Patent GB-511993-A (GB)
Title: Hydraulic presses
IPC: B30B15/18
Filed: 1938-04-08
Abstract: 511,993. Hydraulic presses. BLISS CO., E. W. April 8, 1938, No. 10835. Convention date, April 9, 1937. [Class 69 (ii)] In a hydraulic press having a surge valve for admitting slack liquid to the main work chamber during rapid advance of the ram by pressure liquid admitted to auxiliary chambers, the valve is hydraulically closed, and a passage is provided, controlled by movement of the surge valve, so that when the latter is in its closed position, said passage affords substantially unimpeded liquid communication between the valveclosing chamber and the main work chamber. In the arrangement shown in Fig. 1, pressure liquid is introduced through tube 42 into the rapid advance chamber 44 in the ram 34, the surge valve 18 being held open by springs 19 to admit liquid from the surge tank 50 to the work chamber 39; the interior of the tube 42 also communicates through ports 47, elongated passage 48 and ports 48a in the surge valve with the valve-closing chamber 37. The valve 18 has passages 41 establishing communication between the work chamber 39 and a balance chamber 36. When the valve 18 is in its closed position, grooves 49 therein are uncovered; pressure liquid then passes from the valve closing chamber 37 to the balance chamber 36 and thence through the passages 41 to the work chamber 39. In normal operation, the ram is advanced rapidly by liquid introduced into 44, the valve 18 remaining open; when the work is contacted, the pressure in 44 rises, and causes the valve 18 to close, pressure then being admitted to the work chamber 39 to complete the stroke of the ram at pressing speed. Alternatively, just before the ram contacts the work, back pressure may be set up, as for example by a throttle valve in the exhaust line leading from the pushback chamber 40, whereby a rise in pressure in space 44 is artificially generated, causing the valve 18 to close and the slow working stroke to be initiated. As a further alternative, the adjustment of the valve-opening springs 19 and/or the value of the back-pressure opposing the advance of the ram, as determined by the setting of an adjustable back-pressure valve in the exhaust line leading from the push-back chamber 40, may be such that the valve 18 closes before, or simultaneously with, downward movement of the ram, so that the whole stroke is performed at pressing speed. In a modification, Fig. 3, a single valve-opening spring 51 is provided. The area A of the balance chamber 36 is greater than the area B of the valve seat 14, so that when the valve 18 is moving upwardly with the grooves 49 therein covered, and the lower end of the valve still in closing engagement with the seat, diminution in volume of space 36 is greater than the increase in volume of the space 39; excess liquid passes from space 36 to exhaust through an adjustable throttle valve 55, whereby the upward, i.e., opening, movement of the valve 18 can be variably cushioned. In a further modification, Fig. 4, the valve is opened hydraulically by liquid supplied through pipe 58; separate rams (not shown) are provided for effecting the rapid advance of the ram, and these are fed with pressure liquid in common with the valve-closing chamber 37. Specification 509,925 is referred to.