GB1153438A - Improvements in or relating to the Injection of Disaerated Plastic Materials - Google Patents

Abstract

1,153,438. Injection moulding machines. P. PONCET. 18 Aug., 1966, No. 36942/66. Heading B5A. Plastics material is de-aerated prior to injection by continuous cycling between an injection cylinder 37, a valve 27 and a heated vacuum chamber 18 which includes a perforated plate 17 for forming fine filaments of the material. With the valve 27 in the position shown, plasticized material is fed by a screw 23 from the chamber 18 to a chamber 39 of the cylinder 37, thereby forcing a piston 38 to the right. At the right-most position of piston 38 the valve 27 is moved to connect chamber 18 through pipes 26, 36 with a chamber 40 of the cylinder 37 which in turn forces piston 38 leftwardly and expels plasticized material through pipes 35, 32 and 34 into the entry part 15 of the chamber 18. The material is successively recycled in this way until it is substantially gas-free with the piston 38 in its right-most position. Valve 27 is then moved to close pipe 35, screw 23 is stopped, and the material is injected into a mould 45 by action of an hydraulic ram 43 on the piston 38. The material is preplasticized by a screw 10 and fed thereto from a hopper 1 under a partial vacuum of about 1 mm. Hg. The vacuum obtained by a pump 20 in the chamber 18 is about 10<SP>-4</SP> mm. Hg. and the screws are driven by electric motors 7, 11, 24 respectively. The injection nozzle (Fig. 4, not shown) includes a head (61) screwed to a body (62) the outlet (61a) being normally closed by an axial plunger (63) urged thereinto by a spring (65) acting on a washer (64) attached to an inner end of the plunger. During injection the pressure of the plastics material overcomes the spring pressure and retracts the plunger from the nozzle.