Patent GB-643980-A (GB)
Title: Thermo-injecting molding press and process
Inventor: HALL KEITH WILLIS
IPC: B29C45/02
Filed: 1946-08-02
Abstract: 643,980. Injection - moulding machines. BALDWIN LOCOMOTIVE WORKS. Aug. 2, 1946, No. 23050. [Class 87 (ii)] [Also in Group XXIX] An injection moulding press in which thermosetting plastic material is raised to moulding temperature frictionally by forcing it under high pressure through a restricted orifice from a pressure chamber to a transfer chamber from which it is forced into mould cavities comprises a base 1 with a hydraulic cylinder 7 cast integral therewith, supported on sub-bases 2 from which extend rods 3 supporting an intermediate head 4. The rods 3 also act as guides for shoes 12 of a platen 11 which is raised by a hollow piston 8 working in the cylinder 7 and lowered by a pair of pistons 17 working in cylinders 16 at the sides of the press. The lowest position of the platen 11 is determined by adjustable stop-rods 13. The lower mouldplate 24 included in the press carries a number of inserts 91 determining the lower part of the shape of individual moulds and is supported on a steam plate 25 itself supported on a grid 26 above and secured to the platen 11. An ejector grid 27 carrying ejector pins 29 is held stationary to eject the moulded articles as the platen 11 and mould half 24 move down by means of stoprods 32 engaging the base 1. Springs 31 retract the grid 27 and pins 29 when the platen 11 is raised. A piston 34 carrying a ram 37 works in the hollow piston 8, the upper end of the ram 37 working in a pot 39 secured in the lower mould plate 24. The intermediate head 4 is clamped on the rod 3 between nuts 71 and split collars 72 engaging recesses 74 in rods 3 and 73 in head 4. A number of recesses 74 are provided in each rod 3 to permit adjustment of the height of the head 4. Depending from the head 4 is a steam plate 54 which carries the upper mould plate 53 with mould cavities 87. An annular ram 86 surrounding a circular core 77 fixed relative to the mould plate 53 may be lowered by a movable cylinder 57 working round a fixed piston 56 and retracted by pull-back cylinders and pistons 65, 66. The piston 56 is secured to the fixed head 6 of the press, the cylinders 65 to the intermediate head 4 and the pistons 66 to the cylinder 57. The core 77 is supported from a block 78 passing through a diametral slot in the ram 86. A moulding cycle starts by filling the pot 39 with moulding material. Fluid is then injected through a port 33 in cylinder 7 to raise piston 8 and platen 11 and force the two mould plates 24, 53 together, pressure being maintained above piston 34 through a port 41 to prevent operation of the ram 37 until the moulds are closed. In this position (Fig. 10) a chamfered surface 98 on the upper end of pot 39 co-operates with the lower bevelled surface 99 of the core 77 to create a thin annular orifice. Fluid is then injected under high pressure through port 33 to raise piston 34 and ram 37 to force the material in the pot 39 through the thin annular orifice into the annular chamber 75 around the core 77. The work thus done on the material heats it, the conditions being so chosen that the required moulding temperature is reached. Fluid is then injected into the upper cylinder 57 to force the heated material into the mould cavities from the chamber 75 through channels 88 to the mould cavities. Alternatively this can take place simultaneously with the passage of the material through the heating orifice after some has been collected in the chamber 75. Again, the ram 86 may initially be in its lowest position and be forced upwards as material is injected into the chamber 75, this tending to maintain the pressure drop across the orifice constant. After moulding the ram 37 is retracted by injecting fluid through port 41 above the piston 34. On lowering the platen 11 the articles are ejected by the plungers 29. Ejectors may also be fitted to the top mould plate. The speed with which material is forced through the heating orifice may vary during the stroke of the ram 37, e.g. to heat the last part of the moulding charge more than the first. All passages through which the moulding material passes are accessible on opening the press. Specifications 551,468, 605,150, U.S.A. Specification 1,997,074 and German Specification 687,432 are referred to.