Patent Publication Number: US-10781641-B2

Title: Rotary claw drill bit

Description:
RELATED APPLICATION DATA 
     This application is a § 371 National Stage Application of PCT International Application No. PCT/EP2016/050868 filed Jan. 18, 2016 claiming priority of EP Application No. 15152283.6, filed Jan. 23, 2015. 
     FIELD OF INVENTION 
     The present invention relates to a shear claw drill bit having a plurality of cutting teeth and in particular, although not exclusively, to a modular component bit in which the teeth are distributed at the bit to optimise penetration rate and minimising wear. 
     BACKGROUND ART 
     Rotary drill bits are used in a variety of different fields including drilling oil, gas and water wells within the mining industry. Additionally, earth boring bits are commonly used to create blast holes that are then filed with explosives. Various types of drill bit have been developed for this purpose including drag bits, claw bits and conical roller-cone bits. Some drill bits comprise cutting teeth mounted within specific pick holders whilst other bits are formed from a metal-carbide alloy that mounts abrasion wear resistant polycrystalline diamond (PCD) inserts. 
     To facilitate forward drilling and to reduce wear on the bit, debris from the borehole is transported rearwardly by applying a fluid (typically air) down the drill string to the bit that channels the fluid back though the space between the outside of the drill string tubes and the inner surface of the bore hole. A reduction in the efficiency of removal of the loosened material within the borehole may result in jamming of the bit and the accelerated wear of the cutting teeth. The teeth may also wear prematurely when drilling hard rock or when the bit deviates laterally during drilling. Example rotary drill bits are described in FR 2643414; GB 2,238,736; DE 3,941,609; U.S. Pat. No. 5,666,864; GB 2,345,930; WO 2008/069863; US 2009/0057030; US 2010/0270086. 
     However, conventional bit designs are disadvantageous for a number of reasons. For a single piece bit, when the cutting teeth become unacceptably worn, the entire bit requires replacement which is an inefficient use of material. Additionally, the distribution of the cutting teeth at the bit head is not optimised to minimise teeth wear. Accordingly, what is required is a rotary drill bit that addresses the above problems. 
     SUMMARY OF THE INVENTION 
     It is an objective of the present invention to provide a rotary drill bit optimised to flush axially rearward cut rock fragments and fines to facilitate axially forward penetration of the bit during drilling. It is a further specific objective to both minimise wear of the cutting picks and to minimise, as far as possible, a non-uniform or differential rate of pick wear at the head so as to maximise the time period between servicing, repair or interchange of the bit and/or the picks. It is also a further objective to maintain or improve the guidance or steering characteristic of the bit whilst optimising penetration rate and minimising bit wear. 
     It is a further specific objective to provide a drill bit that is energy efficient and in particular to provide a re-buildable modular drill bit in which component parts of the bit may be recycled for subsequent use following repair or replacement of other components of the modular assembly. 
     The objectives are achieved by providing a modular drill bit having a drill bit head attachable to a drill bit body. Advantageously, different heads may be interchanged at the body as they become worn such that the body is considered to be a recyclable component of the bit. Accordingly, and preferably the head and body comprise respective mating components that facilitate alignment and attachment together. The present head and body are further configured to facilitate secure attachment typically by welding. In one aspect, the head and body comprise approximately planar mating attachment surfaces between which suitable weld material may be deposited to rigidly attach the head at the body. 
     To optimise the axially rearward flushing of cut material and to both minimise pick wear and in particular differential pick wear, the majority of the picks are located at different radial and optionally axial positions at the head. Accordingly, an axially forwardmost cutting tip of each pick is configured to contact the rock face during rotation of the pick about its central longitudinal axis to maximise the rock fracturing and crushing characteristics of the bit. Due to the spatial position of the picks, all picks are effectively working at a similar rate to provide substantially uniform wear. The present rotary bit may be considered to comprise one or a plurality of radially inner front picks and a plurality of radially outermost and axially rearwardmost gauge picks. Preferably, the radially inner front picks are each positioned at different radial and axial positions (relative to one another) whilst the gauge picks may be located at approximately the same radial separation from the axis and at similar axial positions (for example relative to the axially rearward facing attachment surface of the head). 
