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[0001]    This application claims the benefit of U.S. Provisional Application No. 60/192,888, filed Mar. 29, 2000. The entire disclosure of U.S. Provisional Application No. 60/192,888, filed Mar. 29, 2000, is expressly incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to equipment for drilling and/or excavating hard material, including drill bits and other tools for drilling into and/or through reinforced material. The present invention also relates to a method of drilling a hole in steel reinforced concrete.  
           [0004]    2. Discussion of the Related Art  
           [0005]    Drill bits for drilling into hard material are known in the art. The known drill bits are unsatisfactory, however. Among other things, the known drill bits are not well suited for drilling large diameter holes in reinforced concrete. Examples of known drill bits and other material handling equipment are shown in U.S. Pat. Nos. 5,326,196 (Noll), 5,161,726 (Francis), 4,056,152 (Lacey), 3,712,753 (Manzi), 2,826,104 (Morin), 2,786,373 (Patton), 2,276,532 (Welty), 1,940,220 (McGrath), 1,747,117 (Klein), 1,387,994 (Lewis), 525,466 (Marsh et al.), and 499,098 (Comstock).  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention relates to tools, such as drill bits, for forming holes in hard, reinforced material, including reinforced concrete. According to one aspect of the invention, wear-resistant inserts are provided in a cross-shaped pattern. The inserts may be arranged to ensure that the entire bottom surface of the drilled hole is engaged during each revolution of the drill bit. Moreover, fluid entry ports may be located between the inserts for efficient handling of drilling fluid and removal of drilled material. The ports may be located in such a way as to not impair the desired structural integrity of the drill bit. According to another aspect of the invention, the drilling surface (which may be formed by the wear-resistant inserts) is separated into two or more stages to increase drilling efficiency, especially through composite material such as reinforced concrete. In a preferred embodiment of the invention, improved drilling speed through steel reinforcement bars is achieved without significant reduction in the efficiency of drilling through concrete.  
           [0007]    The present invention also relates to a drill tool that has a head portion and inserts for engaging and drilling into hard, reinforced material. The head portion may be provided with conduits and ports for flowing drilling fluid toward the reinforced material, and the inserts may be located in slots in the head portions. The inserts are preferably more wear resistant than the head portion that supports them.  
           [0008]    According to one aspect of the invention, the drill tool may be secured to or integral with a shank that is in turn connected to a drill rig or other drilling apparatus. In operation, the shank applies thrust and torque to the head portion.  
           [0009]    According to another aspect of the invention, fluid passageways are drilled through the head portion to provide fluid communication from an inner portion of the shank to the forward portion of the head portion. The drilled passageways extend along non-parallel paths and intersect each other inside the drill bit. As such, the flow structure for handling the drilling fluid does not degrade the structural integrity of the drill bit. In operation, the drilling fluid may be used to remove drilled material from the cutting edges of the inserts. The drilled material flows along outer paths located along the exterior of the drill bit.  
           [0010]    According to yet another aspect of the invention, the ports for to injecting the drilling fluid into the drilling region are located in recessed portions of the head portion. The recessed portions are such that the ports are spaced axially away from the forward face of the drill bit. The recessed portions are also used to funnel or direct the entrained drilling material into the passageways around the drill bit.  
           [0011]    The inserts may be separated from each other in the plane of their cutting edges. This way, the drilling fluid can flow relatively freely between the inserts to form an efficient flow pattern against the bottom surface of the drilled hole. In a preferred embodiment of the invention, there is an elongated center insert that is surrounded by radial inserts. The radial inserts are arranged to form a cross-shaped pattern. A first group of radial inserts may be longer than the rest of the radial inserts. In one embodiment of the invention, a full face attack cross pattern can be provided, even though none of the inserts extends across the entire forward surface of the head portion. That is, in one embodiment of the invention, the lengths of the cutting edges of the inserts are all much less than the diameter of the head portion. In an alternative embodiment of the invention, one or more of the inserts can extend across the entire forward face of the drill bit.  
           [0012]    According to yet another aspect of the invention, the cutting edges of the wear-resistant inserts each form a roof angle that is in the range of from 34° to about 37°. The desired grade of material, roof-angle, chamfers, size, and orientation of the inserts are preferably constructed so as to obtain maximum cutting speed through steel reinforcement bars with minimal bit wear.  
