GB2175941A

GB2175941A - Rock drills

Info

Publication number: GB2175941A
Application number: GB08612767A
Authority: GB
Inventors: John Arthur Hurt; John Callam Allan Temple Brown
Original assignee: WEAVER AND HURT Ltd
Current assignee: WEAVER AND HURT Ltd
Priority date: 1985-06-07
Filing date: 1986-05-27
Publication date: 1986-12-10
Also published as: GB8612767D0; AU5805286A; EP0204243A2; GB8514505D0; EP0204243A3

Abstract

The invention relates to down the hole percussive rock drills. During the use of down the hole drills chippings and other debris collect in the bottom of the hole and unless such chipping and debris are removed the drilling operation will be impeded. In addition it is a frequent requirement that chippings and debris are brought to the surface for analysis. The object of the present invention is to provide a rock drill facilitating the efficient removal of chippings and debris from the bottom of a hole which objective is met by a construction in which pressure air for the purposes of driving the piston 16 within the rock drill is exhausted through an annular passageway 13 between the end of the wear tube 1 and the drill bit 10 and whereby exhaust air passes entirely around the periphery of the drill bit 10 and to the bottom of the hole from where it enters a centre bore 30 through the drill bit and is exhausted through the centre tube 9 of the drill carrying with it all chippings and debris gathered in the bottom of the hole. <IMAGE>

Description

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SPECIFICATION Rock drills

5 This invention relates to rock drills, and is particularly concerned with rockdrillsforproducing a boreand as are frequently referred to as down-the-hole drills.

Down-the-hole drills are known and in which a compressed airsupply is supplied to thedrill and 10 which, via an air diverter and suitable porting, causes a piston within the drill to reciprocate at high frequency and on its down-stroke to strike the end of a drill bit. Naturally, during operation of such drills, chippings and other debris collect in the bottom of the 15 hole and can impede the drilling operation. Consequently, it is important that such chippings and debris is removed efficiently. Equally importantly, it is frequently so that the nature of the rock or the like through which the bore is being produced needs to be 20 analysed and when again there is a need for a means of bringing such chippings and debris as are created during drilling to the surface foranalysis.

It has therefore been previously proposed to form a down-the-hole drill with a central longitudinal outlet 25 boreforcompressedair,andforappropriateporting to be provided such that air directed below the piston to generate its return stroke and afterthe return stroke has been commenced is directed to the bottom of the hole to be exhausted through the central longitudinal 30 bore with the intention that the exhaust air should carry with itchippingsand debris collecting at the bottom of the hole. The prior art proposal has involved the provision of transverse passageways leading to the centre bore and positioned above the drill bit and 35 longitudinal passageways through the drill bit emerging at its cutting face. The difficulty here is that those longitudinal passageways emerging at the cutting face can become blocked, and when the drill is reliant on a suction effect created by air passing through the 40 lateral passageways and up the centre bore to lift chippings and debris from the bottom of the hole, and whilst some clearing of the bottom of the hole will be effected, it cannot be guaranteed.

The object of the present invention is to provide a 45 rock drill generally of the type referred to above and where clearing of chippings and debris from the bottom of a holecan be substantially guaranteed.

According to the present invention, a rock drill comprises an outer wear tube, an inner centre tube, a 50 drill bit mounted on the end ofthe centre tube, a reciprocal piston slidably mounted on the centre tube, an air diverter located within the drill at a position between a compressed air inlet to the drill and the piston, and porting means forthe selective direction of 55 compressed airto one side orthe other ofthe piston to cause its reciprocation at high frequency, the arrangement being such that the piston, at the end of its down-stroke, strikes the inner end of the drill bit, and there being porting means closed by the piston during 60 its down-stroke and opened on commencement of its retu rn stroke to di rect exh a ust a i r to a n a n n u I a r passageway between the end of the weartube and the drill bit and whereby air is exhausted in its entirety around the periphery ofthe drill bit to the bottom of 65 the hole, from where it enters a central bore through thedrill bitand is exhausted through the centre tube carrying with it all chippings and debris gathered in the bottom ofthe hole. Whilstthe annular passageway can be formed between the end of the wear tube and 70 the drill bit, it is preferred to provide a short extension tube connected to the end ofthe weartube, the annular passageway being formed between the extension tube and the drill bit.

