A drill hammer

Abstract

The invention relates to a pneumatic drill hammer (100). A back-head (104) is secured to a wear sleeve (102). A check valve chamber (112) is provided between the back-head (104) and a chamber dividing wall (118), which supports a check valve (158) and finger valve (128) assembly. A cylindrical skirt (120) extends from the chamber dividing wall (118) along an inside of the wear sleeve (102). An arrangement of passages (136) extends from the check valve chamber (112) to supply air to an annular passage (140) between the skirt (120) and wear sleeve (102). First (189) and second (186) ports from the annular passage (140) through the skirt (120) provide for air distribution paths as the piston (126) reciprocates.

Description

[0001] A DRILL HAMMER

[0002] FIELD OF THE INVENTION

[0003] The invention relates to drill hammer that is pneumatically powered and of the down- the-hole or in-the-hole type. These are well known in the rock drilling industry particularly for drilling into the earth from the surface but also in various underground mining scenarios.

[0004] BACKGROUND TO THE INVENTION

[0005] The components of these drill hammers vary depending on the design that is chosen to achieve a working mechanism. A switching of supply air between a drive chamber and a return or lifting chamber is required to reciprocate a piston that impacts a drill bit. Both chambers need to be exhausted during the cycle and the exhaust air is channelled through a drill bit to flush the drill hole.

[0006] These hammers also have check valves associated with an inlet through a back-head that supplies the pressurised air as the working fluid for the drive mechanism. The check valve is necessary to prevent backflow of water / sludge into the hammer from the borehole.

[0007] The features of an increased flow of air to the drive mechanism (via the check valve) and a simple construction of the parts that are associated with this aspect of the drill hammer would be an advantage. This may translate to improvements in performance, serviceability and / or simplicity in manufacture / assembly, which are important qualities by which a commercial hammer is tested.

[0008] OBJECT OF THE INVENTION It is an object of the invention to provide a pneumatic drill hammer which offers, at least partially, improvements of the kind referred to.

[0009] SUMMARY OF THE INVENTION

[0010] In accordance with the invention there is provided a pneumatic drill hammer comprising: a wear sleeve and a back-head having a cuff that provides a screw-threaded connection into the wear sleeve; an axial inlet to the back-head that opens through a check valve seat; a check valve chamber formed by an enlarged cavity at the check valve seat and along an inside wall of the cuff; a chamber dividing wall provided between the check valve chamber and a drive chamber; a cylindrical skirt that extends from the chamber dividing wall along an inside of the wear sleeve; the chamber dividing wall and skirt configured to provide the drive chamber with a back end of a reciprocating piston and a finger valve that moves into an axial bore of the piston; the cuff engaging against an outer portion of the chamber dividing wall which presses a front end of the skirt against a stop inside the wear sleeve; and the chamber dividing wall including an arrangement of passages that extend from the check valve chamber to a position behind the skirt against the wear sleeve and past a back end of the skirt to supply air to an annular passage that extends between the skirt and wear sleeve.

[0011] The invention further provides for the chamber dividing wall and skirt to be provided as integral parts by a cup-shaped insert.

[0012] The invention further provides for an annular outward step at a front end of the check valve chamber to house a compressible spacer that is biased against a rearward shoulder of the dividing wall. The invention further provides for the arrangement of passages to be formed between the chamber dividing wall and the cuff, preferably as grooves in the rearward shoulder (against which the cuff abuts).

[0013] The invention further provides for a lip on the end of the cuff to locate against an outer portion of the dividing wall that extends forwardly from the rearward shoulder with the grooves formed through the rearward shoulder and open to the lip which locates against lands between the grooves.

[0014] The invention further provides for the chamber dividing wall to have a central opening and supports therethrough a check valve and finger valve assembly:

[0015] - the check valve having a stem that is located in a tube secured within the wall; and

[0016] - the finger valve provided by a part of the tube extending through a drive chamber to interact with the axial bore of the piston.

