Abstract:
A cylindrical hammer drill bit with a central fluid passage and having a first group of circumferentially spaced lowermost cutting surfaces located on lowermost arcuate segments spaced by elongated upwardly extending circumferentially spaced slots and a second group of circumferentially spaced uppermost cutting surfaces located in intermediate arcuate segments at the upper end of the slots. Each of the cutting surfaces has an arcuate segment portion on the outer periphery of the drill bit formed at the intersection of upwardly inwardly sloping surfaces with the periphery of the drill bit; and radially inwardly upwardly inclined radial segment portions located on radially rib portions on the upwardly inwardly sloping surfaces. Each radial rib portion is connected to an elongated inwardly facing fluid slot.

Description:
This application is a continuation of prior applications, Ser. No. 595,838 filed Apr. 2, 1984 and Ser. No. 820,708 filed Jan. 17, 1986, the benefit of which is claimed herein, now abandoned. 
    
    
     BACKGROUND OF INVENTION 
     This invention relates to a drill bit and sub-assembly for use with a reverse circulation hammer type drill pipe. 
     Conventional reverse circulation hammer drill bits have generally been unable to provide a high consistency of recovery of core samples throughout the depth of the drilling operation. Lack of consistent air flow and pressure through the central return has caused inconsistent recovery of samples which has resulted, in many cases, in incorrect and misleading mineral content assays of the sample. Additionally, the design of conventional hammer drill bits has resulted, not only in lack of consistency of recovery of core samples, but also in inefficiency in drilling. 
     The primary object of the present invention is to improve consistency of recovery of core samples and efficiency of drilling. The primary object is achieved by improvements in the construction and design of the drill bit and sub-assembly which improve cutting and removal of chips and maintenance of air pressure in the inner pipe. 
    
    
     BRIEF DESCRIPTION OF DRAWING 
     FIG. 1 is an exploded isometric sectional view of the drill bit and sub-assembly of the present invention; 
     FIG. 2 is a sectional view of the drill bit of the present invention; 
     FIG. 3 is an enlarged cross-sectional view of the drill bit. 
     FIG. 4 is an end view of the drill bit of FIG. 3; 
     FIG. 5 is a cross-section of a drill bit and sub-assembly of the present invention; and 
     FIG. 6 is an alternative embodiment illustrating carbide inserts used in conjunction with the hammer drill bit of the present invention 
    
    
     DETAILED DESCRIPTION 
     As shown in FIG. 1, the drill bit assembly comprises a drill bit 20, known as a Selcon bit, which is connected to the downhole end of a bit sub-connector means 22 which is, in turn, connected to the downhole end of the outer pipe 28 of a section of dual wall drill string 26. The inner pipe 30 of drill string 26 is coupled to bit sleeve 24 by a connector sleeve means 32 which fits over O-rings 34, 36 which are mounted in grooves 38, 40, respectively on bit sleeve 24. 
     In operation, one or more sections of drill string 26 are raised and lowered by a conventional hammer drill type rig to reciprocably drive the drill bit 20 into the earth to cut a drill hole. Compressed air or other fluid under pressure to forced down the outer passage 42 of the dual wall drill string sections, as indicated by arrows 44, 46, and into a central cavity 48 in the drill bit 20, which is connected to center passage 50 of bit sleeve 24 through a center passage in inner pipe 30. Thus, loose bits and pieces of earthen materials are carried upwardly to the surface by air pressure where they can be analyzed and evaluated. 
     The drill bit 20 comprises a one-piece member made from a casting of metallic material such as 4100 to 4300 series steel. Bit sleeve 24 and bit sub 22 are machined from 4140 or 4300 series steel tubing. Drill bit 20 and bit sub 22 are case hardened by electrical induction or sand base hardening to a hardness of between 35 and 50 on the Rockwell scale. The upper end of drill bit 20 is provided with a large diameter bore having threads 52 for connection to the lower threaded end portion 54 of the bit sub 22. The lower end portion of drill bit 20 is provided with a reduced diameter bore which provides an annular seat 76 abutting against lower surface 74 of bit sleeve 24. Annular seal and shock ring 62 is disposed on annular flange 64 to provide an air tight seal between the bottom surface 65 of annular ring 68 and the inner wall of bit sub 22 to ensure passage of air as indicated by arrows 44, 46 and to absorb shock from bit sleeve 24. 
