Drill bit with recessed cutting face

A percussive rock drill bit includes a head having an annular gauge collar and a central island. An annular cutting channel is defined between the collar and the island such that specifically positioned cutting buttons are effective to create an annular ridge in the cut rock face having a reduced rock breaking resistance.

RELATED APPLICATION DATA

This application is a § 371 National Stage Application of PCT International Application No. PCT/EP2015/063308 filed Jun. 15, 2015 claiming priority of EP Application No. 14182068.8, filed Aug. 25, 2014.

FIELD OF INVENTION

The present invention relates to a percussive rock drill bit having a head provided at a shank and configured with a recessed crushing face configured to create a ridge in the rock during cutting so as to reduce the rock breaking resistance.

BACKGROUND ART

Percussion drill bits are widely used both for drilling relatively shallow bores in hard rock and for creating deep boreholes. For the latter application, a drill string is typically used in which a plurality of rods are coupled end-to-end via threaded joints as the depth of the hole increases. A terrestrial machine is operative to transfer a combined impact and rotary drive motion to an upper end of the drill string whilst a drill bit positioned at the lower end is operative to crush the rock and form the boreholes. WO 2006/033606 discloses a typical drill bit comprising a drill head that mounts a plurality of hard cutting inserts, commonly referred to as buttons. Such buttons comprise a carbide based material to enhance the lifetime of the drill bit.

Fluid is typically flushed through the drill string and exits at the base of the borehole via apertures in the drill head to flush the rock cuttings from the boring region to be conveyed rearward through the bore around the outside of the drill string. Further examples of percussive drill bits are disclosed in U.S. Pat. No. 3,388,756; GB 692,373; RU 2019674; U.S. 2002/0153174; U.S. Pat. No. 3,357,507, U.S. 2008/0087473; U.S. Pat. No. 4,113,037; GB 2011286; U.S. Pat. No. 5,890,551; DE 2856205 and WO 2009/067073.

The effectiveness of the drill bit to bore into rock is dependent on the rocks breaking resistance that may be considered to include vertical and horizontal stresses imposed to the rock within the subterranean depth. Drill head design and construction is typically a compromise between maximising the drill bit operational lifetime and maximising the axially forward cutting performance. The drill bit must also facilitate rearward transport of the rock fragments within the borehole that would otherwise decrease forward cutting. Accordingly, what is required is a drill bit and in particular a bit head that is optimised to satisfy the above considerations.

SUMMARY OF THE INVENTION

It is an objective of the present invention to provide a drill bit and in particular a drill bit head for percussive rock drilling that is configured to create a specific topography within the rock that significantly reduces the rock breaking resistance and accordingly increases drilling performance and efficiency. It is a further specific objective to provide a drill bit head configured to be self-guiding during drilling. It is a yet further objective to provide a head that is effective to greatly facilitate the axially rearward transport of rock fragments from the rock face.

The objectives are achieved by providing a drill head with a recessed crushing face positioned radially between a perimeter gauge collar and a central island. In particular, cutting buttons are specifically positioned at the crushing face and respective shear faces that extend axially forward from the crushing face. The present configuration is effective to create a particular ridged topography in the rock that is very susceptible to cracking and fracture to significantly decrease the rock breaking resistance. In particular, the present drill head is configured to create a single annular ridge at the rock face immediately in front of the crushing face of the head to increase the available fracturing directions of the rock at the ridge when impacted by the crushing face mounted buttons.

The as-formed rock ridge is also effective to assist in stabilising and guiding the bit head to reduce lateral deflections due to anomalies such as existing fractures within the rock structure.

The present bit head is also configured with radially and circumferentially extending flushing grooves that interrupt the gauge collar to allow the radially outward and axially rearward transport of the flushings and fines. The present annular channel or groove, recessed in the bit head, is effective to direct the flushing fragments through notches in the gauge collar for optimised axial rearward transport along the borehole.

