Patent GB-976874-A (GB)
Title: Improvements in or relating to the manufacture of pressure cast articles
IPC: B29C45/54
Filed: 1961-02-24
Abstract: 976,874. Injection moulding machines. J. VON STERNBERG. Feb. 24, 1961 [Feb. 26, 1960], No. 6926/61. Heading B5A. [Also in Division B3] In a moulding process e.g. an injection moulding or metal casting process, material to be moulded is pressed into a moulding chamber by an hydraulically actuated piston and an inlet passage leading to the moulding chamber is then sealed with the co-operation of the pressure present in the moulding chamber, whereupon an extremely high pressure is applied to the material, this pressure being developed by the thermal expansion of a medium e.g. mercury or Wood's metal, which is heated in a pressure vessel. In operation synthetic plastics material is fed into a hopper 4 and passes to a screw chamber 5 containing a feed screw 6 rotated by means of gearing 7, 8. The feed screw 6 has an axial bore which contains an annular piston 12 and a piston rod 15 operated independently by hydraulically actuated pistons 14, 17 respectively. The annular piston 12 has a groove 13 so that material may be fed into an injection chamber 10 by the feed screw 6. The chambers 5 and 10 are electrically heated by heaters 9, 11 respectively. The piston 12 is advanced to inject the material into the mould chamber 50 through an injection passage 19. The piston rod 15 is then advanced so that the end 16 thereof enters the passage 19 and a seal 21 fixed to the end 16, having a conical recess seals the passage by virtue of the pressure in the moulding chamber which presses the edges of the seal 21 against the walls of the passage 19. The material in the moulding chamber 50 is now subjected to an extremely high pressure e.g. 300,000 atmospheres, generated by the thermal expansion of a medium heated in chambers 23 connected in parallel to a bore 22 in the apparatus. This heating is effected by a heat exchanger 24 or by induction heating. After cooling of the medium the moulding chamber 50 is opened by movement of the mould half 26 to the right in Fig. 1 and the moulding article e.g. a gearwheel, is ejected by further advance of the piston rod 15. The means used for moving the mould half 26 and for locking it in the closed position is shown in Fig. 8. The mould half 26 is mounted on a block 34 and the moulding chamber is closed by movement of the block to the left in Fig. 8 by an hydraulic cylinder and piston (not shown), whereupon spaced bars 36 are moved clear of the spaces between bars 37 mounted on a plate 38. A cam member 45 is then moved to the left in Fig. 8 to cause the bars 37 to move upwards so that the ends of the bars 36 and 37 engage to hold the moulding chamber closed. Further movement of the cam member 45 causes a wedge 39 to move upwards to lock the bars in this position. All parts of the apparatus which are subjected to the extremely high pressure are pre-treated with this pressure to strengthen them before use. In Fig. 6, a block 30 to form a mould half is pressed against a die by a pressure medium in the passage 19, and is then subjected to the extremely high pressure as before. A seal 33 is provided to prevent leakage of the pressure medium.