GB2030916A - Evacuating moulds - Google Patents

Abstract

A mould or die for the transfer or injection moulding of polymeric materials or the pressure die-casting of metals in which air or other gas is substantially excluded from a hermetically sealed region of the mould or die by a source of vacuum before the commencement and/or completion of final closure of the or each moulding cavity or impression of the mould or die. At least one mould half (3, 5) is surrounded by a shroud ring (9) which is resiliently urged by springs (10) from said mould half (3, 5) towards a companion mould half (4, 6). A constantly effective hermetic seal in the form of a heat-resistant toroidal "O" ring (12a) is provided between the shroud ring (9) and said one mould half (3, 5) whilst a second hermetic sealing ring (11a) of similar formation in a groove (11) on the shroud ring (9) is effective during, and at the completion of, closure of the mould or die (3, 4, 5, 6) but is ineffective when that mould or die (3, 4, 5, 6) is fully open. The surrounding shroud ring (9) is provided with at least one connection point (15) for said source of vacuum and preferably with a plurality of such connection points (15). It is possible to provide each mould or die half with a corresponding shroud ring, (Figs. 3, 4 not shown) the two shroud rings being arranged to cooperate and the shrouded stroke of the mould or die thus being increased. <IMAGE>

Description

SPECIFICATION Improvements in or relating to moulds and dies This invention relates to moulds of the type that are used for the compression, transfer and/or injection moulding of polymeric materials, and to dies of the type that are used for the pressure diecasting of metals.

Moulds of these known types, for the production of mouldings in polymeric materials, and for the die-casting of metals, usually consist of two mold halves or bolsters into which are machined complementary cavities or impressions representing the components to be moulded or die-cast. Alternatively, inserts, each with the cavities or impressions appropriately machined therein, may be arranged in the mould halves. On occasion, such moulds may be provided with ancillary pieces, for example for the production of screwthreaded mouldings or die-castings, or to meet other special requirements.

whilst these known moulds are generally satisfactory, and operate efficiently, there is sometimes a tendency for the mouldings which they produce to be defective, or at least to fall short of the required standard, and this is attributable, under some circumstances, to the air or other gas (for example, nitrogen) which is trapped in the mould, during operation, after final closure thereof.This disadvantage can be overcome, or at least considerably reduced, by providing susceptible moulds and dies with shrouding and one object of the present invention is to provide such a mou Id or die with simple but effective shrouding by which the shortcoming that has been discussed above can be eliminated, or at least very significantly reduced, without appreciably increasing the length of the moulding or casting cycle or the cost of the mouldings or castings. According to the invention, there is provided a mould or die of one of the types set forth, wherein the mould or die comprises shrouds arranged to cooperate with mould halves, bolsters and/or inserts in such a way that at least one substantially hermetically sealed region is formed around at least one moulding cavity or impression which is defined thereby during and/or after the final closure of the mould or die in the use thereof, the or each of said regions being provided with means for the connection thereto of a source of vacuum so that said source of vacuum will evacuate from the or each moulding cavity or impression substantially all of the air or other gas that was present therein before the commencement and/or completion of such final closure.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which.~ Figure 1 is a sectional elevation through a mould provided with shrouding in accordance with the invention, the mould being in a fully closed position, Figure 2 is a part-sectional elevation through the shrouded mould of Figure 1 in a partially closed position with vacuum applied, Figure 3 is a sectional elevation through a mould of an alternative construction, again provided with shrouding in accordance with the invention, the mould being shown in a fully closed position, and Figure 4 is a part-sectional elevation through the shrouded mould of Figure 3 is a partially closed position with vacuum applied.

Referring to the drawings, and firstly to Figure 1 threof, that Figure shows a mould, consisting of two main half moulds, in a fully closed position, the top half mould having a top backing plate 1 and a top bolster plate 3 that are releasably joined together by screws (not illustrated).

The bolster plate 3 carries a number of inserts 5 which are held in position by screws 7.