     Bottom surface portion 74 of bit sleeve 24 abuts against surface 76 such that air passing between the outer wall surface 78 at bit sleeve 24 and annular ring 68 flow through notched air passage means 80, 82 which extend through shortened and elongated cutting teeth 84, 86, respectively. Threaded portion 70 of bit sub 22 engages threaded portion 72 of drill string 26 for assembly of the drill bit assembly illustrated in FIG. 1. 
     FIG. 2 illustrates a plurality of circumferentially and alternately spaced shortened intermediate cutting means 90 located on an intermediate side wall portion of the drill bit and elongated lowermost cutting means 92 on the lower end portion of the drill bit. Each shortened intermediate and elongated lowermost cutting means have shortened and elongated cutting teeth 84, 86, respectively, with notched air passage means formed therein for enabling compressed air to flow into central cavity 48, as set forth above. 
     FIGS. 3 and 4 illustrate axially extended cutting means 92 which comprises an arcuate segmental peripheral cutting edge means 94 formed by the intersection of annular drill bit outer surface 96 and beveled surfaces 98, 100 located on opposite sides of a radially inwardly extending rib portion forming elongated cutting tooth 86 having an upwardly and inwardly sloping cutting edge 102. Each cutting tooth 86 has flat circumferentially spaced axially extending side surfaces 104, 106 connected by curved end surfaces 108, 110 which intersect to form cutting edge 102. Each cutting tooth 86 also has arcuate segmental inner surfaces 112. Air passage means 82 are centrally located in cutting tooth 86 and open through surfaces 112. Each axially extended cutting means is further defined by axially extending side wall portions 116, 118 which define lateral circumferentially spaced gaps 120 therebetween. Surfaces 116, 118 comprise a flat parallel outermost portion 122 and a concave innermost portion 124. 
     Each axially shortened cutting means 90 comprises an arcuate segmental peripheral cutting edge portion 126 formed by the intersection of annular outer drill bit surface 96 and slightly beveled surfaces 128, 130 located on opposite sides of a radially inwardly extending cutting tooth 132 having a laterally inwardly sloping cutting edge 134 on the lower end thereof. Each cutting tooth 132 has flat circumferentially spaced axially extending side surfaces 136, 138 connected by curved end surfaces 140, 142 which intersect to form cutting edge 134. Each rib portion also has arcuate segment and inner surfaces 144 defining circumferentially spaced portions of bore 48. Air passage means 80 are centrally located in cutting tooth 132 and open through surfaces 144. 
     Each of the cutting teeth 86, 132 extend downwardly in the drilling position from a common plane 146 spaced downwardly from surface 148 a relatively short axial distance. Each of the air passages 80, 82 begin at annular lateral surface 150 which defines the end of threaded portion 52. Air passages 82 extend axially downwardly beyond cutting surfaces 126 with a lowermost portion 152 located radially opposite gaps 120 below lateral surfaces 128, 130. Thus, gaps 120 provide the additional function of air flow between adjacent ones of the axially extended cutting means. The oppositely curved side walls 124 form pockets to facilitate collection of cuttings and facilitate flow of cuttings into central cavity 48 and upwardly into connector tube passage 50. 
     In the presently preferred embodiment, the angles of the beveled surfaces 98, 100, 128, 130 are approximately 65 degrees from the vertical axis of the drill bit. The angle of cutting edges 102, 134 is approximately 83 degrees from the vertical axis of the drill bit. Thus, the drill bit provides a plurality of axially extended lowermost cutting means circumferentially disposed on circumferentially spaced lowermost arcuate segmental side wall portions which are of uniform size and shape and which have opposite parallel circumferentially spaced side surfaces forming a plurality of uniform size and shape circumferentially spaced radially inwardly and axially upwardly extending end slots spaced around the periphery of the drill bit and extending radially between the generally cylindrical outer peripheral surface portion of the drill bit and the generally cylindrical central opening extending axially through the drill bit; and a plurality of axially shortened intermediate cutting means axially upwardly spaced from the axially extended lowermost cutting means and disposed on circumferentially spaced arcuate intermediate segmental sections of the drill bit of uniform size and shape which are located axially adjacent and in part define the end slots and are disposed between the opposite parallel circumferentially spaced side surfaces of the lowermost segmental portions. 
