Patent Publication Number: US-9428968-B2

Title: Rotary drill bit with cutting insert having edge preparation

Description:
BACKGROUND OF THE INVENTION 
     The invention pertains generally to an excavating tool such as, for example, a rotary drill bit useful for drilling through various earth strata. More specifically, the invention pertains to a rotary drill bit with a cutting insert such as, for example, a roof drill bit useful for drilling bore holes in an underground mine. 
     The expansion of an underground mine, such as for example, a coal mine, requires digging a tunnel. Initially, this tunnel has an unsupported roof. Because the roof is not supported, there is an increased chance for a mine cave that, of course, adds to the hazards of underground coal mining. Furthermore, an unsupported roof is susceptible to rock and debris falling from the roof. Falling rock and debris can injure workers as well as create hazardous clutter on the floor of the tunnel. In order to support and stabilize the roof in an underground tunnel, bore holes are drilled in the roof, i.e., earth strata. 
     The apparatus used to drill these holes typically comprises a drill with a long shaft, i.e., drill steel, attached to the drill. A roof drill bit is detachably mounted to the drill steel at the distal end thereof. In certain roof drill bits, a hard cutting insert is mounted on a body of the roof drill bit. The roof drill bit is then pressed against the roof, and the drilling apparatus operated so as to drill a bore hole in the roof. The bore holes extend between about two feet and about twenty feet into the roof depending upon the particular situation. The roof support members, such as roof panels, are then attached to roof bolts. In one alternative procedure, these bore holes are filled with resin and roof bolts are fixed within the bore holes. In another alternative procedure, the roof bolts use mechanical expander shells to affix the roof bolts in the bore holes. The end result of using either procedure is a roof which is supported, and hence, is of much greater stability than the unsupported roof. This reduces the hazards associated with underground mining. The roof bolting process is considered to be an essential underground mining activity. 
     Roof bolting accounts for the largest number of lost time injuries in underground mining. During the roof bolting process, the roof is unsupported so that it does not have optimum stability. Furthermore, the roof bolting process exerts stresses on the roof so as to further increase the safety hazards during the roof bolting process. Thus, a decrease in the overall time necessary to bore holes reduces the time it takes to complete the roof bolting process. This is desirable since it contributes to the overall speed, efficiency and safety of the roof bolting process. Thus, many solutions have been proposed to decrease the overall time to complete the drilling of the necessary bore holes. For example, roof drilling bits with various cutting inserts and various cutting geometries have been developed. Efforts have also been made to increase the overall useful life of roof drilling bits. 
       FIGS. 1 and 1A  set forth an example of a known cutting insert  2  (for use with a roof drilling bit) having a leading face  4 , a top surface  6  that includes a primary relief surface  7  adjacent to the leading face  4  and secondary relief surface  8 . The leading face  4  and the primary relief surface  7  intersect at an angle M (90 degrees or less) to form a cutting edge  9  which results in a positive or neutral axial rake angle N. However, it has been determined that this configuration results in a large amount of stress on the cutting edge  9  which in turn leads to the failure of the cutting edge  9  (e.g. as a result of breaking or chipping of the cutting edge) and, thus, the cutting insert  2  needing to be replaced. 
     Accordingly, there is a need for improved roof drilling bits that overcome disadvantages, limitations and shortcomings of known roof drilling bits. For example, it would be desirable to provide an improved roof drill bit that facilitates the prompt completion of the roof bolting process. It would also be desirable to provide an improved roof drill bit that has a longer useful life. It would also be desirable to provide an improved roof drill bit that has an increased penetration rate. 
     SUMMARY OF THE INVENTION 
     In accordance with an aspect of the invention, a rotary drill bit for engaging an earth strata material includes an elongate drill bit body having an axial forward end and an axial rearward end, and a cutting insert attached to the axial forward end of the elongate drill bit body, the cutting insert having an elongate insert body rotatable about a central axis. The elongate insert body includes a pair of symmetrical halves symmetrical about the central axis, each symmetrical half comprising: a leading face; a top surface having a relief surface; a T-land surface extending between the leading face and the relief surface of the top surface; and a cutting edge formed at the intersection of the T-land surface and the relief surface of the top surface. In one aspect, the cutting edge has a negative axial rake angle. In another aspect, the relief surface includes a primary relief surface and a secondary relief surface. 
     In accordance with another aspect of the invention, a cutting insert for use in connection with a rotary drill bit for engaging an earth strata material includes an elongate insert body rotatable about a central axis. The elongate insert body includes a pair of symmetrical halves symmetrical about the central axis, each symmetrical half comprising: a leading face; a top surface having a primary relief surface and a secondary relief surface; a T-land surface extending between the leading face and the primary relief surface of the top surface; and a cutting edge formed at the intersection of the T-land surface and the primary relief surface of the top surface. In one aspect, the cutting edge has a negative axial rake angle. 
