AU730523B2

AU730523B2 - Wear sleeve

Info

Publication number: AU730523B2
Application number: AU42762/97A
Authority: AU
Inventors: Ian Graeme Rear
Original assignee: Sandvik Mining and Construction Australia Production Supply Pty Ltd
Current assignee: Sandvik Mining and Construction Australia Production Supply Pty Ltd
Priority date: 1996-10-22
Filing date: 1997-10-21
Publication date: 2001-03-08
Anticipated expiration: 2017-10-21
Also published as: AU4276297A

Description

11 P/00/011 28/5/91 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Name of Applicant: Actual Inventor(s): Address for service is: lan Graeme Rear lan Graeme Rear WRAY ASSOCIATES 239 Adelaide Terrace Perth, WA 6000 Attorney code: WR Invention Title: Wear Sleeve Details of Associated Provisional Application No(s): P03149 The following statement is a full description of this invention, including the best method of performing it known to me:-

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-2- TITLE: WEAR SLEEVE The present invention relates to down hole hammers and in particular relates to down hole reverse circulation hammers.

In recent times a form of down hole hammer which has been used in rock drilling has comprised a reverse circulation hammer whereby fluid exhausted through and from the hammer, during operation or when the hammer is in the blow down mode (not operating), is caused to pass around the outer radial face of the drill bit and across the bit cutting face, to return the surface through apertures provided in the face of the drill bit. In this regard proposals have been made to modify such hammers to prevent the leakage of exhausted fluid between the side wall of the bore hole and the outer face of the hammer. Examples of such arrangements are the subject of Australian patent specifications 656724 and 638571 and each arrangement relates to the use of a shroud which serves to provide a seal between the outer face of the hammer and the bore hole in the region of the drill bit and to direct the flow of exhausted fluid to the cutting face of the drill bit when in the bore hole. It is a deliberate function of such shrouds that they have an outer diameter which enables the shroud to substantially seal :'•the space between the shroud and the bore hole in order that there is little or no S"fluid flow between the bore hole and the sides of the hammer. An effect of such 20 an arrangement is that when the reverse circulation hammer, drill bit and shroud assembly is used in ground conditions which do not comprise solid rock, such as broken ground, loose rock, old river bed conditions (such as loose gravels) and underwater conditions where there is water flow into the bore hole, there is a tendency for debris to collect in the annular space above the shroud between the bore hole and the side of the hammer. This is particularly the case when the fluid flow through the hammer is stopped as is the case in circumstances when drill rods are being changed. This collection of debris then creates a difficulty when it becomes necessary to extract the hammer from the bore hole and can result in the jamming of the hammer and drill string within the bore hole. This is due to the very minimal fluid flow up the bore hole past the sealing engagement t I tJ -3formed between the shroud and bore hole wall. In addition when drilling through clay formations it is common for such formations to swell with the presence of moisture and it is not uncommon difficulty that the bore hole behind the hammer assembly will reduce in diameter, which makes it very difficult to withdraw the hammer assembly incorporating a shroud through the now reduced diameter bore hole.

As a result of the abovementioned difficulties many hours can be lost in withdrawing the hammer and it is not uncommon for the hammer and at least a portion of the drill string to become so severely jammed that it cannot be recovered from the bore hole.

It is an object of this invention to provide a wear sleeve which can be utilised with a reverse circulation down hole hammer which can at least partially seal the space between the hammer and the borehole to minimise the flow of exhaust fluid past the sleeve while the hammer, drill bit and wear sleeve is rotating and which at the same time is capable of promoting the passage of debris past the wear sleeve to the drill bit while the drill bit is rotating and also of promoting the delivery of the exhaust fluid to the apertures in the drill bit to clear the cuttings from the bore hole.

Accordingly the invention resides in a wear sleeve for reverse circulation down hole hammer where the wear sleeve is adapted to be mounted to the hammer to extend axially from the casing in the direction of the cutting face of the drill bit to surround at least a portion of the outer radial face of the drill bit, the inner radial face of the wear sleeve and the outer radial face of the drill bit being adapted to enable fluid flow therebetween from the hammer in the direction of the cutting face of the drill bit, the outer radial face of the wear sleeve being provided with a :l :plurality of grooves spaced at circumferentially spaced intervals around the outer radial face, said grooves extending between the end faces of the wear sleeve, said grooves being inclined to the central axis of the hammer to, under circumstances where the hammer is rotating, resist the passage of exhaust fluid

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-4from the hammer past the wear sleeve and to enable the downward passage of debris from the space between the bore hole and the hammer to the drill bit.

It is a preferred object of this invention that when the drill bit is not rotating the wear sleeve will allow some fluid flow into the space to assist in the clearance of debris from the space.

It is a preferred object of the invention to provide a means which may facilitate the withdrawal of the hammer from bore hole in difficult ground conditions.

According to a preferred feature of the invention the wear sleeve is adapted to be clampingly engaged between the casing of the hammer and the drill bit support.