     Optionally, to assist optimisation of the cutting and wear characteristics of the bit, the picks may be arranged into groups according to their angular alignment with each group comprising a radially innermost and a radially outermost (gauge) pick. In particular, each group may comprise picks having the same or a similar angular alignment that is different to the angular alignment of the picks of another group. To further optimise the rock breaking and axially rearward flushing characteristics whilst minimising pick wear, an angular alignment of each pick within each group may be slightly different where the difference between the angular alignment of picks within the same group is less than the difference in the angular alignment between the picks of different groups. 
     According to a first aspect of the present invention there is provided a rotary claw drill bit comprising: a body having a rearward region for attachment of the bit to a drill string, a bore extending axially through the body; a head provided at a forward end of the body and having an axially extending bore to align with the bore of the body; a plurality of picks mounted at the head, each pick having a cutting tip; the picks including radially inner front picks and radially outermost gauge picks; characterised in that: the head and body are non-integrally formed; and a radial separation distance of the tips of each of the front picks from the axis is different. 
     Within the specification reference to ‘angular alignment’ of the cutting picks refers to the angular alignment of a longitudinal axis of each pick relative to the longitudinal axis of the bit, the longitudinal axis of other picks at the head and/or the angular alignment relative to the circumferentially extending rotational path of each pick (the rotational direction). The angular alignment of each pick is generally axially forward facing such that a base of each pick is positioned closest to the longitudinal axis of the bit relative to a cutting tip of each pick. Additionally, each pick is also tilted in the rotational direction of the head such that the cutting tip represents the leading part of the pick during rotation. Each pick therefore is aligned at the head at a compound angle to be tilted axially relative to the bit axis and to lean forward in the circumferential rotational direction. Due to the differential positioning of each pick at the head, the radial and axial positions of the circular orbital path of each tip is different to optimise rock breaking and flushing and to provide uniform pick wear. 
     Preferably, the bore of the head exits the head as a single opening positioned at the axis of the bit. Such a configuration is advantageous to optimise the radially outward and axially rearward flow of the flushing fluid (typically air) that entrains the cut material. A single opening minimises turbulence and flow disruptions that would otherwise inhibit the axially rearward transport of the cuttings and fines. A single opening also provides space for the differential positioning of the picks at the head. However, according to further specific implementations, the bit may comprise additional or auxiliary fluid flow outlet passageways exiting the head at different regions. 
     Optionally, the radial and an axial position of the cutting tip of each pick is unique. Accordingly, the front picks are positioned asymmetrically at the head when the bit is viewed along its axial centre. The present bit therefore does not comprise what may be considered symmetrical cutting rows or wings distributed around the axis. 
     Advantageously, the present bit comprises a plurality of pick holders formed integrally or non-integrally with the head, the picks being detachably mounted at the head via the pick holders. Such a configuration is beneficial for material efficiency as worn picks may be replaced without a need to replace the entire head or bit. Also, picks of different shapes and sizes may be interchanged at the head to optimise the cutting characteristics to suit particular applications and rock types. According to the preferred embodiments, the picks comprise a generally conical configuration having a generally sharp conical cutting tip. Preferably, the picks comprise a pick head mounted on a pick shaft that is received within regions of the head to releasably mount each of the picks via conventional pick mounting arrangements involving internal or external retainers. However, according to further specific implementations, the bit may comprise substantially fixed or non-interchangeable picks being fused, encapsulated and/or bonded to the drill bit, drill head or bit body. 
     Optionally, where the picks are considered to be arranged into groups according to their angular alignment of each pick at the head relative to the central axis of the bit, the cutting tips of the front picks of each group are positioned at different axial positions. Optionally, the axial position of the cutting tips of the front and gauge picks may be different for all picks at the head such that no two picks comprise a cutting tip positioned at the same axial and radial position. 
     Preferably, the head comprises a plurality of shoulders extending radially outward and axially rearward from a forward end of the head, each shoulder mounting one of the groups of picks. Preferably, the shoulders comprise tiered sections with each section mounting a respective pick at a particular compound angle and radial and axial position. Accordingly, the orientation of a mount surface of each of the sections according to the preferred embodiment is different to determine the angular alignment of each pick within each group. The tiered sections are advantageous to provide a secure mount for each pick to resist the loading forces during rotation and axially forward advancement into the rock. The tiered sections are also optimised to fit all picks at the head and to distribute them around the single passageway opening. 
