AU2009202750A1

AU2009202750A1 - Pneumatic drill

Info

Publication number: AU2009202750A1
Application number: AU2009202750A
Authority: AU
Inventors: Bernard Lionel Gien
Original assignee: BERNARD GIEN
Current assignee: BERNARD GIEN
Priority date: 2008-07-10
Filing date: 2009-07-07
Publication date: 2010-01-28
Also published as: CN101676514A; CA2670999A1; AU2009202750A8; AU2009202750A9; ZA200904814B; KR20100007762A; CL2009001562A1

Description

S&F Ref: 913386 AUSTRALIA PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT Name and Address Bernard Lionel Gien, of 7 Pillemar Street, Morningside, of Applicant: Sandton, Gauteng Province, Republic of South Africa Actual Inventor(s): Bernard Lionel Gien Address for Service: Spruson & Ferguson St Martins Tower Level 35 31 Market Street Sydney NSW 2000 (CCN 3710000177) Invention Title: Pneumatic drill The following statement is a full description of this invention, including the best method of performing it known to me/us: 5845c(2191087_1) 1 PNEUMATIC DRILL Field Of The Invention This invention relates to pneumatic drills and more particularly to the kind of 5 drills known as "down-the-hole" drills. Background To The Invention Drills of this kind usually include a pneumatically powered piston reciprocating to impact on a drill bit. The gauge of the drill bit must provide a hole large enough for the 10 passage through the drilled rock of the operating mechanism. The operating mechanism can then be located at the working surface and the compressed air to power the operating mechanism conveyed down the hole through a drill stem to the operating mechanism. This air must be caused to act intermittently to drive the piston and to return the piston to a position at the start of its power or impact stroke. It is also necessary that the air be 15 exhausted from the mechanism. Preferably this air is used to clear drilled rock from the working surface particularly when the bit is raised from the working surface and allowed to fall onto its retaining rings in the bit chuck. These well known and widely used mechanisms are necessarily compact and the 20 air passages confined. It is an ongoing challenge to improve the efficiency of the supply of air to these drills while maintaining the strength of the component parts in the down the-hole working conditions against failure and unacceptable wear rates. A particular down-the-hole drill of the kind referred to is disclosed in the 25 specification of my South African Patent No. 2005/03406 and that specification is included in this document in its entirety by reference. The drill disclosed in the above specification uses a chamber divider to direct the air supply from the backhead end into spaced cutouts in the inner wall of the wear sleeve 30 and around the piston. The latter forms at least one shoulder exposed to air pressure during operation of the drill. This gives rise to difficulties in balancing the air pressure forces to reciprocate the piston. More particularly unless adequate exhausting from the chamber formed to provide the return stroke of the piston is obtained the piston will continue to reciprocate when the bit is withdrawn from the working surface. This is 35 explained more fully below. The cutouts in the wall of the cylinder also makes its 2 necessary overall wall thickness such that it can withstand the operating stresses at its parts of minimum material thickness. This limits the dimensions of the piston that can be used in a drill designed to drill a specific hole size. Any use that can be made of the space occupied by wall thickness material having excess strength characteristics relative to the 5 basic minimum requirement enables an overall increase in effectiveness of the drill to be achieved. Object Of The Invention It is an object of the present invention at least in its preferred form(s) to address 1o the problems referred to and mitigate their effects on the overall efficiency of such down the-hole hammer drill assemblies. Summary Of The Invention In accordance with the invention there is provided a down-the-hole pneumatic 15 hammer drill assembly which includes: a backhead secured to a wear sleeve for an impact piston; a drill bit mounted in a chuck in the wear sleeve for limited reciprocation remote from the backhead and providing an anvil for the piston; the piston having a stem of reduced diameter for impacting the bit; the stem guided in a piston stem bush; and an exhaust flow passage provided passed the piston stem bush into a bore through the bit to 20 vent air from a chamber around the piston stem when the bit is lifted from a working surface. The invention further provides for the exhaust flow passage to be provided through the piston stem bush; or for the exhaust flow passage to be provided by a recess 25 partway along the piston stem. A further feature of one aspect of the invention provides for the drill assembly to include fluid paths formed by cut-outs in the walls of the piston and the wear sleeve with a longitudinal annular passage through the wear sleeve for the supply of pressurized fluid 30 to drive the piston, the annular passage extending from the backhead end of the assembly and having spaced apart ports communicating with an air supply passage through the backhead at one end and with the interior of the wear sleeve at the other end. Further features of the invention provide for the annular passage to extend 35 between the outer surface of a part of the wear sleeve having a reduced diameter and the 3 inner surface of a shroud radially spaced from the surface of reduced diameter and secured to the wear sleeve; and for the shroud to be releasably located in position by attachment of the backhead to the end of the wear sleeve. 