US20060000646A1

Movatterモバイル変換

Info

Publication number: US20060000646A1
Application number: US10/529,614
Authority: US
Inventors: Joseph Purcell
Original assignee: Individual
Current assignee: Minroc Technical Promotions Ltd
Priority date: 2002-10-04
Filing date: 2003-09-30
Publication date: 2006-01-05
Also published as: ATE323210T1; AU2003273513A1; ZA200502866B; IES20020794A2; EP1549819B1; DE60304593D1; CA2500949A1; EP1549819A1; WO2004031530A1

Abstract

A down-the-hole hammer is described. It comprises an external cylindrical outer wear sleeve (10), an inner cylinder (9) mounted co-axially within the outer wear sleeve (10), a sliding piston (11) mounted for reciprocating movement within the inner cylinder (9) and the outer wear sleeve (10), to strike a hammer bit (40) mounted at the lower end of the outer wear sleeve (10) and an elongate cylindrical air distributor (3) positioned within the hammer assembly. The lower end of the air distributor (3) is positioned substantially concentrically within the upper end of the inner cylinder (9). A shoulder (38) on the air distributor (3) engages the underside of a complementary shoulder (15) on the inner cylinder (9). The top end of the outer wear sleeve (10) is screw-threadably engaged with the lower end of an annular air distributor mount (2), and the top end of the inner cylinder (9) abuts the lower end of the distributor mount (2) such that the inner cylinder is rigidly mounted in the drill assembly relative to the outer wear sleeve (10).

Description

TECHNICAL FIELD OF THE INVENTION

The present invention relates to “down-the-hole” hammers or fluid-operated percussion drill tools operated by a supply of compressed air.

BACKGROUND TO THE INVENTION

Some designs of conventional down-the-hole hammers and fluid-operated percussion drill tools comprise an external cylinder or outer wear sleeve, within which is mounted an inner cylinder which in turn engages with a backhead assembly. A sliding reciprocating piston co-operates with the inner cylinder and backhead assembly, which when air pressure is supplied through the backhead assembly, acts with a percussive effect on a drill bit retained within a chuck on the outer wear sleeve.

In down-the-hole hammers the energy created is in part dependent on the cross sectional area of the reciprocating piston. This is because the force is determined by the formula P×A (where P=air pressure and A=cross sectional area of the piston). In most modern down-the-hole hammers the piston is a sliding valve, which reciprocates between a strike position on a bit and a top of stroke position. The length and timing of the stroke is determined by the supply and exhaust of air to a lift chamber and top pressure chamber.

In known conventional arrangements, the inner cylinder is effectively suspended within the outer wear sleeve by means of a compressible retaining ring, such as a circlip, which has to be slid up the inner cylinder so as to seat against a shoulder or lip at one end thereof, being compressed when the inner cylinder is dropped down within the outer wear sleeve, and then expanding outwardly into a groove or shoulder formed on the inner diameter of the outer wear sleeve with a snap action. When in this position, the circlip seats within the groove and abuts against the lip of the inner cylinder, by which the inner cylinder is suspended within the outer wear sleeve.

EP1004744A, of the same applicant, discloses a segmented ring mounting for retaining the inner cylinder within the outer wear sleeve in a fluid-operated percussion drill tool, such as a down-the-hole hammer.

The retaining ring seats the smaller diameter inner cylinder within the larger diameter outer wear sleeve. The outer wear sleeve is formed with a groove cut on its inside diameter, or a shoulder for seating the retaining ring against a lip of the inner cylinder. The ring is capable of radial compression and expansion so as to expand radially into the seating groove or shoulder for retaining the components one within the other in use. The retaining ring comprises at least three segments, which when touching end to end form a complete circle, and an expansible O-ring, for holding the segments together but allowing the segments to expand radially and move apart by sufficient amount so as to seat the segments in the groove or against the shoulder.

The inner cylinder of EP1004744A is integral to the porting of the hammer. In the system the piston runs on the inner diameter of the inner cylinder and also on the inner diameter of the outer wear sleeve. It is essential that the fit between the outer diameter of the inner cylinder and the bore of the outer wear sleeve be a tight/close fit to ensure optimum alignment of the two bores. This means that the clearance and hence the efficiency of the hammer is optimised because the operation of the hammer relies on a partial seal between the piston and the top and bottom chambers, i.e. the tighter the clearance the greater the energy (within reason). In the seating ring system of EP1004744A effective operation relies on a difference in wear sleeve bore diameter above and below the seating ring groove. This means the usable diameter for the piston, and thus the energy, is reduced. This is because the inner diameter of the wear sleeve above the seating ring has to be larger than below to ensure that the seating ring is located in position. This results in an effective reduction in the cross-sectional diameter of the piston, which reduces the force on the piston.