The bottom half mould consists of a bottom backing plate 2 and a bottom bolster plate 4 that are also releasablyjoined together by screws (not illustrated), the bolster plate 4 carrying a corresponding number of inserts 6. Each of the inserts 5 and 6 has cavities 8a and 8b representing the shape of the moulding or diecasting which is to be produced. A shroud ring 9 surrounds the top bolster plate 3 and is held captive by the top backing plate 1, the shroud ring 9 carrying a plurality of compression springs 10 at regularly spaced intervals around its centre.There is a small projection 9a on the inner surface of the shroud ring 9 at the top of the latter and there is also a machined groove 1 1 on its lower surface which houses a heat resisting and sealing toroidal "0" ring 1 lea. Several threaded connection points 1 5 (of which only one is illustrated) provide coupling locations for corresponding pipes from a vacuum pump or other source of vacuum (not illustrated). The top bolster plate 3 has, at its bottom, a small projecting lip 3a machined on its outer periphery into which lip is machined a groove 12 that houses a heat resisting and sealing toroidal "0" ring 1 2a.

Figure 2 shows the shrouded mould of Figure 1 in a partially closed position in which the lower surface of the small projection 9a of the shroud ring 9 is in contact with the upper surface of the bolster plate lip 3a. The compression springs 10 are extended in this position, the mould inserts 5 and 6 have space between their opposed faces, and vacuum can be applied at the connection points 1 5 so as to remove air or other gas from the whole of the shrouded space that is bounded by the inner surface of the shroud ring 9, the lower face of the top bolster plate 3 and the upper face of the bottom bolster plate 4. The vacuum just referred to is maintained whilst the two half moulds are closed together to adopt the position that is shown in Figure 1, in which latter position the vacuum may continue to be maintained, or can be released, as may be desired.

Figures 3 and 4 show a mould of alternative design that is provided with shrouding in accordance with the invention, the mould consisting of two main half moulds which are illustrated in a fully closed position in Figure 3, the top half mould having a top backing plate 1A and a top bolster plate 3A that are releasablyjoined together by screws (not illustrated). The bolster plate 3A carries at least one insert 5A which is held in position by a screwed plug 7A. The bottom half mould consists of a bottom backing plate 2A and a bottom bolster plate 4A that are releasably joined together by screws (not illustrated), the bolster plate 4A carrying a corresponding number of inserts 6A. Each of the inserts 5A and 6A again has the cavities 8a and 8b which represent the shape of the moulding or die-casting to be produced.A shroud ring 9A surrounds the top bolster plate 3A and is held captive by the top backing plate 1 A, the shroud ring SA carrying a plurality of compression springs 1 Oa at regularly spaced intervals around its centre. The small projection 9a and the threaded connection points 15 are again provided together with the small projecting lip 3a of the top bolster plate 3A and the groove 12 which houses the toroidal "0" ring 12a.

A second shroud ring 13 surrounds the bottom bolster plate 4A and is held captive by the bottom backing plate 2A. The second shroud ring 13 carries several compression springs 1 Ob which are spaced at regular intervals around the centre of that ring. There is a small inward projection 1 3a on the inner surface of the second shroud ring 13 and the machined groove 11 is again provided on the upper surface of the latter, the groove 1 1 again housing the toroidal "0" ring 1 1 a. The bottom bolster plate 4A has a small projecting lip 4a machined on its outer periphery and also a machined groove 14 which houses a heat resisting and sealing toroidal "0" ring 1 4a.

Figure 4 shows the shrouded mould of Figure 3 in a partially closed position in which the small projection 9a of the shroud ring 9A is in contact with the upper surface of the lip 3a on the top bolster plate 3A. The springs 1 Oa are then extended and the mould inserts 5A and 6A have a space between their opposed faces. The small inward projection 1 3a of the second shroud ring 13 is in contact with the lower surface of the lip 4a on the bottom bolster plate 4A. The springs 10b are also extended and vacuum may be applied via the connection points 15 and may be maintained as the two half moulds are closed together thereby taking up the position shown in Figure 3 in which position the vacuum may continue to be maintained or can be discontinued, as may be desired. With this construction, the hermetically sealed stroke of the mould is increased as compared with the embodiment of Figures 1 and 2.

