GB2124970A - Injection mould assembly - Google Patents

Abstract

A mould assembly for injection moulding a container includes an elongate core member 6 supported at one end and a cavity member 2 into which the core member may be moved to define together with the cavity member a container mould space. That surface of the core member which partially defines the base of the container is substantially planar and affords at least one projecting formation 10 which defines a recess 14 which does not extend substantially through the plane of the said surface of the core member, thereby preventing the formation of projections on the inner surface of the container base. The assembly further includes a core restraining member 18 associated with each recess and arranged to be moved between a first position in which it extends into the respective recess 14 and a second position in which it does not. In an alternative embodiment not illustrated the movable restraining members are mounted in the core member and their face ends are provided with a respective recess 14 for cooperation with a fixed insert in the cavity member. <IMAGE>

Description

SPECIFICATION Injection mould assembly The present invention relates to a mould assembly for injection moulding containers, particularly those having one or more integral partitions, and is particularly concerned with such an assembly for moulding thin-walled, multi-partitioned containers of plastics material for use as containers for automotive electric storage batteries.

Moulding assemblies of this type generally comprise two or more elongate cores supported at one end only by a common support to form a yoked core member and a cavity member into which the cores may be moved to define together with the cavity member the bottom, side walls and partitions of the container. When moulding electric storage battery containers the gaps between adjacent cores and between the cores and the inner surfaces of the cavity member may be 2 mm or even less.The plastics material is injected through one or more moulding apertures and the high moulding pressures which are used together with the fact that the cores are of necessity supported at one end only results in the fact that the cores may be subjected to transient pressure differentials which result in the cores being moved relative to one another and to the mould cavity whilst the plastics material is being injected. It will be appreciated that such movement will result in one or more of the container walls or partitions being of increased thickness and one or more being of decreased thickness. Electric storage battery containers are designed so that their walls and partitions have the minimum thickness which is consistent with their desired mechanical strength, and any reduction in this thickness may result in a container which is unacceptably weak.This also may cause difficulty in extracting the cores from the mould cavity.

For this reason the cores of such moulding assemblies have been provided with means which stabilise them against relative movement during the injection process. This stabilising means commonly comprises one or more retractable pins associated with each core which are movable between a first position in which they engage in a recess formed in the unsupported end surface of the core and a second position in which plastics material can flow around them. In use, the pins are extended into their first position and plastics material is injected into the mould. The engagement of the pins in their associated recesses results in the cores being restrained against relative movement.Shortly before the injection process is complete the pins are retracted to their second position in which they project only slightly into the mould cavity and the plastics material can then flow around them and into the recesses formed in the cores. It has also been proposed that the cavity member may be provided with one or more projections on its base surface associated with each core and that each core is provided with a movable restraining member having a recess in its end surface whose shape corresponds to that of the associated projection.This construction operates in a manner similar to that described above in that the restraining members are moved into engagement with the projections thereby restraining the cores against movement during the injection process and are retracted back into the cores shortly before the end of the injection process to permit plastics material to flow between them and the associated projections.

However, both these constructions result in each compartment of the finished container having a projection on the interior surface of its floor corresponding to the position of the recess in the associated core or restraining member. The projection in each compartment is normally of no consequence since electric storage batteries are generally provided with integral so-called "mud ribs" on which the plates rest which project above the projections and define a space into which active material dislodged from the battery plates can accumulate without leading to internal short circuits in the battery.

However, in certain types of battery, such as so-called recombination batteries in which the plates and separators are under sufficient compression to prevent shedding of active material, mud ribs are not required. In these batteries the plates simply rest on the floor of the container and thus the presence of projections on the floor of the container prevents the plates from reaching the bottom of the container and therefore take up valuable space within the container.

The problem of the movement of the core or cores can occur even when a single compartment container is being formed and thus only a single core is used.

It is an object of the present invention to provide an assembly for injection moulding containers, in particular those having one or more integral partitions, the internal surface of the floor of which is substantially planar and has no projections extending above its plane thereby permitting battery plates within the container to sit flush on the floor of the container.

According to one aspect of the present invention a mould assembly for injection moulding a container includes an elongate core member supported at one end and a cavity member into which the core member may be moved to define together with the cavity member a space which corresponds to the bottom and side walls of the container, the cavity member having at least one aperture through which plastics material may be injected, that surface of the core member which, in use, partially defines the base of the container being substantially planar and affording at least one projecting formation which defines a recess which does not extend substantially through the plane of the said surface of the core member, the assembly including a restraining mem ber associated with each recess, part of whose shape corresponds to that of the associated recess, dis posed within a respective aperture in the cavity member and arranged to be moved between a first position in which it extends into the respective recess and a second position in which it does not.

