stacked a simple sloped, or domed, surface to allow water run-off is not possible.

Reliable stacking, inter-stacking and cross-stacking requires a suitable level stacking surface and a suitable inter-locking feature.

This aspect, not in accordance with the present invention, aims to provide a lid design which both facilitates water run-off and provides uncompromised stacking capabilities.

Fig. 32 schematically shows an example which achieves this aim. Fig. 32a is a side view of a lid 40, Figs. 32b and care sectional views through the lid at different axes, and Figs. 32d and e are enlarged views of details of Figs. 32b and c respectively.

The lid 40 shown in Fig. 32 incorporates a flat stacking surface defined by the upper surfaces 44 of an array of male projections (interlocking features). However the lid also has an underlying convex (e.g. domed or arc or sloping flat surfaces) support surface 45between the stacking features providing good rain water run-off. In other words, the interlocking features, which project from the support surface, vary their length throughout the array so that they are longer towards the edges of the lid than toward the middle, but the tops are kept at the same height forming a substantially planar top surface.

In addition, the lid is what is known in Rotational moulding terms as "double skinned".

The benefit of this is that protrusions 46 on the underside of the lid can "kiss-off' and support the upper surface, further reducing the chance the lid becoming concave. Figs. 32b-e show such protrusions in more detail.

F-i) Catch plates fitted without additional components -not dependent on multi-part moulding As with the previously-described latches, catch plates for rotationally moulded cases are generally either fitted by drilling and riveting, or moulding in plates to receive the rivets.

Drilling and riveting is liable to break the case lid wall, and so the seal is re-established by using a suitable 0-ring or gasket.

The alternative of moulding in a plate adds to machine time (time to fit the insert plates) and also adds cost (i.e. the additional cost of the mould-in insert plate itself).

This aspect, not in accordance with the present invention, aims to overcome these problems, and eliminate the need for moulded inserts and rivets whilst maintaining the integrity of the lid wall.

Fig. 33 schematically shows an exemplary case lid 40 in accordance with this aspect.

Figs. 33a and b provide perspective views of a catch plate fitting 47, with Fig. 33c showing a front view of the lid and Fig. 33d showing a part-sectional view of a catch plate fitting from above. The lid has a plurality of catch plate fittings provided around its circumference, which take the form of recesses 48 extending into the lid. Each recess is moulded with narrow slots running down each side of a recess for a catch plate, as most clearly shown in Fig. 33d.

Fig. 34 schematically shows, in perspective view, a catch plate 49 formed from a sheet of rigid material, preferably metal, which is designed to fit into these slots either side of the latch recess. The catch plate is made slightly oversize for this recess and has serrated edges 50. The catch plate also comprises reception means, in this case a hole 51, for receiving a latch blade. In alternative examples (not shown), the reception means could comprise a hook for example.

Figs. 35a, b are similar to Fig. 33d, b respectively, but show the recess with the catch plate 49 inserted.

To assemble, the catch plate 49 is pushed into the narrow recess immediately after the lid has been demoulded and is still warm. The plastics part will generally shrink by about 3% once cooled so the receiving slots for the catch plate will be further apart when warm than when cool.

The plate is dimensioned so as to be a tight fit in the recess when the moulding is still warm and as the moulding cools it will shrink on to the serrations down the side of the plate which then grip into the still relatively soft plastics material.

The slots 48 are made wider than the thickness of the catch plate 49 in order to reduce the risk of the plastics material thinning unduly over a narrow detail, and also to make the metal of the mould itself stronger. To prevent the catch plate moving back to front in the slot, ribs 52 are provided on the rear wall of the recess next to the slots, which act to push the plate forwards. Holes / cutouts 53 provided in the bottom of the catch plate help ensure drainage from the recess behind the plate.

F-u) Locking of lid using the catch plate -not dependent on multi-part moulding One way to lock ruggedized cases is via a draw latch with a padlock hole, similar in function to a hasp and staple. A problem with this technique is that the staple that the padlock passes through will generally end up protruding past the outer perimeter of the case wall.

This is far from ideal and as an alternative, a cable link solution is frequently used. One end of a cable is attached to the butterfly wing of the latch whilst the other is padlocked to a hasp in a nearby recess on the case. Once the cable is held tight by the padlock, the butterfly latch cannot be lifted or turned, and therefore the latch cannot be opened.

This is a fairly basic solution with limited security (for example cutting the cable defeats the lock) but it does act to prevent mere tampering.

However, an example not in accordance with the present invention enables any standard case to be padlocked at any latch position around the case. The case does not need to be ordered with the locking facility.

The catch plate 49 shown in Fig. 34 is provided with a slotted hole 51 as its reception means to receive the latch blade. This slotted hole is tall enough to allow the latch blade to lift and clear the lower edge of the catch plate.