     Optionally, where the picks are considered arranged into groups, the tips of the picks within at least some of the groups are positioned along an axially rearward and radially outward extending path that is curved or bent in the radial direction. Optionally, the path of the respective groups comprises a generally helical profile that extends axially rearward a short distance around the bit axis. The generally helical path configuration enables the relatively close positioning of the picks at the head where each pick is positioned and orientated at a different compound angles and radial and axial positions. The helical distribution also facilitates the radially outward and axially rearward transport of the cut material. 
     Preferably, a size and a shape of each of the picks is the same. Optionally, the cutting picks within each group may comprise a different size, cone shape or material. In particular, the gauge picks of each group may be generally larger than the radially inner front picks so as to be more resistant to wear. 
     Optionally, at least the tips of each of the front and gauge picks are located at different radial and/or axial positions at the head. Such a configuration optimises the bit for rock cutting during rotational advancement. 
     Preferably, the head comprises a mounting flange provided at a rearward end and the body comprises a mounting flange at a forward end to mate with the flange of the head. More preferably, the flange of the head is a male projection and the flange of the body is a recess to receive the projection. Such an arrangement is advantageous to facilitate reattachment of a replacement head onto the body. In particular, the respective male and female mountings at the head and body allow the head to be separated from the body, by for example, cutting the body axially above the male projection such that the male projection is retained within the cavity. The cavity may then be milled conveniently to mate with a replacement head. The material of the body is accordingly preserved. Preferably, the body and the head are fixed together by a weld material. Preferably, the head and body comprise substantially planar attachment faces between which the weld material may be applied. Additionally, the head and body may comprise radially inward tapered regions that when the head and body are mated together define an annular channel or groove within which the weld material may be applied to provide secure attachment of the head and body. 
     According to a second aspect of the present invention there is provided a kit of parts for a rotary claw drill bit as claimed herein wherein the body, the head and the picks are separate pieces attachable together. 
     According to a third aspect of the present invention there is provided a rotary claw drill bit comprising: a body having a rearward region for attachment of the bit to a drill string, a bore extending axially through the body; a head provided at a forward end of the body and having an axially extending bore to align with the bore of the body; a plurality of picks mounted at the head, each pick having a cutting tip; wherein the head and body are non-integrally formed; and wherein the tips of each of the picks are located at different radial and/or axial positions out the head so as to be distributed asymmetrically at the head. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       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: 
         FIG. 1  is a perspective view of a rotary claw drill bit comprising a body and a head mounting a plurality of picks arranged into cutting groups according to a specific implementation of the present invention; 
         FIG. 2  is a side view of the bit of  FIG. 1 ; 
         FIG. 3  is an upper perspective view of the bit head of  FIG. 2 ; 
         FIG. 4  is a partial exploded perspective view of the bit of  FIG. 2 ; 
         FIG. 5  is a plan view of the bit of  FIG. 2 ; 
         FIG. 6  is a magnified side view of the bit head of  FIG. 3 ; 
         FIG. 7  is a longitudinal cross sectional perspective view of the bit of  FIG. 2 ; 
         FIG. 8  is a further perspective view of the bit head of  FIG. 3  with selected cutting picks removed from the head; 
         FIG. 9  is a perspective view of a rotary claw drill bit according to a further specific implementation of the present invention; 
         FIG. 10  is a plan view of the cutting head of the bit of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT OF THE INVENTION 
     Referring to  FIGS. 1 to 3 , bit  100  comprises a head indicated generally by reference  101  rigidly attached to a body indicated generally by reference  102 . Head  101  comprises a plurality of cutting picks  103  having cutting tips  204  that project generally axially forward at head  101  so as to represent the cutting end of bit  100 . Body  102  comprises an axially rearward portion comprising threads  104  to mount bit  100  to a drill string (not shown). Head  101  comprises three radially and axially extending shoulders indicated generally by reference  200  with three picks  103  mounted at each respective shoulder  200 . Each shoulder  200  comprises a mount surface indicated generally by reference  203  into which is mounted each of the cutting picks  103 . Mount surface  203  along each shoulder  200  is divided into three tiered regions that form stepped sections with the mount surface  203  of each section separated by a step surface  205  that is aligned transverse and in particular perpendicular to the mount surface  203  of each section. The mount surface  203  at each shoulder section is aligned at different compound angles so as to be tilted relative to a longitudinal axis  106  of bit  100  and to lean or slope rearwardly relative to the rotational direction R of the bit  100 . 