[0017] The invention further provides for a drill hammer as defined in which a first port and a second port are provided extending across the skirt from the annular passage; the first port located adjacent a front end of the skirt, and the second port located in spaced apart relationship between a rear end of the skirt and the first port; in which the first port connects the annular passage into a first flow path along a length of the piston to the return chamber, and the second port connects the annular passage into a second flow path through the piston to an enlarged region of the axial bore and around the finger valve to the drive chamber.

[0018] The invention further provides for the stop inside the wear sleeve to be provided by a removable clip, preferably a circlip.

[0019] The invention further provides for a drill hammer as defined in which: the clip locates against a rearward facing shoulder in the wear sleeve; and the rearward facing shoulder is provided at a front end of an enlarged diameter portion of the wear sleeve that forms the annular passage around the skirt.

[0020] BRIEF DESCRIPTION OF THE DRAWINGS

[0021] These and other features of the invention will become more apparent from the following description of one embodiment, made by way of example, with reference to the accompanying drawings, in which:

[0022] Figure 1 shows a cross-sectional side view of a top half of a drill hammer in accordance with the invention; and

[0023] Figure 2 shows a cross-sectional side view of a bottom half of the drill hammer in Figure 1.

[0024] DETAILED DESCRIPTION OF THE INVENTION

[0025] Referring to the drawings, a pneumatic drill hammer (100) is provided with a wear sleeve (102) and a back-head (104). The back-head has an annular cuff (106) with an external screw-thread. The cuff provides a connection into the wear sleeve, which has a corresponding internal screw-thread.

[0026] An axial inlet (108) extends along part of the back-head (104) and opens through a check valve seat (110) into an enlarged check valve chamber (112). The check valve chamber is formed by an outward, inclined step (114) between the inlet (108) and a sidewall (116) of the cuff.

[0027] A chamber dividing wall (118) is provided between the check valve chamber (112) and a drive chamber (DC) of the drill hammer (100). The dividing wall (118) in this embodiment is formed integrally with a skirt (120) by a cup-shaped insert (122). The skirt (120) is cylindrical and extends along an inside of the wear sleeve (102). The chamber dividing wall (118) and skirt (120) of the cup-shaped insert (122) are configured to provide the drive chamber (DC) together with a back end (124) of a reciprocating piston (126) and a finger valve (128) that moves into an axial bore (130) of the piston.

[0028] The cuff (106) of the back-head (104) engages against an outer portion of the dividing wall (118) providing a rearward outer shoulder (132), which presses a front end of the skirt (120) against a stop (134) inside the wear sleeve (102). The stop is provided by a removable clip (134), preferably a circlip.

[0029] The chamber dividing wall (118) includes an arrangement of passages (136) that extend from the check valve chamber (112) to a position at (138) behind the skirt (120) against the wear sleeve (102) and past a back end of the skirt to supply air to an annular passage (140). The annular passage (140) extends between the skirt and wear sleeve. The passages (136) in the arrangement are formed between the chamber dividing wall and the cuff, preferably as grooves (136) in the rearward shoulder, against which the cuff is pressed.

[0030] An annular outward step (144) adjacent the front end of the cuff (106) houses a compressible spacer (146) that is biased against the rearward shoulder (132) of the dividing wall. A lip (148) on the end of the cuff (106) locates against an outer portion of the dividing wall (118) that extends forwardly from the rearward shoulder. The grooves (136) in the arrangement extend in this region of the part and are open to the lip (148) on the cuff. The lip locates against lands provided between the grooves (136).

[0031] The compressible spacer (146) in this embodiment is provided by an O-ring with a L- shaped cross-section cover ring. A washer locates against one side of the cover ring which can move or slide to accommodate the compression of the O-ring. Alternative arrangements may also be used, such as a Belleville washer for example. A check valve (158) is provided in an assembly with the finger valve (128). The chamber dividing wall (118) has a central opening (156) which has the check valve (158) and finger valve (162) assembly supported therethrough. The check valve has a stem (162) that is located in a tube (164) having a press-fit into the opening (156). A coil spring in the tube biases the check valve onto the check valve seat. The finger valve is provided by a part of the tube that extends through the drive chamber (DC) to interact with the axial bore (130) of the piston (126). An enlarged head on the back end of the tube locates against the dividing wall.