Other manufacturers have in the past made the inner cylinder as part of a threaded component which screws into the outer wear sleeve. The disadvantage of this is that the hammer wears externally and in many cases it is rebuilt by replacing all external components. This would obviously be extremely expensive in the above scenario. There is also the issue of the clearance which would be necessary, between the external diameter of the inner cylinder portion and the bore of the wear sleeve, to allow the component to screw into the wear sleeve. As will be explained below the clearance needs to be minimised to optimise the concentricity of the inner cylinder bore and the wear sleeve bore.

In other known prior art percussion hammers the inner cylinder is mounted within the outer wear sleeve by means of a compressible retaining ring, such as a circlip, which is expanded outwardly to seat into the groove or shoulder formed on the inner diameter of the outer wear sleeve.

The outer wear sleeve of down-the-hole hammers is subject to very strong abrasive forces when in use causing significant wear of, and removal of metal from, the outer sleeve. This weakens the outer wear sleeve to the point where it has to be replaced. In the prior art hammers described the provision of circumferential seating grooves for circlips, seating rings and the like, in the inner face of the wear sleeve reduce the wear thickness of the outer sleeve. This means that the outer wear sleeve has to be replaced more quickly than would be the case if the wear sleeve contained no more grooves.

In other prior art down-the-hole hammers (e.g. those having a seating ring) the inner cylinder is located on a shoulder provided by a groove in the wear sleeve. It is then locked in position by the application of torque at the backhead, which locks down on a compression ring or the like. The result is that there is a significant locking force which acts between the shoulder and the threads of the wear sleeve. The possibility that this force could cause distortion on the wear sleeve will increase as the external wear on the wear sleeve outer diameter increases.

Another type of locking system relies on a collet type system (e.g. WO9967065 Azuko). This system applies not only a force down an shoulder on the wear sleeve but also an outward force on the wear sleeve. Again the effect of these forces increases as the wear sleeve wears.

In summary, the disadvantages of the prior art systems are as follows.

Where a seating ring is used this results in:

- a reduction of the available piston cross-section due to shoulder requirements for the seating ring;
- a reduction of wear sleeve cross-section due to the requirement to provide a seating ring groove;
- high locking forces required on the seating ring shoulder of the wear sleeve.
  Where a compressible/expandable circlip is used this results in:
- a reduction of the wear sleeve cross-section due to the requirement to provide a seating ring groove;
- high locking forces required on the seating ring shoulder of the wear sleeve.
  Where an integral inner cylinder and threaded component is used, this results in:
- a requirement for clearance between the inner cylinder and the wear sleeve resulting in concentricity problems;
- it is expensive to rebuild.

OBJECT OF THE INVENTION

It is an object of the invention to provide a down-the-hole hammer, or other fluid operated percussion drill tool, having means for rigidly mounting the inner cylinder in the outer wear sleeve while still maximising the bore of the wear sleeve. It is also an object of the invention to obviate the need for a seating groove in the outer wear sleeve, and to minimise areas of weakness in the outer wear sleeve.

SUMMARY OF THE INVENTION

The invention provides a fluid-operated percussion drill tool, in particular a down-the-hole hammer, comprising an external cylindrical outer wear sleeve, an inner cylinder mounted co-axially within the outer wear sleeve, a sliding piston mounted for reciprocating movement within the inner cylinder and the outer wear sleeve, to strike a hammer bit mounted at the lower end of the outer wear sleeve, characterised in that the inner cylinder is formed with an inwardly-directed abutment which in the assembled tool is clamped between a complementary engagement means and a locking means such that the inner cylinder is rigidly mounted and held in the drill tool assembly relative to the outer wear sleeve.

Preferably, an elongate cylindrical air distributor is positioned within the hammer assembly, and a lower end of the air distributor is positioned substantially concentrically within the upper end of the inner cylinder and an abutment on the air distributor engages the underside of a complementary abutment on the inner cylinder. Preferably, the top end of the outer wear sleeve is screw-threadably engaged with the lower end of an annular air distributor mount, and the top end of the inner cylinder abuts the lower end of the distributor mount such that the inner cylinder is rigidly mounted in the drill assembly relative to the outer wear sleeve when a top locking member is threadably mounted onto the air distributor.

The air distributor is threadably engaged at its upper end with a top locking member which abuts the top of the air distributor mount.

