GB2196291A

GB2196291A - Moulding apparatus

Info

Publication number: GB2196291A
Application number: GB08719582A
Authority: GB
Inventors: Daniel Taylor
Original assignee: AUTO ALLOYS
Current assignee: AUTO ALLOYS
Priority date: 1986-08-23
Filing date: 1987-08-19
Publication date: 1988-04-27
Anticipated expiration: 2007-08-19
Also published as: GB2196291B; GB8719582D0; GB8620563D0

Abstract

Apparatus for producing a moulded polystyrene component 13 comprises two mould parts (10, 11) which, in use, are positioned in face- to-face relationship to define a mould cavity corresponding to the component to be moulded. A chamber (13, 14) is associated with each of said mould parts, and each mould part provides communication (15, 16) between the associated chamber and the mould cavity. The mould parts are adapted to define a further chamber (17) surrounding the joint line of the mould cavity, and which is being in communication with the mould cavity and with the exterior of the mould parts. The apparatus enables quicker steam pressure equalisation giving shorter cycle times together with more even steam distribution through the mould cavity resulting in a better moulding. <IMAGE>

Description

SPECIFICATION Moulding apparatus The present invention relates to moulding apparatus for producing expanded polystyrene components.

Expanded polystyrene components are required for a number of applications, e.g. for the lost foam casting process. In this process, the polystyrene component is buried in refractory sand and then 'burnt-off' by the introduction of liquid metal so that (after cooling) there remains a cast part of the same shape as the original polystyrene component.

Conventional polystyrene moulding apparatus comprises two separable die halves carried on plattens. Each die half has a part die cavity such that when the die halves are closed together, a die cavity of the shape of the component to be moulded is defined. The back face of each die half is contained within a respective closed chamber in which temperature and pressure may be varied to suit the process conditions. Additionally conduits are provided in each die half to provide communication between the closed chamber and its part die cavity and its associated chamber.

During the moulding operations, a first one of the closed chambers is pressurised with steam which thus passes via the conduits in the associated die half into the die cavity.

This steam passes through the polystyrene being moulded and then out through the conduits in the other die half into the other of the closed chambers. This operation is continued until there is an equalisation of pressure in the two chambers. This procedure is then repeated in reverse so that steam 'flow' through the die cavity is in the opposite direction to that in the first stage. Finally, both chambers are pressurised simultaneously to complete the moulding operation.

It is a disadvantage of such apparatus that the pressurisation is required to be effected sequentially which thus increases the time required for the moulding operations.

It is therefore an object of the present invention to provide apparatus for moulding polystyrene components which obviates or mitigates the abovementioned disadvantage.

According to the present invention there is provided apparatus for producing a moulded polystyrene component comprising two mould parts which, in use, are positioned in face-toface relationship to define a mould cavity corresponding to the component to be moulded, two first chambers each associated with a respective one of said mould parts, and conduit means provided in each mould part to provide communication between the associated chamber and the mould cavity, wherein the mould parts are adapted to define a second chamber surrounding the joint line of the mould cavity, said second chamber being in communication with the mould cavity and with the exterior of the mould parts.

Thus in the apparatus of the invention, there is a second chamber which encircles the joint line of the mould cavity, (i.e. the line defined as a result of the faces of the mould parts being in juxtaposed relationship). This second chamber may for example be annular. Irrespective of its shape, the chamber is preferably formed by channels provided in the face of each mould part such that when the mould parts are juxtaposed the channels together define the chamber.

The communication between the mould cavity and the second chamber may be provided by a slight spacing between those sections of the faces of the mould parts between the mould cavity and the chamber. Alternatively, these sections may be in abutting relationship and have channels formed therein for providing said communication.

In a preferred construction of apparatus in accordance with the invention, each of the mould parts is in the form of a platten and its back face is contained within the respective first chamber, in which temperature and pressure may be varied to suit the desired moulding process.

Preferably also each mould part may comprise a plurality of plates or the like positioned together in very closely spaced relationship. In this case the conduit means between the mould cavity and the first chambers are provided by the spacing between the plates. This construction is particularly advantageous for the avoidance of 'blemishes' on the surface of the moulding such as are caused by the ports used in the conventional moulding apparatus to provide communication between the cavity and the first chambers.

