GB491026A - Improvements in or relating to hydraulic presses - Google Patents

Abstract

491,026. Hydraulic presses. MACMILLIN, H. F. Feb. 27, 1937, No. 5961. Convention date, April 22, 1936. [Class 69 (ii)] A hydraulic press of the kind in which the platen is connected to a ram having two piston surfaces and wherein control means for the pressure liquid are provided whereby the latter can first be admitted to the first of said piston surfaces only, so as to cause a rapid approach of the platen to the work, and subsequently admitted to both the first and second surfaces so that the pressing stroke of the ram may be effected at a slower rate but under a higher pressure, includes a main cylinder divided into outer and inner chambers, a main ram arranged in said cylinder and having its two piston surfaces in or communicating with the outer and inner chambers respectively and a surge tank adapted for communication with said cylinder through surge-valve-controlled ports opening into the outer chamber and inner chamber. The platen 17 is actuated by a ram 16 having a central face 42 subject to pressure of liquid in the chamber 36 and having also an annular surface 41 subject to pressure of liquid in the annular chamber 33. The chambers 33, 36 communicate with the surge tank 31 through surge valves 35, 30 which may be of the kind described in U.S.A. Specification 1,892,568. The chamber 36 communicates through port 60 and pipe 59 with one side of a reversible variable-delivery pump 39 which may be provided with control mechanism of the kind described in U.S.A. Specification 1,861,116. The other side of the pump communicates through pipe 63 with push-back cylinders 23. For a rapid approach stroke liquid is exhausted by the pump from the push-back cylinders and is delivered to the chamber 36, the filling of which is assisted by liquid passing from the surge tank 31 through the surge valve 30, so that the advance is accelerated by gravity. The chamber 33 is prefilled by liquid passing from the surge tank through the surge valves 35. At an adjustable predetermined point in the advance stroke a member 78 on the platen actuates valve mechanism 40 opening a valve therein to permit pressure liquid to pass also into the chamber 33 to effect the pressing operation. To effect the return stroke, the pump is set to deliver to the pushback cylinders ; the pressure liquid also passes through pipes 65, 66, 67, 68 to open the surge valves 30, 35 to put the chambers 33, 36 into communication with the surge tank 31. Pressure liquid is also delivered by pipes 65, 69, 70 to opposite ends of the valve 40, these ends being of different areas, whereby the valve is held open by differential pressure against its closing spring, despite the fact that it is released by the member 78 during the upward movement of the platen ; the chambers 33 and 36 thus remain in communication, and liquid passes therefrom to the intake of the pump. A make-up valve 49 of usual construction is provided. The mechanism for actuating the valve 40 by the member 78 on the platen may be rendered inoperative, whereby operation of the press is effected by the delivery of pressure liquid to the chamber 36 only without subsequent admission to the chamber 33. Further, a manually controlled byepass may be arranged around the valve 40 whereby the whole operation of the press is effected by the simultaneous delivery of pressure liquid to both the chambers 33, 36. Independent auxiliary quick-approach booster cylinders may be additionally provided.