MXPA00012605A - Percussive down-the-hole rock drilling hammer, and a piston used therein - Google Patents

Abstract

A down-the-hole percussive hammer comprises a casing (11), a drill bit (13) mounted at a lower end of the casing, a hollow feed tube (15) fixed within the casing and extending along a center axis (CL) thereof, and a piston (16) mounted for axial reciprocation within the casing for transmitting impacts to the drill bit. The piston has a stepped configuration in that a lower portion (16B) thereof is of smaller outer diameter than an upper portion (16A) thereof. The upper portion (16A) forms a downwardly facing surface (22) at the junction between the upper and lower portions. Air-conducting passages are formed in the upper portion of the piston and are supplied with pressurized air from the hollow feed tube. One (18) of those passages intersects the downwardly facing surface of the upper portion of the piston. The present invention also relates to the piston (16) per se.

Description

reach the interface between the piston and the internal surface of the shield, lubricate that interface. However, the presence of the air-guiding notches in the armor serves to weaken the armor and make it more difficult to manufacture. It may be desirable to provide a stronger shield that is relatively simple to manufacture while at the same time providing lubrication of the interface. Another downhole or downhole hammer of the prior art is described in U.S. Patent No. 4,015,670 wherein the piston reciprocates on a hollow air feed tube, which extends through the a central hole in the piston. The passages for conducting the pressurized air from the air supply tube to the chambers above and below the piston, in order to effect the alternating movement of the piston, are formed completely in the piston. That is, some of the passages extend from the central hole towards an upper surface of the piston, and other of the passages extend from the central hole towards a bottom surface of the piston. A problem that occurs in connection with such an arrangement is that when the lower surface of the piston collides with the drill bit, the ends of the passages located in the lower surface are at least partially blocked by the drill bit. Also, impacts can cause cracks in the lower surface around the ends of the passage.

Objectives of the Invention It may be desirable to provide an efficient bottomhole bore hammer which is relatively easy to manufacture and which contains a minimum of parts. An additional objective is to provide a piston for a downhole hammer which provides good lubrication on the cooperating surfaces. A further objective is to provide a piston for a downhole hammer which is economical to produce.

Description of the drawings These and other objects of the present invention will become apparent from the following detailed description of the preferred embodiments thereof in connection with the accompanying drawings, wherein: Figures IA, IB, 1C and ID show a hammer for bottom of well according to the present invention, in a longitudinal section in first, second, third and fourth positions, respectively. Figure 2A shows a piston according to the present invention in a longitudinal section. Figures 2B and 2C show bottom and top views, respectively, of the piston of Figure 2A. Figure 2D shows the piston according to the present invention in a side view. Figure 3A is a longitudinal sectional view of an air feeding tube. Figure 3B is a cross-sectional view taken along line 3B-3B in Figure 3A.

Figure 4 is a longitudinal sectional view of an upper portion of the feed tube and a valve mounted thereon. Figure 5 is a partially exploded view of a tube mounting peg. Figure 6 is a longitudinal sectional view of a shield. Figure 7 is a sectional longitudinal view of a Nylon® bushing. Figure 8 is a longitudinal sectional view through a sealing member.