To assist in the smooth flow of exhaust air past the 75 drill bit to the bottom ofthe hole, it is desirable to provide a number of relatively shallow longitudinally disposed, external grooves around the periphery of thedrill bit.

An inevitable result of producing a bore is the 80 creation of a narrow annular gap between the outer face ofthe weartube and the wall ofthe hole, and up which exhaustaircan pass. It is therefore usualtoseal the upper end ofthe bore at the surface, but this can have the possiby harmful effect of a gradual build-up 85 of pressure in the annular gap. It is therefore a further advantageousfeature ofthe invention that seal means are provided between the outer weartube andthe hole wall to limit the length ofthe annular gap and over which pressurisation can occur. Thus, a sealing 90 ring may be secured to the weartube ofa materialthat combines the two required properties of reasonable flexibility and wear resistance, and which will therefore not impede the passage ofthe drill down the hole or its withdrawal.

95 In a circumstance where the drill ofthe invention is passing through relatively soft material there can be the possible risk of a core of material being formed in the longitudinal bore through the drill bit.Toensure thatthis does not occur, it is a furtherfeature ofthe 100 present invention that the longitudinal bore through the drill bit towards its cutting face is set at an acute angle to the longitudinal axis ofthe drill bit, this offsetting ofthe end ofthe longitudinal bore ensuring that a core of material is not produced, irrespective as 105 to the nature ofthe material through which the drill is passing.

The invention therefore provides a means of cleaning the bottom ofa hole and bringing chippings and other debris to the surface for subsequent 110 analysis that can substantially be guaranteed to function efficiently no matter what drilling conditions are encountered.

One embodiment ofthe invention will now be described with reference to the accompanying draw-115 ing, which is a sectional side-elevation ofa rock drill according to the invention.

In the drawing, a down-the-hole rock drill as an outer wearsleeve 1 secured at one end to a back head 2 and at the opposite end to a chuck 3. Located within 120 theweartubeattheendtowardsthebackheadisa check valve4in sealing engagement with an air diverter 5, an inner cylinder 6 being mounted on the air diverter, and extending to a bearing 7 located within the weartube atthe end towards the chuck3, the outer

The drawing originally filed was informal and the print here reproduced is taken from a later filed formal copy.

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diameter ofthe inner cylinder and the inner diameter ofthe weartube being such asto provide an annular gap 8.

7 The air diverter 5 has a through bore in which is 5 fitted a centre tube Q, a drill bit 10 being mounted on the opposite end ofthe centre tube through an interposed bearing 11 .The outersurfaceofthe drill bit and the inner surface ofthe chuck are correspondingly splfned as indicated at 12, thesplines being so 10 dimensioned as to provide a number of gas passageways 13 around the drill bit 10. Lying within the wear seeve 1 between the chuck3 and the bearing 7 is a split spacer 14 on which is provided a bit retainer 15.

Within the cylinder6 and surrounding the centre 15 tube 9 is a piston 16 having an enlarged bore 17 atone endforsliding engagement over a stem 18ontheair diverter 5 and there being an annulargap 19 between the through bore of the piston and the centre tube 9. The piston 16 hasrtwo inlet ports 20,21, from which, 20 respectively, extend gas passage-ways 22,23, the inlet ports 20,21 respectively selectively co-operating with ports 24,25 through the wall ofthe cylinder6.

Atthe'back-head end, a dual pipejoint26 is provided, locating a centre tube 27 co-axially with a 25 bore through the check valve 4 leading to thecentre tube 9, and an outertube 28 to provide an annular gas passageway 29for incoming pressure air. The drill bit 10 has a centre bore 30 in continuation ofthe centre tube 9, and at its front end, the drill bit is provided with 30 an angled gas passageway 31.