     In accordance with another aspect of the invention, a cutting insert for use in connection with a rotary drill bit for engaging an earth strata material includes an elongate insert body rotatable about a central axis. The elongate insert body includes a pair of symmetrical halves symmetrical about the central axis, each symmetrical half comprising: a leading face; a top surface having a relief surface; a T-land surface extending between the leading face and the relief surface of the top surface; and a cutting edge formed at the intersection of the T-land surface and the relief surface of the top surface. In one aspect, the cutting edge has a negative axial rake angle. 
     In accordance with yet another aspect of the invention, a rotary drill bit for engaging an earth strata material includes an elongate drill bit body having an axial forward end and an axial rearward end, and a cutting insert attached to the axial forward end of the elongate drill bit body, the cutting insert having an elongate insert body rotatable about a central axis. The elongate insert body includes a pair of symmetrical halves symmetrical about the central axis, each symmetrical half comprising: a leading face; a top surface having a relief surface; a T-land surface extending between the leading face and the relief surface of the top surface; and a rounded cutting edge formed at the intersection of the T-land surface and the relief surface of the top surface. In one aspect, the rounded cutting edge has a negative axial rake angle. In another aspect, the relief surface includes a primary relief surface and a secondary relief surface. In another aspect, the leading face and the T-land surface intersect to form a rounded leading edge. 
     These and other aspects of the present invention will be more fully understood following a review of this specification and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric view of a known cutting insert. 
         FIG. 1A  is a sectional view taken along line  1 A- 1 A of the known cutting insert shown in  FIG. 1 . 
         FIG. 1B  is a front view of the known cutting insert shown in  FIGS. 1 and 1A . 
         FIG. 2  is an exploded assembly view of a rotary drill bit, e.g. a roof drill bit, in accordance with an aspect of the invention. 
         FIG. 3  is an isometric view of a cutting insert shown in  FIG. 2 , in accordance with an aspect of the invention. 
         FIG. 4  is a front elevational view of the cutting insert shown in  FIGS. 2 and 3 , in accordance with an aspect of the invention. 
         FIG. 5  is a top plan view of the cutting insert shown in  FIGS. 2, 3 and 4 , in accordance with an aspect of the invention. 
         FIG. 5A  is a sectional view taken along line  5 A- 5 A of  FIG. 5 , in accordance with another aspect of the invention. 
         FIG. 6  is an isometric view of an additional cutting insert, in accordance with an aspect of the invention. 
         FIG. 7  is a top plan view of the cutting insert shown in  FIG. 6 , in accordance with an aspect of the invention. 
         FIG. 7A  is a sectional view taken along line  7 A- 7 A of  FIG. 7 , in accordance with another aspect of the invention. 
         FIG. 7B  is a sectional view similar to  FIG. 7A  but showing an additional cutting insert, in accordance with another aspect of the invention. 
         FIG. 8  is an isometric view of an additional cutting insert, in accordance with an aspect of the invention. 
         FIG. 9  is a top plan view of the cutting insert shown in  FIG. 8 , in accordance with an aspect of the invention. 
         FIG. 9A  is a sectional view taken along line  9 A- 9 A of  FIG. 9 , in accordance with another aspect of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is for purposes of illustrating various aspects of the invention only and not for purposes of limiting the scope of the invention. 
     Referring to the drawings,  FIG. 2  illustrates a rotary drill bit in the form of a roof drill bit generally designated as  10 . Roof drill bit  10  has an elongate drill bit body  12  typically made of, for example, steel. Drill bit body  12  presents a generally cylindrical geometry. Drill bit body  12  has an axial forward end  14  and an axial rearward end  16 . Drill bit body  12  contains a transverse slot  18  in the axial forward end thereof  14 . Drill bit body  12  also may include a debris evacuation or collection port  20  that is mediate between the axial forward end  14  and the axial rearward end  16 . During the drilling operation, dirt and debris may pass through the port  20 . 
