Abstract:
A cutting bit includes a body having a front surface and a side surface, the side surface including a shoulder below the front surface and extending substantially perpendicular to a central axis of the body, and a ring that is harder than the body attached to the body at a front surface of the shoulder. Wear life of the cutting bit is enhanced by maintaining particular dimensional relationships regarding the position of the ring on the body, and the diameter of portions of the body.

Description:
BACKGROUND AND SUMMARY  
       [0001]     The present invention relates to cutting tools used to cut through soft ground or through relatively soft material that has been laid on the ground, such as asphalt roadways.  
         [0002]     Mining, excavating, and road resurfacing operations are typically performed by forcing rotary cutting bits through the material being cut. The cutting bits are mounted on a driven support, such as a rotary drum, fixed beam, or the like to be forced through the material. A typical cuffing bit comprises a hard cemented carbide tip that is brazed to the front surface of a steel shank. The shank is to be mounted in a holder by means of a retainer sleeve which permits the bit to rotate freely relative to the holder about the bit&#39;s center axis, while being restrained against axial dislodgment from the holder. Due to being freely rotatable, the tip is basically self-sharpening.  
         [0003]     It should be understood that cutting mechanisms of the type described above have been used to cut through hard materials, such as rock and ice, in addition to cutting through softer materials such as asphalt. During the cutting of rock, the highest rate of bit wear occurs at the carbide tip, so the wear life of the bit is determined by the carbide tip. However, during the cutting of relatively softer material, such as asphalt, coal, and salt, the highest rate of wear occurs at the shank, i.e., erosion caused by cut asphalt rubbing and impacting against the shank. Thus, when cutting asphalt during a road resurfacing operation, the wear life of the cutting bit is determined by the shank.  
         [0004]     It would be desirable to provide a cutting bit that has an increased wear life when used for cutting softer materials such as asphalt.  
         [0005]     Disclosed in U.S. Pat. No. 4,725,098, which is incorporated by reference, is a cutting bit in which a groove is machined in a tapering side surface of the bit head closely behind a carbide tip mounted in the bit head. Hardfacing is deposited into the groove to form an erosion-resistant annular ring which can be flush with, or project slightly radially beyond, the side surface. Despite being formed of hard material, the ring will be subjected to considerable erosion by cuttings and thus will have a somewhat limited life.  
         [0006]     U.S. patent application Ser. No. 10/058,387, filed Jan. 30, 2002, entitled Rotary Cuffing Bit with Material-Deflecting Ledge, naming Kent Peay and Timothy J. Shean as inventors, which is incorporated by reference, discloses a cutting bit having a tapered side surface with a ledge projecting from the tapered surface. The ledge can be integral with the rest of the bit body or formed as a separate ring held on the body. The ledge is of sufficient diameter relative to the portion of the body above it that material cut tends to accumulate on the ledge and shields the body material underneath from erosion. However, it has been found that the ledge in such a cutting bit is highly prone to wear.  
         [0007]     It would be desirable to provide a cutting bit with an erosion-resistant structure which has an enhanced life. It would also be desirable to provide a cutting bit that is simple to manufacture and involves relatively few manufacturing operations.  
         [0008]     In accordance with an aspect of the present invention, a cutting bit includes a body having a front surface and a side surface, the side surface including a shoulder below the front surface and extending substantially perpendicular to a central axis of the body, the body being no larger in diameter above the shoulder than at the shoulder, and a ring that is harder than the body attached to the body at a front surface of the shoulder.  
         [0009]     In accordance with another aspect of the present invention, a cutting bit includes a body having a front surface and a cylindrical side surface portion, the cylindrical side surface portion including a shoulder below the front surface and extending substantially perpendicular to a central axis of the body, and a ring that is harder than the body attached to the body at a front surface of the shoulder. A distance between the front surface and a top of the ring divided by a distance between the front surface and a bottom surface of the body is 0.15 to 0.5.  
