Patent Publication Number: US-6698537-B2

Title: Bit retention system

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to earth boring percussion bits. More particularly, the invention relates to retention systems for ensuring that even when broken during use, the percussion bit remains connected to the drill string. 
     U.S. Pat. No. 5,065,827 discloses a conventional hammer and percussion bit assembly having a percussion bit retention system. The percussion bit retention system includes a retainer which is mounted on the drive sub of the percussion bit assembly. The retainer includes a lower section having an inner chamber and a thread-shaped, inwardly extending projection. The bottom portion of the percussion bit includes a head section, a threaded section and a recess disposed intermediate the head section and the threaded section. The percussion bit is installed by inserting the upper portion of the percussion bit into the retainer until the threaded section of the lower portion abuts the thread-shaped projection of the retainer. The projection is brought into threaded engagement with the threaded section of the retainer and the retainer is rotated until the projection passes completely through the threaded section of the retainer and enters the chamber. If the percussion bit breaks in the shaft portion above the bottom portion of the percussion bit, the projection will be captured within the chamber by the threaded section of the retainer. 
     The threaded section of such retainers may become fouled during drilling operations, making removal of the percussion bit difficult. Bits may be difficult to install due to corrosion and wear induced degradation of the threaded section of the retainer. 
     SUMMARY OF THE INVENTION 
     With the present invention, a novel percussion bit assembly, and associated novel bit retainer member and method of assembling the bit retainer to a percussion bit drill string, can be simply achieved without the requirement for rotating the bit relative to the retainer, and without the risk of thread fouling. 
     In accordance with the invention, a substantially tubular retainer member is provided, having inwardly extending upper and lower lips and a middle portion longitudinally extending between the upper and lower lips. Multiple slots extend from the lower end of the retainer member to a terminal end disposed intermediate the upper and lower ends. The slots form multiple longitudinally extending cantilever beam segments. The percussion bit is connected to the chuck member by inserting the shoulder of the percussion bit into the middle portion of the retainer member. The cantilever beam segments are resiliently, radially deflected by the shoulder of the percussion bit during installation, the outside diameter of the shoulder being greater than the inside diameter of the lower lip. 
     The upper portion of the chuck member is inserted through the retainer member and the cantilever beam segments are resiliently, radially deflected to insert of the lower portion of the chuck member into the middle portion of the retainer member. The chuck member is mounted to the housing such that the upper lip of the retainer member is clamped between the lower end portion of the housing and the lower portion of the chuck member. An inner ramp face on the lower lip of the retainer member slides up an outer ramp face in the lower portion of the chuck member and an outer ramp face on the shoulder of the bit to facilitate deflection of the cantilever beam segments. 
     The upper bearing surface of the lower lip forms an acute angle α with the interior surface and the lower surface of the shoulder forms an acute angle θ with the surface of the bit, angle θ being complementary to angle α. Preferably, angles α and θ are substantially equal to 60 degrees. 
     In a preferred embodiment, the terminal end of each slot defines a substantially circular opening. The length of each slot is preferably greater than half the length of the retainer member. 
     It is thus an object of the invention to provide a new and improved retention system and assembly method for a percussion bit assembly. 
     It is also an object of the invention to provide a retention system and method for a percussion bit assembly that does not require threaded engagement between the percussion bit and the other components of the retention system. 
     Other objects and advantages of the invention will become apparent from the drawings and specification. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention may be better understood and its numerous objects and advantages will become apparent to those skilled in the art by reference to the accompanying drawing in which: 
     FIG. 1 is an elevation view, partly in section and partly in phantom, of a hammer-percussion bit assembly in the drilling mode of operation, having a percussion bit retention system in accordance with a first embodiment of the invention; 
     FIG. 2 is an enlarged elevation view of the bit retainer element of FIG. 1; 
     FIG. 3 is a bottom view of the bit retainer element of FIG. 2; 
     FIG. 4 is a cross section taken along line  4 — 4  of FIG. 3; 
     FIG. 5 is an enlarged view, partly in section and partly in phantom, of the lower end portion of the hammer-percussion bit assembly of FIG. 1, illustrating a disassembly bushing installed for removal of the bit; and 
     FIG. 6 is an enlarged view, partly in section and partly in phantom, of the lower end portion of the hammer-percussion bit assembly of FIG. 1, illustrating the retention of a broken bit. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to the drawings wherein like numerals represent like parts throughout the several figures, a hammer-percussion bit assembly  12 , with bit retention system  10  according to the invention, comprises a hammer housing  14  threadably connected at its upper end portion  16  to a drill string mounting member  18 . An opening  20  in the lower end  22  of the housing  14  receives the upper portion  24  of tubular chuck member  26  and is threadably connected thereto. The outside diameter  28  of the lower portion  30  of the chuck member  26  is greater than the outside diameter  32  of the upper portion  24  of the chuck member  26  to define a shoulder  34 . The chuck member  26  has a plurality of longitudinally extending splines  36  located on the interior surface for matingly receiving splines  38  located on the shank  40  of the percussion bit  42 , to selectively rotate or permit relative axial displacement of the bit. 