     The roof drill bit  10  also includes a cutting insert (or rotary drill bit insert)  22  (see  FIGS. 2-5A ) that is positioned within the transverse slot  18  and the insert  22  is typically affixed therein by, for example, attaching mechanically or otherwise, via brazing, gluing, or press fitting using conventional compositions and techniques known to those skilled in the art. The roof drill bit  10  and the cutting insert  22  have a central longitudinal axis L-L wherein the roof drill bit  10  and the cutting insert  22  are rotatable about the central axis L-L. The cutting insert  22  is made from, for example, a cemented tungsten carbide that is a mixture of cobalt and tungsten carbide. Other super hard, wear resistant materials such as polycrystalline diamond, ceramics, or cermet may be used as a supplement and/or substitute. For example chromium carbide-coated metals and other cermets where titanium carbide or vanadium carbide is added to tungsten carbide may be candidates for inserts materials in accordance to aspects of the invention. Alternate ceramics for such applications include aluminum-based, silicon based, zirconium-based and glass varieties. Still other insert materials alternatives include cubic refractory, transition metal carbides or any other known or subsequently developed material(s) harder than the base material. Also coatings of the inserts such as PVD or CVD coatings can be used. 
     Cutting insert  22  has a cutting insert body, generally designated as  24 , that has a top surface generally designated as  26 , a bottom surface generally designated as  28 , opposite side surfaces generally designated as  30  and  32 , and opposite end surfaces generally designated as  34  and  36 . The cutting insert body  24  is structured and arranged into two opposite symmetric connected portions, i.e. a pair of symmetrical halves, which are symmetric about the central axis L-L; namely, one symmetric portion generally designated by bracket  38  and another symmetric portion generally designated by bracket  138  (see, for example,  FIG. 5 ). 
     Referring to the one symmetric portion  38 , there is a leading face  40  and an opposite rearward or trailing face  42 . In one aspect, the top surface  26  includes a primary relief surface  44 . In another aspect, the top surface  26  also includes a secondary relief surface  46  wherein the primary relief surface  44  and the secondary relief surface  46  are contiguous and non-coplanar. In another aspect, the secondary relief surface  46  extends from the primary relief surface  44  toward the rearward or trailing face  42  of the cutting insert  22 . In another aspect, the secondary relief surface  46  extends from the primary relief surface  44  to the rearward or trailing face  42 . 
     In accordance with another aspect of the invention, the portion  38  of the cutting insert  22  includes edge preparation such as a T-land surface, generally designated as  48 , extending generally between the leading face  40  and the primary relief surface  44  of the top surface  26 . In one aspect, the T-land surface  48  is a planar surface. In another aspect, the T-land surface  48  is contiguous and non-coplanar with the leading face  40 . In another aspect, the T-land surface  48  is contiguous and non-coplanar with the primary relief surface  44 . 
     The portion  38  of the cutting insert  22  further includes a cutting edge  50  formed at the intersection of the T-land surface  48  and the primary relief surface  44  of the top surface  26 . This configuration of having the cutting edge  50  formed at the intersection of the T-land surface  48  and the primary relief surface  44  provides for the cutting edge  50  to have a negative axial rake angle R (see, for example,  FIG. 5A ). In one aspect, the negative axial rake angle R is in the range of about 10 degrees to about 40 degrees. In one specific example, the rake angle R shown in  FIG. 5A  is about negative 25 degrees. 
     The T-land surface  48  is positioned relative to the primary relief surface  44  at an angle X (see, for example,  FIG. 5A ). The angle X may be referred to as a relief angle relative to or in relation to cutting edge  50 . In one aspect, the T-land surface  48  is positioned relative to the primary relief surface  44  at an angle X that is greater than 90 degrees. In one specific example, the angle X shown in  FIG. 5A  is about 115 degrees. 
     In another aspect, the T-land surface  48  may have a width W (see, for example,  FIG. 5A ) in the range of about 0.002 inches to about 0.090 inches. In one specific example, the width W is about 0.010 inches. 
     It will be appreciated that the described configuration of the T-land  48 , cutting edge  50 , negative axial rake angle R and/or the relief angle X individually and/or in combination advantageously avoid a sharp transition for the cutting edge  50  so as to reduce or minimize the possibility of the cutting edge  50  breaking or chipping during operation of the roof drill bit  10 . In addition, the T-land  48  is configured so as to redirect the cutting forces along the cutting edge to reduce the shear stress along the cutting edge. 
     Referring to the other symmetric portion  138  of the cutting insert  22 , the portion  138  is the same or identical to the portion  38  as described herein. More particularly, the portion  138  includes a leading face  140  and an opposite rearward or trailing face  142 . In one aspect, the top surface  26  includes a primary relief surface  144 . In another aspect, the top surface  26  also includes a secondary relief surface  146  wherein the primary relief surface  144  and the secondary relief surface  146  are contiguous and non-coplanar. In another aspect, the secondary relief surface  146  extends from the primary relief surface  144  toward the rearward or trailing face  142  of the cutting insert  22 . In another aspect, the secondary relief surface  146  extends from the primary relief surface  44  to the rearward or trailing face  142 . 