Thus, in the drill assembly of the invention, the inner cylinder is rigidly held relative to the outer wear sleeve.

There is no requirement for a mounting groove for the inner cylinder within the outer wear sleeve, which can be a weak point in the assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of a down-the-hole hammer in accordance with the invention will now be described with reference to the accompanying drawings, wherein:

FIG. 1 is a sectional side elevation of a first embodiment of a down-the-hole hammer of the invention, showing the piston in the strike position;

FIG. 2 is a sectional side elevation of the down-the-hole hammer ofFIG. 1, showing the piston in the top of stroke position;

FIG. 3 is a sectional side elevation of the top part of the hammer ofFIG. 1 to a larger scale;

FIG. 4 is a sectional side elevation, to an enlarged scale, showing a detail ofFIG. 3;

FIG. 5 is a cross-sectional plan view of the down-the-hole hammer ofFIG. 1, on the line C-C ofFIG. 3;

FIG. 6 is a cross-sectional plan view of the down-the-hole hammer ofFIG. 1, on the line B-B ofFIG. 3;

FIG. 7 is a cross-sectional plan view of the down-the-hole hammer ofFIG. 1, on the line D-D ofFIG. 3;

FIG. 8 is a cross-sectional plan view of the down-the-hole hammer ofFIG. 1, on the line E-E ofFIG. 3;

FIG. 9 is a cross-sectional plan view of the down-the-hole hammer ofFIG. 1, on the line F-F ofFIG. 3;

FIG. 10 is a sectional side elevation of a second embodiment of a down-the hole hammer of the invention, showing the piston in the strike position; and

FIG. 11 is sectional side elevation of the top part of the hammer ofFIG. 10 to a larger scale.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIGS.1 to4 of the drawings a first embodiment of a down-the-hole hammer of the invention comprises an external cylindricalouter wear sleeve10. Aninner cylinder9 is mounted co-axially within theouter wear sleeve10. A slidingpiston11 is mounted for reciprocating movement within theinner cylinder9 and theouter wear sleeve10, to strike ahammer bit36 mounted for sliding movement in achuck41 located at the forward end of theouter wear sleeve10, in well known manner.

Referring now toFIG. 3, at the back end of the hammer, atop locking member1 is screw-threadably mounted on anannular air distributor3.Air distributor3 is fitted concentrically throughinner cylinder9 and adistributor mount2 and when assembled an outwardly-directedannular flange38 on the lower end ofair distributor3 abuts the underside of an inwardly-directedannular shoulder15 ininner cylinder9. Thetop end14 ofinner cylinder9, above theshoulder15, in turn abuts the lower end of thedistributor mount2. Thedistributor mount2 is substantially cylindrical and open at both ends. It has anupper part2ahaving an outer diameter which is the same as the outer diameter of theouter wear sleeve10, such that when themount2 is engaged with the wear sleeve (as described below) the outer cylindrical wall of themount2 is flush with the outer wall of thewear sleeve10. Themount2 has alower part2bof reduced diameter which fits within the top end of thewear sleeve10, and is screw-threadably engaged with the inner wall of thewear sleeve10, by means of screw threads39 (see alsoFIG. 8). The transition between the upper and lower parts of thedistributor mount2 is defined by a downwardly facingannular shoulder23, against which the top annular rim of thewear sleeve10 abuts, and is locked in place when themount2 is fully engaged with thewear sleeve10. The bottom of the top locking member I has a flatannular rim12 which engages a complementaryflat shoulder13 on the top end of thedistributor mount2. Theinner cylinder9 is thus effectively locked between a shoulder13 (between top lockingmember1 and mount2) and shoulder15 (betweenair distributor3 and inner cylinder9).Shoulder15 may be tapered if required.

Stated differently, theinner cylinder9, at its upper end, has an inwardly extending annular shoulder orflange14 which is rigidly held between theshoulder15 and the lower end of thedistributor mount2, when thedistributor mount2 has been screwed into position in the top end of thewear sleeve10, and thetop locking member1 has been screwed on to the air distributor. When the top-lockingmember1 is screwed down, by screw-threadably engaging it with the top of the air-distributor3, this acts to pull the air-distributor3 upwardly against theshoulder15, and in turn pulls theinner cylinder9 upwardly against theshoulder14. The whole assembly then locks down onshoulder13.