According to an alternative preferred feature of the invention the wear sleeve is adapted to be threadably engaged with the casing of the hammer.

According to an alternative preferred feature of the invention the wear sleeve is adapted to be threadably engaged with the drill bit support of the hammer.

i 15 According to another alternative preferred feature of the invention the wear S•-sleeve is formed to be integral with the casing of the hammer.

According to another alternative preferred feature of the invention the wear sleeve is formed to be integral with the drill bit support of the hammer.

According to a further preferred feature of the invention the end portion of the 20 wear sleeve remote from the drill bit cutting face is formed with a chamfer.

According to a further preferred feature of the invention the grooves are inclined, from the first end face proximate the drill bit, cutting face to the second end face remote from the drill bit cutting face in the direction of rotation of the hammer when the hammer is drilling.

According to a further preferred feature of the invention the outer radial face has a diameter substantially corresponding to the diameter of the bore hole to be formed by the drill bit.

According to a further preferred feature of the invention the wear sleeve is formed to be sacrificial.

Accordingly the invention also resides in a reverse circulation down hole hammer having a wear sleeve of the form as described above in relation to the invention.

The invention will be more fully understood in the light of the following description of one specific embodiment. The description is made with reference to the accompanying drawings of which: Fig 1. is schematic sectional elevation of a portion of a hammer with a wear sleeve according to the embodiment in position; :Fig 2. is side elevation of wear sleeve according to the embodiment; Fig 3. is a plan view of the wear sleeve according to the embodiment e The embodiment is directed to a wear sleeve which is to be utilised with a down hole reverse circulation pneumatic hammer.

The hammer comprises an outer casing 11 which accommodates a top sub (not shown) at its upper end and a drive sub 12 at its lower end which intended to 20 accommodate a drill bit 13 of substantially conventional form. The hammer casing also accommodates a piston (not shown) which is intended to be caused i to reciprocate within the casing to impact upon the anvil 14 of the drill bit 13 where the piston is caused to reciprocate by the introduction of pressurised fluid into the hammer through the top sub. In addition according to usual practice exhaust passageways are provided between the drill bit 13 and the drive sub 12 to facilitate the passage of exhaust fluid from the piston chamber into the space between the bore hole and the drill bit whereby the exhausted fluid will subsequently flow past the outer radial face 15 of the drill bit, across the cutting face 16 and return to the surface through apertures 17 provided in the cutting face of the drill bit and in so doing carry with it cuttings generated by the action of the drill bit 13.

The wear sleeve 10 of the embodiment is intended to be either clampingly or threadably retained between the lower end of the casing 11 and the drive sub 12 and to extend axially from the lower end of the casing 11 in the direction of the cutting face 16 of the drill bit to overlie a portion of the outer radial face 15 of the drill: bit. The.outer radial diameter of the wear sleeve substantially corresponds with the cutting diameter of the cutting face of the drill bit. The wear sleeve is formed to be sacrificial in order that it will be worn away as the drill bit wears such that the diameter of the outer radial face of the wear sleeve will substantially correspond with the diameter of the bore hole being formed by the drill bit.

o *The inner radial face of the wear sleeve is spaced outwardly from the outer radial face of the drill bit. In addition according to conventional practice the outer radial face of the drill bit is provided with a plurality of axial grooves which 20 will facilitate the delivery of fluid to the cutting face 16 of the drill bit when the hammer is located in the bore hole. As a result of the presence of the wear sleeve the exhaust fluid from the hammer is directed substantially axially along the outer radial face of the drill bit in the direction of the cutting face of the drill bit.

The outer radial face of the wear sleeve 10 is provided with a plurality of grooves 18 which extend between the end faces of the wear sleeve 10 and which are located at spaced intervals around the circumference of the wear sleeve 10 and are substantially equidistant. The axes of the grooves 18 are inclined to the central axis of the hammer and have an inclination from the first -7end face of the wear sleeve proximate the drill bit to the second end face of the wear sleeve remote from the drill bit which is in the direction of rotation of the hammer when in use (this direction is shown by the arrow A in the accompanying drawings).

In addition the end portion of the outer radial face of the wear sleeve which is remote from the drill bit cutting face is formed with a chamfer as shown.

When the hammer is in use and is being caused to rotate in the direction A as shown, the inclination of the grooves 18 in the direction A of rotation serves to provide an fluid seal by providing a resistance to fluid flow through the grooves 18 from the first end to the second end. At the same time the inclination of the grooves will promote the flow of debris which may have collected in the space between the casing and the sides of the borehole through the grooves 18 from the second end to the first end of the wear sleeve. The debris is consequently delivered to the outer radial face of the drill bit 15 where it will be further conveyed to the cutting face of the drill bit 16 by being entrained in the fluid being exhausted into the bore hole from the hammer. This downward movement of debris through the grooves also serves to limit the leakage of fluid past the wear sleeve when the hammer is rotating which serves to maximise the delivery of the exhaust fluid to the cutting face 16 of the drill bit and to the central apertures 17.

