GB2185709A - Mould for injection moulding - Google Patents

Abstract

A mould for the injection moulding of cans or other objects made from thermoplastic material comprises mould halves (1,2) mutually reciprocally arranged in an injection moulder. The halves form between them at least one mould cavity. The cavity is adapted to receive a blank (3) for attaching to the object formed between the mould halves during each work cycle. One mould half (1) is adapted to keep the blank located in the mould during the work cycle with the aid of vacuum applied through an orifice (5) in said half. The orifice is a gap between a valve body (9) and its seating (10). The body (9) is resiliently biassed by springs 15 to assume an open position, such that on closing the mould, and until molten moulding composition is injected into the cavity, it retains the blank (3) in position, but on injection of the composition it is urged thereby against its seating (10). <IMAGE>

Description

SPECIFICATION Mould for injection moulding The invention relates to a mould disposed for the in- jection moulding of cans orotherobjects madefrom thermoplastic material, and comprises two mutually reciprocally movable mould halves in an injection moulder, between them forming at least one mould cavity, for the production of one of the objects during a working cycle. The cavity is adapted to accommodate a new sheet of material, serving for example as alabel,andhereinaftercalleda"blank",atthebe- ginning of each working cycie, for attaching to the object formed between the mould halves.One mould half is disposed to keep the blank located in the mould during a sequence in each work cycle, using vacuum created via at least one orifice in the mould half, this orifice opening out into the cavity and also being in communication with an vacuum source.

Such a mould is already known, e.g. from the British patent specification 1 456036,which interalia illustrates how a can may be provided with a label during injection moulding. It should be noted here how a label resting against the male half ofthe mould during insertion into the female half can be subjected to considerable asymmetrically acting frictional forces as the mould is closed, and musttherefore be kept centred on the male half by considerable suction forces. This results in that a rather large portion of theblanksurfaceneedsto be exposed to one or more suction orifices. Such an orifice is usually formed as a slit, of which the width must be very small, sothatthe molten moulding composition does not penetrate into the slit and the ducts behind it.This requirement makes it difficult to provide the necessary, large suction area on the blank.

The object of the invention is accordingly to provide a mould where one half affords secure retention of a blankwith the aid of suction, by exposing a con siderable suction orifice area to the blank without the risk of moulding composition penetrating into the orifice or orifices.

The desired result is obtained by the orifice mentioned being implemented as a gap between a valve body and its seating situated in the same mould half, the valve body being adapted such that it resiliently and yieldingly assumes an open position for retain ing the blank in position by vacuum, when the mould is closed and up to the moment where the moulding composition is injected, and that it is closed im mediately by the composition pressing it against its seating, thus releasing the blank and preventing the composition from penetrating into the gap.

One embodiment ofthe invention is described in detail in the following, and with reference to the ac companying drawing, on which a small portion of either mould halfisschematicallyillustratedina position where they have not quite been moved completely together by the injection moulder (un illustrated) in which they are assumed to be moun ted. In one mould half, suitably the male half, there is situated the inventive valve body, and it is partially sectioned in the Figure. In the opposing orfemale half, forming the mould cavity in coaction with the plunger, there is an inletforthe moulding composition. Only a small portion of this half showing the sprue brush is illustrated. The unillustrated parts of the mould may be of essentially conventional implementation.

The mould, which is disposed forthe injection moulding of cans and like objects from thermo- plastic material, comprises two halves 1 and 2, which are mutually, conventionally reciprocal in an injection moulding machine (unillustrated). In a closed condition they form between them at least one mould cavity for producing one ofthe objects in each cavity per work cycle. The mould may thus exhibit one or more mould cavities, each provided with means in accordance with the accompanying drawing. In every work cycle a blank3, is fed to each cavity, the blank being retained by suction against one mould half 1 as the mould is closed. The blank3 is schematically illustrated in the Figure by a line drawn spaced from the mould half 1, againstwhich the blank rests in reality. The line is interrupted to indicate a hole 4 in the blank.Such a blank may be supplied to the cavity or cavities as described in the mentioned British patent specification 1 456036,the Australian patent specification 535895 or the Swedish patent specification 8103608-9 (publication number426 668).

During a sequence of the work cycle, after supplying the blankto the cavity, the blank is retained correctly located on the half 1 by suction via an orifice 5 in the half. The orifice opens out into the cavity and is under vacuum via one or more ducts Sin communication with an unillustrated vacuum source.

The half 1 is normally the male half and the half 2 the female half. In the present case, there is a sprue bush 7 with a gate 8 in the half 2, for allowing the moulding composition to come into the cavity.

The orifice 5 is situated immediately opposite the sprue brush 7 and is formed as an annular gap between a mushroom valve head 9 in the mould half 1 and a valve seating 10 in the same half 1.