[0032] A return chamber (RC) is provided at a front end (168) of the piston (126) and is sealed when the axial bore (130) moves over a foot valve tube (170) that protrudes from an anvil end (172) on a drill bit (174). An axial exhaust passage (176) extends from within the foot valve tube (170), along the drill dit (174) and is open through vents at a working face (178).

[0033] The flow of air through the hammer mechanism (100) when in use is described below.

[0034] Compressed air passes through the inlet (108) of the back-head (104), opens the check valve (158) and passes into the check valve chamber (112). Pressure inside the check valve chamber (112) acts on a rear surface area of the dividing wall or chamber divider (118) to keep the insert (122). This biases the insert (122) together with the compressible spacer (146) against the stop (134) in the wear sleeve (102).

[0035] The air from the check valve chamber (112) passes through grooves (136) between the cuff (106) and the dividing wall (118) of the insert (122). The compressed air proceeds to flow down the annular passage (140) provided by the space between the skirt (120) of the insert and the wear sleeve (102).

[0036] In a return part / stroke of the cycle, compressed air from the annular passage (140) flows through a first, forward port (180) across the skirt (120) and down between the piston (126) and the wear sleeve into the return or bottom chamber (RC) below the piston. The compressed air acts on a surface at the front end (168) of the piston and accelerates the piston in an upward movement.

[0037] A front head of the piston that is guided in the wear sleeve (112) includes an annular arrangement of rear slots (181) that extend to a land (183) adjacent the front end (168). The land (183) is a sealing fit to the wear sleeve above an annular recess (185). The annular recess (185) is sized to provide for passage of air around the land (183), which fits between the ends of the recess (185). When these two features are aligned with spaces at the ends of the land (183), compressed air will be supplied to the return chamber (RC).

[0038] The first port (180) thus connects the annular passage (140) into a first flow path along (part of) a length of the piston to the return chamber (RC).

[0039] A bottom end of the axial bore (130) of the piston (126) separates from foot valve tube (170) and return chamber (RC) exhausts down passage (176) through the bit (174) to the atmosphere.

[0040] The piston continues to move on the return stroke and the finger valve (128) enters a top end of the axial bore (130) to seal off the drive chamber (DC).

[0041] In an impact part (drive stroke) of the cycle, a connection passage (182) is provided to extend from a periphery of the piston (126) to an enlarged region (184) at the top of the axial bore (130). The enlarged region (184) is sized to allow a space for upward flow around the finger valve (128), which seals into the portion of the axial bore (130) below the enlarged region (184) to provide the drive chamber (DC). The connection passage (182) is moved into alignment and fluid communication with a second, rearward port (186) through the skirt (120). Compressed air from the annular passage (140) enters the drive chamber (DC) and acts on a surface area at the back end of the piston (126). The upwards travel of the piston is arrested, and the air pressure acting on a surface at the back end (124) generates a force to accelerate the piston (126) in a downward movement towards the bit, providing a drive stroke which leads to the striking of the bit (174) with the piston delivering its blow energy.

[0042] The second port (186) thus connects the annular passage (140) into a second flow path through the piston to an enlarged region (184) of the axial bore (130) and around the finger valve (128) to the drive chamber (DC).

[0043] Following the downward travel of the piston (126), compressed air is again directed to the return chamber (RC) via the first port (180) and the cycle is repeated.

[0044] When the hammer (100) is lifted from a hole bottom, the bit (174) drops forward into a flushing mode. The piston (126) follows the bit and the second port (186) is exposed. Compressed air flows into the space above the piston (126) and out through axial bore (130) and exhaust passage (176) to the atmosphere. The pressure on the surface at the back end of the piston (126) holds the piston down and renders it inactive.

[0045] A person skilled in the art will understand the interaction of parts (to seal or permit flow) in portions of the drill cycle intermediate to those referred to above.

[0046] It is anticipated that the skirt may be provided with an internal cut-out that creates a flow passage around a top, lateral shoulder on a piston when the shoulder moves into the cut-out for supply of compressed air to the drive / top chamber. The cut-out and lateral shoulder replace the connection passage (182) through the piston and the second port (186) through the skirt (120).

