Patent GB-953681-A (GB)
Title: Hydraulic clamping apparatus
IPC: B30B15/00
Filed: 1962-05-11
Abstract: 953,681. Welding by pressure. BRATISLAVSKE ELEKTROTECHNICKE ZAVODY NARODNY PODNIK. May 11, 1962 [May 11, 1961], No. 18234/62. Heading B3R. [Also in Division B5] An hydraulic press having means for clamping workpieces to enable, for example, resistance-welding to be performed in the press, comprises a clamp 2 having an hydraulic cylinder 6 between which and a distributer 15 for the press cylinder 10 is a clamping valve 28 having a piston 31 for controlling the flow of fluid into the hydraulic cylinder, a first chamber 27 connected through a discharge space 26 of the distributer with a delivery space 14 of the press cylinder on one side of the press piston 9, and a second chamber 36 connected with the pressure space 13 of the press cylinder on the other side of the press piston, the piston 31 in the clamping valve being operative in such a manner that in the hydraulic cylinder 6 firstly the fluid escaping from the delivery space is active and then the pressure fluid supplied to the pressure space is active. The clamp 2 is mounted on the lower fixed electrode 1 of the press and has a jaw 4 movable against a spring 7 towards a fixed jaw 3 by fluid pressure in the cylinder 6 which is connected to a central chamber 35 of the clamping valve. The first chamber 22 of the valve is connected to the discharge chamber 26 which, when the distributer is actuated is connected to a chamber 25 and the delivery space 14 of the press, the piston 9 of which carries a movable electrode 8. The second chamber 36 of the clamping valve is in permanent communication through a chamber 21 of the distributer with the pressure space 13 of the press. With the distributer in the position shown, fluid pressure from a pump 24 passes through chambers 23, 25 of the distributer to the delivery space 14 of the press to hold the piston in its upper position. The fluid flow passes through a one-way valve 12 to the pressure space 13 which, with the distributer in the position shown, is connected by chambers 21 and 19 to a conduit c leading to a reservoir 20. The jaw 4 of the clamp is at this time retracted by the spring 7, fluid in the cylinder 6 being connected to the reservoir 20 by chambers 35, 36 in the clamping valve, a conduit d, chambers 21 and 19 in the distributer and the conduit c. When the distributer is moved to its alternative position by operation of an electromagnet 17, the fluid from the pump passes through chambers 23, 21 of the distributer to the pressure space 13 to lower the piston and electrode 8. The fluid pressure in space 13 is prevented from acting in the delivery space 14 by the valve 12 and the fluid expelled from the latter space is connected by the chambers 25, 26 of the distributer to the chamber 27 of the clamping valve and, because of the differential areas of the press piston is greater in value than the pressure in chamber 36 connected to space 13 and moves the piston 31 against its spring 33 so that fluid can flow through chamber 35 to the cylinder 6 to move the jaw 4 and clamp a workpiece. The clamping pressure is at this time controlled by a relief valve 29. When the electrode engages the workpiece, however, the pressure in space 13 rises and acts in chamber 36 to move the piston 31 so that the pressure in space 13 also acts in the cylinder 6 to increase the clamping force, the maximum pressure being determined by a regulator 22. The movement of the piston 31 causes a projection 32 to open the relief valve 29 to connect the delivery space 14 to the reservoir 20.