Abstract:
The present invention provides a rotary cutting bit for use in road milling, mining and/or excavating applications that includes a split wear ring which is harder than the steel cutting bit body. The cutting bit has a cutting tip made of hard material such as tungsten carbide brazed into a nose portion of the steel tool body. The split wear ring is positioned in an annular channel in the tool body near the steel nose of the tool body. In one embodiment, the split wear ring is positioned so that the inner diameter of the split wear ring is smaller than the outer diameter of the cutting tip. Such a configuration allows the split wear ring to be tucked under the outer diameter of the cutting tip, decreasing tool body wear that could otherwise occur, thus providing longer tool life and reduced operating costs. The split wear ring pieces may be retained in place by a retainer such as banding rings, epoxies, tape or wire. Such retainers hold the ring sections in place during the assembly operation, so the ring sections do not move and remain attached to the tool body.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to road milling, mining and excavating tools, and more particularly relates to cutting bits with wear rings that reduce wear of such tools. 
       BACKGROUND INFORMATION 
       [0002]    Cutting bits are used in various road milling, mining and excavating operations. The bits are mounted on a support structure such as a rotary drum. Each bit typically has a hard wear resistant tip made of a material such as tungsten carbide attached to a generally conical steel head of the bit. A problem with such designs is that the softer steel backing material erodes during cutting operations. 
         [0003]    Wear resistant cutting bits have been developed in order to increase erosion resistance. For example, U.S. Pat. No. 4,725,098 to Beach discloses the deposition of a hard facing material on the steel nose of a tool body. U.S. Pat. No. 5,417,475 to Graham et al. discloses the installation of a ring of hard material on the front surface of a steel nose surrounding the hard cutting tip of a cutting tool. U.S. Pat. No. 6,709,065 to Peay et al. discloses the use of an annular ledge of hard material mounted near the steel nose of a cutting tool. Published U.S. Application No. 2005/0035649 to Mercier et al. discloses the installation of hard wear rings on a stepped shoulder of a cutting bit body. Despite these known designs, a need still exists for cutting bits which exhibit improved wear resistance. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention provides a rotary cutting bit for use in road milling, mining and/or excavating applications that includes a split wear ring which is harder than the steel cutting bit body. The cutting bit has a cutting tip made of hard material such as tungsten carbide brazed into a nose portion of the steel tool body. The split wear ring is positioned in an annular channel in the tool body near the steel nose of the tool body. In one embodiment, the split wear ring is positioned so that the inner diameter of the split wear ring is smaller than the outer diameter of the cutting tip. Such a configuration allows the split wear ring to be tucked under the outer diameter of the cutting tip, decreasing tool body wear that could otherwise occur, thus providing longer tool life and reduced operating costs. The split wear ring pieces may be retained in place by a retainer such as banding rings, epoxies, tape or wire. Such retainers hold the ring sections in place during the assembly operation, so the ring sections do not move and remain attached to the tool body. 
         [0005]    An aspect of the present invention is to provide a cutting bit comprising a body having a nose and a shank, a cutting tip mounted on the nose of the body comprising a harder material than the body, and a split wear ring mounted in an annular channel in the body adjacent the nose comprising a harder material than the body, wherein the split wear ring has an inner diameter less than an outer diameter of the cutting tip. 
         [0006]    Another aspect of the present invention is to provide a cutting bit comprising a body having a nose and a shank, a cutting tip mounted on the nose of the body comprising a harder material than the body, a split wear ring mounted on the body adjacent the nose comprising a harder material than the body, and a retainer ring surrounding at least a portion of the split wear ring. 
         [0007]    A further aspect of the present invention is to provide a cutting bit assembly comprising a body having a nose and a shank, a cutting tip mounted on the nose of the body comprising a harder material than the body, a split wear ring mounted in an annular channel in the body adjacent the nose comprising a harder material than the body, and a retainer ring surrounding at least a portion of the split wear ring for maintaining the split wear ring in the annular channel. 
         [0008]    Another aspect of the present invention is to provide a method of assembling a cutting bit. The method comprises providing a body having a nose and a shank, mounting a cutting tip on the nose of the body comprising a harder material than the body, positioning a split wear ring in an annular channel in the body adjacent the nose comprising a harder material than the body, and securing the split wear ring in the annular channel. 
         [0009]    These and other aspects of the present invention will be more apparent from the following description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is an isometric view of a cutting bit with a split wear ring and retaining ring in accordance with an embodiment of the present invention. 
           [0011]      FIG. 2  is a side view of a cutting bit with a split wear ring in accordance with an embodiment of the present invention. 
           [0012]      FIG. 3  is a side view of the body portion of the cutting bit of  FIG. 2  with the cutting tip, split wear ring and retaining ring removed. 