When screw engaging top lockingmember1 toair distributor3,air distributor3 is prevented from turning by means ofdowels8 positioned betweenmount2 andair distributor3. An annular circlip7 (seeFIGS. 3 and 4) is positioned in achamber24 formed between lockingmember1 andmount2 and agroove25 machined onair distributor3. Thecirclip7 serves to retainair distributor3 loosely in position when assembling the hammer.

Instead of thedowels8, other means (not shown) may be provided to prevent theair distributor3 from turning as thetop locking member1 is being screwed in place in assembling the hammer. For example, theair distributor1 may be provided with external flats (flat surface) which mate with complementary flats milled internally in thedistributor mount2.

To ensure maximum alignment between theinner cylinder9 and thewear sleeve10 the fit must be as close to size for size as possible. Due to tolerance restrictions this means that the fit could be a very close sliding fit, a size for size fit, or a slight interference fit. The efficiency of the hammer is partly dependent upon the clearance between thepiston11 and thewear sleeve10, because the sliding contact between thepiston11 and the inner diameter of thewear sleeve10 acts as a pneumatic seal. The clearance between these parts is of the order of 0.1 mm. It will be appreciated that thepiston11 is running in the bore of thewear sleeve10 at the lower end of its stroke (seeFIG. 1) and runs in the bore of theinner cylinder9 at the top of the stroke (seeFIG. 2). Again the clearance is of the order of 0.1 mm. It is also important to ensure that the bore of theinner cylinder9 is concentric with the bore of theouter wear sleeve10, and that there is no sideways (i.e. radial) movement. This is achieved by having theinner cylinder9 as a very snug, or interference, fit within the bore of theouter sleeve10.

The tolerance on the bore of theouter wear sleeve10 relative to thepiston11 is about 20 microns and a tolerance of about 10 microns in the outer diameter of theinner cylinder9, relative to the outer diameter of thepiston11. The clearance between these parts should be in the range of 0.11 mm and 0.14 mm. If the clearance is greater than about 0.14 mm there is a loss of efficiency of the hammer because compressed air bypasses the piston.

As mentioned above, themount2 is screw-threadably engaged with the top ofwear sleeve10 by means of screw threads39 (seeFIGS. 3 and 8) which are cut into the inner face of thewear sleeve10. The axial depth of cut of thescrew thread39 is kept to a minimum to minimise the stress on the wear sleeve. When considering the axial depth ofscrew thread39 it is important to note that as the diameter of the hammer increases (hammer models are generally denoted by the nominal size which they are designed to drill e.g. 3″, 4″, 5″, 6″, 8″ etc.) the minimum thread depth would increase. In the case of 3″ and 4″ hammers the minimum depth could be in the range of 1.0 to 1.4 mm. On the larger sizes, e.g. 8″, this minimum depth could be in the range of 1.6 mm to 2.0 mm.

In a preferred method of assembly of the hammer, the bottom end of the hammer is assembled first. The hammer is then placed upright. Thepiston11 is placed into thewear sleeve10. Theair distributor3 is placed into thewear sleeve10 such that theprobe6 is sitting withinpiston11. Theinner cylinder9 is pushed into thewear sleeve10. Thedistributor mount2 is screwed into thewear sleeve10. The assembly is then tipped on end so thatdistributor3 falls down throughmount2 Where thedowels8 are used these are assembled, and an O-ring is placed ondistributor3. Thecheck valve4 and a spring are put in position. Thetop locking member1 is then screwed onto the end ofdistributor3.

There are other ways of assembling hammer but the above method has been found to be convenient.

For example, in an alternative method of assembly, theair distributor3 is inserted into inner cylinder9 (theprobe6 has already been inserted in air distributor3). Thedistributor mount2 is placed overair distributor3.Dowels8 are inserted in position ingrooves26 indistributor mount2, andcomplementary grooves27 in air distributor3 (seeFIG. 6). Once the dowels are in place theair distributor3 cannot rotate. Thecirclip7 is assembled ingroove25 on air distributor3 (seeFIGS. 3 and 4). If the assembly at this stage is stood oninner cylinder9, thenair distributor3 can fall as far ascirclip7 allows it. In thisposition circlip7 is in groove24 (in distributor mount2) and cannot come out. Thus the assembly can be inserted intowear sleeve10 by applying force until thedistributor mount2 is in position to screw intowear sleeve10. On screwing thedistributor mount2 into thewear sleeve10, theinner cylinder9 will be gradually pushed into position. When thedistributor mount2 abuts wearsleeve10 atshoulder23, thetop locking member1 is screwed toair distributor3 by screw threads42 (seeFIG. 7). When the lockingmember1 is locked onshoulder13, theinner cylinder9 is held securely in position, andcirclip7 has pulled up inspace24 to a top position. Thus, the function of thecirclip7 is to prevent theair distributor3 from falling down into the hammer assembly before the lockingmember1 is in place. After the lockingmember1 has been screwed into position theair distributor3 is firmly held in position and thecirclip7 becomes redundant.