         [0010]     In accordance with yet another aspect of the present invention, a cutting bit includes a body having a front surface and a cylindrical side surface portion, the cylindrical side surface portion including a shoulder below the front surface and extending substantially perpendicular to a central axis of the body, a cutting tip attached to the front surface, and a ring that is harder than the body attached to the body at a front surface of the shoulder. A diameter of a bottom of the cutting tip divided by the diameter of the body at the bottom of the cutting tip is 0.72 to 0.95.  
         [0011]     In accordance with yet another aspect of the present invention, a cutting bit includes a body having a front surface and a cylindrical side surface portion, the cylindrical side surface portion including a shoulder below the front surface and extending substantially perpendicular to a central axis of the body, a cutting tip attached to the front surface, and a ring that is harder than the body attached to the body at a front surface of the shoulder. A diameter of the cutting bit divided by an outside diameter of the ring is 0.60 to 0.80.  
         [0012]     In accordance with yet another aspect of the present invention, a cutting bit includes a body having a front surface and a side surface, the side surface including a first shoulder below the front surface and extending substantially perpendicular to a central axis of the body, the body being no larger in diameter above the first shoulder than at the first shoulder, and a second shoulder below the first shoulder, the body being no larger in diameter above the second shoulder than at the second shoulder, and a first ring and a second ring attached to the body at a front surface of, respectively, the first shoulder and the second shoulder.  
         [0013]     In accordance with still another aspect of the present invention, a cutting tip for being attached to a cutting bit includes a base portion, a tip portion, the tip portion being generally convex in shape, and a side portion extending between the base portion and the tip portion, the side portion being generally concave in shape.  
         [0014]     In accordance with still another aspect of the present invention, a cutting bit includes a cutting tip having a base portion, a tip portion, the tip portion being generally convex in shape, and a side portion extending between the base portion and the tip portion, the side portion being generally concave in shape and intersecting with the tip portion at a junction. The cutting bit also includes a body having a front face to which the cutting tip is attached, a bottom portion, and a shoulder below the front surface and extending substantially perpendicular to a central axis of the body, and a ring that is harder than the body attached to the body at a front surface of the shoulder. An imaginary cone is defined by the junction and the bottom portion and the ring is disposed inside of the cone. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The objects and advantages of the invention will become apparent from the following detailed description of preferred embodiments thereof in connection with the accompanying drawings in which like numerals designate like elements and in which:  
         [0016]      FIG. 1  is a side elevational view of a rotary cutting bit according to an embodiment of the present invention;  
         [0017]      FIG. 2  is a side elevational view of a rotary cutting bit according to an embodiment of the present invention showing an accumulation of cut material on the bit; and  
         [0018]      FIG. 3  is a side elevational view of a rotary cutting bit according to another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0019]     A cutting bit  21  according to an embodiment of the present invention is shown in  FIGS. 1 and 2 . The cutting bit  21  includes a body  23  having a front surface  25  and a side surface  27 . The side surface  27  includes a shoulder  29  below the front surface  25  and extending substantially perpendicular to a central axis of the body. A cutting tip  31  is preferably attached to the front surface  25 , usually by brazing, the cutting tip preferably being harder than the body  23 .  
         [0020]     A ring  33  that is preferably harder than the body  23  is attached to the body at a front surface  35  of the shoulder  29 , such as by brazing. The body  23  is preferably no larger in diameter above the shoulder  29  than at the shoulder and, preferably, at least a portion  37  of the side surface  27  of the body  23  is cylindrical, more preferably circularly cylindrical, above the shoulder  29  so that a ring having a circular inside diameter can be slid over the body to the shoulder. Because the body  23  is preferably no larger in diameter above the shoulder  29  than at the shoulder, it is not necessary to incur machining costs for machining a groove in the body. Also, the body  23  can be cold formed. The ring  33  is preferably positioned above the shoulder  29  and brazed to the body  23  in the same operation, which can minimize manufacturing costs, particularly when compared with bits wherein a groove must be formed. If desired or necessary, however, the shoulder  29  can be part of a groove in the side surface and the ring can be, for example, a split ring that is held in place by upper and lower surfaces of the groove. The ring  33  is illustrated as being a substantially circular shape, however, it will be appreciated that the ring can be any desired shape, such as hexagonal, octagonal, etc.  
