GB1340229A - Devices for applying hammer blows to a body - Google Patents

Abstract

1340229 Power hammers H BRIDEN 4 Sept 1972 [14 Sept 1971] 42734/71 Heading B3H [Also in Divisions B4-B5 and F1] An hydraulically-actuated hammer substantially as described in Specification 1,177,765, has its spring loaded pilot valve spool 31, Figs. 2 and 5, controlled by valve-operating gear comprising a thrust member 50 disposed between the spool and a pivoted lever 43, a spring 53, Fig. 4, for rotating the lever about an axis 44 to depress the spool against the action of its spring 33, a latch 38 for holding the thrust member, a push rod 34, Fig. 2, controlled by the movements of the hammer 19 for rotating the lever against its spring action, and means, such as a lost motion link 42, controlled by the lever for releasing the latch when the push rod has rotated the lever clear of the thrust member far enough to allow the spool to travel to its other end position. The hammer 19 is connected by a rod to a driving piston 21 which is moved on its leftward stroke by hydraulic pressure (oil) and on its rightward stroke by gas or spring pressure stored in a chamber 16 during the leftward stroke and acting through an accumulator piston 26 and a liquid column. A port 24 connects the first chamber containing the rod of the driving piston 21 with a second chamber 25 adjacent the accumulator piston 26. The main valve in its first state admits hydraulic fluid both to the first chamber to move the driving piston leftwards and the second chamber 25 to cause the accumulator piston 26 to compress the gas or springs in the chamber 16. In its second state the main valve connects the first chamber to the second chamber 25 via valve 63 to cause hydraulic fluid to flow from the second chamber 25 under the influence of the gas or spring pressure in the chamber 16 to cause the driving piston to move the hammer 19 rightwards to apply an impact force on the head 263 of the tool carrier shaft 2. The pilot valve 30 ensures that the main valve changes from its first to its second state when the hammer has been retracted to a predetermined position and a predetermined quantity of energy has been stored in the chamber 16. Pilot valve 30 controls hydraulically-actuated valves 255, 216. On the return stroke, the righthand side of the driving piston 21 is connected to hydraulic pressure source 205 via port 24, and chamber 25 and the lefthand side is connected to exhaust via chamber 23. The driving piston 21 impacts a third piston 28 which moves with the driving piston and accumulator piston 26 to pressurize gas or springs in the chamber 16. During this movement the hammer 19 actuates the push rod 34 and causes the latch 38 to lift to allow the pilot valve spool 31 to move and cut off the chamber 25 from the hydraulic pressure source except for a small by-pass 62, cut off chamber 23 from exhaust and connect chamber 25 to chamber 23. The stored pressure in the chamber 16 then acts on the accumulator piston 26 to drive the hydraulic fluid out of the chamber 25 into the chamber 23 to move the driving piston 21 and the hammer 19 on the forward stroke. The rod 211 of the accumulator piston displaces hydraulic fluid in the chamber 23 so that the driving piston 21 moves faster than the accumulator piston 26 until the hammer 19 strikes the head 263 of the tool carrier shaft 2. The forward movement is cushioned in the event of a full stroke by piston and cylinder assemblies 7, 8 operating in two stages and connected by a line 10 to a fourth piston 15 via a chamber 11 which is also connected to the hydraulic pressure source 205 via a restriction 12. When the shaft comes to rest in its forward stroke, the piston 15 returns leftward and a valve plate 18 closes to allow hydraulic fluid stored behind the piston 15 to flow back into the chamber 11 at a controlled rate so that the shaft returns at a controlled speed. During the forward movement, the push rod 34 is released by the hammer. Reversal of the valve 255 is delayed by a restriction 218 in the pilot valve. The chamber 23 is connected to exhaust and the chamber 25 to pressure for the return stroke of the hammer. The hammer is cushioned by a resilient sleeve 266 and the head 263 is resiliently connected to the shaft 2 by a resilient collar (262), Fig. 1 (not shown). The hammer 19 includes an impact block (19B), Fig. 6 (not shown), in its head and is connected resiliently to the driving piston by a pivoted connecting rod (74) having resilient sleeves (83, 85). The apparatus may be carried by an hydraulic excavator and can be used for breaking rock, cutting metals or for actuating extrusion dies or driving piles.