GB1416860A - Earth cutting machines - Google Patents

Abstract

1416860 Earth-cutting machines D FIRTH K FOSTER and C J HOOKE 9 Nov 1972 [19 Oct 1971 4 Aug 1972] 30055/75 and 30056/75 Divided out of 1416859 Heading E1F [Also in Division Fl] An earth cutting (e.g. boring) machine, Fig. 7A, includes a cutting tool 202 driven by a fluid operated reciprocatable device, the device comprising an outer member 200, 208 carrying the tool 202, an inner member 212, 214 reciprocable relative to the outer member, and a resilient member 210 sealingly connected between the members 208, 212, the resilient member 210 having an average length in the direction of reciprocation greater than the average thickness measured normal to the direction of reciprocation. In operation an hydraulic system produces a pulsating pressure in a working chamber 222 defined by the outer member 200 and the flexible member 210. The pulses cause vibration of masses 216, 218, the latter being arranged to vibrate freely or to strike the tool 202. In the system shown, Fig. 4, a gear pump 70 controlled by a relief valve 80 delivers a substantially constant pressure past a non-return valve 78 to the device 10. At the same time a reciprocating pulse generator 84 delivers a pulsating supply to the device 10 downstream of the non-return valve 78, a relief valve 96 controlling the maximum pressure supplied to the device 10. An alternative system, Fig. 3 (not shown) consists of an oscillating spool valve which connects the device alternatively to a pump (40) and a reservoir (66). The hydraulic systems may be arranged to produce a forward stroke of the device which is of greater speed than the return stroke. The device 10 may be of circular, rectangular, square, triangular, polygonal, elliptical or irregular cross section. The inner member 32 of the rectangular construction of Fig. 2 is provided with a tool steel or tungsten carbide cutting edge 34. Such a construction is suitable for use as the cutting blade 32 of an earth cutting machine 300, Fig. 8, movable on crawler tracks 302, the blade being positionable by an hydraulic jack 306. The resilient member 22 is preferably of rubber having a uniform steel or tapering thickness and is 'bonded to the inner and outer members of mild steel. To improve the mechanical properties of the device the resilient member 22 is placed under compression by swaging the outer member inwardly by approximately 10% of its initial dimensions. Pressure may be applied to the inner end of the inner member via a floating piston (120), Fig. 6 (not shown).