[0047] One of the improvements represented by the hammer is that the back-head is separate from the dividing wall and skirt (integral insert) which means that the back-head part can be made from a less expensive steel. The wall of the skirt is required to be relatively thin. For this reason, a material that is stronger and more expensive is required and this may also be machined to a higher tolerance for guiding of the reciprocating piston. The drill hammer of the invention may be used with a regular standard bit (whether it is with a foot valve tube, as shown, or with a piston stem and stem bush, or other possible versions depending on the design of a particular embodiment), which means that replacement bits should be more easily available at most times and places.

[0048] In prior art versions of these hammer drills, it is common for a check valve chamber to be provided in a narrow bore of the back-head or in a tube. The check valve chamber of the current invention provides a plenum for the pressurised working air. The arrangement provides for favourable flow through the grooves, past the dividing wall and to the annular passage between the skirt and wear sleeve.

[0049] The construction of the dividing wall and skirt is also unique in that it avoids having a skirt with openings through a skirt wall to an annular passage down the wear sleeve - the arrangement of the invention feeds the air to a position behind the back end of the skirt.

[0050] A person skilled in the art will appreciate that a number of variations (in addition to those specifically mentioned) may be made to the features of the embodiments described without departing from the scope of the invention.

Claims

CLAIMS1 . A pneumatic drill hammer comprising: a wear sleeve and a back-head having a cuff that provides a screw- threaded connection into the wear sleeve; an axial inlet to the back-head that opens through a check valve seat; a check valve chamber formed by an enlarged cavity at the check valve seat and along an inside wall of the cuff; a chamber dividing wall provided between the check valve chamber and a drive chamber; a cylindrical skirt that extends from the chamber dividing wall along an inside of the wear sleeve; the chamber dividing wall and skirt configured to provide the drive chamber with a back end of a reciprocating piston and a finger valve that moves into an axial bore of the piston; the cuff engaging against an outer portion of the chamber dividing wall which presses a front end of the skirt against a stop inside the wear sleeve; and the chamber dividing wall including an arrangement of passages that extend from the check valve chamber to a position behind the skirt against the wear sleeve and past a back end of the skirt to supply air to an annular passage that extends between the skirt and wear sleeve.

2. A drill hammer as claimed in claim 1 in which the chamber dividing wall and skirt are provided as integral parts by a cup-shaped insert.

3. A drill hammer as claimed in claim 1 or claim 2 which includes an annular outward step at a front end of the check valve chamber to house a compressible spacer that is biased against a rearward shoulder of the dividing wall.

4. A drill hammer as claimed in claim 3 in which the arrangement of passages is formed between the chamber dividing wall and the cuff.

5. A drill hammer as claimed in claim 4 in which the arrangement of passages is provided as grooves in the rearward shoulder.

6. A drill hammer as claimed in claim 5 in which a lip on the end of the cuff locates against an outer portion of the dividing wall that extends forwardly from the rearward shoulder with the grooves formed through the rearward shoulder and open to the lip which locates against lands between the grooves.

7. A drill hammer as claimed in any one of claims 1 to 7 in which the chamber dividing wall has a central opening and supports therethrough a check valve and finger valve assembly:- the check valve having a stem that is located in a tube secured within the wall; and- the finger valve provided by a part of the tube extending through a drive chamber to interact with the axial bore of the piston.

8. A drill hammer as claimed in claim 8 in which a first port and a second port are provided extending across the skirt from the annular passage; the first port located adjacent a front end of the skirt, and the second port located in spaced apart relationship between a rear end of the skirt and the first port; in which the first port connects the annular passage into a first flow path along a length of the piston to the return chamber, and the second port connects the annular passage into a second flow path through the piston to an enlarged region of the axial bore and around the finger valve to the drive chamber.

9. A drill hammer as claimed in any one of claims 1 to 3 in which the stop inside the wear sleeve is provided by a removable clip.

10. A drill hammer as claimed in claim 9 in which the clip locates against a rearward facing shoulder in the wear sleeve.

11. A drill hammer as claimed in claim 10 in which the rearward facing shoulder is provided at a front end of an enlarged diameter portion of the wear sleeve that forms the annular passage around the skirt.

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