EP0088705A1 - Down-the-hole pneumatic hammer - Google Patents

Abstract

1. Down-the-hole pneumatic drilling hammer, which comprises a tubular body (1) supplied with compressed air and carrying a drilling bit (3) and in which a ramming piston (21) is made to perform a reciprocating movement inside an internal sleeve (7) forming a casing by means of a mechanism for distributing compressed air alternately above and below the ramming piston in such a way that it cyclically strikes the bit and rises again, characterised in that the hammer has two separate sources (16, 18) of compressed air, a high-pressure one and a low-pressure one respectively, the distribution mechanism ensuring alternately the supply of high-pressure air to the upper chamber (51) above the piston (21) so as to project the latter towards the bit, while the lower chamber (50) allows the air to escape, and the supply of low-pressure air to the lower chamber (50) so as to cause the piston (21) to rise again, while the upper chamber (51) allows the air to escape.

Description

The present invention relates to a pneumatic drilling hammer, and more particularly a hammer of the "down-the-hole" type, that is to say intended to work at the very bottom of the hole that is being drilled.

Such devices are therefore placed at the end of a set of tubes which serve to transmit the compressed operating air to it as well as the thrust and the general rotational movement to regularize the action of the perforating cutter.

Such pneumatic hammers intended to work at the bottom of the hole generally comprise a tubular body supplied with compressed air, a distribution mechanism, a striking piston, and a cutting edge receiving the impacts of the striking piston to transmit them to the rock. The striking piston is movable in a cylinder formed by an inner jacket, and between the jacket and the inner wall of the hammer body are provided longitudinal passages serving to bring the compressed air acting on the piston, other passages serving the exhaust of air after its action on either side of the striking piston. When such hammers are provided for an independent supply of a cuttings flushing fluid, they comprise an axial connection piece to the piping for supplying the fluid through the drilling tubes, and an axial tube passing right through the whole assembly of the hammer, that is to say in particular the striking piston, to come out in an axial bore formed in the cutter. Such a pneumatic hammer has been described for example in the French patent published under number 2,044,939.

To obtain sufficient forces to strike the striking piston on the cutting edge, and consequently on the rock to be broken, compressed air is used under high pressure, at 20 to 25 bars for example. Consumption which can be of the order of 10 to 15 Nm 3 per minute, for example, therefore requires the use of high flow compressors under high pressure, that is to say heavy and bulky equipment. It is also expensive equipment, both in terms of purchase and fixed assets, and in operating cost because energy consumption is high.

The present invention allows a significant reduction in these costs, and in particular, with the same drilling efficiency, a significant reduction in energy consumption.

The invention therefore relates to a pneumatic drilling hammer of the type "downhole", comprising a tubular body supplied with compressed air carrying a perforating cutter, and in which a striking piston is set in reciprocating motion in an inner sleeve forming a sheath by a mechanism for distributing compressed air alternately to - above and below the striking piston so that it cyclically strikes the cutting edge and goes up.

According to the invention the hammer comprises two separate supplies of compressed air, respectively at high and low pressure, the distribution mechanism alternately ensuring the supply of high pressure air to the upper chamber above the striking piston to project it towards the cutting with exhaust from the lower chamber, then the low-pressure air supply from the lower chamber to raise the piston with exhaust from the upper chamber.

According to a particular embodiment of the invention, the supply of low pressure air to the lower chamber is provided by an internal axial chamber of the striking piston, while the supply of high pressure air to the upper chamber is provided by lights. crossing the sheath and longitudinal grooves formed externally in the thickness of the sheath.,

The invention will be better understood by referring to a particular embodiment given by way of example and represented by the accompanying drawings.

Figure 1 is a general view in longitudinal section, in two parts, of a pneumatic hammer produced according to the invention.

Figures 2 to 5 are partial views which show the successive positions of the striking piston during an operating cycle.

Referring firstly to the assembly of the two parts of FIG. 1, it will be seen that the main body 1 of the hammer is screwed at its lower part onto a nozzle 2 in which slides the grooved tail of the perforating cutter 3. The tail of the cutter is stopped in rotation relative to the body, and limited in axial displacement by a tangential key 4 which bears on a clearance 5 of the tail.

