GB470814A - Improvements in hydraulically operated injection moulding presses - Google Patents

Abstract

470,814. Hydraulic presses ; valves ; machinery guards. SHAW & SONS (SALFORD), Ltd., J., and SHAW, J. B. Feb. 15, 1936, No. 4629. [Classes 69 (ii) and 135] [Also in Groups V and XXIV] A hydraulically-operated injection moulding press for the manufacture of articles from cellulose acetate and other thermoplastic products, synthetic resins and the like, and of the kind in which two parts of a mould are first closed together and then fed with the moulding paste by means of a heated injector comprises a centrifugal pump and an electric motor to drive the same, a tank from which liquid is supplied to the pump, a byepass being provided to relieve the pump when the press is not working, a press having a small diameter lifting or closing cylinder and a large diameter pressure cylinder, and valve gear between the pump and cylinders for operating the press, such valve gear consisting of an externallyoperated valve under the control of the operator to feed and exhaust the lifting and push-back cylinders, and an automatically operated valve influenced by build-up of pressure in the lifting cylinder to feed the pressure cylinder from the pump, means being provided to feed the pressure cylinder with slack water prior to the opening of such automatic valve. The press comprises, Fig. 1, a large diameter hollow ram e working in a cylinder d; the hollow ram comprises the lifting or closing cylinder, and the annular space the pressure cylinder. Liquid from the supply tank 1c is forced by the centrifugal pump b driven by the electric motor a, through the distributing valve g to the quick-lift cylinder ; slack water enters the pressure cylinder from a supply not shown, through a non-return valve. When the piston has completed its travel, the pressure liquid opens a valve m, Fig. 3, which is normally held closed by a spring m<1>, and pressure liquid passes through passage o and port o<1> into the pressure cylinder to hold the mould parts together. During these operations, the exit of liquid from the pressure cylinder is prevented by a spring-pressed valve p; the pushback cylinders s exhaust through the distributing valve g back to the supply tank c. The valve g is then moved by hand pressure liquid is now supplied to the push-back cylinders s, and also to a piston r which lifts the valve p, so that liquid from the pressure cylinder can now exhaust through the port q and pipe x to the supply tank c; liquid from the quicklift cylinder exhausts through the distributing valve g back to the supply tank c ; the valve m is closed by its spring during this time. The distributing valve comprises, Fig. 4, a sliding piston g provided with slots g<1> constituting longitudinal ports ; it is manually actuated by safety mechanism necessitating the use of both hands of the operator ; two hand levers u are provided, these being pivoted on a bracket u<1> and each pivotally connected to a link v pivoted in the end of the valve g; to be effective, both levers must be operated. To ensure that both hands are used, a metal shield w is provided between the levers, or one lever may be shorter than the other, or the levers may be cranked in opposite directions. A spring returns the valve to the "press open position when one or both hands are removed. A relief pipe y byepasses the pump when the press is inoperative ; a pressure gauge t indicates the pressure in the space o. The invention is stated to be particularly applicable to a press as described in Specification 429,769, [Group V].