The mushroom valve head 9 is adapted for resiliently and yieldingly assuming the illustrated open valve state. More specifically, the shank 11 ofthe valve is axially movable in a complementary bore in the body of the male half. At the end ofthe shank 11 away from the mushroom head the shank has a valve base 12 fastened to it, e.g. by a threaded joint. The base 12 has limited axial movement in a space 13 in a fastening plate 14 associated with the male half 1.

Helical compression springs 15 are arranged between the valve base 12 and the bottom ofthe space 13 and are situated in holes in the valve base. These springs urge the valve base against a stop 16 formed by the body of the male half 1. In the illustrated position against this stop the valve fastening 12 keeps the mushroom head 9 open, with the outermost face of the mushroom head substantially flush with the front surface of the half 7. The combined bias of the springs 15 is selected such that the pressure of the moulding composition against the mushroom head on injection through the gate 8 is so great that it im mediately presses the mushroom head 9 against its seating 10, so that the composition cannot penetrate into the inner parts of the gap 5 and the vacuum ducts 6.On the other hand, the springs keep the valve open before injection, thus maintaining the blank 3 effectively urged against the male half 1 by suction via the orifices, which can be given a large gap and a correspondingly large suction area as a resuit of this inventive arrangement.

In the illustrated embodiment the blank has a hole 4, so that with the aid of the flow of the composition passing through the hole 4, the blank is taken from the male half 1 to the female half 2, that the blank will be on the outside of the moulded object. If it is desirable to have the blankon the inside ofthe object, twill be made withoutthe hole 4. In this case the valve closes just as efficiently as a result ofthe pressure from the moulding composition being transmitted via the blank to the outer surface ofthe valve, so that both damage to the blank and blocking the gap 5 are prevented.

The axial movement of the shank 11 inwardlyto a closed state of the valve is limited by the valve base 12 being stopped by an abutment 17, which is the bottom ofthe space 13. The valve base comes into contactwith the stop 17 only when the composition has pressed the peripheral portion ofthe mushroom head 9 against the seating 10 and has achieved a certain elastic deformation of the mushroom head 9, which is relieved from further stress by the valve base bottoming. Coolant ducts, not illustrated on the drawing, are disposed in the valve shank 11 up to the mushroom head, which thus has its strength reduced. The limitation of the stress on it is therefore necessary.

To afford a larger suction surface in the plane where the blank is sucked against the mould half, the annular gap 5 is considerably enlarged in a region terminating towards the cavity, such as to form an annu lar, wide ditch along the periphery of the mushroom head 9. The coacting surfaces of the mushroom head 9 and seating 10 are conical and complementary, with the outer edge of the seating merging into the ditch.

Claims (6)

1. Mould disposed forthe injection moulding of cans or other objects made from thermoplastic material, comprising mould halves (1, 2) mutually reciprocally arranged in an injection moulder, and which form between them at least one mould cavity for producing an object one per work cycle, the cavity being adapted to receive a film, foil or plane or planar piece of material, hereinafter called a "blank" (3) for attaching to the objectformed between the mould halves during each work cycle, one half being adaptedto keeptheblanklocatedinthemoulddur- ing a sequence of the work cycle with the aid of vacuum obtained via at least one orifice (5) in said half, said orifice opening out into the mould cavity and being in communication with a source of vacuum, characterized in that the orifice is a gap between a valve body (9) and its seating (10), both situated in one ofthe halves (1 ),the body (9) being adapted resiliently yealdinglyto assume an open valve position, such that on closing the mou Id, and until molten moulding composition is injected into the cavity, it retains the blank(3) in position, but on injection ofthe composition it is immediately urged against its seating (10) by the compositions, the blank (3) thus being released, as well as the composition being prevented from penetrating intothegap.

2. Mould as claimed in claim 1, characterized in that the valve body (9) is formed as a mushroom valve with a shank (11), and in that the gap is annular and is formed between the mushroom head (9) and its seating (10).

3. Mould as claimed in claim 2, characterized in thatthe mushroom head (9) is situated immediately opposite and facing towards a gate (8) situated in the opposing mou Id half (2), for injecting the composition, and such that in the case where the blank (3) has a hole (4) concentric with the gate said mushroom head will be subjected directly to the flow of the in jectedcomposition, or for the case where the blank has no hole, it will be subjected indirectly to the flow of said composition via the intermediary of the blank.

4. Mould as claimed in claim 2 or 3, characterized in that the shank (11) is biassed by at least one spring (15) in the interior of its mould half (1), said spring biassing the mushroom head (9) into its open position, there being stop means (16, 17) arranged for limiting the reciprocal movement ofthe mushroom valve (9, 11) outwards to the open position, and inwards to a closing position also limiting the stress on the mushroom head (9) transferred to itvia its en gagement against its seating (10), and caused by the pressurized molten moulding composition.

5. Mould as claimed in any one of claims 2 - 4, characterized in that the annular gap (S) is made lar- ger, in the region of a portion thereof,terminating towards the cavity to form an annular, wide ditch along the outer periphery of the mushroom head (9).

6. A mould, substantially as herein described with reference to the accompanying drawing.