The purpose of the shrouding which includes the heat resisting toroidal "0" rings 1 a and 1 2a in Figures 1 and 2, and 1 1 a, 1 2a and 1 4a in Figures 3 and 4, is to pressure seal the respective surfaces with which they are in contact so that vacuum may be applied to the hermetically sealed region and be maintained as hereinbefore described thus ensuring that a minimum of air or othe gas remains within that shrouded region so that such air or other gas shall not cause misshapen mouldings or die-castings to be produced.

Claims (12)

1 . A mould or die of one of the types set forth, wherein the mould or die comprises shrouds arranged to co-operate with mould halves, bolsters and/or inserts in such a way that at least one substantially hermetically sealed region is formed around at least one moulding cavity or impression which is defined thereby during and/or after the final closure of the mould or die in the use thereof, the or each of said regions being provided with means for the connection thereto of a source of vacuum so that said source of vacuum will evacuate from the or each moulding cavity or impression substantially all of the air or other gas that was present therein before the commencement and/or completion of such final closure.

2. A mould or die as claimed in claim 1, wherein said shrouding comprises at least one shroud ring which surrounds at least one of said mould halves, bolsters and/or inserts, a hermetic seal being provided between that shroud ring and said mould half, bolster and/or insert and a further hermetic seal being provided for co-operation with the companion mould half, bolster and/or insert during and after the final closure of the mould or die.

3. A mould or die as claimed in claim 1, wherein one mould half, bolster and/or insert is provided with a surrounding shroud ring and the companion mould half, bolster and/or insert is provided with a surrounding second shroud ring, and wherein continuously effective hermetic seals are provided between the first and second shroud rings and the respective mould halves, bolsters and/or inserts and an intermittently effective hermetic seal is provided between opposed faces of the first and second shroud rings, the latter intermittently effective hermetic seal being inoperative at least when the or each moulding cavity or impression is fully open.

4. A mould or die as claimed in claim 2 or3, wherein the or each shroud ring is provided with means which resiliently urges that shroud ring from the mould half, bolster and/or insert which it surrounds towards the companion mould half, bolster and/or insert, a stop being provided to prevent the or each shroud ring from being resiliently urged towards the companion mould half, bolster and/or insert beyond a limit position.

5. A mould or die as claimed in claim 4, wherein the means by which the or each shroud ring is resiliently urged towards the companion mould half, bolster and/or insert comprises a plurality of compression springs.

6. A mould or die as claimed in claim 5, wherein the compression springs which correspond to the or each shroud ring are spaced apart from one another at regular intervals around the centre of that shroud ring.

7. A mould or die as claimed in any one of claims 2 to 6, wherein the means for the connection to the or each hermetically sealed region of a source of vacuum comprises at least one connection point formed on the shroud ring or on at least one of the shroud rings.

8. A mould or die as claimed in any one of claims 2 to 7, wherein each hermetic seal comprises a groove machined in a corresponding one of the mould halves, bolsters and/or inserts or in the shroud ring, or one of the shroud rings, each such groove accommodating a sealing ring.

9. A mould or die as claimed in claim 8, wherein each sealing ring is of toroidal "0" formation.

10. A mould or die as claimed in claim 8 or 9, wherein each sealing ring is formed from heatresistant material.

1 1. A mould or die of one of the types set forth, substantially as hereinbefore described with reference to Figures 1 and 2 or with reference to Figures 3 and 4 of the accompanying drawings.

12. A polymeric material moulding or metallic die-casting when produced by a mould or die as claimed in any preceding claims.