           [0013]      FIG. 4  is a longitudinal sectional view of a cutting bit assembly including a split wear ring, retainer ring and braze ring in accordance with an embodiment of the present invention. 
           [0014]      FIG. 5  is an isometric view of a split wear ring segment in accordance with an embodiment of the present invention. 
           [0015]      FIG. 6  is a front view of the split wear ring segment of  FIG. 5 . 
           [0016]      FIG. 7  is a side view of the split wear ring segment of  FIG. 5 . 
           [0017]      FIG. 8  is an isometric view of a retainer ring for securing a split wear ring on a cutting bit in accordance with an embodiment of the present invention. 
           [0018]      FIG. 9  is a front view of a retainer ring in accordance with an embodiment of the present invention. 
           [0019]      FIG. 10  is a sectional view taken through section  10 - 10  of  FIG. 9 . 
           [0020]      FIG. 11  is an isometric view of a braze ring which may be used during assembly of a cutting bit in accordance with an embodiment of the present invention. 
           [0021]      FIG. 12  is a front view of the braze ring of  FIG. 11 . 
           [0022]      FIG. 13  is a sectional view taken through section  13 - 13  of  FIG. 12 . 
           [0023]      FIGS. 14 and 15  are photographs of different cutting bits before and after they were subjected to wear testing. In each of the photographs, a cutting bit in accordance with an embodiment of the present invention is shown on the left, a cutting bit with a deposited hard facing material is shown in the middle, and a cutting bit with a relatively large unitary wear ring is shown on the right. As shown in  FIG. 15 , the cutting bit of the present invention exhibits significantly improved erosion resistance in comparison with the other designs. 
           [0024]      FIG. 16  is a photograph of a cutting bit in accordance with an embodiment of the present invention after it was subjected to wear testing. 
           [0025]      FIG. 17  is a photograph of a conventional single ring body wear protection cutting bit after it was subjected to wear testing. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    As shown in  FIGS. 1 ,  2  and  4 , a cutting bit  10  comprises a body  12  having a front nose  14  and rear shank  16 . The body  12  is typically made of steel. As shown most clearly in  FIGS. 1 and 2 , a spring sleeve  17  may be installed around the shank  16  of the cutting bit  10 , and a washer  18  may surround the spring sleeve  17 . A cutting tip  20  is mounted in a pocket  21  in the nose  14  of the cutting bit body  12  by known methods such as brazing or epoxy. The pocket  21  extends longitudinally from the front surface of the nose  14  into the body  12  a distance P, shown in  FIGS. 3 and 4 . The cutting tip is made of a relatively hard material, such as tungsten carbide, polycarbonite diamonds, ceramics, or any other material that is harder than the steel body. 
         [0027]    As shown most clearly in  FIGS. 2-4 , an annular channel  19  is provided in the body  12  of the cutting bit near the nose  14 . The annular channel  19  has a front wall  19   a  and a rear wall  19   b,  defining a width W of the annular channel  19 . In the embodiment shown in  FIGS. 2-4 , the front and rear walls  19   a  and  19   b  are generally flat and extend in planes perpendicular to the axial direction of the cutting bit body  12 . However, other wall surfaces, shapes and orientations may be used. For example, curved or faceted wall surfaces may be used instead of the flat wall surfaces shown in the figures. Furthermore, the walls may be oriented at angles other than perpendicular to the axial direction as shown in the figures. The annular channel  19  also has a diameter C D  that is less than a diameter N D  of the nose  14 . 
         [0028]    In accordance with the present invention, a split wear ring  30  is provided in the annular channel  19 . The hardness, size and location of the split wear ring  30  are selected in order to significantly reduce erosion and wear of the relatively soft body  12  of the cutting bit  10 . The split wear ring  30  has an outer diameter R OD , inner diameter R ID , and thickness T, as shown in  FIGS. 2 ,  4  and  7 . The split wear ring  30  may be made of any suitable hard material such as carbides, aluminum oxide, hard ceramic materials, hardened tool steels and the like. For example, the split wear ring  30  may be made of tungsten carbide. In one embodiment, the split wear ring  30  and cutting tip  20  are made of the same hard material. Furthermore, portions of the split wear ring  30  may be made of different materials, e.g., materials having different hardness and/or toughness properties, graded materials, and the like. 