A cylindrical sheath 3 internally doubles the body 1 over almost its entire length. At its lower part the sleeve 7 is supported on a spacer ring 8 of generally conical shape, pierced with radial orifices 9, and which itself is supported on the end piece 2. Similarly the other end of the sleeve 7 is in abutment on a ring 10 provided with radial conduits 11. The ring 10 is held by the end of the rac end cord 13 screwed onto the body 1. By its other end the end piece 13 receives the usual pieces of connection with the tubes and rods for supplying and operating the hammer. The part 15 which transmits the thrust on the hammer forms a first annular conduit 16 around a tube 17; a second annular conduit 18 is formed between the internal face of the tube 17 and a central tube 19.

By its internal surface the sleeve 7 serves as a guide for the sliding striker piston 21 which can move freely between a low position as shown in Figure 1 where it is in contact with the end of the tail of the cutter, and a high position as will be seen later in the description of the operation of the device. The upper part of the striker 21 permanently encloses the lower part of the tube 17, the solid lower end 23 of which has channels 24 which make the annular duct 18 communicate with a central chamber 25 inside the striker 21. The chamber 25 is extended by two axial conduits 26 and 27, the latter opening at the bottom of the batter. Externally the striker 21 has a circular groove 28.

The outer surface of the sleeve 7 has three series of longitudinal grooves; to simplify the drawing, only one groove of each type has been shown here. A first series of upper grooves 30 communicates the annular chamber 31 which surrounds the ring 10 with as many orifices 32 which open out inside the sheath. A second series of lower grooves 34 lead to the annular chamber 35 surrounding the lower ring 8; the orifices 36 and 37 pass through the wall of the sheath 7 and open into these grooves 34. Finally, a third series of grooves 39 connects the orifices 40 and 41 which also pass through the wall of the sheath 7.

It will be noted that the chamber 35, around the ring 8, communicates with the outside of the hammer by the conduits 9, by the games between the grooves of the cutting edge and the conjugate grooves of the end piece 2, and by the chamber 47 which communicates to the outside via the exhaust pipes 48.

The central tube 19 is used for the supply of water used to drive the cuttings down the hole. For this, the tube 19 is extended at the bottom until it enters the tail of the cutter which has a conjugate central channel 43. The penetration of the tube into the tail of the cutter is determined so that the tube remains engaged whatever the position. of the cutting edge in its axial displacement. The central channel 43 is extended by a channel 44 which opens out through orifices 45 at the periphery of the cutting edge to chase the spoils.

The outer annular duct 16 is supplied with compressed air at high pressure, for example under 20 to 25 bars. The inner annular duct 18 is supplied with compressed air at low pressure, for example at 6 bars.

The drawings have not shown the simultaneous hammer supply connections by the three different fluids, flushing liquid for the central tube 19, low pressure air for the duct 18, high pressure air for the duct 16. Such fittings, as well as the structure of the elongate tubes for connection with the surface have already been described for example by the French patent published under the number 2.126.118.

We will now refer to Figures 2 to 5 to understand the operation of the hammer, thus supplied with compressed air under two different pressures. In FIG. 2, as in previous FIG. 1, the striking piston 21 is shown in the low position, just after its impact on the tail of the cutter. In this position the high pressure air fills the conduit 16, the intermediate chamber 49, the conduits 11, the annular chamber 31, the grooves 30 and the orifices 32; but these, inside the sheath, are closed by the striker 21 and the high pressure air remains trapped in the grooves 30. On the other hand the low pressure air which arrives via the conduit 18 passes through the conduits 24 in the chamber 25, and from there via the conduits 26 and 27 fills the lower chamber 50 under the striker 21. The pressure in the lower chamber 50 causes the striker 21 to rise without any reaction other than its own weight because the upper chamber 51 then communicates freely with the exhaust outside the hammer through the orifices 36, the grooves 34 and the chamber 35.