Detailed Description of a Preferred Modality of the Invention In Figures IA, IB, 1C and ID a preferred embodiment of a hammer 10 for the bottom of the well according to the present invention is shown. The hammer 10 comprises a reversible upper cylindrical shield 11 which, by means of an upper base 14, is connectable to a plurality of rotating probes, not shown, through which compressed air is conducted. The upper base has an external screw thread 14A connected to the shield 11. The inner wall of the shield 11 is free from the notches defining the air passage, and is thus strong and relatively simple to manufacture. (Parts retaining notches 11B may be provided in a portion of the inner wall in contact with the piston for retention purposes only if a reversible shield 11 is used - see Figure 6). A hammer piston 16 reciprocates in the cylindrical shield 11, and the compressed working air is alternately directed to the upper and lower ends of the piston to effect its alternating movement in the shield. Each downward stroke of the piston inflicts a blow or impact shock on the anvil portion 30 of a drill bit 13 mounted within an actuator base 12 in the lower portion of the cylindrical shield 11. As is apparent from FIGS. 1A -1D the piston 16 and the drill bit 13 have a substantially reversed (inverted) shape relative to each other. That is, the piston has a broad upper portion and a narrow lower portion, and the drill bit has a wide lower portion and a narrow upper portion.Generally speaking, when the voltage wave energy is transmitted through the pistons and drill bits, it has been found that the influence due to variations in the cross sectional area A, Young's E-modulus and density, they can be summarized in a parameter Z called impedance. The importance of impedance has been discussed in U.S. Patent No. 5305841. The impedance Z = AE / c, where c = (E / p) l / 2, for example, the elastic wave velocity. In this way, Z = 2Ap. The piston 16 according to the present invention (see Figures 2A-2D) includes a lower portion 16B and an upper portion 16A which slidably engages the inner wall of the shield 11. The upper portion 16A has a length LM1 and an impedance ZM1, while the lower portion 16B has a length LT1 and an impedance ZT1. The ratio ZM1 / ZT1 is in the range of 3.5-5.8. In addition, the ratio LM1 / LT1 or TM1 / TT1 in the range of 1.0-3.0, preferably 1.5-2.5, where TM1 is the time parameter of the posterior portion 16A of the piston, and TT1 is the time parameter of the lower portion 16B of the piston. The definition of the time parameter T is T = L / c, where L is the length of the portion in question and c is the elastic wave velocity in the portion in question. Thus, for portion 16A, TM1 = LMl / cMl and for portion 16B, TT1 = LT / cTl. The reason why it is necessary to consider the time parameter T instead of the length L is that different portions of different materials having different values can be formed with respect to the elastic wave velocity c. Each of the portions 16A and 16B have a basic cylindrical shape and the lower cylindrical portion 16B has a reduced diameter, thereby causing an intermediate end face or a shoulder surface 22 to face downwardly be formed on the upper portion 16A whose surface is preferably perpendicular to the center line CL of the hammer. The construction of the piston is based on the idea that the distribution of the mass of the piston 16 is such that initially a smaller mass, for example, the portion 16B, is coming into contact with the drill bit 13. Subsequently, a mass larger, for example, portion 16A follows. It has been found that by such arrangement almost all the kinetic energy a > »The piston is transmitted to the rock via the drill bit. An internal cylindrical wall 37 of the piston defines a central passageway 31 and is accommodated to slide over a coaxial control tube or supply tube 15 that is secured to the upper base 14. The supply tube 15 is hollow and includes radial openings. of air inlet and radial openings 21 of air outlet. The upper portion 16A of the piston is provided with several passage ways 17, 18, 24 and 25 for the transport of pressurized air. A first passageway 17 communicates with the upper end face 19 of the piston, and opens towards the wall 37 of the piston via a third passageway 24 at a separate location along the length of the piston. A second passageway 18 in the piston communicates with the shoulder 22 and opens toward the wall 37 of the piston via a fourth passageway 25 at a spaced-off site in an upward direction of the third passageway 24. In this way , the second passageway 18 does not open to any of the upper, lower faces 19, 27 of the piston. The passageways 17 and 18 are spaced radially from the outer periphery of the piston by a shoulder 38 to reinforce the piston and minimize air leakage. The center lines CL1 and CL2 of the passages 17 and 18, respectively, are substantially mutually parallel, and substantially parallel to the central line CL of the piston. The center