US3529511A - Percussive tools utilizing a reciprocating differential area piston - Google Patents

Description

United States Patent [72] Inventor 21 Appl. No.

[22] Filed [45] Patented [32] Priority Anthony Edward Walter Last, Ipswich, Suffolk, England Jan. 17, 1968 Sept. 22, 1970 The British Steel Piling Company Limited,

a mnrpanyarcreat Britain and flo rthern Ireland Jan. 19, 1967 Great Britain [54] PERCUSSIVE TOOLS UTILIZING A RECIPROCATING DIFFERENTIAL AREA PISTON 299, 300 (Cursory), 321 (cursory) [56] References Cited UNITED STATES PATENTS 1,384,216 7/1921 Smith 91/317 1,494,030 5/1924 Slater..... 91/317 1,662,576 311929 .leschke u. 91/317 2,609,792 9/1952 O'Farrell 91/317 FOREIGN PATENTS 384,730 2/1908 France 169,656 10/1921 g g g g 91/317' 230,388 311925 m ning 91/317 Primary Examiner-Paul E. Maslousky Attorney-Beale and Jones ABSTRACT: In the specification there is described a percussive tool using a compressible fluid as its energy source and having a ram piston with difi'erential area end faces reciprocating in a cylinder. A valve controls the supply of fluid to the cylinder such that the lower, smaller end area of the piston is subjected to fluid pressure to lift the piston and the valve then allows pressure fluid to reach the other end of the piston during its upward stroke by putting both ends of the piston into communication with each other. As the piston approaches the end of its upward stroke, said other end enters a sealed space whereby the pressure acting on it builds up rapidly causing an accelerated reversal into the impact stroke of the piston. Near the end of the impact stroke, exhaust ports are uncovered to release pressure fluid acting on said other side of the piston. The specification further describes how the tool can be adapted for extraction operations, the ram piston first being lifted to a raised position in the inverted cylinder by the application of pressure fluid to said other end of the piston.

PERCUSSIVE TOOLS UTILIZING A RECIPROCATING DIFFERENTIAL AREA PISTON This invention relates to percussive tools arranged to be operated by compressible fluids. in particular compressed air.

In a known compressed air hammer. a differential area ram piston is slidable in a cylinder having bores in its walls which form fluid inlets at opposite ends while a control valve provides a sequential connection of these bores to air under pressure reciprocating the piston in the cylinder. The smaller area side of the piston is at the bottom of the cylinder when at rest and in the cycle of movement. the valve first delivers compressed air to that side to lift the piston. As the piston rises, the valve next places both sides of the piston'in communication with each other so that the piston slows down and after reaching the end of its upward stroke it falls to provide a working impact. The compressed air above the piston is released to atmosphere shortly before the piston impact at the bottom of its stroke.

A disadvantage of this known arrangement is that the speed of movement of the piston is limited by the space that must be allowed for the reversal of its movement at the top of its stroke where the change of velocity is relatively slow since it is determined by the imbalance between the inertia forces on the piston and the net pressure force resulting from the different areas at the top and bottom faces of the piston. One result of this is that the cycle frequency at which the piston operates is restricted. Y

According to the invention, there is provided a percussive tool operable by a compressible fluid and comprising a differential area ram piston slidable in a cylinder having fluid ports at opposite end regions, valve means being arranged to deliver pressure fluid to the smaller area side of the piston to urge it from its associated end of the cylinder and to deliver pressure fluid to the larger area side of the piston as the piston approaches the opposite end of the cylinder to reverse the piston into an impact stroke of its cycle of motion, exhaust means being arranged to release pressure fluid from the cylinder during said impact stroke, the fluid port associated with said larger area side of the piston being spaced from its endof the cylinder whereby travel of the piston into said end region seals off said port and creates a fluid buffer zone in said region accelerating reversal of the piston motion.

' Preferably said sealing of the port is completed when the piston has travelled through substantially no more than 80 percent of the cylinder free space.