           [0013]    Further, the present invention also relates to a multi-stage drill bit for forming a cylindrical hole. The drill bit has a pilot stage portion and at least one subsequent stage. The pilot stage may be provided with the ports mentioned above for flowing drilling fluid into the pilot hole, and wear-resistant inserts for engaging the drilled material. The second or subsequent stage has a larger diameter than the pilot stage to increase the size of the drilled hole. In a referred embodiment of the invention, the second stage is also provided with wear-resistant inserts.  
           [0014]    In addition, the present invention relates to a method of drilling a hole into reinforced concrete. The method includes the steps of (1) using a pilot stage to drill through a steel reinforcement bar; (2) using a larger diameter second stage to drill through the reinforcement bar; and (3) transmitting torque from the shank to the pilot stage through the larger diameter second stage.  
           [0015]    These and other features of the invention will become apparent from the following detailed description of preferred embodiments. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is an end view of a drill bit constructed in accordance with one embodiment of the present invention.  
         [0017]    [0017]FIG. 2 is a partial cross-sectional view of the drill bit of FIG. 1, taken along the line  2 - 2 .  
         [0018]    [0018]FIG. 3 is a partial cross-sectional view of the drill bit of FIG. 1, taken along the line  3 - 3 .  
         [0019]    [0019]FIG. 4 is a perspective view of a drill bit constructed in accordance with another embodiment of the present invention.  
         [0020]    [0020]FIG. 5 is an end view of the drill bit of FIG. 4.  
         [0021]    [0021]FIG. 6 is a cross-sectional view of the drill bit of FIG. 4, taken along the line  6 - 6  of FIG. 7.  
         [0022]    [0022]FIG. 7 is a partial cross-sectional view of the drill bit of FIG. 4, taken along the line  7 - 7  of FIG. 5.  
         [0023]    [0023]FIG. 8 is partial cross-sectional view of the drill bit of FIG. 4, taken along the line  8 - 8  of FIG. 5. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0024]    Referring now to the drawings, where like reference numerals designate like elements, there is shown in FIG. 1 a drill bit  10  constructed in accordance with the present invention. The drill bit  10  is well suited for drilling through reinforced concrete and/or other composite materials. The drill bit  10  has a shank  12  (FIG. 2), a larger diameter head portion  14 , long radial inserts  16 ,  18 , short radial inserts  20 ,  22  (FIG. 1), and a center insert  24 . The shank  10  and the head portion  14  may be made of steel or another suitable material. The inserts  16 - 24  may be formed of tungsten carbide, or another suitable wear-resistant material. In a preferred embodiment of the invention, the inserts  16 - 24  are designed to drill through steel reinforcing rods and/or other tough materials embedded in concrete.  
         [0025]    The inserts  16 - 24  are located within respective slots or pockets  26 ,  28 ,  30 ,  32 ,  34 . The inserts  16 - 24  are sized to fit snugly within the slots  26 - 34 . If desired, the inserts  16 - 24  may be connected to the forward face  36  of the head portion  14  by a suitable brazing material (not shown). The inserts  16 - 24  have grinding or cutting edges  38 ,  40 ,  42 ,  44 ,  46  that lie within a common plane. In the illustrated embodiment, the cutting plane (contains the edges  38 - 46 ) is perpendicular to the rotational axis of the drill bit  10 . Each cutting edge  38 - 46  forms a roof angle α (FIG. 2) that is in the range of from about 34° to 37°.  
         [0026]    In operation, an axial force is applied by the shank  12  in the direction of arrow  60  to press the cutting edges  38 - 46  against the bottom of the hole being drilled (not shown), and a torque is simultaneously transmitted through the shank  12  in the direction of arrow  62  (FIG. 1) to rotate the cutting edges  38 - 46  to grind or drill the bottom surface of the hole. Drilling fluid (not shown) flows through the center of the shank  12  in the direction of arrow  60 , and then through four conduits (only two of which are shown in FIG. 3 designated by reference numerals  67 ,  69 ) and ports  66 ,  68 ,  70 ,  72  (FIG. 1) toward the bottom surface of the hole.  