lines CL3 and CL4 of the passages 24 and 25 are substantially mutually parallel and substantially perpendicular to the centerline of the piston. The diameters of the way of passage 17, 24, 18 and 25 are substantially identical. The center lines CL1 and CL3 of the passages 17 and 24, respectively, intersect preferably one with the other, and the central lines CL2 and CL4 of the passages 18 and 25, respectively, also intersect preferably one with the another, for reasons of resistance to fatigue and blasting. The passages 24 and 25 open towards the outer cylindrical periphery of the piston, which provides a good lubrication of the sliding surfaces of the piston, and facilitates the manufacture of the piston, such as the perforation and blasting steps. That is, the oil that is entrained in the pressurized air will constantly be deposited on (and thus will lubricate) the inner wall of the shield even when the radially outer ends of the passages 24 and 25 are substantially constantly sealed by the wall. internal The ways of passage 17 are spaced by approximately 90 °, and the routes of passage 18 are spaced by approximately 18 °. Four first passages 17 are described which open towards the upper surface 19 (Figure 2C) and only two second passages 18 of passage 18 that open towards the intermediate end face 22 (Figure 2B). However, other combinations of ways of passage could be used, such as the first three ways of passage and the three second ways of way, for example. The lower portion 16B slides within a central passageway 39 of a seal member of the lower chamber that rests on the retainers 33. The outer wall 40 of the lower portion 16B will slide against an inner wall of an upper portion 39a of the central passageway 39 to form a seal between them. The seal member 36 of the lower chamber is of a generally cylindrical basic shape, and has notches 36a for receiving o-ring seals which engage the internal surface HA of the shield 11. The anvil portion 30 of the auger 30 The perforation 13 is positioned within an enlarged portion 39b, lower, of the central passageway 39. In this way, the seal member 36, together with the lower base 12, form a structure of auger assembly. A lower chamber 26 is continuously formed between the piston 16 and the seal member 36. During a downward stroke of the piston, the lower portion 16B of the piston reaches a position shown in Figure IB, wherein the upper part of the central passageway 39 of the seal member 36 is closed. At that time, the air outlet openings 21 in the feed tube are also closed. In this way, the lower chamber 26a is formed, which closes to the outside. Therefore, the air in the lower chamber begins to be compressed as the piston descends further. Eventually, the piston collides with the drill bit 13 (see Figure 1C), whereby a lower chamber 26b is formed. The pressurized air is constantly distributed to a central hole 41 of the upper base, while the hammer is in use. He orifice 41 is connected to a valve seat The conical tube 42 which in turn is connected to an expanded central cavity 43. The feeding tube 15 extends into the central cavity 43 of the upper base 14. A bushing 45 extends around a portion of the control tube 15 at a site below the air inlet 20 to stabilize the supply tube within the cavity. The bushing includes annular grooves 45b at an outer periphery thereof (see Figure 7) for the reception of the O-ring seals which form a seal against the inner surface of the upper base. The bushing can be formed of any material, but preferably it is formed of a light weight material such as plastic (for example Nylon®) in order to minimize the weight acting on the spikes 44 which are described below. Due to the use of bushing 45 to stabilize the feed tube, there is no need to manufacture the outer diameter of the feed tube with narrow dimensional tolerance in relation to the internal diameter of the upper base, because the bushing ensures that the feeding tube will be stabilized, and that no air of aag = * ißÉiÉaá? te «-? work may leak away down the bushing. The feeding tube is mounted to the upper base by means of the two lateral pegs 44 (see also Figure 5), each extending through the aligned radial holes formed in the lower portion of the upper base, the hub 45, and the upper portion of the tube 15. The holes 15a and 45a formed in the control tube 15 and in the hub 45, respectively, are shown in Figures 3A and 3B. Each pin 44 extends from the tube 15 towards the external screw threads 14a of the upper base, and does not extend inside the tube to an appreciable extent, and thus does not decrease the air conduction capacity of the tube as It could happen if the spikes extended completely through the tube. The upper portion of the tube 15 carries a check valve 35 that is elastically accommodated on the tube 15 by means of a compression coil spring 50 (see Figure 4) which deflects the closed valve during periods when the openings 21 of the tube supply 15 are blocked by the internal wall 37 of the piston 16.

