The present invention relates to a percussive rock drill bit and in particular, although not exclusively, to a drill bit having a head with a plurality of flushing grooves that are optimised via their orientation relative to an axis of the bit that greatly facilitate axially rearward flushing of fragments and fines cut from the rock face.
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 typically 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 backward and through the bore around the outside of the drill string. Further examples of percussive drill bits are disclosed in DE 3519592; U.S. Pat. No. 3,388,756; GB 692,373; RU 2019674; US 2002/0153174; U.S. Pat. No. 3,357,507, US 2008/0087473; WO 2009/067073 and WO 2013/068262.
Typically, a plurality of flushing grooves are recessed in the drill head to allow the fractured material to be transported rearwardly from the drill bit via the flushing fluid. U.S. Pat. No. 5,794,728 discloses a percussion rock drill bit having a plurality of fluid passageways that extend from a central bore of the bit to emerge at flushing grooves at the front face. However conventional bits are disadvantageous for a number of reasons. In particular, conventional flushing grooves are not optimised to facilitate fluid flow axially rearward from the front face and this reduces accordingly the drilling performance and in particular the penetration rate of the bit. Additionally, it is not uncommon for the axially forwardmost part of the flushing fluid passageway to become damaged due to contact with the rock that in turn decreases the delivery of fluid to the front face and also the efficiency of rearward flushing of fines and debris material cut from the rock face. Accordingly, what is required is a drill bit that addresses the above problems.
It is an objective of the present invention to provide a percussive rock drill bit that is optimised for drilling efficiency and in particular to provide an enhanced drilling penetration rate. It is a further specific objective to provide a drill bit that is effective to optimise the axially rearward flushing of rock debris and fines cut from the rock face. It is also a specific objective of the present invention to reduce as far as possible damage to the fluid flushing passageways due to contact with the rock face during cutting.
The objectives are achieved by providing a drill bit having flushing grooves that extend radially outward from a central axis of the bit and axially rearward from the bit head to the bit shank having optimised fluid flow path lengths. The optimisation is achieved as the fluid flow path length within the grooves (from the axially forwardmost region of the head to the radially outer perimeter of the head at the region of the shank) is devoid of ridges or sharp angled transitions that would otherwise perturb the fluid flow and accordingly reduce the efficiency with which the cut fragments and fines (that are entrained in the flushing fluid) flow axially rearward through the grooves. Additionally, the present bit is optimised to protect the axially forwardmost region of the fluid flow passageways from damage by the rock face via the position of emergence of the passageways within the flushing grooves. That is, the annular leading edge that defines the exit aperture (in the vicinity of the front face) of the flushing passageway is positioned at the trough region of each respective flushing groove such that this aperture edge is positioned axially rearward from the front face and is accordingly set back from the rock face during cutting to avoid frictional contact damage with the rock. The shape profile of the passageway exit aperture is accordingly preserved following extended use. Accordingly, the intended fluid flow pathways of the fluid delivered by the passageways remain unaffected by use of the drill head and in particular damage or wear at the front face.
Advantageously, the flushing grooves have a fluid flow path that is generally convex relative to an axis of the bit and that is continuously angled rearwardly away from the front face (relative to the axis) to facilitate the axially rearward flow. As such, the present flushing grooves are devoid of any regions in the fluid flow length that could be regarded as perpendicular to the axis that would otherwise deflect the fluid flow radially outward. Such arrangements are common to existing bit configurations and have the effect of disrupting the axially rearward fluid flow by presenting obstructions to the particles and fines as they travel radially outward from the axis and axially rearward from the bit face.
According to a first aspect of the present invention there is provided a percussive rock drill bit comprising: a 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 having a front face and a plurality of collar segments spaced circumferentially around a longitudinal axis of the bit and positioned at a perimeter of the front face, the front face being generally dome-shaped; a plurality of front cutting buttons provided at the front face and a plurality of gauge cutting buttons provided at the collar segments; a plurality of flushing grooves extending in a direction radially outward from the axis at the front face and continuing in a direction axially rearward to define and circumferentially separate the collar segments, each of the grooves terminating at the vicinity of the shank; at least one fluid passageway connected to the bore and emerging as an aperture in the vicinity of the front face within at least one of the flushing grooves, the aperture being recessed axially from the front face within the at least one groove; characterised in that: a flow path length of each of the flushing grooves is generally convex in the direction from the front face to the shank relative to the axis of the bit; and the flow path length is aligned to extend continuously axially rearward from the region of the aperture towards the shank such that no part of the flow path length is aligned perpendicular to the axis of the bit so as to provide an unhindered axially rearward flow path for fluid to flow from the aperture towards the shank and between the collar segments.