         [0029]    The distance N between the front surface of the nose  14  and the front wall  19   a  of the annular channel  19  in which the split wear ring  30  is installed is minimized in order to provide improved wear resistance. For example, the distance N may be less than or equal to the width W of the annular channel  19 , and may be less than or equal to the thickness T of the split wear ring  30 . The distance N, width W of the annular channel  19  and thickness T of the split wear ring  30  are selected in order to provide the desired wear resistance for the body  12 . In one embodiment, the distance N may be from about 0.05 to about 0.5 inch, the width W of the annular channel  19  may be from about 0.1 to about 0.3 inch, and the thickness T of the split wear ring  30  maybe from about 0.1 to about 0.3 inch. 
         [0030]    As shown most clearly in  FIGS. 3 and 4 , the annular channel  19  and pocket  21  are arranged such that the distance P which the pocket  21  extends axially into the body  12  from the front surface of the nose  14  is greater than the distance N between the front surface of the nose  14  and the front wall  19   a  of the annular channel  19 . In the embodiment shown in the figures, the distance P is such that the rear surface of the pocket  21  is located between the front wall  19   a  and the back wall  19   b  of the annular channel  19  in the axial direction of the body  12 . Thus, the annular channel  19 , and the split ring  30  mounted therein, surround the rear surface of the pocket  21  and the rear face of the cutting tip  20  mounted in the pocket. 
         [0031]    As shown in the embodiment of  FIGS. 1 and 4 , a retainer ring  32  is used to secure the split wear ring  30  within the annular channel  19  of the body  12 . The retainer ring  32  may be made of any suitable material such as spring steel, stainless steel, or any other material capable of withstanding the assembly attachment process for the split wear ring and cutting tip. As more fully described below, the retainer ring  32  is used to hold the split wear ring  30  in place during assembly of the cutting bit  10 , and may be retained on the cutting bit  10  after it has been fabricated. 
         [0032]    As shown in the embodiment of  FIG. 4 , a braze ring  34  may be positioned adjacent to the split wear ring  30  and the nose  14  of the cutting bit body  12  during fabrication of the cutting bit  10 . The assembly shown in  FIG. 4  may be heated by any suitable means such as induction heating to melt the braze ring  34  to form a braze joint between the split wear ring  30  and the annular channel  19  of the body  12 . A braze alloy  22  may also be provided between a recess in the nose  14  of the body  12  and the rear portion of the cutting tip  20 . In one embodiment, the braze joint  22  is formed during the same heating step which melts the braze ring  34  to form the joint between the split wear ring  30  and the body  12 . The braze ring  34  and the braze joint  22  may be made of any suitable braze alloys such as high or low temperature copper based alloys. In one embodiment, the same braze alloy is used for the braze ring  34  and braze joint  22 . In an alternative embodiment, epoxy may be used to secure the split wear ring  30  in the annular channel  19 . 
         [0033]    As shown in  FIG. 4 , the inner diameter R ID  of the split wear ring  30  is smaller than an outer diameter T OD  of the cutting tip  20 . This arrangement provides significantly improved wear resistance by preventing steel wash more effectively. The inner diameter R ID  of the split wear ring  30  is also smaller than the diameter N D  of the nose  19 . The location of the split wear ring  30  in the annular channel  19  a relatively close distance N to the nose  14  of the tool body  12  provides significantly better wash protection. If the split wear ring  30  was not tucked under the nose  14  of the tool body  12 , it would rub in the cut due to its close proximity to the cutting tip  20 , causing decreased wear protection and tool performance. The outer diameter R OD  of the split wear ring  30  is also smaller than a diameter S D  of a shoulder of the body  12 . The shoulder diameter S D  is measured at the edge where the rear wall  19   b  of the channel  19  meets the generally frustoconical portion of the cutting bit body  12 . The smaller outer diameter R OD  of the split wear ring  30  in comparison with the larger diameter S D  of the tool body shoulder prevents the outside edge of the split wear ring  30  from rubbing in the cut. 
         [0034]    With the split wear ring  30  located relatively close to the tool body nose  14 , the steel body  12  is better protected and it holds its original conical shape, creating less drag and reducing operating costs. If the wear ring was moved further down the body  12 , it would tend to blunt or become club-like during operation, slowing the machine down and increasing operating costs. The position of the split wear ring  30  in the upper portion of the body  12  can help aid in rotation by acting as a “steering wheel” in the cut. Thus, in addition to decreasing the body wear under the cutting tip  20 , the split wear ring  30  attached to the cutting tool body  12  can also aid in tool rotation, lessen cutting bit frictional forces in the cut of the material, and reduce operating costs. The split wear ring may optionally include features such as ribs, flutes, veins and/or dimples for aiding in tool rotation. 
