WO1990015220A1

WO1990015220A1 - Rock drilling bit

Info

Publication number: WO1990015220A1
Application number: PCT/AU1990/000248
Authority: WO
Inventors: William Lister
Original assignee: William Lister
Priority date: 1989-06-09
Filing date: 1990-06-07
Publication date: 1990-12-13
Also published as: ZA904380B

Abstract

A rock drilling bit for a pneumatic percussion hammer has a bit head (11), its periphery (11a) substantially cylindrical and perpendicular to a working face (11b). An axial aperture from the top of the bit is in two diameters, the lower (21a) closely slidable on the bottom of an air exhaust tube (22) of the hammer, the upper (21) forming a high pressure air inlet connected to a series of primary and secondary air outlets (25, 26) from the periphery (11a) of the bit head (11), the primary air outlets (25) being connected through the bit to the air exhaust tube (22), the secondary air outlets (26) so directing air under pressure as to form a pressurized air shroud about the bit head (11).

Description

TITLE: "ROCK DRILLING BIT"

BACKGROUND OF THE INVENTION THIS INVENTION relates to a rock drilling bit. The specification of my Patent No. 493847 describes and illustrates a pneumatic percussion hammer with a bit drive sub fitted with a rock drilling bit. The present invention has been devised with the general object of providing a rock drilling bit applicable to a pneumatic percussion hammer of the general type described in that patent specification and which is of notably improved performance, particularly in drilling through water-bearing or fractured strata.

SUMMARY OF THE INVENTION

Broadly, the invention resides in a rock drilling bit for a percussion hammer, the bit including a bit head with a substantially cylindrical periphery and a working face substantially perpendicular, thereto, the bit being axially apertured to accept an exhaust tube of the hammer and with a high pressure air inlet passage thereabout, wherein: formed in the periphery of the bit head are a series of primary and secondary air outlets, connected to the high pressure air inlet passage, the primary air outlets are connected, through channels in the working face of the bit, to air return passages in the bit leading to the exhaust tube, and the secondary air outlets are arranged to direct air under pressure from the periphery of the bit head to form a pressurized air shroud about the bit head.

Other features of the invention will become apparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS In order that a preferred embodiment of the invention may be readily understood and carried into practical effect, reference in now made to the accompanying drawings, wherein:

FIG. 1 is a perspective view of a rock drilling bit according to the invention. FIG. 2 is a bottom view of the bit shown in Fig. 1,

FIG. 3 is a sectional view of the bit taken along line 3-3 in Fig. 2, and shown within the lower part and drive sub of a pneumatic percussion hammer,

FIG. 4 is a sectional view of the bit taken along line 4-4 in Fig. 2, and

FIG. 5 is a sectional view taken along line 5-5 in Fig. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The bit 10 includes a bit head 11, with a substantially cylindrical periphery 11a and a working face lib in which are fixed tungsten bit buttons 12.

The bit head is made integrally with a coaxial splined section 13 and a coaxial shank 14 which, as shown in

Fig. 3, is slidable in a drive sub 15 screwed into the lower end of a percussion hammer casing 16. The upper part of the bit shank is a reduced-diameter neck portion

14a which is surmounted by an anvil 17. During the operation of the hammer the anvil is struck repeatedly by a rapidly reciprocating piston 18 slidable in the hammer casing. The splined section 13 is formed with a series of equally spaced splines 19 and is slidably but non-rotatably engaged in corresponding keyways 20 in the drive sub.

An axial high pressure air inlet passage 21 is formed through the top of the anvil and bit unit, its lower part 21a being of reduced diameter. Within this passage a coaxial exhaust tube 22 depends within the hammer, its lower end engaged closely but slidably in the reduced-diameter lower part 21a of the passage. The bit head 11 has two series of air outlet channels formed in its periphery, extending upwards from the bottom of the bit head and closed at their upper ends. The four primary air outlet channels 23 are somewhat deeper than the four alternating secondary air outlet channels 24. From the high pressure air inlet passage 21 four oblique ducts 25 within the bit lead into the upper parts of all the primary air outlet channels 23 and four oblique ducts 26 of lesser diameter lead into the secondary air outlet channels 24.

