Patent GB-673054-A (GB)
Title: Improved method and apparatus for injection moulding, pressure casting or transfer moulding
IPC: B29C45/00
Filed: 1950-01-02
Abstract: 673,054. Casting - machines. LESTER ENGINEERING CO. Jan. 2, 1950 [July 16, 19491, No. 27095/49. Class 83 (i). [Also in Groups V and XXIX] The pressure exerted on the metal to force it into a two-part mould is so high that if it were maintained subsequent to the filling of the mould, minute separation of the two parts of the mould would occur: but at a time when the mould has been filled but before such minute separation has occurred the pressure on the metal is reduced to a value insufficient to cause such separation. A test run may be made to ascertain when the pressure should be reduced. Figs. 1 and 4 show a machine in which the injection piston 9 is hydraulically operated by pressure lines 27, 28, reversing valve 23, pressure line 21 and pump 18. The pressure line 27 which advances the injection piston is connected by line 32 to relief valve 31, which communicates by line 80 with reservoir 17 and by line 33 with solenoid-operated valve 34. Valve 34 communicates with pilot relief valve 36 by way of line 81. Solenoid 35 in valve 34 is energized by operation of a timing device 37. Operation. Valve 22 is operated (manually or in timed sequence by solenoids, cams, &c.), to close the mould parts 15, 16, and valve 23 is similarly operated to advance injection piston 9. During the advance of the piston the valves 31, 34, 36 are in the positions shown, in which the injecting pressure in line 27 extends also through line 32, through valve 31 by way of narrow conduit B and wider conduit C, and through line 33 to valve 34, where it is halted. A spring E urges piston A in valve 31 to the left to shut off the relief line 80. The solenoid 35 in valve 34 is de-energized, and passage 83 in solenoid valve D is connected to the reservoir through line 82a. The timer 37 is set in operation by initiation of the injection stroke, and after a predetermined time a switch therein is closed to energize solenoid 35. Solenoid valve D is thus moved to the left, and passage 84 therein connects lines 33 and 81, whereby the pilot valve 36 is unseated and pressure in lines 81 and 33 and in chamber G in valve 31 escapes to the reservoir through line 82. The high pressure in line 32 thereupon moves piston A in valve 31 to the right and pressure escapes through line 80, whereby the pressure in the mould is reduced. This reduced pressure is maintained whilst the metal in the mould cools and solidifies, whereupon valves 23, 22 reverse, piston 9 retracts, and timer 37 and solenoid 35 are de-energized. A check valve 30 retains pressure in line 24 to keep the mould closed. The passage C may be connected to a valve that opens at, say, 1000 pounds per square inch, to preclude strain, the valve 36 being set to open at, say, 200-300 pounds per square inch. Fig. 3 shows a modification in which a high-pressure pump 49 fills the mould and a low-pressure pump 50 maintains reduced pressure whilst the metal cools and solidifies, the pumps delivering through a solenoid-operated valve 47 controlled by a timer 37. The pressure-reducing devices described in Specification 673,120, [Group V], may be used. Specification 631,641 also is referred to.