     According to the specific implementation, picks  103  comprise a generally conical shape configuration having a respective central axis  209  that is orientated perpendicular to the mount surface  203  at each stepped section. Additionally, each of the pick axes  209  is aligned at a compound angle being transverse to bit central axis  106  and to lean into the bit rotational direction R such that the tip  204  of each bit represents the leading part. At least some of the picks are orientated to tilt towards the axis  106  (such that tip  205  is radially closer to axis  106  than a base of the pick) whilst some picks are tilted such that their tips  204  are inclined to be pointing away from the axis  106 . Each shoulder  200  comprises a corresponding rearward surface  206  positioned behind mount surface  203 . 
     Referring to  FIGS. 2 and 8  each pick  103  comprises a frusto-conical pick body  800  that mounts a cutting tip piece  801 . Body  800  is provided at one end of an elongate pick shaft (not shown) that extends through shoulder  200  and in particular a pick bore  803  extending from shoulder mount surface  203  to shoulder rearward surface  206 . Optionally, a pick washer  802  positionally supports pick body  800  at mount surface  203  with each pick shaft extending through each bore  803  and is secured in position via a retainer indicated generally be reference  207 . As shown in  FIG. 8 , each of the three shoulders  200  comprises a series of tiered sections including a first shoulder section  804   a  a second shoulder section  804   b  and a third shoulder section  804   c . Each section  804   a ,  804   b ,  804   c  is positioned to extend radially outward from axis  106  and to extend generally axially rearward in the general direction of bit head  101  towards bit body  102 . 
     Referring to  FIGS. 2 and 4 , head  101  comprises an axially rearward annular attachment face  201  configured to mate in touching contact with an axially forward annular attachment face  202  of bit body  102 . An annular attachment neck or flange  402  projects axially rearward from head attachment face  201 . A corresponding annular collar  400  projects axially forward from body attachment face  202  and is configured to receive neck  402  within a cavity region  401  defined by collar  400 . Via the appropriate mating of neck  402  within collar  400 , bit head  101  may be appropriately aligned and mounted onto body  102 . A weld material is applied between and at the junction of the attachment faces  201 ,  202  so as to secure head  101  to body  102 . A bore  306  extends centrally through head  101  and is aligned radially with a corresponding bore  403  extending within body  102  such that the two bores  306 ,  403  define a single bore that extends axially from a rearwardmost annular edge  704  at body  102  to a single bore opening  307  at head  101  referring to  FIGS. 3 and 7 . 
     As illustrated in  FIGS. 3 and 5 , the three shoulders  200  project radially outward around bore opening  307  to form three radially extending wings mounting each of the picks  103  at their respective tiered sections. In particular, a first shoulder  303  provides a mount for a first group of picks  300   a ,  300   b ,  300   c ; a second shoulder  304  provides a mount for a second group of picks  301   a ,  301   b ,  301   c ; and a third shoulder  305  provides a mount for a third group of picks  302   a ,  302   b ,  302   c . As illustrated with reference to  FIG. 8 , each of the three shoulders  303 ,  304 ,  305  comprises a corresponding mount surface  203  that is divided into stepped sections  804   a ,  804   b ,  804   c  such that each pick of each of the groups is positioned at a respective step S 04   a ,  804   b ,  804   c  at each of the respective shoulders  303 ,  304 ,  305 . The mount surface  203  of each shoulder  303 ,  304 ,  305  is positioned to sit on a generally helical path that extends radially outward and axially rearward around axis  106  from the region of bore opening  307  that is centred on axis  106 . As illustrated in  FIG. 3 , within each group of picks, each pick comprises an angular alignment that is generally similar and that is different to the angular alignment of the picks of the remaining groups. As the picks within all groups are positioned on a path having a generally helical profile that extends around axis  106 , the alignment of each pick  300   a ,  300   b ,  300   c  within each group is not identical but is generally similar so as to define a collective set of picks that are configured to cut the rock in a coordinated manner and to create concentric grooves in the rock that act to stabilise axially forward drilling and bit steering. In particular, the axis  300   d  of the first group of picks  300   a ,  300   b ,  300   c  is transverse to the axis  301   d  of the second group of picks  301   a ,  301   b ,  301   c  that is in turn aligned transverse to the axis  302   d  of the third group of picks  302   a ,  302   b ,  302   c.    
