GB1382950A - Fluid operated impact device - Google Patents

Abstract

1382950 Percussive tools CONSTRUCTION TECHNOLOGY Inc 18 Sept 1973 [18 Sept 1972 25 Sept 1972] 43686/73 Heading B4C An hydraulically operated impact device for applying repetitive impact forces to a tool 20 comprises a hammer 28 carrying a piston 70, an energy storage device 45, first and second chambers 90, 60 on opposite sides of the piston and a valve sleeve 75 movable to a rearward first position when the fluid pressure is to move the hammer rearwardly against the energy storage device and movable forwardly away from the piston to place the first and second chambers in fluid communication with each other to permit the energy storage device to drive the hammer forwardly. As shown, the hammer 28 is secured to a bearing plate of the energy storage device which may be a compression spring or an air spring chamber 42, the hammer being arranged to pass through a cushion plate 30 and deliver blows on the tool 20 through an anvil 120. The valve sleeve 75 has radial notches 87 on its rear end face and operates as a differential piston between abutments 55 and 65 by having a larger area at its rear end operating in a bore 52 which is larger than the bore 53. A safety device in the form of a valve sleeve 100 prevents operation until the tool is pressed against a work surface. In the inactive position shown in Fig. 4, a groove 105 in the sleeve 100 communicates a port 106 with a port 112 to allow the fluid pressure supply to the inlet port 91 to be by-passed through a line 107 to a reservoir 63. When the force applied to the tool 10 and anvil 120 overcomes the differential hydraulic bias caused by the larger end area 115 of the groove, the sleeve moves back to close port 112. The build up of fluid pressure in the chamber 90 first causes the valve sleeve 75 to move into engagement with the abutment 55 to close exhaust port 79 and then causes the piston 70 to move the hammer 28 rearwardly to compress the air spring 42. When in the fully retracted position, Fig. 6 (not shown), the piston 70 is in engagement with the abutment 55 to allow the pressure fluid in the chamber 90 to pass through the radial notches 87 and cause the valve sleeve to move forwardly into engagement with the abutment 65. With the valve sleeve now in its forward position the chamber 90 is open to communication with the chamber 60 and the exhaust port 79. The energy stored in the air spring 45 is then able to drive the hammer 28 forwardly, Fig. 7 (not shown). The hammer impacts the anvil 120 just before the rear end of the hammer engages the cushion plate 30. So long as the device is pressed against a work surface, the hammer will cycle at a rate determined by the flow rate of the pressure fluid. In an alternative embodiment, Figs. 8 and 9 (not shown), the rearward force of the hammer for compressing the air spring is increased by adding the area of the valve sleeve (80<SP>1</SP>) to the area of the piston (70<SP>1</SP>), the valve sleeve becoming part of the piston during the rearward movement under fluid pressure.