Advantageously, the increase of pressure at said opposite end of the cylinder is achieved by interconnecting the fluid ports as the piston approaches said opposite end to equalise pressures at both ends of the cylinder. For this purpose, the valve means may itself comprise a reciprocable piston having differential area faces, the smaller area face being in communication with fluid line pressure and the larger area face being in communication with said other end of the cylinder. The cylinder inlet conduit associated with said smaller area side of the ram piston can then extend to a valve chamber within which said body is reciprocable, said conduit being located axially intermediate the connections from said chamber to the pressure line and to the port for said other end of the cylinder whereby movement of the valve body brings said conduit into alternate communication with each of said two connections.

In a preferred feature of the invention, means are provided comprising a passage connected to the fluid pressure line and communicating with said opposite end of the cylinder for starting the motion of the ram piston on the stroke away from said opposite end of the cylinder. In this way, the tool can be readily adapted for inverted operation so that, for example, it can be employed for extraction as well as the driving of piles.

One particular form of the invention operable as a piling 'hammer or a rock breaker will now be more particularly described with reference to the accompanying drawings in which:

FIG. 1 is a sectional elevation of the hammer, and

'FIG. 2 is a corresponding section to a larger scale of the distributing valve of the hammer.

Referring to the drawings, the hammer comprises a rectangular section casing 2 having a main cylindrical bore 4 forming a pressure cylinder within which a piston 6 is reciprocable. The limits of the pressure cylinder are defined by a sealing disc 20 at its upper end secured by a circlip 19 and by a closure ring 10 at its lower end secured by a circlip 9. The piston 6 has an integrally formed impact stem 12 that sealingly slides in a metallic gland ring (not shown) clamped within the closure ring 10. The top plate 2Q comprises a suspension eye 2l and at the bottom end of the casing an anvil block 22. that is struck by stem 12 when the pistondescends. is attached to the casing by a wire sling (not shown) passing through lower hole 21' of the suspension eye.

Reciprocation of the piston is actuated by compressedair which can reach the cylinder by upper and lower inlet conduits 24. 26 respectively. The conduit 24 is secured in position in a recess 23 of the casing by a block 25 bolted to the casing and bearing on the curved end of the conduit. Pairs of exhaust conduits 28 each equidistant from the sectional. plane of FIG. I, extend through opposite sides of the casing intermediate the length of the cylinder, their position being such that they are uncovered by the piston 6 shortly before it reaches the bottom of its stroke.

Flow of pressure fluid through the conduits 24, 26 is controlled by valve 30 shown in more detail in FIG. 2. This comprises a block 32 having a vertical bore 33 that forms a cylindrical chamber 34. A counterbore 35 at the top of the bore 33 receives the open end of the conduit 24 which seats against a resilient buffer ring 37. An annular recess 38 intermediate the length of the chamber 34 communicates with the conduit 26 through an opening 39. A tapping 40 on the block 32 receives a connection 41 (FIG. I) from a source of compressed air and communicates with the chamber 34 through an annular recess 42 immediately above a reduced diameter bore 36 continuing downwardly from the bore 33.

The valve has a double-headed piston 44 comprising a smaller diameter lower head 45 sealing with the lower bore 36 and a larger diameter upper head 46 sealing against the bore 33 forming the chamber 34. The two sides of the piston thereby have different areas exposed to the pressures within the chamber and, similarly to the main hammer piston 6, the smaller face area is to the underside of the piston. A resilient buffer 52 is secured in a counterbore 50 at the bottom of the bore 36 to limit the downwards displacement of the piston.

The sequence of operation of the hammer mechanism can be considered from the position shown in the drawing where the hammer piston 6 is at the bottom of its stroke while the valve piston 44 is at the top of its stroke. The upper end of the hammer cylinder is then in communication with atmosphere through the exhaust outlets 28. The tapping 40 is connected to a line carrying compressed air, in this example at a pressureof I05 lbs. per square inch absolute, and this is transmitted through the chamber 34 and opening 39 to the underside of the hammer piston. In this condition the valve piston 44 is supported in its uppermost position by the net pressure force on the different areas of its upper and lower heads.