Thus in this embodiment the core member affords one or more recesses which co-operate with associated restraining members but which are situated beyond the plane of that surface of the core member which defines the base of the container, that is to say on the side of that plane remote from the remainder of the core member. In use, the or each restraining member is extended into a position in which it engages in the associated recess in the core member thereby restraining the core member against movement whilst plastics material is injected and towards the end of the injection process the or each restraining member is retracted again to permit plastics material to flow into the or each recess in the core member.By virtue of the fact that the or each recess in the core member does not extend substantially through the plane of that surface which partially defines the base of the container, the inside surface of the base of the finished container has no projection on it and thus when used as a battery container the battery plates can sit flush on the base of the container. It will be appreciated that the projecting formation which defines the recess will produce a recess in the base of the container but this does not impair the flush engagement of the base by battery plates.

According to a second aspect of the present invention a mould assembly for injection moulding a container includes an elongate core member supported at one end and a cavity member into which the core member may be moved to define together with the cavity member a space which corresponds to the bottom and side walls of the container, the cavity member having at least one aperture through which plastics material may be injected, that surface of the core member which, in use, partially defines the base of the container being substantially planar and the core member accommodating at least one movable restraining member whose end defines a recess, the assembly including a projecting formation on the cavity member associated with the or each restraining member, part of whose shape corresponds to that of the recess in the restraining member, the or each restraining member being arranged to be moved between a first position in which the recess in it is situated wholly beyond the plane of the said surface of the punch member and the projecting formation extends into the said recess and a second position in which it does not, and the recess in the restraining member does not extend substantially through the said plane. This embodiment may be thought of as being the reverse of the first in that the movable restraining member is accommodated in the core member rather than the cavity member but otherwise its operation and advantages are much the same.

The recess formed in the base of the container by the projecting formation in the first embodiment or by the outer edge of the end of the restraining member in the second embodiment may lead to a local weakening of the base, and for this reason the cavity member may be provided with a recess extending around each restraining member or projecting formation respectively and thus at each of these positions the exterior surface of the base of the finished container will extend somewhat beyond the remainder of this surface. The or each recess in the cavity member is preferably so dimensioned that the thickness of the base of the finished container is substantially constant.

In the preferred embodiment the assembly is for injection moulding a container having at least one integral partition, and in this case the core member comprises a plurality of spaced cores each of which has at least one projecting formation and associated restraining member associated with it. In this construction adjacent cores define a space which corres ponds to a partition in the finished container and each core is restrained against movement by engagement of a restraining member with the or each projecting formation associated with it.

The projecting formations may be formed by appropriate machining of the core member or the cavity member or the or each such formation may be afforded by a separate insert secured in a recess in the said surface of the core member or the cavity member respectively.

Preferably the recess in the or each restraining member or in the end of the or each projecting formation and the co-operating end of the or each projecting formation or the or each restraining member respectively are of tapered cross-section and therefore act as a lead-in when the restraining member is extended into the mould cavity and thus ensures engagement of the or each restraining member with its associated cavity even if the core member or its constituent cores should be somewhat displaced with respect to the restraining members.

Further features and details of the present invention will be apparent from the following description of one specific embodiment which is an assembly for injection moulding a polypropylene compartmented container for a six cell lead acid automotive battery which is given by way of example only with reference to the accompanying diagrammatic drawings in which: Figure 1 is an underneath view of the core member of the assembly; and Figure 2 is a transverse sectional view on the line Il-Il in Figure 1 showing the cavity member also.

The assembly comprises a cavity member 2 (seen in Figure 2) affording an open-topped rectangular section cavity and a core member 4 (seen in Figure 1) comprising a plurality of spaced elongate cores 6, each connected at one end to, and supported by, a support plate 8. The cavity member and core member form part of a moulding machine whose construction is conventional and will therefore not be described in detail but which includes means for moving the core member to a position within the cavity member in which together with the cavity member it defines the spaces corresponding to the base, side walls and intercell partitions of a battery container.

Each core has two spaced recesses, each of which accommodates a circular section insert 10 which has a circular section flange 12 which projects beyond the plane of the underside (as seen in Figure 2) of the associated core and defines a circular section recess 14 whose side walls taper upwardly and inwardly and whose base is coplanar with the underside of the punch.

The cavity member has six spaced injectiion apertures 16 disposed along its centre line, each of which is positioned to be beneath the centre of an associated core 6. The cavity member 2 also affords two spaced apertures associated with each core, one on each side of the respective injection aperture 16, each of which slidably accommodates a respective restraining member 18. The restraining members 18 are disposed at positions corresponding to those of the inserts 10 and are of circular section with their free ends being of tapered shape corresponding to those of the recesses 14. All the restraining members 18 are connected to a common actuation device (not shown) for movement between the position shown in Figure 2 to a position in which they are accommodated in a respective recess 14.