Thus, atthe commencement of operations, and with the piston 16 at its position of restas is indicated by the upper part of the section through the piston, the piston extends through the bearing 7 and is in contact with 35 the end ofthe drill bit. Here, the piston the bearing 7 and the cylinder 6 definea chamber 32 into which the passageway 22 in the piston emerges, and the port 20 irithe piston is in register with the port24 through the cylinder walLOn the admission of pressure air 40 through the annular passageway 29, air passes through the checkvalve 4 and air diverter 5 into the annular gap 8, from where it passes through the ports 20,24 and down the passageway 22 to pressurisethe chamber32and applyan upward force on the piston 45 sufffcientto carry the piston to the position indicated by the lower part of the section through the piston, where the piston has, atone end, cleared the bearing 7, and atthe other end engaged the stem 18 on the diverter,the piston, the stem 18 and the cylinder 50 forming a chamber33 into which the passageway 23 in the piston emerges. Atthe commencement ofthe up orreturn stroke ofthe piston the instantthe piston leaves the end ofthe drill bit,thechamber33is eommunicatedwiththepassageways 13aroundthe 55 drillbittoexhaustanypressureair,andasthepiston clears the:bearing 7, pressure air in the chamber32 is also exhausted through the passageways 13. Atthe end of the up or return stroke ofthe piston, the port 21 in the piston is in register with the port 25 in the 60 cylinder, to direct pressure airto the chamber33, to apply a downward force onthe piston to drive it into contactwith the end of the drill bit.

Thus, for so long as pressure air is provided the piston is caused to reciprocate at high speed, with 65 pressure air in the chambers 32 and 33 being alternately exhausted through the passageways 13 around the exteriorof the drill bit. Consequently, all of the exhausted air passesaround the exteriorof the drill bitandintothebottom ofthe hole being drilled from where it escapes through the angled passageway 31 inthebitand up through the centre ofthe drill, carrying with it dirt and debris congregating in the bottom of the hole. The angled disposition.ofthe gas passagewaythrough the drill bit has the effect of avoidingthat passageway becoming blocked as drilling of a hole progresses.

Claims

1. A rock drill comprising an outer weartube, an inner centre tube, a drill bit mounted on the end ofthe centre tube, a reciprocal piston slidably mounted on the centre tube, an air diverter located within the drill at a position between a compressed air inlet to the drill and the piston, and porting meansforthe selective direction of compressed airto oneside orthe otherof the piston to cause its reciprocation at high frequency, the arrangement being such thatthe piston, atthe end of its down-stroke, strikes the inner end ofthe drill bit, and there being porting means closed by the piston during its down-stroke and opened on commencement of its return stroke to direct exhaust airto an annular passageway between the end of the weartube and the drill bit and whereby air is exhausted in its entirety around the periphery ofthe drill bitto the bottom ofthe hole,from where itenters a central bore throughthedrill bitandisexhaustedthroughthe centre tube ca rrying with itall chippings and debris gathered in the bottom of the hole.

2.-- ArockdrillasinClaim 1,whereintheannular passageway is formed between the end ofthe wear tube and the drill bit.

3. A rockdrill as in Claim 1, wherein theannular passagewayisformed between a short extension tube connected to the end ofthe wear tube and the drill bit.

4. ArockdrillasinanyofClaims1to3,whereina number of relatively shallow longitudinally disposed external grooves are provided around the periphery of thedrill bit.

5. ArockdrillasinanyofClaims1to4,wherein externally of the weartube and part way along its length annularseal means are provided to seal against the wall ofthe hole being cut.

6. ArockdriirasinanyofCiaims1to5,whereinthe gas inletto the longitudinal bore through the drill bit is set at an acute angle to the longitudinal axis ofthe drill bit

Printed in the United Kingdom for Her Majesty's Stationery Office, 8818935, 12/86 18996, Published atthe Patent Office, 25 Southampton Buildings, London WC2A 1 AY, from which copies may be obtained.

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