5 Still further features of invention provide for the annular passage to extend between the inner surface of part of the wear sleeve having an increased diameter and the outer surface of a skirt depending from the backhead and for the skirt to be screw threaded to engage within a screw-thread at the end of the wear sleeve for attachment of the backhead to the wear sleeve. 10 In accordance with still another aspect of the invention there is provided for the drill assembly to include fluid paths formed by cut-outs in the walls of the piston and the wear sleeve with a longitudinal annular passage through the wear sleeve for the supply of pressurized fluid to drive the piston, the annular passage extending from the backhead end is of the assembly between the outer surface of a part of the wear sleeve having a reduced diameter and the inner surface of a shroud radially spaced from the surface of reduced diameter and secured to the wear sleeve. In accordance with yet another aspect of the invention there is provided for the 20 drill assembly to include fluid paths formed by cut-outs in the walls of the piston and the wear sleeve with a longitudinal annular passage through the wear sleeve for the supply of pressurized fluid to drive the piston, the annular passage extending from the backhead end of the assembly between the inner surface of part of the wear sleeve having an increased diameter and the outer surface of a skirt depending from the backhead; and in which the 25 skirt is screw-threaded to engage within a screw-thread at the end of the wear sleeve for attachment of the backhead to the wear sleeve. Brief Description Of The Drawings These and other features of this invention will become apparent from the 30 following description of embodiments of the invention described below with reference to the accompanying drawings in which: Figure 1 shows a longitudinal cross-section through the drill assembly and the insert shows a modification; 35 4 Figure 2 shows a longitudinal cross-section through an alternative embodiment of a drill assembly; and Figure 3 shows an enlarged view of part of Figure 2. 5 Detailed Description Of The Preferred Embodiments In the embodiment illustrated in Figure 1 compressed air is introduced into the drill assembly (1) through an inlet passage (2) in the backhead (3). The air is then passed through distribution passages (4) into a passage (5) around the circumference of the 10 backhead (3). A wear sleeve or cylinder (6) has at its operatively upper, outer end an annular recess providing reduced wall thickness. A longitudinally extending, annular passage (7) is formed by securing a shroud (8) at its ends over the reduced wall thickness portion of 15 the wear sleeve (6). This securing will include seals (9) and may be effected by welding or the like. In this embodiment, a screw-thread attachment of the backhead (3) to the wear sleeve (6) is used to secure the shroud (8) in position. The backhead includes a known assembly of a check valve (10) and control rod 20 (11). Figure 1 shows the location of the necessary cut-outs in the inner wall of the wear sleeve (6) and along the outer wall of a piston (12). The cutouts provide the necessary flow paths for the compressed air through the assembly to reciprocate the 25 piston (12) which strikes the anvil at the operatively upper end of the bit (13). In the condition shown, the check valve (10) is closed and the control rod (11) withdrawn from the piston (12). When compressed air is applied, the check valve (10) opens against its spring bias to allow flow through passages (4) into the passage (5) in the 30 backhead (3) and thence through inlet ports (7A) to outlet ports (7B) via annular passage (7) in the wear sleeve (6). The passage (7) feeds the interior of the wear sleeve (6) and thus the chamber (14) formed between the upper cutouts in the piston (12) and wear sleeve (6) through 35 outlet ports (7B). This chamber (14) remains pressurized while the check valve (10) is 5 open and alternately provides pressure to both ends of the piston (12) for power and return strokes as is set out below. While the drill (1) is operating, the head or operatively upper end of the piston 5 (12) never moves down the wear sleeve (6) passed the outlet ports (7B). The piston (12) has a reduced diameter in a lower region of chamber (14) and is stepped outwardly to form a shoulder at (15). Cutouts (16) in the enlarged step (15) are provided as shown. The shoulder (15) together with the bottom of the cutouts (16) provides a stepped surface area on the piston (12) which in use will be under the influence of pressurized air in the io chamber (14). This surface area will be referred to as shoulder (15). An axial bore (17) is provided through the piston (12) and the piston has a stem (18) of reduced diameter at its operatively lower free end. The free end of the stem (18) forms the striking face which acts on the anvil of the bit (13). 15 A piston stem bush (20) fitted in the wear sleeve (6) acts as a guide for the stem (18) of the piston (12) and upper end of the bit (13) when the latter is in the impact zone during operation of the drill. 20 The reduced diameter of the piston stem (18) forms a second chamber (21) in the assembly (1) and a usual form of chuck (22) with retaining ring (23) is located in the bottom of the wear sleeve (6). This allows limited free axial movement of the bit (13) when it is not in contact with a working surface. 25 In the described embodiment of this invention shown in Figure 1, exhaust venting ports (24) and (25) are shown from the chamber (21) around the stem (18) through the piston stem bush (20). An alternative arrangement of piston stem bush (20) is illustrated in the insert shown. In this latter arrangement recesses in the form of slots (27) are provided partway along the piston stem (18) to provide the venting passage from the 30 second chamber (21) when the bit (13) is in its extended position. In operation the compressed air supplied through the annular passage (7) enters the chamber (14) and from there passes into the second chamber (21).

