GB1424473A - Pneumatic spring hammers - Google Patents

Abstract

1424473 Percussive tools ROBERT BOSCH GmbH 19 Feb 1973 [21 Feb 1972] 8009/73 Heading B4C A pneumatic spring hammer comprises either a strike-piston 54 or cylinder 45 reciprocated to cause a hammer blow via an air cushion, and an air pump 9 at the rear of the piston and cylinder whose suction is connected to atmosphere by a check valve 60 and whose discharge is connected to the air cushion space 57 by a second valving arrangement such as a groove 44 and port 58 in the housing and cylinder respectively controlled by movement of the cylinder and strike piston. As shown, the air pump is formed by the crankcase 9 and the motor-driven crank disc 10 drives the cylinder 45 to cause reciprocation of a strike piston 54 to hammer the end 29 of an anvil 21 against a tool 26. When the hammer is started up and the cylinder 45 is moved forwards a vacuum appears in the crankcase 9 to draw in air through a filter 62 and the check valve 60. As the cylinder moves forwards it compresses air in the space 57 to cause forward movement of the strike piston. The air in the space 56 is compressed and when the edge 45<SP>11</SP> of the cylinder has passed over the edge 44<SP>1</SP> of the groove 44, this air flows into the crankcase to close the check valve 60. As the strike piston approaches the anvil 21 the air pressures in the spaces 56 and 57 are equalized through a longitudinal groove 55 in the cylinder. During subsequent rearward movement of the cylinder 45 the strike piston 54 is accelerated rearwards and the air in the crankcase 9 is compressed to flow into the space 56 via the groove 44 to assist acceleration. When the hammer is removed from the workpiece, the strike piston 54 drives the anvil 21 into a non-operative forward position where a resilient ring 37 of rubber or plastics snaps into a groove 31 and the air in the spaces 56 and 57 are equalized with the strike piston remaining in its end position with the port 58 uncovered. Cooling air from a fan on the motor drive shaft flows between inner and outer casings 12, 13 and out through openings 17 and 18.