The operation of the hammer is as follows. Referring toFIG. 3, compressed air is supplied through top lockingmember1 and forces checkvalve4 open by pushing down on acompression spring5. The compressed air is then supplied through anannular chamber16 formed betweenair distributor3 and probe6 (seeFIGS. 3 and 7). The air then passes throughports17 inair distributor3 and into four chambers18 (seeFIGS. 3 and 8), which are segmental in plan, and are formed betweendistributor mount2 andair distributor3. From there the compressed air passes down throughports19 ininner cylinder9 and into the segmentally-shaped chambers20 (seeFIG. 9) between theinner cylinder9 and thewear sleeve10. From here the air is supplied throughports21 in theinner cylinder9.

When thepiston11 is in the strike position (FIG. 1), air is supplied from theports21 into thechamber28 between thepiston11 and thewear sleeve10. From here it is supplied through thechannels29 in thepiston11 to undercut30 and intolift chamber31.

At the back end of the piston, in atop chamber32, air is free to exhaust through piston bore33 and bit bores34 and35 to atmosphere. As a result a pressure differential exists between thelift chamber31 and thetop chamber32 and the piston lifts to the top of stroke position (FIG. 2).

In this position air is cut-off from enteringchamber31, and air can exhaust fromchamber31 through bit bores34 and35 to atmosphere. Pressurised air is supplied fromports21 to achamber38 betweenpiston11 andinner cylinder9. From here it is supplied thoughchannels37 ininner cylinder9 totop chamber32 which is prevented from exhausting byprobe6 which is in piston bore33. As there is now a pressure differential between

chambers

31 and32 the piston is driven down to strike thebit36 and the cycle repeats itself.

A second embodiment of the down-the hole hammer is now described with reference toFIGS. 10 and 11 of the drawings. This embodiment is substantially similar in construction and operation to the first embodiment of FIGS.1 to9, and like reference numerals denote like parts.

It has been found in use of the first embodiment that there is a risk that thedistributor mount2 may crack if excessive force is applied to it from thetop locking member1 due to torqueing up of the assembly in operation. This risk may be avoided by providing a stop for the downward movement of thetop locking member1 on the top end of theair distributor3.

As shown inFIG. 11, the stop is provided by means of an annularflat shoulder50 on the inner surface of thetop locking member1, which abuts the top flatannular end51 of the air-distributor3, when theinner cylinder9 is locked in position. In practice the locking is achieved, by arranging the length tolerances to be such that, as theinner cylinder9, is locked, there is a small gap between theend51 of the air-distributor3 andshoulder50. As the hammer tightens due to applied torque in operation, this gap is closed. Alternatively, a compression ring (not shown) may be positioned between theend51 and theshoulder50 which absorbs forces as the assembly tightens. This also makes up for variation in lengths due to tolerances.

The length tolerances referred to are the length ofdistributor3 fromend51 toshoulder15; the length ofinner cylinder9 fromshoulder15 to thetop end14 of the inner cylinder; the overall length ofmount2, and the length fromshoulder12 on top lockingmember1 toshoulder50. These lengths are chosen to achieve a small gap between theshoulder50 and theflat end51. As explained about, this gap closes in operation of the hammer. If it is not desired to be restricted to tight length tolerances then a compression ring may be inserted betweenshoulder50 and theflat end51 as explained above.

In this embodiment, theair distributor3 is all in one piece which improves the strength of the assembly.

As shown inFIG. 11, in this embodiment theannular circlip7 shown inFIGS. 3 and 4, is replaced by a rubber O-ring53 positioned between the lower inner end of the lockingmember1 and the air-distributor3.

From the foregoing, it will be apparent that numerous modifications and variations can be effected without departing from the true spirit and scope of the novel concept of the present invention. It will be appreciated that the present disclosure is intended to set forth the exemplifications of the invention which are not intended to limit the invention to the specific embodiments illustrated. The disclosure is intended to cover by the appended claims all such modifications as fall within the scope of the claims.

Where technical features mentioned in any claim are followed by reference signs, these reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly, such reference signs do not have any limiting effect on the scope of each element identified by way of example by such reference signs.

The words “comprises/comprising” and the words “having/including” when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components and groups thereof.