GB1577034A - Injection moulds - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO INJECTION MOULDS (71) I, THE SECRETARY OF STATE FOR INDUSTRY, London do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to injection moulds.

A conventional injection mould comprises two relatively movable parts which can be brought together to define between them a cavity of desired shape into which heated polymeric material is injected and which, when the material has cooled, are separated to permit the removal of the article formed in said cavity.

In the usual arrangement one of the mould parts remains in a fixed position throughout the moulding process, the other mould part being reciprocable relative to it. One of the mould parts - usually the fixed part -comprises a duct through which the material is injected into the mould cavity directly and/or indirectly via a duct in the other mould part, and one or both of the mould parts comprise ducts for the flow of a fluid, typically water or oil, for cooling the material in the mould.

The manner in which the material cools is of importance if the structure of the moulded article is to be controlled and if the generation of undesirable internal stresses and/or warping of the moulded article is to be avoided, and the need for a well defined and repeatable mode of cooling is particularly great in the injection moulding of small precision pieces such as, for example, gearwheels or electrical components. Common practice today is to provide the mould parts with fixed mould cavity-defining surfaces and a fixed arrangement of cooling fluid ducts, the aim being to provide optimum cooling for the particular form of mould cavity which the mould parts define. This practice can be wasteful, however, in that different, complete moulds usually need to be made up for each form of article which it is desired to produce. In order to achieve economy in the usage of mould components and to permit some variation in the form of the mould cavity in a particular mould, mould parts have been proposed which comprise a so-called bolster having a fixed arrangement of ducts for the flow of a cooling fluid, and an impression unit demountably attached to the bolster, the form of the mould cavity being variable by replacing the impression unit with other such units of different form. With this arrangement, however, in which cooling is effected by the flow of fluid through the bolster only, it is impossible to provide optimum cooling for all the different forms of impression unit usable with the same bolster.

The present invention seeks to provide an injection mould in which both the form of the mould cavity and the arrangement of cooling fluid ducts can be varied without the necessity of constructing completely new mould parts, and accordingly the invention resides in an injection mould in which one or each mould part comprises a bolster and an impression unit demountably attached thereto, the impression unit comprising a pair of plates having profiled faces arranged in abutment with one another and defining therebetween one or more ducts for the flow of coolant, and the face of one plate remote from its said profiled face defining a part of the boundary of the mould cavity.

The bolster itself may or may not be provided with cooling fluid ducts.

The invention makes possible designs in which there is provision for varying the form of the mould cavity-defining surface(s) and/or the arrangement of the cooling fluid ducts. The impression unit can be desinged to include an assembly capable of disassembly and reassembly with differently configured components to thereby achieve such variation.

The invention will now be more particularly described, by way of example, with reference to the drawing filed with the provisional specification, in which: Figure 1 indicates schematically an embodiment of an injection mould in accordance with the invention; Figure 2 is a longitudinal section through the impression units of Figure 1; and Figure 3 is a section on the lins III-III of Figure 2.

Referring to Figure 1, the illustrated injection mould comprises a fixed mould part 1 and a movable mould part 2 reciprocable relative to the fixed mould part in the sense of arrow 'A'. Figure 1 shows the mould parts in the 'open' condition which permits removal of the moulded article from the mould, in Figure 2 the mould parts being 'closed' and ready for the injection of polymeric material into the mould cavity 9.

The mould parts comprise respective bolsters 3 and 4 which may be provided with cooling fluid ducts as indicated schematically at 3A and 4A, and respective impression units 5 and 6 demountably attached by bolts, screws or otherwise to the appropriate bolster. The fixed mould part is provided with a duct 7 through which the polymeric material is supplied from the cylinder 8 to the mould cavity.

Details of the construction of the impression units 5 and 6 are shown in Figures 2 and 3. As illustrated, the units are configured to define between them a mould cavity 9 for the production of test pieces in the form of circular discs, to this end unit 6 providing a circular recess 9A for cooperation with a flat face 9B on unit 5.The unit 6 comprises two circular cross-section plates 10 and 11 having profiled faces disposed in abutment upon the axis 'X' of relative movement between the mould parts and secured together by screws 12. The assembly of plates 10 and 11 together with a packing plate 13 and a spacing ring 27 is secured by screws 14 to an outer block 15. The flat end face 10A of plate 10 defines the base of recess 9A, the peripheral boundary of the recess being defined by a gate ring 16 demountably secured to block 15. Gate pads 16A and 16B are provided for edge injection if desired. A spring loaded ejector pin 17 is borne centrally by plate 10.

The profiled end face 10B of plate 10 and the profiled end face 11A of plate 11 define between them a series of ducts for the flow of cooling fluid through the impression unit, the ducts communicating with ducts 18, 19 and 20 bored in plate 10 as shown in Figure 3.

