GB1336066A - Injection moulding machine - Google Patents

Abstract

1336066 Injection moulding machine KRAUSS-MAFFEI AG 19 April 1971 [24 April 1970] 9873/71 Heading B5A In an injection moulding machine having an injection ram 1 operated by a piston 3, the piston is subjected on the injection pressure side 3b to pressure from a compressed gas supplied from a reservoir 5 and on the return pressure side 3a to an hydraulic pressure medium (oil) supplied by a pump 8; the return stroke of the piston 3 after an injection process serves to build up the gas pressure in the reservoir 5, and the pressures on both sides of the piston are compared and regulated to give a constant pressure head during the return stroke by a differential pressure meter 12, the oil pressure being additionally controlled by a pressure regulating valve 15. The pressure meter 12 has a chamber 20 in communication with gas reservoir 5, and a chamber having parts 21a, 21b in communication, via the pressure regulating valve 15, with the oil supply, the chambers 20, 21a, 21b being interconnected by a bore through which passes a piston 23. An adjustable spring 24 serves to bias the piston 23 in the same direction as does the oil pressure i.e. in opposition to the gas pressure, the gas pressure tending to close a valve defined by a conical portion 23c on the piston and the wall of chamber 21a, and the oil pressure tending to open this valve. In operation, when the piston 3 is in its extreme left hand position i.e. after an injection stroke, oil is pumped into chamber 2a to effect the return movement of the piston 3, the oil also passing into chamber 21b through valve 15 and tending to lift off the conical portion 23c of the piston 23 to allow oil to flow into chamber 21a against the gas pressure and into a container 27 through conduit 26, thus decreasing the oil pressure. As the piston 4 moves to the right the gas pressure increases and "throttles" the oil flow through the meter 12, thus balancing the pressures on either side of the piston 4 and ensuring that the piston is returned at a suitable rate.