The hammer operates as follows with reference to Figures IA to 1C. Figure 1C shows the impact position of the piston 16. It should be noted that during a drilling operation, the lower chamber 26 positioned between the piston and the sealing member 39 does not become shorter than the length L2 of the lower chamber 26a shown in Figure 1C. The front end 27 of the piston has impacted just above the anvil portion 30 of the auger 13. A shock wave will be transferred through the auger to the cemented carbide buttons on the front surface of the auger, thereby shredding the rocky material. The hammer is simultaneously rotated via the string of drill rods, not shown. The piston will then move upwardly due to bounce from the auger and due to the supply of pressurized air from the air outlet openings 21 of the control tube 15 by way of the passage ways 25 and 18. The piston will close the openings 21 while moving in an upward direction, such that no more pressurized air will be emitted through the openings 21. Accordingly, the spring 50 will push the valve 35 in an upward direction to a position that closes the passage 41 (see Figure IB), since the flow of air is blocked. The piston 16 is still moving in an upward direction due to its momentum and due to the expanding air in the lower chamber. This movement of the piston will continue until the force acting down on the upper surface 19 of the piston becomes greater than the force acting in an upward direction on the intermediate end face 22 of the piston. In the mean time, neither the upper chamber 32 nor the lower chamber 26 communicates with the air supply or the outlet channels (see Figure IB). In the position shown in Figure IA the lower chamber 26 has been opened outwards, since the inner wall 39 of the sealing member 36 of the lower chamber, and the outer wall 40 of the lower portion 16B no longer engage one with the other. In this way, air will push from the lower chamber through the drill bit 13 to blow away the drilling dust. The upper chamber 32 is now supplied by pressurized air by means of the openings 21 and the passage ways 24, 17. The piston, however, is still moving in an upward direction such that eventually the openings 21 ti ^ áÉUÉd¿MaÉg¡jil | ^ _ ^ ___ ^ lfc ^^ _ itH ^ a > The ends of the air are closed while the pressure of the compressed air in the closed upper chamber 32 is increased to a level approximately equal to the pressure of the supply air that is distributed. to the control tube 15. At this stage the piston stops its upward movement. A downward movement is then initiated due to the spring force of the compacted air in the closed upper chamber 32. The downward movement is accelerated by the air pressure added by the opening of the air supply to the upper chamber 32, when the openings 21 become aligned with the passageway 24. The piston will continue its downward movement until the surface 27 of the elongated lower portion 16B impacts on the auger 13 as shown in Figure 1C. The cycle described above will continue as long as the pressurized air is supplied to the hammer or until the anvil portion 30 of the drill bit comes to rest on the bit retainers 33, as shown in Figure ID. The last case may occur when the auger finds an empty space in the rock or when the hammer is raised. Then, to avoid impacts on the retainers 33, the air supply will not move the piston but rather will come out through the openings 21 and follow the path indicated by the arrows in Figure ID to the front exterior of the hammer. However, when the hammer makes contact with the rock again, the drill 13 will be pushed into the hammer to the position of Figure 1C and the drill hole will be resumed with the condition that pressurized air is supplied. Tests have shown that the hammer according to the present invention drills at least 33% faster than the most competitive known hammer, and this requires 15% less air consumption. In addition, according to the present invention, the air flow conduction passage ways, formed in the piston, never become clogged when the piston collides with the drill bit or with the mounting structure of the auger. The mounting of the feeding tube by pins extending through the threaded portion of the upper base reduces the height of the hammer. Since the spikes do not pass through the AÉBMHa £ ttaHj || a ^ feeding tube, these do not obstruct the flow of air. The use of a bushing between the feeding tube and the upper base makes it possible for the feeding tube to be mounted in a stabilized manner without the need for its outer diameter to correspond closely to the internal diameter of the upper base. In this way, the feeding tube can be manufactured in a simple and cheaper way. The disclosures in U.S. Patent Application No. 09 / 099,686, of which this application claims priority, and in the extract attached to this application, are incorporated by reference herein. Although the present invention has been described in connection with a preferred embodiment thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made, without departing from the spirit and scope of the invention. invention as defined in the appended claims.

