GB1074240A - Improvements in or relating to hydraulic cushion for dies - Google Patents

Abstract

1,074,240. Presses. DI-DRO ENGINEERING CO. Dec. 8, 1964 [Jan. 6, 1964], No. 49883/64. Heading B3H. [Also in Division G3] A press 10 having a crank-operated die 18 and a fixed die 22, includes a die pad 24 for cushioning the impact of die 18 without offering too great a back pressure. Beneath the pad 24 are positioned two pistons 28 which are hydraulically connected through a back pressure relief valve 32 with a fluid reservoir 36 at relatively low pressure, the valve permitting fluid to flow from cylinders 26 back to the reservoir 36 when a predetermined pressure is exceeded. In operation, the increase in pressure beneath the pistons 28 during a working operation is transmitted through a conduit 30 to the valve 32. If the pressure exceeds a predetermined value, a pilot valve 100 is lifted off its seat, against the pressure of an adjustable spring 102, by the fluid pressure, thus allowing fluid to pass into passages 106 and 108. Should the pressure in the cylinders 26 exceed a second predetermined value, the pistons 120 and 66 of a pair of unloading valves are lifted by a pressure differential against spring bias to open ports 110, thereby by-passing fluid from the high pressure side of the system to the low pressure side. A one-way ball check valve 54 is biased by a light spring 56 to allow fluid to pass only from chamber 48 to passage 44. A piston 86 and a bore 84 form an expansible chamber, for reducing the back pressure on the unloading valves, the piston being raised, by an increase in the fluid pressure, against an adjustable stop 92, the top side of the piston being open to atmosphere or alternatively to the supply pipe 34 from the reservoir.