From the bottoms of an opposed pair of the primary air outlet channel 23, radial channels 27 extend towards each other before leading into a pair of inclined air return passages 28 in the bit head converging upwardly to lead into the bottom end of the exhaust tube 22. Oblique channels 29 in the bottom or working face of the bit head connect the radial channels 27 which lead from one pair of the primary outlet channels 23 to the bottoms of the other two primary outlet channels 23.

Small cleaning air ducts 30 lead from oblique ducts 25 to the lower part of the splined section 12 and are normally closed by the drive sub 15 except when the bit head 11 is advanced some distance from the bottom of the drive sub.

When the hammer is in operation, the bit anvil 17 being repeatedly struck by the piston 18 while the hammer casing 16 and bit 10 are rotated, the bit buttons 12 break up the rock to which the hammer is applied. Air under high pressure passes through the ducts 25 and 26 and into all of the air outlet channels 23 and 24. Air expelled into the primary air outlet channels 23 (the bit being close to the wall of the bore-hole) is directed into the oblique channels 29 and radial channels 27, entraining rock particles and carrying them through the inclined air return passages 28 and thence into the exhaust tube 22 and up to the surface of the drilling site. At the same time, the air under pressure directed into the secondary air outlet channels 24 forms about the bit and within the bore hole a pressurized shroud of air. Some of this air under pressure sweeps under the working face of the bit, further cleaning rock fragments into the exhaust tube, but an important function of the air shroud is to reduce greatly the likelihood of any water or mud, which may be about the hammer, drive sub and bit, from flowing into the bit and up through the exhaust tube. Therefore even if the hammer should drive the bit through water-bearing strata, the rock fragments emitted from the upper end of the hammer casing will be substantially dry, greatly simplifying their disposal. Moreover, if the hammer should drive the bit into a rock formation in which there is a crevice or hollow leading from the part of the bit so that some compressed air is lost in the crevice, the air expelled from the air outlet channels not opening into the crevice will maintain the effective operation of the hammer. Compressed air expelled through the small cleaning air ducts 30 on each stroke of the bit extending it from the drive sub clears rock fragments from the annular space between bit and drive sub.

Rock drilling bits according to the invention will be found to be very effective in achieving the objects for which they have been devised. It will, of course, be understood that the particular embodiment of the invention herein described and illustrated may be subject to many modifications of constructional detail and design, ,_?which will be readily apparent to persons skilled in the art, without departing from the scope of the invention hereinafter claimed.

Claims

1. A rock drilling bit for a percussion hammer, the bit including a bit head with a substantially cylindrical periphery and a working face substantially perpendicular thereto, the bit being axially apertured to accept an exhaust tube of the hammer and with a high pressure air inlet passage thereabout, wherein: formed in the periphery of the bit head are a series of primary and secondary air outlets, connected to the high pressure air inlet passage; the primary air outlets are connected, through channels in the working face of the bit, to air return passages in the bit leading to the exhaust tube; and the secondary air outlets are arranged to direct air under pressure from the periphery of the bit head to form a pressurized air shroud about the bit head.

2. A rock drilling bit according to Claim 1 wherein: the primary and secondary air outlets alternate in a series of channels in the periphery of the bit head closed at their upper ends and opening at their lower ends to the working face of the bit head.

3. A rock drilling bit according to either of the preceding claims wherein: the primary and secondary air outlets are connected to the high pressure inlet passage by ducts in the bit, the ducts leading to the primary air outlets being of greater cross-sectional area than those leading to the secondary air outlets.

4. A rock drilling bit according to claim 3 wherein: cleaning air ducts lead from ducts connecting air outlets to the high pressure inlet passage, are closed when the bit is retracted in the drive sub and, when the bit is advanced on its working stroke, are opened to clear rock fragments from an annular space between the drive sub and the bit head.

5. A rock drilling bit substantially as herein described with reference to the accompanying drawings.