     FIG. 5 is a cutaway assembly drawing of the drill bit assembly of the present invention in an assembled configuration. Drill string 26 is attached to bit sub 22 by way of threaded portions 72 of drill string 26 and threaded portions 70 of bit sub 22. In a similar manner, bit sub 22 is coupled to drill bit 20 by way of male threaded portions 54 of bit sub 22 and female threaded portions 52 of drill bit 20. Bit sleeve 24 is disposed in the central opening formed by the assembly of drill bit 20, but sub 22 and drill string 26. Bit sleeve 24 is disposed between flange portion 32 of inner pipe 30 and annular seal 62 disposed in bit sub 22. Bit sleeve 24 forms an annular cylindrical cavity having a center passage 50 for movement of air and collected bit samples in an upward direction. Bit sleeve 24 separates center passage 50 from external air passage 42. O-rings 34, 36 provide an airtight seal between outer passage 42 and center passage 50. Air is pumped down the outer passageway 42 of the drill string from the surface and proceeds along the outer passage as indicated by arrows 44, 46. Air passes between the inner surface of annular ring 68 and outer surface 78 of bit sleeve 24 into notched portions 80, 82 of cutting teeth 84, 86. Annular ring 62 provides an airtight seal between annular ring 68 and the inner wall of bit sub 22 and absorbs shock transmitted by bit sleeve 24. 
     The configuration of air passage means 80, 82 directs the airflow in an inward and upward direction to provide a more consistent air return. Both pressure and velocity of the air return remain more constant during the drilling process because of the inward and upward angle at which the air is directed through air passages 80, 82. The air medium functions to blow the sample away from the cutting edges of the bit and direct the sample through opening 48 into the void area of central passage 50 such that the sample is directed along the path of least resistance through central passage 50. In this manner, the consistency of the sample by volume is constant during the entire drilling process so as to provide a sample of mineral content which remains constant with vertical drilling depth. This is of high importance in exploratory drilling, especially of desert aluvials and placer exploration, to accurately determine mineral content of samples to accumulate data for the purpose of evaluating the feasibility of a mining operation. Failure to efficiently and consistently return the sample to the surface may affect the accuracy of the percentage per ton of rare metals of the sample retrieved during the drilling process. 
     The present invention also provides extra cutting edge. The axially shortened cutting means 90 provides room for expansion of samples which have been cut by axially extended cutting means 92 until the sample is removed through central opening 50. The cutting edges are beveled to increase the feed angle and to streamline the removal of sample from the cutting surfaces during the drilling process. The angle of the cutting edges provides for more cutting edge as the cutting process proceeds into the cut material. Moreover, the design of the present invention provides for additional cutting teeth to further increase the efficiency of the hammer drill bit of the present invention. 
     FIG. 6 illustrates an alternative embodiment which utilizes carbide inserts 160, 162, 164, 168 adjacent cutting edges in drill bit 20. Each of the carbide inserts is inserted into a groove such as groove 170 adjacent the cutting edge and secured in place by gluing or other suitable means of attaching the carbide inserts in the grooves. The carbide inserts function to increase the hardness of the cutting edges and consequently extend the effective use of the drill bit and premature wear of the cutting edges. The grooves in the cutting edges are machined in drill bit 20 prior to the hardening process. Once the grooves are machined in the drill bit 20, the surfaces are case hardened by electrical induction, as described above. 
     The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and other modifications and variations may be possible in light of the above teachings. The embodiment was chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and various modifications as are suited to the particular use contemplated. It is intended that the appended claims be construed to include other alternative embodiments of the invention except insofar as limited by the prior art.