     A lock cylinder  44  and a split lock ring  46  are positioned within the interior of the housing  14 . The upper end of the lock cylinder  44  abuts a shoulder ring  48  fixedly mounted within the housing  14  and the lower end of the lock cylinder  44  and the upper end of the lock ring  46  abut each other. When the chuck member  26  is installed, the upper end  50  of the chuck member  26  abuts the lower end of the lock ring  46  to hold the lock ring  46  and lock cylinder  44  in place. The upper portion  52  of the percussion bit shank  40  is disposed within the lock ring  46  and lock cylinder  44  such that an upper radially extending shoulder  54  on the upper portion  52  is positioned within the lock cylinder  44  and above the lock ring  46 . The inside diameters of the lock cylinder  44  and the lock ring  46  and the outside diameter of the upper shoulder  54  are selected such that the upper shoulder  54  is free to move up and down within the lock cylinder  44  and is captured by the lock ring  46 . 
     The upper shoulder  54  has a plurality of vertically extending grooves (not shown) that correspond to the splines  36  on the chuck member  26 . The upper portion  52  of the percussion bit shank  40  also includes an upper bearing surface  56 . The percussion bit shank  40  has a lower shoulder  57  including an upper bearing surface  58  adapted for bearing against the lower surface  60  of the chuck member  26 . The bottom surface  62  of the hammer  64  impacts against the upper bearing surface  56  to impart a percussive force to the bit  42 . Alternatively, the percussive force may be transmitted through the lower surface  60  of the chuck member  26  to upper bearing surface  58  of the bit  42 . A lower radially extending shoulder  66 , preferably an annular rim, is disposed below upper bearing surface  58  and adjacent to the head  68  at the lower end of the percussion bit  42 . As shown in FIG. 5, upper bearing surface  58  may define the upper face of the lower shoulder  66 . 
     A percentage of all percussion bits shanks  40  fail due to cyclic fatigue by fracturing below the lock ring  46  and above the bit head  68 . When this occurs during the drilling operation, the lower section of the percussion bit is left at the bottom of the hole, requiring a costly and cumbersome fishing operation. 
     The percussion bit retention system  10  of the subject invention employs a substantially cylindrical (tubular) retainer member  70  having upper and lower ends  72 ,  74  and interior and exterior surfaces  76 ,  78 . The interior surface  76  is disposed around the lower portion  30  of the chuck member  26  and the shoulder  66  of the bit  42 . The upper and lower ends  72 ,  74  are each formed as a lip  80 ,  82 , preferably annular, which extend radially inward toward the axis of the retainer member  70 . The upper lip  80  defines upper and lower bearing surfaces  84 ,  86 , which are clamped between the housing lower end  22  and the shoulder  34  of the chuck member  26 , in a manner substantially similar to that shown in U.S. Pat. No. 5,065,827. The lower lip  82  defines an upper bearing surface  88  forming an acute angle α with interior surface  76 . The lower surface  90  of lower shoulder  57  also forms an acute angle θ with the bit surface  92 , where angle θ is complementary to angle α. In a preferred embodiment, angles α and θ are each equal to 60 degrees. As shown in FIG. 6, the acute angles α and θ of the mating surfaces  88  and  90  urges the lower lip  82  inwards on engagement thereby providing a more secure retention of a broken bit  42 ′. 
     A longitudinal channel  94  is defined between the upper lip  80  and the lower lip  82  of the retainer member  70 , in the middle portion  95  of the retainer member  70 , having a length selected to receive the lower portion  30  of the chuck member  26  and to allow free vertical movement of the lower shoulder  66  of the percussion bit  42 . The inside diameter of the retainer member  70  between the upper and lower lips  80 ,  82  is preferably uniform and slightly larger than the outside diameter of the lower shoulder  66 . Multiple radially spaced slots  96  extend from the lower end  98  of the retainer member  70  to a terminal end  108  positioned intermediate the upper and lower ends  100 ,  98  thereby forming a series of cantilever beam segments  102 . 