     In accordance with another aspect of the invention, the portion  138  of the cutting insert  22  includes a T-land surface, generally designated as  148 , extending generally between the leading face  140  and the primary relief surface  144  of the top surface  26 . In one aspect, the T-land surface  148  is a planar surface. In another aspect, the T-land surface  148  is contiguous and non-coplanar with the leading face  140 . In another aspect, the T-land surface  148  is contiguous and non-coplanar with the primary relief surface  144 . 
     The portion  138  of the cutting insert  22  further includes a cutting edge  150  formed at the intersection of the T-land surface  148  and the primary relief surface  144  of the top surface  26 . This configuration of having the cutting edge  150  formed at the intersection of the T-land surface  148  and the primary relief surface  144  provides for the cutting edge  150  to have a negative axial rake angle (not shown). It will be appreciated that the negative axial rake angle for the portion  138  is the same as negative axial rake angle R, as described herein and illustrated herein. In one aspect, the negative axial rake angle is in the range of about 10 degrees to about 40 degrees. In one specific example, the rake angle is about negative 25 degrees. 
     The T-land surface  148  is positioned relative to the primary relief surface  44  at an angle (same as angle X shown, for example, in  FIG. 5A  and described herein), which may be referred to as a relief angle for the cutting edge  150 . In one aspect, the T-land surface  148  is positioned relative to the primary relief surface  144  at a relief angle that is greater than 90 degrees. In one specific example, the relief angle is about 115 degrees. 
     It will be appreciated that the described configuration of the T-land  148 , cutting edge  150 , negative axial rake angle and/or the relief angle individually and/or in combination advantageously avoid a sharp transition for the cutting edge  150  so as to reduce or minimize the possibility of the cutting edge  150  breaking or chipping during operation of the roof drill bit  10 . 
     The Cutting insert  22  is made, for example, with a powder metallurgy process using a press comprising of a die and top and bottom ram/punch to press the complete shape. Parts can be pressed to finished shape or modified with a wet/dry blast, or diamond ground other material shaping processes such as but not limited to EDM (electrical discharge machining), EDG (electrical discharge grinding), green machining, laser ablation into final shapes. Advantageously, the invention provides for moving the critical cutting edge of the insert from the intersection of the die case and ram during manufacturing. In accordance with an aspect of the invention, the critical cutting edge is now formed entirely in the ram/punch. This eliminates the flash from forming on the cutting edge. Flash is undesirable because, for example, it is a stress concentrator. It will be appreciated that these and other aspects of the invention as set forth herein contribute to the desired edge, i.e. cutting edge, preparation for the cutting insert. 
     Referring to  FIGS. 6-7A , there is illustrated an additional cutting insert  222 , in accordance with another aspect of the invention. Cutting insert  222  has a cutting insert body, generally designated as  224 , that has a top surface generally designated as  226 , a bottom surface generally designated as  228 , opposite side surfaces generally designated as  230  and  232 , and opposite end surfaces generally designated as  234  and  236 . The cutting insert body  224  is structured and arranged into two opposite symmetric connected portions, i.e. a pair of symmetrical halves, which are symmetric about the central axis L-L; namely, one symmetric portion generally designated by bracket  238  and another symmetric portion generally designated by bracket  238 A (see, for example,  FIG. 7 ). It will be appreciated that the symmetric portion  238 A of the cutting insert  222  is the same or identical to the portion  238  which will be described in detail herein. 
     Referring to the symmetric portion  238 , there is a leading face  240  and an opposite rearward or trailing face  242 . In one aspect, the top surface  226  includes a relief surface  244 . In contrast to the cutting insert  22  described herein, the top surface  26  does not include a secondary or additional relief surface. In another aspect, the relief surface  244  extends to the rearward or trailing face  242 . 
     In accordance with another aspect of the invention, the portion  238  of the cutting insert  222  includes a T-land surface, generally designated as  248 , extending generally between the leading face  240  and the relief surface  244  of the top surface  226 . In one aspect, the T-land surface  248  is a planar surface. In another aspect, the T-land surface  248  is contiguous and non-coplanar with the leading face  240 . In another aspect, the T-land surface  248  is contiguous and non-coplanar with the relief surface  244 . 
       FIG. 7B  illustrates an additional cutting insert  222   b , in accordance with another aspect of the invention. Cutting insert  222   b  is similar to cutting insert  222  except that cutting insert  222   b  includes a rounded or curved, i.e. non-planar, T-land surface  248   b . Cutting insert  222   b  still includes a negative axial rake angle R 1   b.    
