Injection compression moulding

Abstract

A mould for injection compression moulding of an article includes a female mould part and a core for mounting in use on the platens of an injection moulding machine for movement towards and away from one another between an open and a closed position. A sealing ring surrounds the core for effecting a seal between the female mould part and the core. The core, the female mould part, and the sealing ring together define a closed mould cavity as the core approaches the closed position. The sealing ring has tapering sections, each tapering section having a tapering surface that seals against a tapering surface on the core only after the core has reached the closed position, leaving a venting clearance between the tapering surfaces of tapering sections of the sealing ring and the tapering surface of the core as the core approaches the closed position.

1 . A mould for injection compression moulding of an article, the mould comprising: 
 a female mould part;    a core, the core and the female mould part being movable relative to one another between an open and a fully closed position; and    a sealing ring surrounding the core for effecting a seal between the female mould part and the core, wherein the core, the female mould part, and the sealing ring together define a cavity when the core is in the fully closed position, such that the sealing ring makes sealing contact with the female mould part prior to the core reaching the fully closed position and such that the sealing ring has a tapering section that seals against a tapering surface on the core only after the core has reached the fully closed position, the mould including a venting clearance between the tapering section of the sealing ring and the core as the core is advanced towards the fully closed position to compress plastics material injected into the mould cavity.    
   
   
       2 . The mould of  claim 1 , wherein the tapering section of the sealing ring has an angle of taper measured relative to a direction of movement of the core of less than 5°.  
   
   
       3 . The mould of  claim 2 , wherein the angle of taper is substantially 1°.  
   
   
       4 . The mould of  claim 1 , including a venting gap to vent gas from the mould cavity, the venting gap located between the tapering section of the sealing ring and the core.  
   
   
       5 . The mould of  claim 4 , wherein the mould includes only a single venting gap.  
   
   
       6 . The mould of  claim 4 , wherein the sealing ring is mounted on the core so as to be capable of a limited movement relative to the core, the sealing ring being urged by at least one of a spring and gas pressure in a direction to increase a size of the venting gap.  
   
   
       7 . The mould of  claim 1 , wherein at least one of the core and the female mould part is adjustably mountable on a platen of an injection moulding machine to permit the core and the female mould part to be axially aligned with one another, wherein a plurality of guide fingers is provided on one of the mould parts and distributed about an axis of the core to be received in recesses of complementary shape in the other mould part as the mould parts approach the fully closed position, each finger having two parallel-sided locating sections that are spaced from one another along a length of the finger, the locating section nearer a free end of the finger being narrower than the other and a length of each locating section being at least equal to a final part of a stroke of platens during which compression of injected plastics material takes place.  
   
   
       8 . The mould of  claim 7 , wherein a part of each guide finger lying between the two parallel-sided locating sections is continuously tapering.  
   
   
       9 . The mould of  claim 7 , wherein each guide finger is flat and is secured to the core and the recesses are formed in a plurality of flat inserts releasably secured to the female mould part.  
   
   
       10 . An injection compression moulding machine, comprising: 
 a mould, the mould including,    a female mould part,    a core, the core and the female mould part being movable relative to one another between an open and a fully closed position, and    a sealing ring surrounding the core for effecting a seal between the female mould part and the core, wherein the core, the female mould part, and the sealing ring together define a cavity when the core is in the fully closed position, such that the sealing ring makes sealing contact with the female mould part prior to the core reaching the fully closed position and such that the sealing ring has a tapering section that seals against a tapering surface on the core only after the core has reached the fully closed position, the mould including a venting clearance between the tapering section of the sealing ring and the core as the core is advanced towards the fully closed position to compress plastics material injected into the mould cavity.    
   
   
       11 . The injection compression moulding machine of  claim 10 , wherein the tapering section of the sealing ring has an angle of taper measured relative to a direction of movement of the core of less than 5°.  
   
   
       12 . The injection compression moulding machine of  claim 11 , wherein the angle of taper is substantially 1°.  
   
   
       13 . The injection compression moulding machine of  claim 10 , including a venting gap to vent gas from the mould cavity, the venting gap located between the tapering section of the sealing ring and the core.  
   
   
       14 . The injection compression moulding machine of  claim 13 , wherein the mould includes only a single venting gap.  
   
   
       15 . The injection compression moulding machine of  claim 13 , wherein the sealing ring is mounted on the core so as to be capable of a limited movement relative to the core, the sealing ring being urged by at least one of a spring and gas pressure in a direction to increase a size of the venting gap.  
   
   
       16 . The injection compression moulding machine of  claim 10 , wherein at least one of the core and the female mould part is adjustably mountable on a platen of an injection moulding machine to permit the core and the female mould part to be axially aligned with one another, wherein a plurality of guide fingers is provided on one of the mould parts and distributed about an axis of the core to be received in recesses of complementary shape in the other mould part as the mould parts approach the fully closed position, each finger having two parallel-sided locating sections that are spaced from one another along a length of the finger, the locating section nearer a free end of the finger being narrower than the other and a length of each locating section being at least equal to a final part of a stroke of platens during which compression of injected plastics material takes place.  
   
   
       17 . The injection compression moulding machine of  claim 16 , wherein a part of each guide finger lying between the two parallel-sided locating sections is continuously tapering.  
   
   
       18 . The injection compression moulding machine of  claim 16 , wherein each guide finger is flat and is secured to the core and the recesses are formed in a plurality of flat inserts releasably secured to the female mould part.