GB2147845A - Forming plastics sheet to provide a reclosable opening - Google Patents

Abstract

Plastics sheet material moulded to form a container or a part therefor and having an outwardly projecting portion including an internal part which may be broken away so that the outwardly projecting portion provides a filling opening, the moulding being such that at least a part of the periphery of the broken away part and at least a part of the filling opening which corresponds thereto are inwardly sloped such that the broken away part may subsequently be lodged in the filling opening to act as a plug therefor. <IMAGE>

Description

SPECIFICATION Forming plastics sheet to provide a reclosable opening This invention relates to forming plastics sheet to provide a reclosable opening, and apparatus for such forming. It has been particularly developed for vacuum-drawn casings for heavy duty electric cable joints but is not limited to this technical application.

Such casings are generally made in two mating halves of similar shape, the shape being a standard shape depending on the number of cables entering the casing etc. After the joint is made the two parts of the casing are assembled around it and are held together by clipping their peripheral flanges together. A liquid insulating material is then poured into the casing and allowed to set usually by a chemical reaction. Once the insulating material has set, the casing is no longer of importance; in other words, it serves principally as a mould for the insulating material.

These casings are currently made from a polys tyrene sheet which is heated and vacuum drawn onto a wooden former at the bottom of the mould.

This former gives it a suitable shape which mini mises the amount of insulating material needed to fill the final casing and which gives the casing sufficient rigidity.

The invention is concerned with the provision of a filling opening in formed plastics sheet, particularly polystyrene sheet which is moulded to form a cable joint casing half. Heretofore the moulding operation has been used to form a filling operating with a rounded peripheral lip the free edge of which faces towards the cable casing interior, a separate plug being provided to close offthe opening after the casing has been filled with insulating material. It has now been found to be possible to mould the plastics sheet in such a way that a part of the moulded sheet may be broken out to give a filling opening and that the broken away part has a taper which permits it to be replaced in the opening after filling such that it lodges in the opening, but does not pass completely through it. In other words, the broken out part acts as a plug.

A problem which was encountered in putting this idea into practice arises from the necessity of tapering both the wall of the broken out part and the wall of the filling opening so that the tapered walls engaged when the broken out part was used as a plug after filling. If a fixed former blade is used to form the two tapered walls on the respective sides thereof it cannot be withdrawn after the forming operation is completed. Thus special resiliently mounted former blades were designed to allow the plastics sheet to be moulded into the correct shape.

It is in fact surprising that it suffices to pivotally mount the former blades at their base without providing for a complex retraction mechanism to disengage them before the plastics sheet is stripped from the former. The reason for this is that the vacuum drawing does not pull the plastics sheet tightly against the blade particularly at the undercut side, so that after the plastics sheet has cooled and set the blade is a fairly loose fit in a sloping polystyrene channel.

According to one aspect, the invention provides plastics sheet material moulded to form a container or a partthereforand having an outwardly project ing portion including an internal part which may be broken away so that the outwardly projecting portion provides a filling opening, the moulding being such that at least a part of the periphery of the broken away part and at least a part of the filling opening which corresponds thereto are inwardly sloped such that the broken away part may subsequently be lodged in the filling opening to act as a plug therefor.

According to another aspect, the invention provides a former for use in vacuum or pressure moulding thermoplastic plastics sheet material which comprises upstanding blade means arranged to form a substantially continuous closed ridge in the plastics material, at least two opposite parts of the blade means being outwardly sloped and pivoted at or adjacent their base to permit the moulded sheet material to be disengaged from the former.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a side elevation of part of an assembled cable joint casing; Figure 2 is a perspective view of the top part of the casing of Figure 1 (with slight modifications); Figure 3 is a section on line Ill-Ill of Figure 2; Figure 4, Figure 5 and Figure 6 are a plan view, a longitudinal section and a tranverse section respectively of a lower former member; Figure 7, Figure 8 and Figure 9 are a plan view, a longitudinal section and a transverse section respectively of an upperformer member; Figure 10 and Figure 11 are a plan view and side elevation respectively of an end former blade; Figure 12 and Figure 13 are a side elevation and an end elevation respectively of a side former blade; and Figure 14 is a view partly in section of the assembled former.

Referring now to Figures 1 - 3 of the drawing, Figure 1 shows one end of a cable joint casing made from flanged polystyrene sheet mouldings 1 and 2 joined together by clips (not shown) which fit over the edges of the facing flanges 3, 4 of the respective mouldings. The top part of the box has an upwardly projecting ridge 6 designed to form a filling opening as will be explained below. As shown in Figures 2 and 3 the ridge 6 has outer and inner walls 7, 8, the inner walls 8 being continuous with a flat bottom 9.