The subject invention is to be contrasted with existing drill bits that typically comprise a ridge, shoulder or relatively sharp angled transition that is aligned perpendicular to the elongate main length of each groove and positioned at the transition between the generally radially extending front face and the generally axially extending rearward region of the head. Accordingly, the subject invention is advantageous to allow the unhindered axially rearward flow of entering rock particles within the flushing fluid. In particular, and preferably each of the grooves comprise a first region positioned generally at the front face and a second region positioned generally between each of the collar segments wherein a transition between the first and second regions is seamless and is devoid of any ridge or edge aligned perpendicular to the fluid flow path of each of the grooves. The transition region between the axially forward region of the head and the axially rearward region of the head has been optimised according to the subject invention to have the effect of channelling or funnelling the fluid axially rearward and not directing the fluid flow radially outward. Accordingly, the flushing fluid is retained within each groove and this provides optimisation of the axially rearward transport of the cut rock fragments that in turn increases the penetration rate of the drill bit and hence a reduction in the overall drilling time for a given depth.
Preferably, each of the grooves extend axially forward beyond each aperture. Such an arrangement is advantageous to capture cut rock particles at the very forwardmost region of the drill head.
Preferably, an angle of alignment of the flow path length of each of the grooves in the first region axially forward and axially rearward of the aperture is substantially equal. The relative orientation of each groove at the region of the aperture provides for the unhindered flow of fluid and efficient transport of rock particles from the first (axially forward) to the second (axially rearward) ends of the grooves. The present grooves are configured to provide minimal disruption to the fluid flow and hence the undesirable ‘ gathering’ or accumulation of rock particles at regions of the grooves that may otherwise hinder the axially rearward flow. Preferably, each of the grooves at the transition between the first and second regions comprises a convex curve in the flow path length relative to the axis.
The curvature at the transition region may be represented by an arc of a circle having a single radius corresponding approximately to a radius of the head and/or cylindrical shank.
Optionally, the flow path length in the first region is aligned to be declined to slope towards the axis at an angle in the range 40 to 80°, 45 to 65° or 50 to 60° relative to the axis. Optionally, the flow path length in the second region is aligned to be declined to slope towards the axis at an angle in the range 5 to 30°, 10 to 25° or 10 to 20° relative to the axis. The angle of inclination corresponds to the angle extending between the axis and a trough region of each groove through an axial cross section of the drill bit. When viewed as a cross section through each groove in an axial plane bisecting the groove trough region, each groove comprises a generally convex shape profile relative to the axis having a generally dome-shaped profile. Sidewalls that define each groove may be curved in a circumferential direction around the axis such that the width of the groove perpendicular to its flow path length may increase according to a generally V- or U-shaped profile. Such an arrangement is advantageous to maintain the fluid flow within the grooves and to optimise the axially rearward flow of particles within each groove.
Preferably, the front face is generally dome-shaped and is devoid of regions aligned substantially perpendicular to the axis. Such regions aligned perpendicular to the axis may otherwise significantly disrupt the axially rearward transport of rock particles.
Preferably, each collar segment comprises gauge buttons and the front face comprises front buttons. Optionally, the drill bit comprises three front buttons and six gauge buttons. Optionally, two gauge buttons are provided on each collar segment and are positioned circumferentially between each of the grooves. Having the same number of grooves and front buttons has been found to optimise the rate of rock fracture relative to the rate by which the fractured particles are transported axially rearward. Similarly, the subject invention comprises twice the number of gauge buttons relative to the number of grooves to optimise cutting without compromising axially rearward transport of fractured debris material.
Preferably, a depth of each of the grooves increases generally from the front face towards the shank. The groove depth is optimised so as to provide a greater volume towards the axially rearward end of each groove so as to accommodate an increasing volume of debris particles transferred to the groove from the region of the gauge buttons. Again, such an arrangement is advantageous to optimise cutting and flushing of the rock particles.