The inflow of pressure air to the underside of the hammer piston 6 lifts it in the cylinder and as it rises it seals off the exhaust outlets so that its continuing movement causes an increasing pressure to be developed in the upper region of the cylinder. This upper region pressure is exerted upon the valve piston 44 in opposition .to the line pressure acting in the chamber 34 and because of the different areas of the piston heads, the piston is returned to its bottom position when the upper cylinder region pressure reaches some 45 lbs. per square inch absolute. In the illustrated example. where the free axial space of the cylinder in the state shown in FIG. 1 is some 9 inches, the switching of the piston 44 may occur when the piston 6 has risen some 5 inches. Depression of the valve piston brings its upper head 46 below the annular recess 38 and therefore the cylinder spaces on both sides of the hammer piston 6 are placed in communication with each other, through conduit 24, connecting passages in valve 30 and to conduit 26, and their pressures are equalised at some lbs. per square inch absolute.

Due to the larger area of the upper face of the piston 6. a resultant pressure force is developed urging the piston downwards but its inertia causes the piston to continue on its upward stroke while the pressure increases due to the decreasing free volume in the cylinder as the stem 12 enters the cylinder. As the top of the piston 6 passes the upper end of the conduit 24 in its continuing upward motion. the space above the piston is sealed off and there is a sharper rise in pressure there which accelerates the termination of the piston upward stroke and also its initial downwards motion. This sealing off of a buffer space at the top of the cylinder takes place as it passes the upper end connection of conduit 24 when the piston has risen through not less than some 70 percent of the free space in the cylinder as measured from the piston bottom position. Preferably, the sealing occurs when the piston has risen through not more than about 80 percent of that free space, as shown in the illustrated example.

As the piston 6 descends, the cylinder pressure falls to some 46 lbs. per square inch by the time the exhaust outlets 28 are uncovered and the pressure air is released. This release of pressure removes the downward force on the valve piston keeping it at its lowered position. The line pressure once again urges the valve piston up to its illustrated position so that a further cycle of movements is able to begin as the hammer piston reaches the bottom of its stroke and delivers a working impact to the anvil block 22. It is clear that the cycle will repeat itself as long as line pressure is applied to the tapping 40.

It is to be noted that the passages provided for the flow of air to and from the hammer cylinder are relatively large and abrupt changes of direction, e.g. in the flow from the valve to the top of the cylinder, are avoided. By so avoiding throttling of the flow, the cycle of movement of the hammer piston is further accelerated and the operative effectiveness of the machine is thereby increased.

As described so far, with the anvil block at the bottom of the structure, the hammer operates as a pile driver but a feature of the design is its ability to be used alternatively to extract piles. For this mode of operation the unit is, of course, inverted and is connected to the pile through wire bridles in a conventional manner. Before being connected to line pressure, however, the hammer piston will now be in the opposite end position to that shown in the drawing and no movement will take place if pressure is simply applied through the tapping 40. For this reason, an auxiliary tapping 48 is provided on the line to the top of the cylinder with which it communicates through a nonretum valve 49. Initially, therefore, pressure air is admitted into the cylinder through the tapping 48 to raise the hammer and valve pistons and as soon as the exhaust ports 28 are uncovered the piston 6 drops and the cyclic operation described above begins, the anvil block being impacted at each upward stroke of the piston 6. The pressure flow through the tapping 48 is maintained during operation of the hammer both in the normal and inverted positions; this flow is strongly throttled however so that while the hammer is operating the amount of pressure air bypassing the valve 30 is too small to have any effect and it is therefore unnecessary to provide shut-E means in the tapping 48.

lclaim:

1. A percussive tool operable by a compressible fluid and comprising in combination, a cylinder, a ram piston slidable within the cylinder and having different area ends within the cylinder, fluid inlet ports arranged at opposite end regions of the cylinder. valve means for controlling the flow through said ports, and conduit means connecting the ports to the valve means, said valve means being arranged to deliver pressure fluid to the smaller area end of the cylinder and to bring said ports into communication with each other through said conduit means to apply fluid pressure to the larger area end of the piston as the piston approaches the opposite end of the cylinder to reverse the piston into an impact stroke of its cycle of motion. exhaust means in the cylinder being arranged to release pressure fluid from the cylinder during said impact stroke, the fluid inlet port associated with said larger area end of the piston being spaced from its end of the cylinder whereby travel of the piston into said end region seals off said inlet port and creates a fluid buffer zone in said region accelerating reversal of the piston motion.