According to a first aspect of the present invention there is provided a percussive rock drill bit head provided at one end of an elongate shank having an internal bore extending axially from one end of the shank towards the head, the head comprising: an axially forward facing annular crushing face; a generally annular gauge collar projection axially forward from the crushing face at a perimeter of the head and having a gauge surface positioned axially forward of the crushing face; a central island being axially raised from the crushing face and having a front face positioned axially forward from the crushing face; a first and second generally annular shear face extending axially between the crushing face and the gauge face and the crushing face and the front face respectively; at least one cutting button provided respectively on each of the crushing, gauge, front and first and second shear faces; flushing grooves in communication with the internal bore and extending radially outward from the island towards and through the gauge collar to separate the gauge collar into collar segments; and an annular channel being defined between the island and the gauge collar configured to create an annular ridge in the rock and accordingly reduce the rock breaking resistance.

The present bit is configured to create a hole topography comprising shelves and ridges that have lower k-values (rock breaking resistance) such that the cutting buttons mounted at the crushing face have significant reduced k-values than other buttons of the drill head. The total k-value of the present drill head is significantly lower (of the order of 20% less) than that of existing bits due to the specific grouping and positioning of the cutting buttons at respective gauge, front, crushing and shear faces that interact with synergy during cutting. Accordingly, by reducing the rock k-value the present bit head is configured to drill greater diameter boreholes with less power consumption (or in less time using the same power) with respect to known bits.

Optionally, the crushing face is substantially planar or concave relative to a plane extending perpendicular to a longitudinal axis of the shank. A concave crushing face is advantageous to further increase the axial depth of the groove and accordingly increase the axial height of the as-formed annular ridge within the rock to reduce the rock breaking resistance.

Preferably, the flushing grooves extend radially inward within regions of the island. Additionally, and preferably the flushing grooves are recessed into the crushing face. A desired flow path for the flushing fluid from a central region of the head to the head perimeter is accordingly created to entrain rock particles and debris to flow radially outward and axially rearward from the head. The various notches at the island and the collar greatly facilitate flushing and prevent the flushing slurry flowing along an extended flow path in the circumferential direction around the head.

Preferably, the front face is positioned axially forward of the gauge face. Such an arrangement is advantageous to stabilise the forward drilling and to maximise the axial length of the annular ridge formed with the rock to produce the rock breaking resistance.

Preferably, the front face comprises an axial depression to provide a fluid flow pathway between radially inner regions of the flushing grooves. The axial depression accordingly provides a recessed pocket for the flow of flushing fluid to facilitate the radially outward and axially rearward transport of rock fines from the centre of the head.

Preferably, the head comprises flushing bores in communication with the internal bore and extending through the gauge collar to exit at the gauge face. The flushing bores within the collar act to further facilitate radially outward and axially rearward flushing are beneficial to maximise crushing performance and efficiency.

Optionally, the first and second shear faces are inclined to extend transverse to a longitudinal axis of the shank. Optionally, the first and second shear faces may be aligned parallel to the longitudinal axis or comprise annular sections aligned parallel to the axis with other annular sections being aligned transverse to the axis. That is, the first and second shear faces may each comprise a plurality of faces being angularly disposed relative to one another. The shear faces are configured to create the desired topography in the cut rock having an unstable ridge that is susceptible to breaking.

Where the first and/or second shear faces are inclined relative to the axis, the angle by which the first shear face may be inclined relative to the axis is in the range 1 to 20°. Optionally, the angle by which the second shear face may be inclined relative to the axis is in the range 20 to 40°.

Optionally, along a radius extending from a centre of the head to a radially outermost perimeter, a separation distance between a radially innermost part of a cutting button on the first shear face and a radially outermost part of a closest cutting button on the second shear face is in the range 10 to 30% of the radius of the head. Optionally, the range is 15 to 25% or more preferably 18 to 22%.