Figs. 36a, b schematically show an assembled latch, with attached padlock, in two differing perspective views. The latch comprises a latch body 54 and a latch blade 55, the latch blade being vertically extensible with respect to the latch body. The height of the slot is made large enough to accept both the latch blade in the closed position and a suitable size shackle of a padlock 56. Once the padlock shackle is locked through the catch plate, the latch blade cannot be lifted above the lower edge of the catch plate and therefore cannot be separated from the lid.

This method does not stop the butterfly wing of the latch from being lifted or turned but it does stop the latch blade from being removed from the catch plate. As a result the lid can be lifted by the travel distance of the latch (about 3-4mm) so the seal of the case may be broken, but the lid cannot be removed.

Additional components (not shown) can be post-fitted to the latch to offer further security and prevent the lifting if required.

F-ui) Lid hinge -providing compression to maintain a good seal -not dependent on multi-part moulding Most cases have simple lift-off lids with compression latches equally spaced around the perimeter of the lid.

If a hinge lid is required, the latches on one side are replaced with hinges. The mounting point for these hinges needs to be carefully set in order to ensure the correct compression on the seal. If the hinges are not set correctly, and the gap is too small, the lid may jam and not close properly. If the gap is too big, air or water can ingress.

This provides a hinging solution which enables a standard compression latch, with additional components, to be converted into a hinge. The uniform compression and good seal produced by the compression latches is therefore maintained. A lift-off lid case could also be converted to a hinged lid with minimal effort.

Fig. 37 schematically shows a standard compression latch 57. This operates on a butterfly mechanism, such that turning the latch effects vertical movement of a latch blade 58. The latch blade has, as standard, a hole 59 drilled therethrough.

A catch plate as shown in Fig. 33, which would be affixed to the lid, has a corresponding hole and when the latch is in its closed position the holes align. Fig. 38 schematically shows, in perspective view, the latch 57 and catch plate 49 riveted together, so that both the lid and the latch blade will operate as one, so turning the latch will lift the blade, catch plate and the lid together. This creates a connection between the body and lid and allows the latch to be used as a hinge.

The latch has its own hinge, which allows it to swing out clear of the plate once disengaged, and so once latch compression is released, the lid is free to hinge open.

In a latch and catch" configuration, compression of the latch will always pull the shrink fit catch plate further into its recess. Once turned into a hinge, the opening action (if a load is applied to the lid) puts force in the opposite direction which could potentially loosen the catch plate.

A method of improving the security of the catch plate provides additional fixing points in the catch plate. Fig. 39 schematically shows, in perspective view, a modified catch plate 60 attached to a latch 57. Here the catch plate includes a right-angle bend at the top, relative to the serrated edges, with two additional screw or rivet points 62 provided in the bent portion 61 which can be used to secure the catch plate to the lid moulding.

A minor downside to this method is that with this configuration a lift-off lid case cannot be converted, e.g. after purchase, to a hinge lid.

Figs. 40, 41 schematically show a methodology which allows for such conversion using a latch-based hinge fitting including, inter alia, a standard latch and the flat catch plate 49 of Fig. 38. Fig. 40a is a sectional view of the latch-based hinge fitting taken orthogonally to the plane of the catch plate. Fig. 40b is a front view, and Figs. 40c and 40d are perspective views from opposing angles showing the back and front of the fitting respectively. Fig. 41 meanwhile is a perspective view of a case with such a fitting in place.

In more detail, with this system, flat catch plates 49 are fitted to all lid locations.

Clamping means, in this case additional (right angled) catch cover plates 63 are then fitted on the side of the case to be converted to a hinge. Cover plate 63 includes projections 67 which are dimensioned to be snugly received within the catch plate reception means, hole 51, preventing relative vertical movement therebetween Moulded self-tapping screw/rivet holes are included as standard on one side of the case. The assembly of catch plate 49, latch blade 58 and cover plate 63 are then riveted (rivet shown at 64) together, effectively clamping the latch blade. The cover plate 63 provides additional security for the catch plate in a similar way to that of Fig. 39, i.e. a right-angled portion 65 with fixing holes 66 but is retro-fittable.

Perspective views of two cases constructed according to the present invention are schematically shown in Fig. 42 and Fig. 43. The case 9 of Fig. 42 is higher, using a mould configuration similar to that shown in Fig. 8a, while that 9' of Fig, 43 is lower, since a wall section of the mould was omitted, similarly to the arrangement shown in Fig. 8b.

The above-described embodiments are exemplary only, and other possibilities and alternatives within the scope of the invention will be apparent to those skilled in the art.

Claims (5)

1. Claims 1. An insert for attaching a latch to a plastics product formed by a rotational moulding process, comprising a metal sheet folded to form a polyhedron, the metal sheet including holes for attaching the latch.
2. 2. An insert according to claim 1, wherein the polyhedron comprises a triangular prism.
3. 3. An insert according to claim I wherein the polyhedron comprises a tetrahedron.
4. 4. A plastics case comprising an insert according to any of claims 1 to 3.
5. 5. A case substantially as herein described with reference to the accompanying figures.