When in its ascent stroke the striker reaches the position shown in Figure 3, the supply of low pressure air is interrupted by sealing the orifices 24 by the walls of the chamber 26. At the same time the chamber 50 is turned on. the exhaust through the opening of the orifices 37 which then make it communicate with the grooves 34.

Under the impulse given, the striker 21 will continue its upward stroke and the groove 28 will face the orifices 32 and fill with high pressure air.

When the striker reaches the position shown in Figure 4 the groove 28, already full of air under high pressure, directly communicates the holes 32 and 40, so that by the grooves 39 and the holes 41 the chamber 51 is filled high pressure air.

The exhaust ports 36 are already closed, the high pressure in the chamber 51 violently pushes the striker 21 downwards, without back pressure since the lower chamber 50 is then exhausted through the exposed orifices 37.

During its downward stroke (FIG. 5), the striker 21 first closes the high pressure supply to the chamber 51, then puts the latter in the exhaust by uncovering the orifices 36. A little before the impact on the end of the tail of the cutting edge the exhaust of the chamber 50 is closed by closing the orifices 37, then the low pressure air is again brought into the chamber 50 by opening the orifices 24 on the chamber 25, and the cycle can start again.

It can be seen that thus at each cycle, that is to say at each round trip of the hitter 21, only the active phase of throwing from the hitter towards the cutting edge consumes high pressure air, while the inactive phase of ascent consumes only air under low pressure; the force generated by the low pressure in the chamber 50 is sufficient to ensure the free rise of the hitter who also benefits from the rebound effect upon impact on the end of the tail of the cutting edge. The consumption of air at high pressure is therefore globally divided substantially by two, which makes it possible, for the same perforation power, to use a material that is much less bulky, less expensive to purchase and less costly in energy consumption. The supply of compressed air under low pressure of the order of 6 bars in fact requires only a connection to a usual distribution network, or a compressor group with low purchase and consumption costs.

It will be noted that at the exhaust, both the high pressure air after action in the upper chamber 51 and the low pressure air after working in the lower chamber 50 are found mixed in the chamber 35, then at the outlet of the hammer in conduits 48.

Naturally the invention is not strictly limited to the mode of re _w ing which has been described as an example, but it also covers the achievements that do differ only in details, by variants 'execution, or by the use of equivalent means.

Thus, although the above description has been made for a pneumatic hammer having a central flushing fluid supply, the same advantage in energy consumption reduction would be observed for a hammer without flushing fluid, and the cuttings do not would be evacuated only by the exhaust air from the conduits 48.

Claims (4)

1.- Pneumatic perforation hammer of the "down-the-hole" type, comprising a tubular body (1) supplied with compressed air and carrying a perforating cutter (3), and in which a striking piston (21) is set back and forth movement in an inner jacket (7) forming a sheath by a mechanism for distributing the compressed air alternately above and below the striking piston so that it cynically strikes the cutting edge and reassemble, characterized in that the hammer comprises two separate supplies of compressed air (16, 18), respectively at high and low pressure, the distribution mechanism alternately ensuring the supply of high pressure air to the upper chamber (51 ) above the piston (21) to project it towards the cutting edge with exhausting of the lower chamber (50), then the low pressure air supply to the lower chamfer (50) to raise the piston ( 21) with exhaust from the cham upper bre (51). 2. A pneumatic hammer according to claim 1, characterized in that the supply of low pressure air to the lower chamber is ensured by an internal axial chamber (25) of the striking piston (21), while the supply of high air pressure of the upper chamber (51) is provided by openings (32, 40, 41) passing through the sheath (7) and longitudinal grooves (30, 39) formed externally in the thickness of the sheath. 3. A pneumatic hammer according to claim 1, characterized in that the exhaust ducts (36, 37), respectively of the high pressure air from the upper chamber (51) and the low pressure air from the lower chamber (50 ), have a common part (34) opening at the bottom of the hammer. 4. A pneumatic hammer according to any one of the preceding claims, characterized in that it further comprises an axial duct (19) for supplying the cuttings flushing fluid.

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