WO1992007706A1

WO1992007706A1 - A device in injection moulding machines

Info

Publication number: WO1992007706A1
Application number: PCT/SE1991/000744
Authority: WO
Inventors: Carl Gustaf LANGENSKIÖLD; Stefan Olin
Original assignee: Disc & Cassette Manufacturers
Priority date: 1990-11-05
Filing date: 1991-11-05
Publication date: 1992-05-14
Also published as: SE469686B; SE9003519L; SE9003519D0

Abstract

The invention relates to a device in injection moulding machines, particularly for the manufacture of articles (6) of plastic with high accuracy and at high speed, such as compact discs, comprising a mould with two mutually reciprocable mould halves with a cavity therebetween and a gripping means (5) which is adpated to be introduced into the space between the mould halves for removing finished articles (6) therefrom. For providing a further reduction of the time for each injection operation the invention suggests that the gripping means is made disc-like with at least one through-hole (7) with a circumferential contour (8) corresponding to that of the article (6) to be produced and adapted to constitute in introduced position between the mould halves a third mould part forming the outer limitation of the cavity and by which the article produced is retained after moulding for being removed from the moulding zone.

Description

A device in injection moulding machines

The invention relates to a device in injection moul¬ ding machines, particularly for the manufacture of articles of plastic with high accuracy and at high speed, such as compact discs, comprising a mould with two mutually recipro¬ cable mould halves with a cavity therebetween and a gripping means which is adapted to be introduced into the space bet¬ ween the mould halves for removal of finished articles therefrom.

In injection moulding of articles of plastic and parti¬ cularly in the form of compact discs an injection moulding machine of the above-mentioned type is frequently used. The halves of the mould have a matrix side and a mirror side, respectively, facing each other. The minor side, in which an inlet passage for plastic is formed in the centre, is provided with a recess with the same shape as the article or the disc to be produced, the recess forming the cavity.

A gripping means is adapted to be introduced between the halves of the mould for withdrawal of the finished disc. The gripping means is usually provided with suction cups, which are placed against the disc at the centre there¬ of, whereupon vacuum is applied to the cups and the disc is gripped. Thereafter, the gripping means have to be moved a short distance axially away from the cavity and then away from the mould radially in the plane of the disc.

The time for forming of each disc, the so-called "cycle time" is in known devices at least 6, 5 and usually 7-8 seconds. The drawbacks of the above-mentioned gripping means are the bulkiness and great mass thereof and hence its great inertia. Due to this and since the gripping means grips the disc at its centre, the halves of the mould have to be moved apart relatively far in order to make space for the gripping means. Moreover, the suction cups of the grip¬ ping means are to be applied to the only available area, namely at the centre of the disc, which is very restricted, in order not to affect above all the readability of a com- pact disc. The gripping means also have to have time to recognize that it really has gripped the disc, and the grip¬ ping force further has to be very accurately adjusted, since the disc still is somewhat soft at the gripping. To sum up this makes the cycle time unnecessary long.

Therefore, the object of the invention is to provide a device, which grips the articles or discs in a different way and hence allows a reduction of the cycle times, but which also results in the achievement of several other ad- vantages.

This is achieved according to the invention substan¬ tially in that the gripping means is made disc-like with at least one through-hole with a circumferential contour cor¬ responding to that of the article or disc to be produced, said gripping means being adapted in its introduced posi¬ tion between the mould halves to form a third mould part, which when the mould is closed is sealingly confined bet¬ ween the mould halves and forms the outer limitation of the cavity and by which the article or disc produced is retained after the moulding for being removed from the moulding zone.

The greatest advantage of the invention is that the cycle time can be substantially reduced down to about 4,5 seconds due to the fact that the mould halves do not have to be brought apart so far thanks to the slender form of the gripping means and that the gripping means grips the article or disc around its circumferential edge. This also result in several further advantages and possibilities. One such advantage is that the sprue can be knocked off from the article or disc outside the mould, which contributes to the reduction of the cycle time.

A non-limiting example of the invention will now be described with reference to the accompanying drawings, in which Fig. 1, is a plan view of a first embodiment of mould and gripping means according to the invention, one of the mould halves being removed, Fig. 2 is an enlarged and partly sectional side view of the halves of the mould with inter¬ posed gripping means, in which the mould halves are separa¬ ted after a just finished moulding and with the moulded article remaining in the gripping means, Fig 3. is a view similar to that in Fig. 2 but with the mould halves brought together against the gripping means, so that the mould is ready for a new moulding cycle (a so called shot) , Fig. 4 is a plan view of another embodiment of the gripping means according to the invention, said means being arranged in a so called three-pillar-press, and Fig. 5 is a sectional side view of the gripping means taken along the line V-V in Fig. 5. Figs. 1-3 illustrate a first embodiment of a mould 1 with two mutually reciprocable mould halves 2, 3 with a cavity 4 therebetween and a gripping means 5 which is intro- duceable into the space between the mould halves 2, 3 for removal of a finished article 6 form the cavity 4. Accor- ding to the invention, the gripping means 5 is formed disc¬ like (see Figs. 2 and 3) with at least one through-hole 7 with a circumferential contour 8 corresponding to that of the article 6 to be produced. Preferably, the hole 7 is formed in an insert 9 fixed to the gripping means 5 and suitably made of litium.

