Patent GB-296090-A (GB)
Title: Improvements in fluid pressure operated metal-shaping and like machine tools
IPC: B23D7/00
Filed: 1928-08-20
Abstract: 296,090. Waterbury Tool Co., (Assignees of Francis, D. R.). Aug. 26, 1927, [Convention date]. Shaping - In a hydraulically actuated metal cutting machine such as a shaping mschine, the ram 12 is of hollow cylindrical form and coacts with a fixed piston 16 having a hollow piston rod 17 which conveys pressure fluid to the front of the piston, the piston rod being surrounded by a, sleeve 19 which conveys fluid to the rear of the piston through ports 19a. The fluid is preferably pumped from a variable-delivery pump 20 comprising a number of cylinders 23 whose stroke is controlled by a swash plate 24. The tilting of the swash plate to control the pump delivery is effected from a hand-wheel 32. The pump is driven from an electric motor 33 and the delivery passes to the ram through a reversing valve 40 which is of the type described in Specification 278,683, [Class 69 (ii), Hydraulic pressure &c.]. The pipe 38 leading to the hollow piston rod communicates through the port 43 with the central portion of a piston valve 46, while the pipe 39 leading to the sleeve communicates through port 44 to the end ports 44<a>, 44b of the valve chamber. The valve rod 47 is actuated automatically from the ram. Each projecting end of the rod carries a collar coacting with a spring-pressed latch 49 pivoted at 50. Arms 52 located at the ends of the rams are forked to enclose the spindle 47 and each arm carries a roller 54 coacting with the latch. At the end of a stroke the arm 52 first compresses a spring 53 and the roller then rides up a tapered portion of the latch which is thereupon disengaged so that the valve rod is shifted by its spring to reverse the movement. The movement of the valve rod causes the opposite latch to be engaged and this in its turn is disengaged to reverse the movement at the other end of the stroke. In a modification, Fig. 4, the valve, rod 72 is shifted by means of a small fluid pressure cylinder 71 controlled by a four-way valve 73 which is actuated through a lever 81 by tappets 80 on the ram. The area exposed to fluid on the front of the piston is considerably greater than that at the rear so that the return stroke is made at higher speed. In order to compensate for the difference in the volume of fluid to be pumped to the front and rear of the piston an expansion tank 55 connected by pipes 58, 59 to the pipes 38, 39 respectively is provided with valves which are connected by means of a rod, 64 so that when one valve is open the other is simultaneously closed. The arrangement is such that the tank is closed to the pipe which is under pressure, and open to the one under suction. Thus when, in operation, the pump delivery passes through the pipe 39 and sleeve 19 to the rear of the piston, the suction is from the space in front of the piston and the excess of the fluid exhausted from this space over that required by the pump flows through the pipe 58 to the expansion tank. When, after reversal, the pump delivery passes through the pipe 38 and hollow piston rod to front of the piston, the valve, 63 will be automatically opened and the excess amount of fluid required by the pump over that exhausted from the rear of the piston is withdrawn from the tank 55. In some cases the wheel 32 which controls the pump delivery may be fitted with means for indicating in feet per minute the working speed of the ram.