2. A percussive tool according to claim 1 wherein the seal ing of the port is completed when the piston has travelled through at least percent of the cylinder free space.

3. A percussive tool according to claim 1 wherein said seal ing of the port is completed when the piston has travelled through substantially no more than percent of the cylinder free space.

4. A percussive tool operable by a compressible fluid and comprising in combination. a cylinder. a ram piston slidable within the cylinder and having different area ends within the cylinder. fluid ports arranged at opposite end regions of the cylinder. valve means in communication with said ports and being arranged to deliver pressure fluid to the smaller area end of the piston to urge it from its associated end of the cylinder and to deliver pressure fluid to the larger area end of the piston as the piston approaches the opposite end of the cylinder to reverse the piston into an impact stroke of its cycle of motion. exhaust means in the cylinder being arranged to release pressure fluid from the cylinder during said impact stroke. the fluid port associated with said larger area end of the piston being spaced from its end of the cylinder whereby travel of the piston into said end region seals off said port and creates a fluid buffer zone in said region accelerating reversal of the piston motion, wherein said valve means comprises a cylinder, a piston reciprocable therein having differential area end faces, the smaller area face being in communication with fluid line pressure and the larger area face being in communication with the fluid port in the region of said cylinder opposite end, said valve piston being displaceable to interconnect the cylinder fluid ports as the ram piston travels towards said opposite end of the cylinder so that pressures on both sides of the ram piston are equalized, during the upward motion of the ram piston.

5. A percussive tool according to claim 4 wherein the valve piston comprises a pair of heads at opposite ends and different area bores are formed in the valve cylinder to receive the respective heads, fluid line pressure being directed to the space between the piston heads and a fluid conduit being provided from the outer end of the larger area head to said cylinder opposite end region.

6. A percussive tool operable by a compressible fluid and comprising in combination, a cylinder, a ram piston slidable within the cylinder and having different area ends within the cylinder, fluid ports arranged at opposite end regions of the cylinder, valve means in communication with said ports and being arranged to deliver pressure fluid to the smaller area end of the piston to urge it from its associated end of the cylinder and to deliver pressure fluid to the larger area end of the piston as the piston approaches the opposite end of the cylinder to reverse the piston into an impact stroke of its cycle of motion, exhaust means in the cylinder being arranged to release pressure fluid from the cylinder during said impact stroke, the fluid port associated with said larger area end of the piston being spaced from its end of the cylinder whereby travel of the piston into said end region seals off said port and creates a fluid buffer zone in said region accelerating reversal of the piston motion, said valve means comprising a cylinder having two different area bores in series, a valve piston reciprocable in the cylinder and having a pair of heads spaced at opposite ends fitting the respective bores of the cylinder, an inlet opening being formed in the cylinder in the space between the piston heads for the admission of fluid at line pressure and a fluid conduit being provided at that end of the valve cylinder beyond the larger area piston head to said cylinder opposite end region.

7. A percussive tool according to claim 6 wherein said fluid conduit comprises a main portion located co-axially with the valve cylinder bores and a curved transition portion extending therefrom to said cylinder end region.

l0.'A percussive tool operable by a compressible fluid and comprising in combination. a cylinder. a ram piston slidable within the cylinder and having different area ends within the cylinder, fluid ports arranged at opposite end regions of the cylinder. valve means in communication with said ports and being arranged to deliver pressure fluid to the smaller area end of the piston to urge it from its associated end of the cylinder and to deliver pressure fluid to the larger area end of the piston as the piston approaches the opposite end of the cylinder to reverse the piston into an impact stroke of its cycle of motion, exhaust means in the cylinder being arranged to release pressure fluid from the cylinder during said impact stroke. the fluid port associated with said larger area end of the piston being spaced from its end of the cylinder whereby travel of the piston into said end region seals off said port and creates a fluid buffer zone in said region accelerating reversal of the piston motion. and starting means comprising a fluid conduit bypassing the valve means and interconnecting the fluid pressure line with the said opposite end of the ram cylinder through non-return flow means to displace the piston from said opposite end of the cylinder independently of the valve means. whereby operation of the tool in an inverted position can be initiated.

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