     In a preferred implementation of the invention, the retainer member  70  is composed of carbon steel and is substantially tubular, with a wall thickness of 0.2425-0.2475 inches, and an outer diameter of approximately 7⅝ inches. The overall length  104  of the retainer member  70  is 8{fraction (3/32)} inches, with the slots  96  having a length  106  substantially equal to 5.0 inches. Preferably, there are twelve (12) slots  96  which have terminal ends  108  in the form of a circular opening having a ⅜ inch diameter  110 . It should be appreciated that the material of the retainer member  70 , the wall thickness, the length  106  of the slots  96  and the diameter  110  of the openings are selected, in combination, to allow the lower lip  82  to deflect over the lower portion  30  of the chuck member  26  and the shoulder  57  of the bit  42  (as described below) without exceeding the elastic limit of the material. Further, the cantilever beam segments  102  should be sufficiently stiff to prevent inadvertent deflection which would release the bit  42 . 
     A bit  42  is installed by inserting the upper portion  24  of the chuck member  26  through the retainer member  70  such that the lower end  74  of the retainer member  70  is proximate to shoulder  34  of the chuck member  26 . An inner ramp face  112  of the lower lip  82  is thereby disposed next to an outer ramp face  114  of shoulder  34 . Pressing the retainer member  70  downward causes ramp face  112  to slide up ramp face  114  to deflect the cantilever beam segments  102  radially outward. Continued pressure causes the lower lip  82  of the retainer member  70  to pass over the lower portion  30  of the chuck member  26 , the radially inner face  116  of the lower lip  82  sliding over the radially outer surface  118  of lower portion  30 . The cantilever beam segments  102  resiliently return to their original configuration when the lower portion  30  of the chuck member  26  is disposed in channel  94 . 
     The assembled chuck member  26  and retainer member  70  are then positioned above the bit  42  such that the inner ramp face  116  of the lower lip  82  is proximate to an outer ramp face  120  of shoulder  57  of the bit  42 . Pressing the retainer member  70  downward causes ramp face  112  to slide up ramp face  120  to deflect the cantilever beam segments  102  radially outward. Continued pressure causes the lower lip  82  of the retainer member  70  to pass over shoulder  57 . The cantilever beam segments  102  resiliently return to their original configuration when shoulder  57  is disposed in channel  94 . 
     Preferably, a press is used to provide the pressure for installing the bit  42 . However, experimentation has shown that using a sledgehammer to strike the upper end  100  of the retainer member  70  provides sufficient force to deflect the cantilever beam segments  102  and to drive the retainer member  70  over the lower portion  30  of the chuck member  26  and the shoulder  57  of the bit  42 . In an alternative method of installing the bit  42 , the chuck member  26  may be positioned over the bit  42  and the retainer member  70  pressed over the lower portion  30  of the chuck member  26  and the shoulder  57  of the bit  42 . 
     To remove the bit  42 , the bit is positioned such that the shoulder  57  of the bit  42  is disposed below the lower lip  82  of the retainer member  70  and two halves of a split disassembly bushing  122  are positioned around the bit  42  between the lower lip  82  of the retainer member  70  and the bit head  68 . Pressing the bit  42  and the disassembly bushing  122  toward the chuck member  26  moves the bit  42  longitudinally until the upper bearing surface  58  of the bit  42  engages the lower surface  60  of the chuck member  26  and moves the disassembly bushing  122  longitudinally until an outer ramp face  124  on the upper end  126  of the disassembly bushing  122  engages the ramp face  112  on the lower lip  82  of the retainer member  70 , the retainer member  70  being held in position by the clamping mechanism of the housing lower end  22  and shoulder  34 . Continued pressure causes ramp face  112  to slide up ramp face  124  and thereby deflect the cantilever beam segments  102  radially outward. The lower lip  82  then slides over shoulder  57 , releasing the bit  42 . 
     In a preferred embodiment, the longitudinal length  128  of the radially inner face  116  of the lower lip  82  is longer than the longitudinal length  130  of ramp face  120  such that inner face  116  slidingly engages the radially outer surface  118  of lower portion  30  before ramp face  112  may slide down ramp face  120 . Such structure facilitates removal of the retainer member  70  from the chuck member  26  with the disassembly bushing  122 . 
     Thus, according to the method of the invention, a percussion bit assembly  12  is formed by securing a bit  42  for longitudinal movement within a housing  14 , and securing a substantially tubular retainer member  70  in fixed relation to the housing  14  so that the retainer member  70  surrounds and extends below an outwardly projecting shoulder  57  formed on the bit  42 . A lip  82  at the lower end  98  of cantilever beam segments  102  of the retainer member  70  are resiliently deflected during installation, but restricts downward movement, serving as a stop to engage the bit shoulder  57  during use. 
     While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.