         [0027]    Each of the four ports  66 - 72  is connected to a respective one of the four conduits  67 ,  69 . There may be four conduits  67 ,  69 —one for each port  66 - 72 , although only two conduits are shown in FIG. 3 for the sake of clarity. The other two conduits would be seen on another cross section through the drill bit  10 , extending from the respective ports to the center of the shank  12 . In the preferred embodiment of the invention, there are four conduits  67 ,  69  and four respective ports  66 - 72 . The present invention should not be limited, however, to the specifics of the preferred embodiments shown and described in detail herein.  
         [0028]    The drilling fluid may be liquid or air, for example. The drilling fluid entrains drilled material from the bottom of the hole and transmits it through scalloped passageways  74 ,  76 ,  78 ,  80  formed in the cylindrical side surface  82  of the head portion  14 . The drilled material flows with the drilling fluid away from the bottom of the hole in the direction of arrow  84  (FIG. 2).  
         [0029]    If desired, the shank  12  may be connected to a drill rig or extension (not shown) by an internal rope thread  86  (FIG. 3) or by another suitable connection mechanism. Other connection threads can be provided with adapters or during manufacture of the bits. In an alternative embodiment of the invention, the bit  10  is permanently mounted on a drill string (not shown) of any suitable length.  
         [0030]    As shown in FIG. 1, the length of the cutting edge  46  of the center insert  24 , along with the lengths and locations of the radial inserts  16 - 22  provide radial overlap. This way, the entire circular surface of the hole is excavated as the bit  10  is rotated. In other words, as the bit  10  is rotated in the hole, the sweep of the cutter inserts  16 - 24  engages and cuts every part of the hole face. Preferably, the entire circular surface of the drilled hole facing the cutting edges  38 - 46  is engaged by the cutting edges  38 - 46  during each rotation of the drill bit  10 . In the illustrated embodiment of the invention, the center cutting edge  46  is longer than the long radial edges  38 ,  40 , and the long radial cutting edges  38 ,  40  are longer than the short radial cutting edges  42 ,  44 . The present invention should not be limited, however, to the preferred embodiments shown and described in detail herein.  
         [0031]    If desired, concave or recessed portions  90 ,  92 ,  94 ,  96  may be provided for spacing the conduit openings or ports  66 - 72  axially away from the forward face  36  of the head portion  14 . In the illustrated embodiment, there is one concave portion  90 - 96  for each port  66 - 72 . If desired, however, the invention may be practiced with more or less than four concave portions  90 - 96  and ports  66 - 72 . Preferably, the concave portions  90 - 96  form funnel-like structures that help to guide or direct the drilling fluid into the respective scalloped passageways  74 - 80 . The conduits  67 ,  69  connecting the ports  66 - 72  to the shank  12  are formed by drills to have constant diameters. The conduits  67 ,  69  extend in straight lines from the recessed portions  90 - 96  to a common point  71  where they meet at the central axis of the shank  12 . This way, the conduits  67 ,  69  do not degrade the structural integrity of the drill bit  10 .  
         [0032]    The drill bit  10  may have an operating diameter  98  (FIG. 2) that is in the range of from about one inch to about two and one-half inches. Thus, for example, the drill bit  10  may be used to drill a hole into 5000 psi compressive strength concrete made of crushed limestone aggregate, reinforced with number  11  rebar (steel reinforcement bars) on four-inch centers each face, each way. The drill apparatus may have an operating pressure of about 2250 pounds per square inch; the impact energy may be between about 100 to 120 foot-pounds; the impact frequency may be between about 3300 to 3600 bpm; with a rotation speed of about 0 to 250 rpm. In operation, the bit  10  of the present invention, with an outside diameter in the range of from about 1.25 to 2.00 inches may provide a drilling speed that is 20% to 40% higher than can be achieved by conventional cross-face bits. The present invention should not be limited, however, to the preferred embodiments shown and described herein.  
         [0033]    Referring now to FIG. 4, there is shown a two-stage drill bit  100  constructed in accordance with another aspect of the present invention. The two-stage bit  100  provides multiple attack stages to reduce the total area of rebar being excavated at any one time. The first stage (or pilot stage)  102  has the inserts  16 - 24 , ports  66 - 72 , recessed areas  90 - 96 , and downstream fluid pathways  74 - 80  of the drill bit  10  of FIGS.  1 - 3 . The first stage  102  is followed by a larger diameter second stage  104 . The second stage  104  has four inserts  106 ,  108 ,  110 ,  112  (FIG. 5) with cutting edges  114 ,  116 ,  118 ,  120  (FIG. 6) that are constructed like the cutting edges  38 - 46  of the first stage  102 . The second stage inserts  106 - 112  are separated from each other by recessed portions  122 ,  124 ,  126 ,  128  that funnel the drilling fluid into scalloped passageways  130 ,  132 ,  134 ,  136 .  