Preferably, the device further comprises a trench axially recessed in the font face and extending circumferentially around the axis and perpendicular to the grooves, with each aperture positioned on the circumferential path of the trench such that an axial depth of the trench and each groove at the vicinity of each aperture is substantially equal. The trench is effective to provide a recessed region for each aperture of the passageways. In particular, the radially inner part of the trench is defined by a shoulder that acts to deflect and shield the annular edge (that defines the aperture) from the rock face and debris material.
Optionally, the drill bit comprises three flushing passageways and three grooves. Accordingly, each groove is provided with its own respective fluid flow. As will be appreciated, the specific number and configuration of front buttons, gauge buttons and grooves may vary within the scope of the subject invention having consideration of cutting efficiency without compromising or being detrimental to the axially rearward transport of cut material.
A specific implementation of the present invention will now be described, by way of example only, and with reference to the accompanying drawings in which:
Referring to
Front buttons 105 are located at front face 103 in close proximity to apex 112 and axis 102. The radially outer gauge buttons 106 are provided on the collar segments 104. According to the specific implementation, head 100 comprises three front buttons 105 and six gauge buttons 106, with each collar segment 104 comprising two gauge buttons 106. Front face 103 encompasses the forward facing surface 116 of collar segments 104 and is generally continuously tapered axially rearward from apex 112 to a head perimeter edge 115 that represents the maximum outside diameter of head 100.
A plurality of flushing grooves indicated generally by reference 107 are arranged over head 100. A first groove region 109 extends generally radially outward from axis 102 and a second groove region 110 extends generally axially rearward from front face 103 and in particular apex 112. Each groove 107 is recessed into head 100 such that a trough region 117 of each groove 107 is recessed axially rearward of the front face 103. Each groove 107 is further defined by sloping side faces 200 that provide a generally smooth transition from collar segment surfaces 116 and groove trough region 117. Grooves 107 comprise a generally V-shaped profile and configuration as defined by wall surfaces 200 and trough 117. The V-shaped profile extends generally along the full length of each groove 107 in the vicinity of apex 112 and a transition region 113 between shank 101 and head 100.
The drill bit further comprises a plurality of apertures 108 located at front face 103 and in particular at the trough region 117 of each groove 107. Each aperture 108 is defined by a substantially circular edge 114 having a diameter being smaller than a diameter of cutting buttons 105, 106. According to the specific implementation, the drill bit comprises three apertures 108 each located within a respective groove 107 and positioned radially between front buttons 105 and gauge buttons 106. However, apertures 108 are positioned off-set or to one side of an imaginary radial spoke extending through each of the front buttons 105 and gauge buttons 106. That is, the region of head 100 radially inward and radially outward from aperture 108 is devoid of a cutting button 105, 106 respectively.
Head 100 further comprises a plurality of channels 111 that extend axially within the outer perimeter of collar segments 104 having an axial length corresponding approximately to the axial distance between head perimeter edge 115 and transition region 113. According to the specific implementation, head 100 comprises three channels 111 positioned respectively at each one of three collar segments 104. According to the specific implementation, a depth (in a radial direction) of channels 111 is appreciably less than a corresponding depth of grooves 107. Additionally, channels 111 do not extend radially inward beyond collar segment surface 116 and gauge buttons 106.
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Specifically recessing the aperture edge 114 at the groove trough 117 prevents damage to the edge 114 so as to maintain the desired delivery and flow of flushing fluid within each groove 107. As will be appreciated, should edge 114 become damaged or worn so as to be misshapen, the fluid delivery path would be affected and the flushing performance decreased. The specific radial positioning of each aperture 108 radially intermediate the radial positions of front buttons 105 and gauge buttons 106 further optimises the protection of edge 114 from damage during cutting. Protection of edge 114 is further enhanced by a generally circumferentially extending trench 118 that is positioned radially between front buttons 105 and gauge buttons 106. In particular, each aperture 108 is located at the trough region of each trench 118. Furthermore, a generally circumferentially extending shoulder 119 defines a radially inner region of trench 118 that has the effect of providing a shield for edge 114 by way of deflecting or guiding rock debris appropriately into grooves 107.
Number | Date | Country | Kind |
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14153364.6 | Jan 2014 | EP | regional |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2014/077784 | 12/15/2014 | WO | 00 |