6 The pressure in the chamber (21) acts on the bottom surface of piston (12) and urges it upwards. In this travel (a) on the piston (12) passes (b) in the bore of the wear sleeve (6) to prevent the air from entering the chamber (21). The piston stem (18) withdraws from the piston stem bush (20) and the air in the chamber (21) exhausts s through bore (28) in the bit (13) to atmosphere. Point (c) in the bore (17) of the piston (12) passes (d) on the control rod (11) thereby sealing off the upper chamber (26) formed around the control rod (11) from exhausting through the bore (17) in the piston (12). As (e) on the piston passes (f) in the 10 bore of the wear sleeve (6) compressed air from the pressurized chamber (14) enters the upper chamber (26). The air pressure from this chamber (26) acts on the upper end of the piston (12) and combines with pressure applied to the shoulder (15) on the piston (12) to provide the propulsion of the piston to strike the anvil of the bit (13). 15 At this time, (c) in the bore of the piston (12) has moved downwardly passed (d) on the control rod (11) and chamber (26) can exhaust through the bores in the piston (12) and bit (13) to atmosphere. When the drill is raised in the bore hole, the bit (13) drops in the chuck (22) and 20 falls against the retaining rings (23). As a result the piston (12) follows the bit (13) and (g) on the piston passes (h) in the wear sleeve (6) to seal chamber (21) from chamber (14). Simultaneously, downward movement of bit (13) has opened the ports (24) and 25 (25) through the piston stem bush (20) to release the pressure from the chamber (21) and allowing exhaust through the bore (28) in the bit (13). It is important to release the pressure from chamber (21) when the drill (1) is in this flushing condition. Otherwise, the piston (12) will bounce back and continue reciprocating. 30 Also (i) on the piston (12) has passed (j) in the bore of the wear sleeve (6) to open ports (7B) into chamber (26) and thus permitting a pressurized air supply to flow through the piston (12) and the bit (13) to atmosphere and flush the bore hole. The flushing mode will only take place when the piston (12) is inactive and the ports (7B) can flush through (17) and (28). 35 7 Referring again to the insert in Figure 1, it will be appreciated that downward movement of the bit (19) when it is lifted off the working face at the bottom of the drill hole causes the piston (12) to move downward and this is accompanied by location of the slots (27) on the stem (18) across the stem bush (20). In this way, the necessary venting of 5 the chamber (21) is also achieved. Once the bit (13) is replaced onto the working surface and moved back into the wear sleeve (6) the reciprocating action of the piston will restart. 10 As mentioned, while the piston (12) is stroking, chamber (14) is continually pressurized and alternately supplies upper chamber (26) and lower chamber (21). Compressed air on the shoulder (15) acts continuously against the lifting of the piston (12) during the return stroke. The smaller surface the area of the shoulder (15), the smaller will be the force acting against the return stroke. To achieve this, as compared 15 with existing drill assemblies, one solution is use of the shroud described above. Referring now to Figures 2 and 3, an alternative construction of a drill assembly (31) which also enables this result to be obtained is illustrated and described below. The drill (31) has a backhead (32) with an axial inlet (33) for operating air at one 20 end. The backhead (32) has inclined, radially extending distribution passages (34) and the usual spring biased inlet control valve assembly (35) A control rod (36) extends from the backhead (32) into a wear sleeve (37) for the operating assembly. This assembly consists of a pneumatically operated piston (38) 25 forming the hammer for a drill bit (39). The drill bit (39) is retained in a well known chuck assembly (40) mounted in the end of the wear sleeve (37) remote from the backhead (32). A piston stem bush (41) is mounted in the wear sleeve (37) above the bit 30 retaining ring (42). This ring (42) permits a limited free fall of the bit (39) when the latter is raised from the working position shown in Figure 2. The stem bush (41) has an annular exhaust passage (43) extending longitudinally to meet radial outlet ports (44). When the bit (39) is raised from the working surface and moved outwardly from the wear sleeve (37) in the usual manner to achieve flushing, operating air will discharge from the 35 assembly (31) via the axial passage (45) through the bit (39).