         [0021]     In the cutting bit  21 ′ shown in  FIG. 3 , the body  23 ′ includes a second shoulder  39  below the first shoulder  29 . Again, the body  23 ′ is preferably no larger in diameter above the second shoulder  39  than at the second shoulder to facilitate sliding a second ring  41  over the body to the second shoulder where it is attached to the body at a front surface of the second shoulder. Again, if desired or necessary, however, the shoulder  39  can be part of a groove in the side surface and the ring  41  can be, for example, a split ring that is held in place by upper and lower surfaces of the groove.  
         [0022]     A distance A between the front surface  25  and a top  43  of the ring  33  divided by a distance B between the front surface and a bottom surface  45  of the body is preferably 0.15 to 0.5. It is intended that material being cut will accumulate on the ring  33  and the material will prevent erosion of the body  23  between the ring and the cuffing tip  31  by deflecting further material. A flange  47 , which is preferably integral with the body, is preferably provided at the bottom of the body  23 . Cut material tends to accumulate on the flange  47  in a manner similar to the manner in which material accumulates on the ring  33 .  
         [0023]     In the past, a wear pattern between a cutting tip and a bottom flange on a body would tend to approximate the “golf tee” shape shown by the dotted line X in  FIG. 2 . It has been found that providing the ring  33  in a region that would ordinarily be subject to significant erosion results in a substantially reduced volume loss of material from the body  23  and tends to approximate the double “golf tee” shape shown as the shaded area Y in  FIG. 2 . While it is desirable to prevent body wear, it is also desirable to ensure that the ring  33  is at a sufficient distance from the cutting tip  31  to avoid a dulling of the cutting action, which can be achieved by keeping the relationship between distance A and distance B in the range of 0.15 to 0.5. If a second shoulder  39  and ring  41  are provided as in  FIG. 3 , it is preferred that a distance A′ between the front surface  25  and a top  49  of the second ring  41  divided by the distance B between the front surface and a bottom surface  45  of the body is, as with the first ring  33 , 0.15 to 0.5. This tends to place both the first ring  33  and the second ring  41  in what would otherwise be a region of maximum erosion on the body  23 .  
         [0024]     A diameter C of the cutting tip  31  divided by a diameter D of the body  23  at the bottom of the cutting tip is preferably 0.72 to 0.95. The front surface  25  is preferably recessed to define a dam wall  51  in which the cutting tip  31  is attached by brazing. Purposes of the dam wall  49  include preventing brazing liquid from flowing out from between the cutting tip  31  and the front surface  25  and acting as a stress reliever when the body  23  cools off. As C/D becomes closer to 1, the thickness of the dam wall  49  is reduced and less material is needed to form the body  23 . As C/D moves from 1 toward 0, the body  23  has more material and its useful life span tends to approach that of the cutting tip  31  made of harder material.  
         [0025]     The diameter C of the cutting tip  31  divided by an outside diameter E of the ring is preferably 0.60 to 0.80. As seen in  FIGS. 1-3 , the cutting tip  31  preferably has a bottom surface  52  that is brazed to the front surface  25  inside the dam wall  49 , a concave surface portion  53  extending upwardly to a break point  55 , and a tip portion  57  that is generally convex. As seen in  FIGS. 2 and 3 , an imaginary cone  59  extends through a point  61  on the outer edge of the flange  47  and the break point  55  to a point  63  above the tip portion  57  along the center axis of the body  23 . It has been found desirable to keep all points on the cutting bit  21 , including points on the ring  33 , inside or at least substantially inside of this cone  59 . Points extending outwardly beyond the cone tend to be too vulnerable to erosion. By keeping C/E in the range of 0.60 to 0.80, particularly when A/B is 0.15 to 0.50 and C/D is 0.72 ton  095  the outermost point on the ring  33  tends to fall on or inside of the cone  59  and is less subject to wear. The relationships described above in connection with the cutting bit having only the ring  33  are preferably also true for bits having two or more rings, e.g., the bit  21 ′ including the ring  41  shown in  FIG. 3 .  
         [0026]     Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without departing from the spirit and scope of the invention as defined in the appended claims.