In addition in circumstances where the drill bit has been stationary in the bore hole without fluid flow through the hammer it is very likely that debris will have become deposited in the space defined by the bore hole annulus above the :wear sleeve. In this regard the presence of the grooves 18 facilitates the clearance of such debris from the space above the wear sleeve when the drill bit oo am is initially caused to rotate by causing such debris to be conveyed downwardly through the grooves on the commencement of the rotation of the drill bit -8- When the hammer assembly is operating and is not rotating or when the hammer assembly is not rotating and is not operating, such as under "blow down" conditions, the presence of the grooves 18 in the outer face of the wear sleeve 10 enables the flow of some of the fluid which is exhausted into the bore hole from the hammer to travel upwardly past the wear sleeve into the space between the bore hole and the hammer while the hammer is not rotating. This controlled flow of a proportion of the fluid which is exhausted into the bore hole serves to carry to the surface any debris which may have collected in that space.

This serves to reduce the likelihood of the hammer becoming jammed in the bore hole as a result of the presence of such debris.

In addition when it becomes necessary to withdraw the hammer from the bore hole the presence of the grooves 18 in the wear sleeve 10 serve to facilitate passage of any debris downwardly past the wear sleeve. This clearance of debris can be further enhanced by causing the hammer to rotate in the direction A as shown while being withdrawn from the bore hole which further causes the debris or clays to be channelled downwardly past the wear sleeve 10 through the grooves 18. In addition in conditions where drilling is being conducted through clay formations which will swell with the presence of moisture the presence of the wear sleeve facilitates the withdrawal of the hammer through a 20 reduced diameter bore hole with rotation of the hammer in the direction A shown since the wear sleeve acts like an auger to facilitate the passage of the hammer assembly through the reduced diameter bore hole.

The wear sleeve according to the embodiment enables the creation of a seal ~between the hammer and the bore hole and/or the controlled delivery of debris 25 collecting in the space between the hammer and the bore hole above the wear, sleeve downwardly into the region of the drill bit to be carried out of the bore by the fluid exhausted into the bore hole when the drill bit is in operation (ie rotating) and the controlled flow of a portion of the fluid exhausted into the bore hole past the wear sleeve to facilitate clearance of debris which may collect in the space between the hammer and the bore hole when the drill bit is stationary.

-9- It should be appreciated that the scope of the present invention need not be limited to the particular scope of the embodiment described above. In particular the wear sleeve can be formed to be integral with the drive sub or may be mounted to the drive sub or according to any suitable arrangement which is appropriate according to the circumstances.

*o• *oo oo *o o* *o

Claims

1. A wear sleeve for a reverse circulation down hole hammer where the wear sleeve is adapted to be mounted to the hammer to extend axially from the casing in the direction of the cutting face of the drill bit to surround at least a portion of the outer radial face of the drill bit, the inner radial face of the wear sleeve and the outer radial face of the drill bit being adapted to enable fluid flow therebetween from the hammer in the direction of the cutting face of the drill bit, the outer radial face of the wear sleeve being provided with a plurality of grooves spaced at circumferentially spaced intervals around the outer radial face, said grooves extending between the end faces of the wear sleeve, said grooves being inclined to the central axis of the hammer to, under circumstances where the hammer is rotating, resist the passage of exhaust fluid from the hammer past the wear sleeve and to enable the downward passage of debris from the space between the bore hole and the hammer to the drill bit.

2. A wear sleeve as claimed at claim 1 wherein the wear sleeve is adapted to be clampingly engaged between the casing of the hammer and the drill bit support.

3. A wear sleeve as claimed at claim 1 wherein the wear sleeve is adapted to 20 be threadably engaged with the casing of the hammer.

4. A wear sleeve as claimed at claim 1 wherein the wear sleeve is adapted to be threadably engaged with the drill bit support of the hammer. lll i A wear sleeve as claimed at claim 1 wherein the wear sleeve is formed to be integral with the casing of the hammer.

6. A wear sleeve as claimed at claim 1 wherein the wear sleeve is formed to be integral with the drill bit support of the hammer. -11

7. A wear sleeve as claimed at any one of the preceding claims wherein the end portion of the wear sleeve remote from the drill bit cutting face is formed with a chamfer.

8. A wear sleeve as claimed at any one of the preceding claims wherein the grooves are inclined, from the first end face proximate the drill bit, cutting face to the second end face remote from the drill bit cutting face in the direction of rotation of the hammer when the hammer is drilling.

9. A wear sleeve as claimed at any one of the preceding claims wherein the outer radial face has a diameter substantially corresponding to the diameter of the bore hole to be formed by the drill bit. A wear sleeve as claimed at any one of the preceding claims wherein the wear sleeve is formed to be sacrificial.

11. A wear sleeve substantially as herein described.

12.A reverse circulation down hole hammer having a wear sleeve of the form as claimed at any one of the preceding claims. Dated this TWENTY-FIRST day of OCTOBER 1997. IAN GRAEME REAR Applicant Wray Associates Perth, Western Australia Patent Attorneys for the Applicant