Claims (9)

1. A percussion hammer for the bottom of a well, to drill rock, which includes: a shield or case in general cylindrical; an auger assembly structure mounted on a lower portion of the shield and forming an open central passageway in an upward direction; a drill bit mounted on the auger assembly structure, and including an anvil portion projecting upwardly into the central passageway of the auger assembly structure, the drill bit comprises means for blowing away the drilling dust, beyond the hammer; a top base mounted on an upper portion of the shield; a hollow feed tube closed at a lower end mounted to the upper base and extending in a downward direction along a longitudinal central axis of the shield, and defining a central passage adapted to drive pressurized air containing lubricant; feeding tube includes axially spaced upper and lower radial openings; and a piston mounted for axial alternating movement within the shield and positioned below the upper base and above the auger mounting structure, the piston including the upper and lower portions, the lower portion that is cross-sectional smaller than the upper portion whereby the upper portion forms a face-down surface at a junction between the upper and lower portions, the piston includes: an axial side-to-side hole that slidably receives the feed tube; a first passageway extending in a downward direction from an upwardly facing surface of the piston; a second passageway extending in an upward direction from the face-down surface of the upper portion of the piston; a third passageway extending from the axial hole from side to side to an outer peripheral side surface of the piston, and intersecting a lower end of the first passageway; and a fourth passageway extending from the axial hole from side to side to the outer peripheral side surface of the piston, and intersecting an upper end of the second passageway; each of the third and fourth ways of passage are arranged for communication It is intermittent with the lower opening of the feeding tube during alternating movement of the piston to expose an internal surface of the shield to the air containing lubricant; the lower portion of the piston is accommodated to travel downwardly within the central passageway of the auger mounting structure and collide with the anvil portion of the drill bit, with the surface facing downwardly of the bore. upper portion of the piston, spaced above the drill bit and the auger mounting structure.

2. The hammer according to claim 1, wherein the upper and lower piston portions have first and second impedances, respectively, a ratio of the first impedance to the second impedance is in the range of 3.5 to 5.8, wherein the impedance is equal to 2Ap where A is a cross-sectional area of the respective piston portion, and p is the density of the respective piston section.

3. The hammer according to claim 1, wherein the upper base includes táhM | rißi ||| áfiafla? akM | ^^ an external screw thread for coupling the upper base to the shield, the hammer further includes a plurality of pins mounted on the upper base and extending radially through the thread of external screw and inside a side wall of the feeding tube to secure the feeding tube to the upper base, the pins are located outside the central passage of the feeding tube.

4. The hammer according to claim 3, wherein the upper base includes a central hole, the feed tube mounted in the central hole, an outer diameter of the feed tube is smaller than a diameter of the central hole, and a bushing mounted on an outer periphery of the feeding tube inside the central hole and pressed between the upper base and the feeding tube, the pins extend through the hub.

5. The hammer according to claim 4, wherein the bushing is formed of plastic. • 'ii *?

6. The hammer according to claim 1, wherein the upper base includes a central hole, the feeding tube mounted in the central hole, an outer diameter of the feeding tube is smaller than a diameter of the central hole, and a bushing mounted on an outer periphery of the feeding tube inside the central hole and pressed between the upper base and the feeding tube.

7. The hammer according to claim 1, wherein the internal surface of the shield is free of notches that conduct air.

8. A piston adapted for use in a percussion hammer, at the bottom of a well, wherein the hammer is designed to pass the drilling dust on the outer side of the hammer, comprising: upper and lower portions, the lower portion being of cross section smaller than the upper portion, the upper portion forms a face-down surface at a junction between the upper and lower portions; an axial hole from side to side extending through the upper and lower portions; a ^^^ & ^^^ Z! Zj ^ ¡cj ^^ $ i a * ¿the first way of passage that extends in a downward direction from an upward facing surface of the upper portion; a second passageway extending in an upward direction from the face-down surface of the upper portion; a third passageway extending between the axial side-to-side hole and an outer peripheral side surface of the piston, and intersecting a lower end of the first passageway; and a fourth passageway extending between the axial hole from side to side and the outer peripheral side surface of the piston, and intersecting an upper end of the second passageway.

9. The piston according to claim 8, wherein the upper and lower piston portions have first and second impedances, respectively, a ratio of the first impedance to the second impedance is in the range of 3.5 to 5.8, where the impedance is equal to 2Ap where A is a cross-sectional area of the respective piston portion, and p is the density of the respective piston section. ~ * ~ * * »~" ~