     Referring to  FIGS. 5 and 6 , an apex cutting tip  600   a ,  600   b ,  600   c  (illustrated with reference to the first group of picks  300   a ,  300   b ,  300   c ) are aligned on helical path  500  that projects radially outward and axially rearward relative to axis  106 . The cutting tips of the picks of the second and third groups  301 ,  302  are similarly aligned on respective helical paths  501 ,  502  that extend radially outward and axially rearward at head  101 . The axial and radial position and alignment of each respective mount section  804   a ,  804   b ,  804   c  at each shoulder  303 ,  304 ,  305  is different so as to provide a different axial and radial position and alignment of each of the respective picks  103  of each of the groups of picks such that a radial and axial position of each cutting tip (for example  600   a  to  600   c  and  601   a  to  601   c ) is different for all picks  103  at head  101 . 
     Referring to  FIGS. 3 and 5 , one pick  300   a ,  301   a ,  302   a  is positioned radially innermost; a corresponding second pick of each group  300   c ,  301   c ,  302   c  is positioned radially outmost relative to axis  106  and a third pick of each respective group  300   b ,  301   b  and  302   b  is positioned radially intermediate the respective first and second picks to create three cutting wings that are bent in the radially outward direction from axis  106 . Accordingly, the first and third picks  300   a ,  301   a ,  302   a ,  300   b ,  301   b  and  302   b  may be termed front picks and the second picks  300   c ,  301   c ,  302   c  may be termed gauge picks. Each of the radially innermost front picks  300   a ,  301   a ,  302   a  are positioned radially inside and axially forward of all the intermediate front picks  300   b ,  301   b ,  302   b . Additionally, the intermediate front picks  300   b ,  301   b ,  302   b  are positioned radially inside and axially forward of all of the gauge picks  300   c ,  301   c ,  302   c . The cutting tips  204  of the gauge picks  300   c ,  301   c ,  302   c  represent a radially outermost part of bit  100  and determine the diameter of the borehole during drilling. 
     According to the specific implementation, a radial separation distance of the tip  204  of each of the radially innermost set of front picks  300   a ,  301   a ,  302   a  is different and a corresponding radial separation distance from axis  106  of the intermediate front picks  300   b ,  301   b ,  302   b  is also different within these two sets of front picks. Also, as can be seen from  FIG. 6 , the axial position of each tip  204  of the front picks  300   a ,  300   b ,  301   a ,  301   b ,  302   a ,  302   b  relative to, for example, the axially rearward attachment surface  201  is different. This individual radial and axial positioning of each tip  204  of the inner front picks is advantageous to contact different radial and axial positions of the rock face to optimise rock fracture during rotation of bit  100 . Such a configuration also facilitates uniform wear across the different picks to maximise the period between which the picks are required to be interchanged when worn. 
     According to the specific implementation, the radial separation distance of the tip  204  of each of the gauge picks  300   c ,  301   c ,  302   c  and the axial position relative to the rearward attachment surface  201  is approximately equal. Such a configuration is advantageous to stabilise forward drilling and facilitate steering/guidance of the bit in use. However, according to further specific implementations, the radial and axial position of the respective tips  204  of the gauge picks  300   c ,  301   c ,  302   c  may be different within this set of picks so as to enhance the rock breaking characteristics of the bit and hence the drilling rate. 
       FIGS. 9 and 10  illustrate a further embodiment of the present invention in which pick head  700  comprises three corresponding shoulders  701 ,  702 ,  703 . Three picks  103  are provided at the first and second shoulders  701 ,  702  whilst two picks  103  are provided at third shoulder  703 . As with the embodiment of  FIGS. 1 to 8  each of the shoulders  701 ,  702 ,  703  extend generally along a radially outward and axially rearward extending path relative to axis  106  and comprise the corresponding tiered sections and mount surfaces  804   a ,  804   b ,  804   c.