     The portion  238  of the cutting insert  222  further includes a cutting edge  250  formed at the intersection of the T-land surface  248  and the relief surface  244 . This configuration of having the cutting edge  250  formed at the intersection of the T-land surface  248  and the relief surface  244  provides for the cutting edge  250  to have a negative axial rake angle R 1  (see, for example,  FIG. 7A ). In one aspect, the negative axial rake angle R 1  is in the range of about 10 degrees to about 40 degrees. In one specific example, the rake angle R 1  shown in  FIG. 7A  is about negative 25 degrees. 
     The T-land surface  248  is positioned relative to the relief surface  244  at an angle X 1  (see, for example,  FIG. 7A ). The angle X 1  may be referred to as a relief angle relative to or in relation to the cutting edge  250 . In one aspect, the T-land surface  248  is positioned relative to the relief surface  244  at an angle X 1  that is greater than or equal to 90 degrees. In one specific example, the angle X 1  shown in  FIG. 7A  is about 95 degrees. 
     It will be appreciated that the described configuration of the T-land  248 , cutting edge  250 , negative axial rake angle R 1  and/or the relief angle X 1  individually and/or in combination advantageously avoid a sharp transition for the cutting edge  250  so as to reduce or minimize the possibility of the cutting edge  250  breaking or chipping during operation of the roof drill bit  10 . 
     Referring to  FIGS. 8-9A , there is illustrated an additional cutting insert  322 , in accordance with another aspect of the invention. Cutting insert  322  has a cutting insert body, generally designated as  324 , that has a top surface generally designated as  326 , a bottom surface generally designated as  328 , opposite side surfaces generally designated as  330  and  332 , and opposite end surfaces generally designated as  334  and  336 . The cutting insert body  324  is structured and arranged into two opposite symmetric connected portions, i.e. a pair of symmetrical halves, which are symmetric about the central axis L-L; namely, one symmetric portion generally designated by bracket  338  (see, for example,  FIG. 9 ) and another symmetric portion generally designated by reference number  338 A (see, for example,  FIG. 8 ). It will be appreciated that the symmetric portion  338 A of the cutting insert  322  is the same or identical to the portion  338  which will be described in detail herein. 
     Referring to the symmetric portion  338 , there is a leading face  340  and an opposite rearward or trailing face  342 . In one aspect, the top surface  326  includes a primary relief surface  344 . In another aspect, the top surface  326  also includes a secondary relief surface  346  wherein the primary relief surface  344  and the secondary relief surface  346  are contiguous and non-coplanar. In another aspect, the secondary relief surface  346  extends from the primary relief surface  344  toward the rearward or trailing face  342  of the cutting insert  322 . In another aspect, the secondary relief surface  346  extends from the primary relief surface  344  to the rearward or trailing face  342 . While the primary relief surface  344  and the secondary relief surface  346  are shown, it will be appreciated that the insert  322  may include a single relief surface or more than two relief surfaces in accordance with aspects of the invention. 
     In accordance with another aspect of the invention, the portion  338  of the cutting insert  322  includes a T-land surface, generally designated as  348 , extending generally between the leading face  340  and the relief surface  344  of the top surface  326 . In one aspect, the T-land surface  348  is a planar surface. In another aspect, the T-land surface  348  is contiguous and non-coplanar with the leading face  340 . In another aspect, the T-land surface  348  is contiguous and non-coplanar with the relief surface  344 . 
     The portion  338  of the cutting insert  322  further includes a rounded cutting edge  350  formed at the intersection of the T-land surface  348  and the relief surface  344 . In another aspect, the leading face  340  and the T-land  348  intersect to form a rounded leading edge  341 . 
     The configuration of having the rounded cutting edge  350  formed at the intersection of the T-land surface  348  and the relief surface  344  provides for the cutting edge  350  to have a negative axial rake angle R 2  (see, for example,  FIG. 9A ). In one aspect, the negative axial rake angle R 2  is in the range of about 10 degrees to about 40 degrees. In one specific example, the rake angle R 2  shown in  FIG. 9A  is about negative 25 degrees. 
     The T-land surface  348  is positioned relative to the relief surface  344  at an angle X 2  (see, for example,  FIG. 9A ). The angle X 2  may be referred to as a relief angle relative to or in relation to the rounded cutting edge  350 . In one aspect, the T-land surface  348  is positioned relative to the primary relief surface  344  at an angle X 2  that is greater than 90 degrees. In one specific example, the angle X 2  shown in  FIG. 9A  is about 115 degrees. 
     Whereas particular aspects of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.