Optionally, a radial distance of the crushing face defined between the first and second shear faces is 5 to 20% of a radius of the head defined between a centre of the head and a radially outermost perimeter part of the cutting buttons at the gauge collar. Optionally, the range is 10 to 15% and more preferably 11 to 14%.

Optionally, an axial separation distance between the front face and the crushing face is in the range 25 to 45% of an axial length of the head defined between an axially forwardmost part of the cutting button at the front face and an axially rearwardmost part of a skirt that represents an axially rearwardmost part of the gauge collar extending directly from the shank. Preferably, the range is 30 to 40% and more preferably 33 to 38%.

Referring toFIGS. 1 to 4, a percussive drill bit comprises an elongate shank120having a drill head100provided at one end. Head100is flared generally radially outward from shank120and comprises a gauge collar101formed at a perimeter and a raised central island indicated generally by reference104to define an annular channel (indicated generally by reference105) located radially between collar101and island104.

Gauge collar101comprises a skirt117that flares radially outward from shank120to form an annular junction between head100and shank120. Collar101comprises a forward facing gauge face121being declined to slope downwardly away from a central longitudinal axis119extending through shank120and head100. Collar101is divided in a circumferential direction into three arcuate collar segments being separated by generally v-shaped notches108that project axially rearward from gauge face121towards shank120. A plurality of gauge buttons112are distributed on the gauge face121of each collar segment and are orientated to tilt radially outward from axis119. A plurality of sludge grooves207are also recessed into the perimeter of collar101to facilitate rearward transport of debris cut from the rock face. A radially innermost side of gauge face121is terminated by a first shear face109aligned transverse to gauge face121and being generally inclined to slope upwardly from axis119. First shear face109extends axially forward from a substantially planar crushing face indicated generally by reference102. Crushing face102is generally annular and extends circumferentially around central island104to represent a trough or base of the recessed annular channel105defined radially between island104and collar101. A plurality of crushing buttons118are distributed circumferentially over crushing face102. Crushing face102is terminated at its radially innermost end by a second shear face110extending axially forward from face102to define a perimeter of island104. First and second shear faces109,110are positioned radially opposed one another and collectively define channel105such that channel105comprises an axial depth being approximately equal to an axial height of collar101and island104. However, according to the specific implementation, an axial height of island104is greater than the axial distance by which collar101extends forward from crushing face102.

Each of the first and second shear faces109,110comprises respective sets of shear buttons113,114. Second shear face110is also aligned transverse to axis119such the opposed shear faces109,110define at least part of a generally v-shaped circumferentially extending channel. Accordingly, the respective first and second sets of shear buttons113,114are orientated to be tilted axially inward and outward relative to axis119, respectively.

Island104comprises a generally circular configuration in a plane perpendicular to axis119having a generally dome shaped profile in an axial plane extending through head100. An axially forwardmost end of second shear face110is terminated by an annular front face103being generally planar and positioned perpendicular to axis119and aligned parallel to crushing face102. A recess111is indented into front face103being positioned centrally within head100such that central island104comprises a slightly recessed cavity at its axially forwardmost apex region. A plurality of front buttons115are provided on front face103and a single front button116is mounted to project from a base of recess111.

A plurality of notches106extend in a generally radial direction to be indented within island104at circumferentially spaced apart positions. Each notch106comprises a radially innermost first end202that terminates at the region of recess111whilst a radially outermost part210terminates at the radially innermost end of crushing face102. A plurality of curved grooves indicated generally by reference107extends in both the radial and circumferential directions to be recessed within crushing face102. Each groove107comprises a radially innermost first end200and a radially outermost second end201. First end200is positioned within a respective island notch106whilst second end201is located within a respective v-shaped notch108at gauge collar101. Accordingly, notches106,108and grooves107collectively define flushing grooves to facilitate the radial and axially rearward transport of rock fragments and fines created during drilling. Each island notch106is terminated at its radially innermost end by an axially projecting bore401that is provided in fluid communication with a larger central bore400extending axially through shank120. Accordingly, flushing fluid (typically air) may be supplied to head100via bores400,401to emerge at island notches106. Accordingly, the fluid is configured to circulate within channel105(and grooves107) to exit head100via the v-shaped notches108together with the entrained rock fragments.