8 It will be appreciated that the annular exhaust passage (43) may alternatively be provided between the outside of an upper portion of the stem bush (41) having a reduced diameter and the wear sleeve (37) instead of extending through the stem bush (41) as 5 shown. The wear sleeve (37) and piston (38) have cut-outs respectively to provide flow passages for the pneumatic operation of the piston (38) on the bit (39). This embodiment also has a chamber (46) in which pressurized air continuously acts on shoulder (47) of the io piston (38). The operation of the assembly has already been described with respect to the first embodiment shown in Figure 1. What is important in this embodiment is the flow path (51) provided for inlet pressurized air into the operating assembly. 15 The backhead (32) is screw-threaded into engagement in the end of the wear sleeve (37) and to enable this to be done an externally screw-threaded skirt (49) extends from the body of the backhead (32) into the wear sleeve (37). An annular passage (51) is provided between the inner surface of the wear sleeve (37) and the skirt (49). The 20 distribution passages (34) provide inlet ports (5 1A) adjacent the upper end of the skirt (49) which open into the annular passage (51). Outlet ports (51B) adjacent the lower end of the skirt (49) open from the passage (51) into the interior of the wear sleeve (37) and into cutouts at the upper end of the piston (38). These components can be seen more clearly in Figure 3. 25 To maintain an adequate wall thickness to the wear sleeve (37) the operatively upper end is made this enough to accommodate the provision of an internal screw-thread to receive the external screw-thread on the skirt (49). 30 In this embodiment, the outside diameter of the skirt (49) is initially provided to be larger than what would normally fit through the internal thread (37A) at the top of the wear sleeve (37). The outside of the skirt (49) is then threaded to engage in the top of the wear sleeve (37), as shown. The thread on the skirt (49) serves the purpose of adding thickness to the wall of skirt (49). The thread depth in the embodiment shown is 3mm. 35 The thread depth is added to the wall thickness of the skirt (49) making it much stronger.