In use, the core member is lowered into the cavity member and the spaces between the cores then correspond to the intercell partitions of a battery container whilst the space between the core member and the cavity member correspond to the base and side walls of a battery container. Before injection of plastics material through the injection apertures 16 is commenced, the restraining members 18 are moved from the position shown in Figure 2 to a position in which they each engage within a recess 14 in the associated insert 10. By virtue of this engagement each core of the core member is restrained against movement and the side walls and intercell partitions of the container are thus formed to the desired thickness.Shortly before the injection is terminated, the restraining members 18 are retracted again to the position shown in Figure 2 and plastics material then flows into the recesses 14 and into the space between the inserts 10 and restraining members 18. Once the plastics material has solidified the core member is withdrawn and the moulding is ejected in the conventional manner.

As may be seen from Figure 2, the internal surface of the base of the container has no projections on it, and whilst it will have a number of annular recesses corresponding to the positions of the circular flanges 12 these will not impair the flush engagement of battery plates with the base of the container.

In the illustrated construction the restraining members are retracted to a position in which they are proud of the base of the recesses 20 since the free ends of the restraining members are tapered and thus if they were retracted any further plastics material would leak into the recesses accommodating the restraining members which would remain as "flash" on the underside of the finished container. It will be appreciated that if the restraining members were of constant cross-section it would be possible for these to be retracted to a position in which their upper surface is flush with the base of the recesses 20.

In the illustrated embodiment the restraining members and the injection apertures are quite separate but it will be appreciated that it would be possible to combine these by forming some or all of the restraining members as hollow injection members. In such a modified construction it is of course necessary to provide either the surfaces of the recesses 14 or the surfaces of the free ends of the restraining members 18 with one or more grooves or the like or some alternative flow passage to enable plastics material to flow into the mould cavity even when the restraining members engage the inserts 10 since otherwise this engagement would prevent such flow of plastics material.

In a second embodiment, which is not illustrated, the movable restraining members are positioned in the cores and have free ends whose shape corresponds to that of the inserts 10 in Figure 2 whilst the cavity member is provided with inserts projecting into the mould cavity whose shape corresponds to that of the ends of the restraining members in Figure 2. In use, the restraining members are moved between a position in which the cavities in their ends occupy the position shown for the cavities 14 in Figure 2 and a position in which these cavities mate with the upstanding inserts in the cavity member and the operation and advantages are otherwise the same as those described above.

Claims (8)

1. A mould assembly for injection moulding a container including an elongate core member supported at one end and a cavity member into which the core member may be moved to define together with the cavity member a space which corresponds to the bottom and side walls of the container, the cavity member having at least one aperture through which plastics material may be injected, that surface of the core member which, in use, partially defines the base of the container being substantially planar and affording at least one projecting formation which defines a recess which does not extend substantially through the plane of the said surface of the punch member, the assembly including a restraining member associated with each recess, part of whose shape corresponds to that of the recess, disposed within a respective aperture in the cavity member and arranged to be moved between a first position in which it extends into the respective recess and a second position in which it does not.

2. A mould assembly for injection moulding a container including an elongate core member supported at one end and a cavity member into which the core member may be moved to define together with the cavity member a space which corresponds to the bottom and side walls of the container, the cavity member having at least one aperture through which plastics material may be injected, that surface of the core member which, in use, partially defines the base of the container being substantially planar and the core member accommodating at least one movable restraining member whose end defines a recess, the assembly including a projection formation on the cavity member associated with each restraining member, part of whose shape corresponds to that of the recess in the restraining member, the or each restraining member being arranged to be moved between a first position in which the recess in it is situated wholly beyond the plane of the said surface of the punch member and the projecting formation extends into the said recess and a second position in which it does not, and the recess in the restraining member does not extend substantially through the said plane.

3. An assembly as claimed in Claim 1 or Claim 2 for injection moulding a container having at least one integral partition, the core member comprising a plurality of spaced cores each of which has at least one projecting formation and associated restraining member associated with it.

4. An assembly as claimed in any one of the preceding claims in which the cavity member affords a recess extending around each restraining member or projecting formation respectively.

5. An assembly as claimed in any one of the preceding claims in which the or each projecting formation is afforded by a separate insert secured in a recess in the said surface of the punch member or in the cavity member respectively.

6. An assembly as claimed in any one of the preceding claims in which the recess in the or each restraining member or in the end of the or each projecting formation and the co-operating end of the or each projecting formation or the or each restraining member respectively are of tapered crosssection.

7. An assembly as claimed in any one of the preceding claims including two or more restraining members, each of which is connected to and arranged to be moved by a common actuating member.

8. A mould assembly for injection moulding a container substantially as specifically herein described with reference to the accompanying drawings.