Plate 10 is provided with a continuous annular recess 10C and plate 11 is provided with a circumferential spine 11B having a gap therein through which coolant can flow from one side of the spine to the other. A radial fence 11C within the gap extends across the recess 10C so that there are defined two outer circumferential ducts 21A and 21B, two inner circumferential ducts 22A and 22B communicating with respective outer ducts 21A and 21B adjacent to fence 11C, and a radial duct 23. With this arrangement a number of different cooling fluid flows are possible. Thus, with duct 19 blanked off cooling fluid can be supplied to duct 18 to flow through ducts 21A, 22A, 22B and 21B and exit via duct 20 (or vice versa); or cooling fluid can be supplied to duct 19 to flow through duct 23, bifurcate, and flow through ducts 22A and 21A to exit via duct 18 and through ducts 22B and 21B to exit via duct 20; or cooling fluid can be supplied to ducts 18 and 20 to flow through ducts 21A and 22A and through ducts 21B and 22B, unite, and flow through duct 23 to exit via duct 19.

The impression unit 5 comprises two circular cross-section plates 24 and 25 having profiled faces and disposed in abutment upon the axis 'X' being so configured as to collectively define, in a similar manner to plates 10 and 11 of unit 6, a series of cooling fluid ducts 26. In this embodiment, the arrangement of ducts 26 is a mirror image of the ducts in impression unit 6, equivalent cooling of each side of the mould cavity 9 being effected by the flow of fluid through the impression units 5 and 6 (together with any cooling flows through the bolsters 3 and 4).

Changes in the thickness of the discs produced in the mould cavity 9 can be effected by replacing the packing plate 13 and the spacing ring 27 in unit 6 with other such rings of different thicknesses. Other changes in the form'of article produced by the mould can be effected by replacing one or more of elements 10, 16, 16A, 16B and 24 with other such elements having mould cavity-defining surfaces of different forms. Changes in the arrangement of cooling fluid ducts in the impression units to enable optimum cooling to be maintained with different forms of mould cavity can also be effected by suitably configured replacement plates 10 and 24, and /or by replacing plates 11 and 25. It will also be appreciated that the form of construction exemplified above permits changes in the arrangement of cooling fluid ducts in the impression units to be made without changing the form of the mould cavity, this being of use in the experiment determination of the best mode of cooling for a particular form of mould cavity. As in the arrangement of ducts exemplified in Figure 3, in any particular duct arrangement there may be a number of different cooling flow options.

Although in the embodiment of the invention described above the mould comprises but one pair of impression units 5 and 6, it is equally within the scope of the invention for the mould parts to comprise a plurality of pairs of demountable, fluid-cooled impression units sharing common bolsters, and fed with polymeric material from a common cylinder, thereby enabling a plurality of articles of the same or different forms to be moulded simultaneously by one machine.

The invention is applicable also to injection moulds in which one of the mould parts comprises a fixed bolster plate and a movable middle plate to form with the other mould part a so-called three plate mould.

WHAT I CLAIM IS: 1. An injection mould including a mould part comprising a bolster and an impression unit demountably attached thereto, the impression unit comprising a pair of plates having profiled faces arranged in abutment with one another and defining therebetween one or more ducts for the flow of coolant, and the face of one plate remote from its said profiled face defining a part of the boundary of the mould cavity.

2. An injection mould according to claim 1 wherein the profiled face of one of the plates is formed with an annular recess therein and the profiled face of the other plate is formed with an upstanding spine extending circumferentially within the annular recess and abutting the base thereof to define, with the walls of the recess, ducts for the flow of coolant, the spine having a gap through which coolant can flow from one side of the spine to the other, a fence being located within the gap but spaced from the spine, the fence barring direct flow of coolant in the circumferential direction of the recess, the spine also having a protuberance in seal ing contact with a wall of the recess at a location remote from the gap, and ducts through one or both of the plates communicating with the recess, one duct on either side of the protuberance.

3. An injection mould according to claim 2 wherein a further duct is provided through one or both plates to communicate with the recess on the side of the spine remote from the protuberance.

4. An injection mould substantially as hereinbefore described with reference to Figures 1 to 3 of the drawings filed with the provisional specification

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. the mould parts to comprise a plurality of pairs of demountable, fluid-cooled impression units sharing common bolsters, and fed with polymeric material from a common cylinder, thereby enabling a plurality of articles of the same or different forms to be moulded simultaneously by one machine. The invention is applicable also to injection moulds in which one of the mould parts comprises a fixed bolster plate and a movable middle plate to form with the other mould part a so-called three plate mould. WHAT I CLAIM IS:

1. An injection mould including a mould part comprising a bolster and an impression unit demountably attached thereto, the impression unit comprising a pair of plates having profiled faces arranged in abutment with one another and defining therebetween one or more ducts for the flow of coolant, and the face of one plate remote from its said profiled face defining a part of the boundary of the mould cavity.

2. An injection mould according to claim 1 wherein the profiled face of one of the plates is formed with an annular recess therein and the profiled face of the other plate is formed with an upstanding spine extending circumferentially within the annular recess and abutting the base thereof to define, with the walls of the recess, ducts for the flow of coolant, the spine having a gap through which coolant can flow from one side of the spine to the other, a fence being located within the gap but spaced from the spine, the fence barring direct flow of coolant in the circumferential direction of the recess, the spine also having a protuberance in seal ing contact with a wall of the recess at a location remote from the gap, and ducts through one or both of the plates communicating with the recess, one duct on either side of the protuberance.

3. An injection mould according to claim 2 wherein a further duct is provided through one or both plates to communicate with the recess on the side of the spine remote from the protuberance.

4. An injection mould substantially as hereinbefore described with reference to Figures 1 to 3 of the drawings filed with the provisional specification