9 This allows for a larger bore within the skirt (49) and a better ratio of the surface areas on the piston (38). At the same time a smaller surface area on shoulder (47) is achieved which improves the piston upward speed of the piston (38) to create more blows per minute and thus better performance. 5 The drill assembly of the invention gives an improved ratio of the surfaces on the piston (38) that result in a positive return stroke and ensure the cessation of movement of the piston (38) when the bit (39) moves into an inoperative position. The construction also maintains satisfactory wall strength for the threaded skirt (49) while still maintaining 10 the described compact construction. The down-the-hole drills described above mitigate the problems referred to and provide efficient easily manufactured products.

Claims

1. A down-the-hole pneumatic hammer drill assembly which includes: a backhead secured to a wear sleeve for an impact piston; a drill bit mounted in a chuck in 5 the wear sleeve for limited reciprocation remote from the backhead and providing an anvil for the piston; the piston having a stem of reduced diameter for impacting the bit; the stem guided in a piston stem bush; and an exhaust flow passage provided passed the piston stem bush into a bore through the bit to vent air from a chamber around the piston stem when the bit is lifted from a working surface. 10

2. A drill assembly as claimed in claim 1 in which the exhaust flow passage is provided through the piston stem bush.

3. A drill assembly as claimed in claim 1 in which the exhaust flow is passage is provided by a recess partway along the piston stem.

4. A drill assembly as claimed in claim 1 which includes fluid paths formed by cut-outs in the walls of the piston and the wear sleeve with a longitudinal annular passage through the wear sleeve for the supply of pressurized fluid to drive the 20 piston, the annular passage extending from the backhead end of the assembly and having spaced apart ports communicating with an air supply passage through the backhead at one end and with the interior of the wear sleeve at the other end.

5. A drill assembly as claimed in claim 4 in which the annular passage 25 extends between the outer surface of a part of the wear sleeve having a reduced diameter and the inner surface of a shroud radially spaced from the surface of reduced diameter and secured to the wear sleeve.

6. A drill assembly as claimed in claim 5 in which the shroud is releasably 30 located in position by attachment of the backhead to the end of the wear sleeve.

7. A drill assembly as claimed in claim 4 in which the annular passage extends between the inner surface of part of the wear sleeve having an increased diameter and the outer surface of a skirt depending from the backhead and the skirt is screw- 11 threaded to engage within a screw-thread at the end of the wear sleeve for attachment of the backhead to the wear sleeve.

8. A drill assembly as claimed in claim 1 which includes fluid paths 5 formed by cut-outs in the walls of the piston and the wear sleeve with a longitudinal annular passage through the wear sleeve for the supply of pressurized fluid to drive the piston, the annular passage extending from the backhead end of the assembly between the outer surface of a part of the wear sleeve having a reduced diameter and the inner surface of a shroud radially spaced from the surface of reduced diameter and secured to the wear 1o sleeve.

9. A drill assembly as claimed in claim 1 which includes fluid paths formed by cut-outs in the walls of the piston and the wear sleeve with a longitudinal annular passage through the wear sleeve for the supply of pressurized fluid to drive the is piston, the annular passage extending from the backhead end of the assembly between the inner surface of part of the wear sleeve having an increased diameter and the outer surface of a skirt depending from the backhead; and in which the skirt is screw-threaded to engage within a screw-thread at the end of the wear sleeve for attachment of the backhead to the wear sleeve. 20

10. A drill assembly substantially as described with reference to Figure 1 or Figures 2 and 3 of the accompanying drawings. Dated 3 July, 2009 25 Bernard Lionel Gien Patent Attorneys for the Applicant/Nominated Person SPRUSON & FERGUSON