         [0034]    In operation, the drilling fluid that flows axially out the drilled hole, through the scalloped passageways  74 - 80  of the first stage  102 , in the manner explained above in connection with FIGS.  1 - 3 , subsequently flows into the recessed portions  122 - 128  of the second stage  104 . The drilling fluid picks up additional drilled material from the second stage  104  and is funneled into the second stage outbound passageways  130 - 136 . Thus, the drilling fluid (with the entrained drilled material) flows axially out of the drilled hole around the second stage  104  in the direction of arrow  138 .  
         [0035]    In the illustrated embodiment, the first stage  102  is integral with the second stage  104 , and the second stage  104  is integral with a shank  12 . Thus, the axial force ( 60 ) and torque ( 62 ) applied by the shank  12  are applied through the second stage  104  to the second and pilot stage inserts  16 - 24 ,  106 - 112 .  
         [0036]    In operation, the two stages  102 ,  104  work together to expand the hole in the concrete to the desired larger diameter. When rebar (not shown) is encountered, the total “crowd force” available from the drill rig is distributed by the drill bit  100  largely on the rebar until it is excavated by the smaller-diameter pilot stage  102 . That is, the pilot stage  102 ,  16 - 24  drills through a length of the rebar equal to approximately the width  98  of the pilot stage  102 . The second and first stages  102 ,  104  then excavate through concrete together until the second stage  104  encounters the rebar. At this point, the total “crowd force” of the drill rig is largely acting on the excavation of the rebar through contact with the cutting edges  114 - 120  of the second stage  104 . Eventually, lengths of the rebar approximately equal to the lengths of the second stage cutting edges  114 - 120  are drilled on either side of the portion of the rebar that was drilled through by the pilot stage  102 . The decrease in bit area (compared to the entire cross sectional area of the fully drilled hole) acting on the rebar at any one time increases the overall drilling efficiency. The pilot stage performance of the bit  100  also assists in drilling a straight hole.  
         [0037]    The two-stage drill bit has four ports  66 - 72  and four respective conduits  101 ,  103  (only two of the conduits are shown in FIG. 8 for the sake of clarity of illustration). That is, the four ports  66 - 72  are connected to the annular interior of the bit  100  by four respective drilled passageways  101 ,  103 . The ports  66 - 72  provide ample flow of drilling fluid to the drilling surface (i.e., the bottom of the drilled hole) without degrading the structural integrity of the bit  100 . The ports  66 - 72  may be present only on the pilot stage  102 , since the fluid will flow from the pilot stage  102  and wash over the second stage  104 . If additional flow is necessary on the second stage  104  for especially difficult applications, additional ports (not shown) and drilled flow passageways (not shown) may be added to the second stage  104 , if desired.  
         [0038]    The two-stage bit  100  provides the full-face attack construction of the bit  10  of FIGS.  1 - 3 . In addition, the two-stage bit  100  provides improved drilling speed through reinforced concrete especially where the diameter of the hole being drilled is greater than about two-inches (or greater than the thickness of the rebar).  
         [0039]    While preferred embodiments of the invention have been described and illustrated, it should be apparent that many modifications can be made to the preferred embodiments without departing from the spirit or scope of the present invention. Accordingly, the invention is not limited by the foregoing description or drawings, but is only limited by the scope of the appended claims.

Summary:
A drill bit is provided for drilling holes in hard, reinforced material, including reinforced concrete. According to one aspect of the invention, wear-resistant inserts are provided in a cross-shaped pattern. The inserts ensure that the entire bottom surface of the drilled hole is engaged during each drill bit revolution. The inserts may be secured in pockets or slots. Fluid entry ports may be located between the inserts for efficient handling of drilling fluid and removal of drilled material, without impairing the structural integrity of the drill bit. According to another aspect of the invention, the drilling surface is separated into two or more stages to increase drilling efficiency, especially through composite material such as reinforced concrete.