         [0035]    Details of a split wear ring section  30   a  are shown in  FIGS. 5-7 . In this embodiment, two of the split wear ring sections  30   a  are used to form the split wear ring  30 . However, any other suitable member of split wear ring sections may be used, such as three sections, four sections, etc. When the split wear ring sections are assembled in the annular channel  19 , they may have flat faces which abut each other as shown in the embodiment of  FIGS. 5-7 . Alternatively, the abutting faces may have other shapes such as tabs or other features which provide a contoured or interlocking connection between adjacent sections. 
         [0036]    In the embodiment shown in  FIG. 7 , the split wear ring  30  has a cross section with beveled corners forming angles A, B, C and D. In accordance with one embodiment, angles A and B are the same, and angles C and D are the same, such that the ring forms a mirror image and is symmetrical in a plane of the ring. Such a configuration facilitates assembly of the cutting bit  10  because when the split wear ring segments are mounted in the annular channel  19 , they are automatically aligned with the opposing split wear ring segment(s). In one embodiment, all of the angles A, B, C and D are the same. Each of the angles A, B, C and D typically range from about 30 to 60 degrees, with an angle of about 45 degrees being particularly suitable. The symmetrical shape allows universal fit in assembly operations, such that no particular orientation is required when fitting the parts. 
         [0037]      FIGS. 8-10  illustrate details of the retainer ring  32 , and  FIGS. 11-13  illustrate details of the braze ring  34 . As shown in FIGS.  4  and  8 - 13 , the retainer ring  32  has an inner diameter less than or equal to the outer diameter R OD  of the split wear ring  30 . The braze ring  34  has an inner diameter equal to or slightly smaller than the outer diameter of the nose  14  of the body  12 . The inner diameter of the braze ring  34  is typically smaller than the inner diameter of the retainer ring  32  and the outer diameter R OD  of the split wear ring  30 . As shown most clearly in  FIG. 4 , the retainer ring  32  is seated against the rearward portion of the split wear ring  30  at the rear edge of the annular channel  19 . The braze ring  34  is seated against the forward portion of the split wear ring  30  and the forward edge of the annular channel  19 . The beveled cross sectional shape of the split wear ring  30  helps maintain the retainer ring  32  and braze ring  34  in their respective positions shown in  FIG. 4 . 
         [0038]    In addition to the split wear rings  30  of the present invention, additional ribs, flutes, veins and/or dimples may be attached to the tool body  12  either independently or in conjunction with the split wear ring  30 . The ribs, flutes, veins and/or dimples may be harder than the steel body  12 , and may be made from similar materials as the split wear ring  30 . Such ribs, flutes, veins and/or dimples may be used to protect the steel body  12  from erosion, e.g., caused by cutting of asphalt material, and to aid in rotation of the tool. 
         [0039]    The retainer ring  32  holds the split wear ring segments  30   a  in place when going through the braze coil or other brazing operations. The wear ring segments  30   a  will tend to move apart by the magnetic action of the braze coil and the floating effect of the braze material if not held in place by the retainer ring. This aids in assembly. Operators do not need to hold the wear ring segments  30   a  together while the braze ring  34  melts, which avoids safety issues associated with operators placing their hands in the braze coil. During the cutting operations, the retainer ring  32  may be removed in the milling cut after a few minutes, and will not interfere with tool cutting performance. 
         [0040]    The braze ring  34  snaps over the nose  14  of steel body  12  allowing easier assembly operation with the split wear ring segments  30   a.  The braze ring  34  helps lock down the split wear ring segments  30   a  to the body shoulder to prevent the rings from moving in the braze coil. Thus, both the braze ring  34  and retainer ring  32  may help secure the split wear ring segments during assembly. The braze material flows down behind the split wear ring segments  30   a  into the annular channel  19  to ensure better braze coverage and a more secure braze joint. 
         [0041]    Comparative wear tests were performed on a cutting bit in accordance with an embodiment of the present invention in comparison with a conventional cutting bit having hard facing material deposited thereon and another cutting bit having a relatively large unitary wear ring. The comparative wear testing was performed by installing tools equally across an entire cutting drum so all tools are subject to similar wear and cutting conditions. The cutting drum was engaged in the material, e.g., asphalt, under normal job site cutting conditions across the full length of the cutting drum to ensure all tools are subject to the same wear pattern and conditions across the entire drum cutting surface. All parts were run in the asphalt material for the same amount of time or square footage. The parts were then removed from the cutting drum and examined and photographed to determine differences in wear. 
         [0042]      FIG. 14  is a photograph showing the cutting bits before they were tested, and  FIG. 15  is a photograph showing the cutting bits after they were subjected to wear testing.  FIG. 16  is a photograph of a cutting bit of the present invention after it was subjected to wear testing.  FIG. 17  is a photograph of a conventional single ring body wear protection cutting bit after it was subjected to wear testing. 
         [0043]    Whereas particular embodiments 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.