GB943072A - Die cushion assembly - Google Patents

Abstract

943,072. Compression moulding machines. DANLY MACHINE SPECIALTIES Inc. June 8, 1962 [June 8, 1961], No. 22251/62. Heading B5A. A die cushion assembly consists of a cylinder and a hollow piston telescoped for relative movement and enclosing a space therebetween, the piston containing a reservoir of fluid under pressure which may be communicated to the space between the members by the actuation of a normally closed valve. Such a die cushion may be used in a press having a fixed lower die and a movable upper die. In a press (Fig. 1) knock-out pins 38 are supported on such a resilient cushion by rods 48 and plate 50. The cylinder 52 co-operates externally with the hollow piston 56 and is raised and lowered by fluid under pressure introduced into the space 70 through the valve 88, 84, Fig. 2, or 176, 172, Fig. 3. During the moulding operation the pins 38 are forced down against the pneumatic pressure, by the upper die, so that upon withdrawing the upper die the pins are raised, thus ejecting the moulded article. In the modification, shown in Fig. 2, the cylinder 52 is normally in its inoperative position, i.e. lowered, in which the valve 88, seated on the upper end of rod 90, is pressed against the aperture 84 by spring 104. The cylinder is raised to the operative position by introducing air under pressure into space 106 and into the space between the piston 112, seated on the lower end of the rod 90, and the fixed cylinder 108. As the piston 112 is of greater area than valve 88, the valve is withdrawn from the aperture so that air under pressure enters the space 70. The upper valve may be closed, by the spring 104, by-releasing the pressure in the lower cylinder and the cushion lowered by releasing the pressure in the space 70 by means of valve 162. To raise the cushion again, the valve 162 is closed and air readmitted to the cylinder 108. In a second modification, Fig. 3, the valve 176, which is adapted to form a restrictive passage between itself and the valve seat 172 when withdrawn slightly, is opened by direct pressure of the compressed air in space 106 upon the upper surface of piston 188. To lower the cushion the upper valve is closed, by equalizing the pressures on both sides of the piston 188 by admitting air under pressure into the space below the piston, and the pressure in space 70 is released through valve 212. The cushion is raised again by introducing compressed air at a slightly reduced pressure, through supply line 222, to the space 70 and at the same time opening the valve 176. By controlling the rate at which the pressure is released from the space below piston 188, by throttle valve 206, the rate of withdrawal of the valve 176 may be controlled and thus the pressure within the space 70 may be built up slowly. The upper valve opens fully only when the cushion has reached the operative position which prevents any undue shock caused by ring 72 and shoulder 74 coming into fierce abutment.