Althought the gripping means 5 according to the inven¬ tion in principle may be provided with a single through- -hole 7, in Figs. 1-3 has been illustrated an embodiment, in which the gripping means 5 is designed as a rectangular disc provided with two holes 7 made in inserts 9 and inten¬ ded to be inserted alternately between the halves 2, 3 of the mould 1.

Fig. 2 shows how the article or disc 6 just moulded is retained by the walls of the hole 7 in one of the inserts 9 of the gripping means 5. The hole-wall of the insert 9 which defines the circumferential contour 8 of the article is preferably slightly concave, as seen in cross-section, for a firmer retaining of the article 6. The halves 2, 3 of the mould 1 are shown in a retracted position, in which the finished article 6 can be withdrawn from the moulding zone of the mould 1 and in which the other emptied insert 9 with its hole 7 can be brought into the moulding zone for the subsequent moulding cycle. Fig. 3 clearly shows that the gripping means 5, when the mould halves are brought together is sealingly confined therebetween and forms by the wall of the hole 7, a third mould part. One of the mould halves 2 is provided with a matrix 10 and the other mould half 3 is provided with an inlet pas¬ sage 11 for plastic located in the middle of that half, which during moulding is pressed against i.a. the matrix 10. The half 3 of the mould 1 forms a mirror side 12 provi- ded with a circular protrusion 13, which produces a thick¬ ness-reducing depression in the article 6 when moulding. This depression will produce a weakening in the material for faciliating removal of a sprue 14 remaining on the ready-shaped article 6. When producing compact discs the circular protrusion has the same diameter as the centre hole of the disc.

Fig. 4 shows a preferred embodiment of the gripping means 5, which is made as a circular disc. In this embodi¬ ment the gripping means 5 is provided with regularly angu- larly spaced through-holes 7. In this Figure the gripping means 5 is provided with six holes 7. The gripping means 5 is shown placed in a so-called three-pillar-press, the pil¬ lars of which are shown in section. As seen from Fig. 4 it is very advantageous to place a circular gripping means in a three-piliar-press with one of the pillars in the centre of the gripping means.

Fig. 5 shows how the inserts 9 are arranged in the gripping means 5 and how the gripping means is arranged relative the mould 1. The holes 7 of the gripping means are arranged to be introduced step-by-step in order into the moulding zone of the mould 1. In this circular and preferred embodiment of the gripping means 5 the finished articles 6 are dischar¬ ged from the mould 1 step-by-step. Since the articles 6 after the moulding are retained with their circumferential edge in the holes 7 of the in¬ serts 9, they can be withdrawn from the cavity 4 after a shorter cooling time than according to prior art. Moreover, the articles 6 are allowed to cool further before their removal, since they can remain in the inserts 9 during the major part of the rotary movement of the gripping means, and the knocking off of the sprue 14 can be done when the article is cooler and less sensitive to damages. Possible further machining can be done while the article 7 remains in the gripping means 1. The articles 6 are removed from the inserts 9 in a manner known per se.

Claims

C l a i s

1. A device in injection moulding machines, particularly for the manufacture of articles (6) of plastic with high accuracy and at high speed, such as compact discs, compri¬ sing a mould (1) with two mutually reciprocable mould hal¬ ves (2, 3) with a cavity (4) therebetween and a gripping means (5) which is adapted to be introduced into the space between the mould halves for removing finished articles (6) from the cavity, c h a r a c t e r i z e d i n that the gripping means (5) is made disc-like with at least one through-hole (7) with a circumferential contour (8) cor¬ responding to that of the article (6) to be produced, said gripping means being adapted in its introduced position between the mould halves (2, 3) to form a third mould part, which when the mould is closed, is sealingly confined bet¬ ween the mould halves (2, 3) and forms the outer limitation of the cavity and by which the article produced is retained after the moulding for being removed from the moulding zone.

2. A device according to claim 1, c h a r a c t e r i¬ z e d i n that the disc-like gripping means (5) is formed as a rectangular disc, which is provided with two through- -holes (7) adapted to be alternately introduced in the moul¬ ding zone.

3. A device according to claim 1, c h a r a c t e r i¬ z e d i n that the disc-like gripping means (5) is formed as a circular disc provided with a plurality of circumferen- tially equally spaced through-holes (7) and adapted to be turned step-by-step for successively feeding the holes (7) into the moulding zone.