GB764757A - Improvements in or relating to mechanical hammers - Google Patents

Abstract

764,757. Pile driving. USUKI, M. March 23, 1955 No. 8480/55. Class 68 (2). Apparatus for driving piles, or for use as a forging hammer, &c. which utilizes the reaction force set up by accelerating a body from rest, comprises an upper cylinder portion 1 which is divided by a piston 5 into an upper pneumatic cylinder 7 and a lower oil pressure cylinder 8 and which is bolted to a lower portion 2 having a cylinder 30 which accommodates a thrust piston 31. A cylinder 17 fitted to the inside of a cover 3 for the cylinder 7 which is open at its upper end to the outer atmosphere, houses a piston 16, the rod 10 of which carries, at its lower end, a main valve 18, and intermediate its ends, an inner cylinder 11 which is provided with valves 12,13 in its upper face and slidingly accommodates an upper part 6 of the piston 5. The main valve 18 has a cylindrical part 19 which, when the valve is raised, fits tightly within a valve seat 21 which is arranged within the top of the cylinder 30 and projects into the bottom of the cylinder 8 to form a seating for the lower face of the piston 5 when this is lowered, a passage 9, leading from the cylinder 8 to the cylinder 30, thus being formed. Oil discharge ducts 23 in the main valve 18 lead to a central bore which houses a spring loaded valve 24 and has a lower discharge opening 43, the upper end of the bore having a cylindrical portion 27 which receives a piston-like projection 25 on the upper part of the valve 24 and communicates with a duct 29 in the rod 10. When the valve 18 is fully raised the duct 29 communicates with a duct 28 in the piston 5 leading to the cylinder 8. In the upper part of the cylinder 30 are provided a safety valve 32, and an oil discharge valve 35 which leads to a chamber 39 having a pipe 41 for returning used oil to the pressure source. In operation, compressed air is forced into the cylinder 7 and through the valve 12 into the inner cylinder 11 to urge the piston 5 downward and also into the cylinder 17 to raise the piston 16 and thus the main valve 18, low viscosity oil at the same time being pumped through a pipe 42 into the cylinder 8 to raise the piston 5 sufficiently to disengage it from the valve seat 21 and allow the oil to enter the passage 9 and slightly depress the valve 18 by an amount which, however, is insufficient to allow oil to leak into the cylinder 30. As the oil feed is increased the piston 5 begins to rise in the cylinder 11 to further compress the entrapped air therein and raise the main valve 18 slightly, back into its original position. The piston 5 continues to rise in the cylinder 11 until it comes into contact with the rod 15 of the valve 13, whereupon the highly compressed air in the cylinder 11 suddenly escapes into the cylinder 7, the resultant superior downward thrust on the valve 18 at that instant causing the valve 18 and its fittings to descend so that oil flows through the passage 9 and into the cylinder 30. At the same time the piston 5 descends rapidly due to the increased pressure of air in the cylinder 7, thus the oil is quickly forced into the cylinder 30 and the piston 31 is suddenly ejected from the end of the unit. The action of the oil discharge valve 35 is delayed sufficiently so that discharge of oil into the chamber 39 does not commence until the shock has subsided. When the ejection of oil from the cylinder 8 has ceased the main valve is raised by the piston 16 and the piston 5 again contacts the valve seat 21, the residual oil in the passage 9 being discharged through the ducts 23 and the opening 43 into the cylinder 30. When the valve 18 is. completely raised the ducts 28,29 correspond, and the pressure of oil in the cylinder 8 closes the valve 24. The operation then commences again.