To facilitate the rearward transfer of flushings, a plurality of boreholes205are provided through head100to extend between central bore400and to emerge at gauge face121. The rearward and radially outward transport of the flushing fluid may also be facilitated by cavities206formed at a trough region208of each v-shaped notch108. Each notch108is further defined by a pair of opposed and axially converging side faces209.

Each of the first and second shear faces109,110comprises trailing annular end faces203and204respectively. Each end face203,204forms an axial junction between crushing face102and each of the sloping shear faces109,110. End faces203,204are aligned parallel with axis119and generally perpendicular to crushing face102to define the axially lowermost trough region of channel105in combination with crushing face102.

Referring toFIGS. 5 to 7, an axially forwardmost region of head100is defined by the respective apex regions500of front buttons115projecting from front face103. Additionally, a radially outermost perimeter of head100is defined by a radially outermost region502of each gauge button112. Gauge button regions502project radially beyond a radially outermost perimeter edge501of gauge collar101such that gauge buttons112determine the diameter of the borehole during cutting. Accordingly, a radial length of head100between central axis119and the perimeter of head100(as determined by the gauge button region502) is represented by reference E.

Referring toFIG. 6, an axial length, represented by reference D, corresponds to an axial separation distance between the axially forwardmost region500of each front button115and an axially rearwardmost region600of skirt117provided at the axial junction with shank120. Additionally, an axial separation distance between front face103and crushing face102is represented by reference C. Additionally, a radial separation distance between the opposed parallel first and second end faces203,204is represented by reference A that corresponds to a radial length of crushing face102.

Referring toFIG. 7a radial separation distance (indicated by reference B) corresponds to the radial separation between a radially innermost part702of first shear button113and a radially outermost part703of a second shear button114that is located closest to the reference first shear button113. The separation distance B lies on the radial line segment700being a straight line between the axial centre701of head100and the head radially outermost perimeter defined by gauge button region502. As buttons113and114do not lie on the same radial line segment, the radially innermost point of separation distance B may be considered to be defined by an imaginary arcuate line extending from part703of second shear button114as illustrated inFIG. 7.

According to the specific implementation, radial distance A is approximately 11 to 14% of radial distance E and radial distance B is approximately equal to 18 to 22% of radial distance E. Additionally, axial length C is approximately equal to 34 to 37% of axial length D.

Additionally, and according to the specific implementation, head100comprises three collar segments each comprising three gauge buttons112and two first shear buttons113. Second shear face110comprises six second shear buttons114, whilst crushing face102comprises three crushing buttons118. Additionally, the annular front face103comprises three front buttons115with recess111comprising a single front button116. Gauge buttons112are generally larger than the crushing buttons118that are in turn larger than the first and second shear buttons113,114. Additionally, front buttons115,116are generally smaller than first and second shear buttons113,114.

In use, head100is rotated about axis119and advanced axially forward to cut into the rock structure. A ridge within the rock is created during forward advancement by the cooperation between the opposed first and second shear buttons113,114with the ridge being defined within the annular channel105between gauge collar101and central island104. The present head100is advantageous to increase the rate of forward drilling and/or to minimise power draw by appreciably lowering the rock breaking resistance (k-value) due to the specific topography created at the rock face by the contours within head100. That is, the specific positioning and orientation of the crushing118and shear113,114buttons, generates an unstable annular ridge at the rock that exhibits at least four directions of breaking when contacted by crushing buttons118. As will be appreciated, the specific topography of the annular ridge may be selectively adjusted by variation of the size and position of the crushing102and shear113,114buttons and accordingly the geometrical relationship between the crushing face102and the first and second shear faces109,110.