Press for moulding gramophone records or the like

Abstract

A press for moulding plastic materials for the manufacture of gramophone disc records or like flat parts comprises a fixed press platen carrying a first mould element, a movable press platen guided along columns fast with the fixed platen and a movable intermediate platen carrying a second mould element. A mechanical device is provided to urge the movable press platen to the fixed press platen. A fluid pressure is supplied between coacting cylinder and piston provided respectively in the movable platens. The intermediate platen is supported and guided by the movable platen without any contact between this intermediate platen and the columns.

I claim: 
     
       1. Press for moulding gramophone disc records, comprising: a fixed press platen adapted to carry a first mould element; parallel guide columns fast with the fixed press platen; a movable press platen mounted on and movable relatively to said columns, a movable intermediate platen adapted to carry a second mould element, said first and second mould elements having cavities which together form the shape of a gramophone disc record, the movable press and intermediate platens co-operating one within the other as an arrangement of a piston in a cylinder with the intermediate platen supported wholly by the movable press platen; means including a constant-stroke closing mechanism of the toggle type for moving the movable press platen along the guide columns, between an operative position close to the fixed press platen and an inoperative position remote from the fixed press platen; a circuit for the admission of fluid under pressure between the movable press and intermediate platens to effect relative movement of the piston of said piston and cylinder arrangement out of its cylinder, and a feed system for plastics material in the fluid state capable of introducing under pressure a metered charge of this plastics material between the two mould elements when the movable press platen occupies its operative position and when the said circuit delivers fluid under pressure as aforesaid between the movable press and intermediate platens, said means for moving the movable press platen and the circuit for the admission of fluid under pressure being operable, after the movable platen has been moved toward the fixed platen by the constant stroke mechanism, to act upon the intermediate platen, on each operation of introduction of plastics material under pressure, in two successive stages, the first of which consists in driving the intermediate platen towards the fixed platen with a resilient force calibrated to a value lower than the opposing force which is produced by the introduction of the plastics material into the mould and which tends to separate the mould elements of the fixed and intermediate platens, and the second of which is a stage of compression with a force sufficient to move the two mould elements one against the other after introduction of the charge of plastics material. 
     
     
       2. Moulding press according to claim 1, wherein the movable press platen comprises the cylinder and the intermediate platen comprises the piston of the piston and cylinder arrangement, the circuit for the admission of fluid under pressure terminating in the movable press platen. 
     
     
       3. Moulding press according to claim 1, wherein a resilient device is interposed between the movable press platen and the intermediate platen to create the aforesaid resilient force by yielding after the intermediate platen, which is carried along at first by the movable press platen in its movement from its inoperative position to its operative position, has stopped by mutual contact of the mould elements of the intermediate and fixed platens, the circuit for the admission of fluid under pressure then operating to exert on the intermediate platen the compressive force corresponding to the aforesaid second stage. 
     
     
       4. Moulding press according to claim 3, wherein the resilient device interposed between the movable press platen and the intermediate platen is formed by at least one pneumatic jack.