The moulding apparatus of the invention may of course be incorporated in an automatic machine which opens and closes the mould parts as required. Whilst the mould is closed, the mould parts may be held in position by a locking force or mechanism. The apparatus will of course be associated with the conventional facilities for introducing polystyrene into the mould cavity.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawing, in which: Fig. 1 is a fragmentary diagrammatic view of a moulding apparatus according to the invention; and Fig. 2 is a sectional detail view of the mould cavity joint line to an enlarged scale.

The moulding apparatus comprises two mould parts 10, 11 positioned as shown in Fig. 1 to define a mould cavity 12. Each mould part 10, 11 has a respective chamber 13, 14 on its back face with respective conduits 15, 16 providing communication between the cavity 12 and each of chambers 13, 14.

A chamber 17 is provided at the joint line 18 of the mould parts 10, 11. The chamber 17 is formed by facing channels 19, 20 in the butting walls 21, 22 of the respective mould parts 10, 11.

The chamber 17 communicates with the mould cavity 12 via a slight spacing 23 between the butting surfaces of the walls 21, 22.

Communication between the chamber 17 and the exterior of the mould parts 10, 11 is also provided and such communication is indicated generally by pipe 24 communicating, in this instance, with the channel 19.

During use of the apparatus in accordance with the invention, the mould parts 10, 11 are initially brought into face-to-face relationship and polystyrene introduced into the mould cavity 12. Air displaced from the cavity 12 passes into the chambers 13, 14 via conduits 15, 16. This displacement can be assisted by generating a reduced pressure in the chamber 17 via-its communication (the pipe 24) with the exterior of the mould parts 10, 11.

In the next step, steam is introduced into chamber 17 via its communication (the pipe 24) with the exterior of the mould parts 10, 11 from which it passes into the mould cavity 12 and thus through the polystyrene. From the mould cavity 12 the steam passes via the conduits 15, 16 into the chambers 13, 14.

This operation may be continued until pressure is equalised between the chambers 13, 14 and the chamber 17. Once this has been achieved, the moulding operation is completed and there is no need to reverse the steam flow as is the case with the conventional moulding apparatus.

The invention thus provides the significant advantage of a shorter cycle time for the moulding operation. Additionally, during the moulding operation, there is a more even distribution of steam through the mould cavity, resulting in a better moulding.

An advantageous development of the apparatus lies in the case where mating ports or passages are provided in each die or die carrier face so that services i.e. water, steam, vacuum etc. can be provided variably in all cavities without the necessity of external pipe work. This is of great advantage on the moving die faces, where'the flexible pipes do hinder the removal of the moulded component and of access to the "Open" die for application of adhesive in the case of the requirements to join multi part mouldings before ejection from the mould cavity.

A further refinement is that the 'pipe less' facility with its 3 chamber system in assembled as a quick change cassette.

Claims

1. Apparatus for producing a moulded polystyrene component comprising two mould parts which, in use, are positioned in face-toface relationship to define a mould cavity corresponding to the component to be moulded, two first chambers each associated with a respective one of said mould parts, and conduit means provided in each mould part to provide communication between the associated chamber and the mould cavity, wherein the mould parts are adapted to define a second chamber surrounding the joint line of the mould cavity, said second chamber being in communication with the mould cavity and with the exterior of the mould parts.

2. Apparatus as claimed in claim 1 which the second chamber is formed by channels provided in the face of each mould part such that when the mould parts are juxtaposed the channels together define the chamber.

3. Apparatus as claimed in claim 1 or 2 in which the communication between the mould cavity and the second chamber is provided by a slight spacing between those sections of the faces of the mould parts between the mould cavity and the chamber.

4. Apparatus as claimed in claim 1 or 2 in which the communication between the mould cavity and the second chamber is provided by channels formed in the butting faces of the mould parts.

5. Apparatus as claimed in claim 1, in which each of the mould parts is in the form of a platten and its back face is contained within the respective first chamber, in which temperature and pressure may be varied to suit the desired moulding process.

6. Apparatus as claimed in claim 1, in which each mould parts comprises a plurality of plates or the like positioned together in very closely spaced relationship.

7. Apparatus as claimed in claim 6, in which the conduit means is provided by spacing between the plates.

8. Apparatus for producing a moulded polystyrene component, substantially as hereinbefore described with reference to the accompanying drawings.