The walls 7, 8 are continuous with each other at the ridge top 10 but at this point the sheet is weakened by internal indentations (not shown) provided by the teeth on the former blades as described below. The walls 7, 8 are upright at the semicircular ends 12,13 of the ridge 6 but are both sloped (see Figure 3) along the longitudinal parts 14 of the ridge 6. In use, when it is desired to provide a filling opening in the moulding, the inner part 18 consisting of inner walls 8 and bottom 9 is removed by hand-breaking the sheet at the ridge top 10. If necessary a knife may be run along the inside of the ridge top 10 to provide a further weakness in addition to the indentations mentioned above. After filling, the inner part 18 can be replaced to act as a plug.In view of the space between the walls 7,8 shown in Figure 3, the inner part 8 will now penetrate further into the filling opening until the sloping walls 7,8 abut. The arrangement is such that the bottom 9 is now flush with the main part of the moulding 1 thus providing a uniform thickness of insulating material around the cable joint.

The former used to provide the moulding shown in Figures 2 and 3 will now be described with reference to Figures 14.

The lower former member 20 is shown in Figures 4 - 6 and comprises a base 21 having screwholes 22 and an integral peripheral wall 23. The inner face of the wall 23 is vertical at the semicircular ends 25 but is outwardly sloped at the longitudinal sections to form a ramp 24.

The upper former member 30 is shown in Figures 7 - 9 and comprises a base 31 with screwholes 32 (matching screwholes 22 in lower member 20) and semicircular end walls 33 arranged to fit within end walls 25. The inner face of end walls 33 is sloped as shown. The longitudinal edges 35 of the base 31 have grooves 36 to receive rubber strips as described belowwith reference to Figure 14 and undercuts 38 are provided around the ends of the base 31 for receiving part of the former blades as described below with reference to Figure 14.

A semicircular end former blade 40 is shown in Figures 10 and 11 and has three inwardly directed nibs 41 at the bottom which on assembly are located in undercuts 38 to prevent removal of the blade from its fixed position sandwiched between the walls of lower and upper former members 20,30. The hollow ground blade 40 has teeth 43 to provide the weakness in the formed polystyrene as described above.

A side former blade 45 is shown in Figures 12 and 13 and has two inwardly directed nibs 42 at the bottom which on assembly are located in undercuts 38 as shown in Figure 14. The blade 45 likewise has teeth 47 at the top.

Figure 14 shows the assembled former consisting of lower former member 20, upper former member 30, two blades 40 and to blades 45. Screws passing through the screwholes 22,32 secure the former together and connect it to a former base (not shown) around which the rest of moulding is formed.

Rubber strips 50 in grooves 36 normally press blades 45 against ramps 24 but after moulding blades 45 may pivot to a vertical position by compressing strips 50 as the moulding is stripped from the former. Thus outer wall 7 can be given an undercut configuration without interfering with the stripping process. As will be seen from Figure 14, the ends of the triangular end walls 33 of former member 30 serve to prevent outer and inner polystyrene walls 7, 8 coming into contact around the ends of the former blades 45.

Claims (16)

1. Plastics sheet material moulded to form a container or a part therefor and having an outwardly projecting portion including an internal part which may be broken away so that the outwardly project ing portion provides a filling opening, the moulding being such that at least a part of the periphery of the broken away part and at least a part of the filling opening which corresponds thereto are inwardly sloped such that the broken away part may subse quently be lodged in the filling opening to act as a plug therefor.

2. Sheet material according to claim 1 wherein the outwardly projecting portion comprises a ridge having a continuous top which forms a line of weakness.

3. Sheet material according to claim 2 wherein the ridge top has internal indentations to weaken it.

4. Sheet material according to claim 1,2 or 3 wherein the outwardly projecting portion has two opposite long sides which correspond to said parts of the periphery.

5. Sheet material according to any preceding claim, which has been moulded to form a cable joint casing part.

6. A method of providing a plug for a filling opening in plastics sheet material moulded to form a container or a part therefor, which comprises break ing said part from plastics sheet material according to any preceding claim.

7. Aformerfor use in vacuum or pressure moulding thermoplastic plastics sheet material which comprises upstanding blade means arranged to form a substantially continuous closed ridge in the plastics material, at least two opposite parts of the blade means being outwardly sloped and pi voted at or adjacent their base to permit the moulded sheet material to be disengaged from the former.

8. A former according to claim 7, wherein said parts of the blade means are resiliently urged into their outwardly sloped position at which they rest against a stop.

9. A former according to claim 8, wherein said urging is effected by a strip of resiliently compressi ble material engaging the inner side of said parts of the blade means.

10. A former according to claim 7,8 or 9 wherein said parts of the blade means extend along two long sides of the closed ridge and wherein the other parts of said blade means are upright but are provided with a sloping inner reinforcing wall to close the gaps at the ends of the said parts of the blade means.

11. A former according to claim 10 wherein said other parts of said blade means are semi-circular.

12. A former according to any one of claim 7 - 11, which comprises a lower former member with an upstanding wall portion and an upper former mem ber and an upstanding wall portion which fits therein, at least part of the blade means being secured between said wall portions.

13. A former according to claim 12, wherein the blade means have lugs engaging under the upper former member.

14. A former according to any one of claims 7 13 wherein the blade means have serrations along their tops.

15. Plastics sheet material according to claim 1, substantially as hereinbefore described with reference to Figures 1 - 3 of the drawings.

16. A former according to claim 7, substantially as hereinbefore described with reference to Figures 4 - 14 of the drawings.