Patent Abstract:
Abrasive tip for abrasive tool and method for forming and replacing thereof are disclosed. The abrasive tip facilitates easy and quick attachment to an abrasive tool.

Full Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 61/151,971 filed on Feb. 12, 2009 and entitled “ABRASIVE TIP FOR ABRASIVE TOOL AND METHOD FOR FORMING AND REPLACING THEREOF”, which is incorporated by reference herein in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present invention relates generally to abrasive tools used for drilling, cutting and grinding concrete, natural stone and other hard materials. More specifically, the present invention relates to a device that secures a plurality of abrasive segments to an abrasive tool and method for forming the device as well as replacing when worn. 
         [0003]    A core bit is one type of abrasive tool that uses abrasive segments containing diamond to drill holes in concrete. A typical diamond core bit that can be used to drill holes in a concrete structure (e.g., a wall, floor, ceiling, column, bridge deck, etc.,) is produced by attaching individual diamond containing segments to the front face of a steel tube. The diamond core bit cuts a hole by using an electrical or hydraulic motor to spin the core bit around its axial axis, while at the same time being pushed forward either manually or by an automatic feeding mechanism to provide penetration. The drilling may be preferably done with coolant (e.g., water) but dry drilling may also be applied. In this manner of operation, an outside wall of a cylindrical opening is generated, while at the same time an inner core element is generated that detaches from the concrete structure once the diamond core bit has fully penetrated through the structure. 
         [0004]    Eventually, the diamond segments become worn and have to be replaced. Replacing the diamond segments on a core bit is known as re-tipping the core bit. A typical re-tipping operation of a core bit will depend on how the diamond segments are secured to the front face of the steel tube. For example, the diamond segments may be brazed, laser welded or direct sintered to the front face of the steel tube. For the case of braze fitted diamond segments, a core bit user may de-braze the residues of the worn diamond segments from the face of the steel tube and braze fit new diamond segments to the same tube face. The steel tube with new diamond segments attached thereto may typically be shortened by a few millimeters as a result of this re-tipping operation. Shortening will only take place generally if the tube is cut up right behind the diamond segments in order to avoid the debrazing and this is typically only done in a repair shop. However, if the re-tipping operation is to be done directly on a construction site, then normally the only option is the debrazing and subsequent braze fitting of new segments. Overall, the re-tipping operation allows reduction in the costs associated with the core bit, which at the end reduces the cost of drilling holes in concrete and similar structures. 
       SUMMARY 
       [0005]    In one embodiment, there is a device for securing a plurality of abrasive segments to an abrasive tool having a rotatable body with an outer diameter and an inner diameter. In this embodiment, the device comprises a carrier element having a first portion that accommodates the plurality of abrasive segments and a second portion opposite from the first portion that attaches to the rotatable body. The second portion comprises a shoulder extending therefrom that facilitates centering with the rotatable body. 
         [0006]    In a second embodiment, there is a core bit tip that comprises a plurality of abrasive segments and a carrier element that accommodates the plurality of abrasive segments. The carrier element has a first portion configured to receive the plurality of abrasive segments and a second portion opposite from the first portion that attaches to one end of a core bit tubular body having an inner diameter and an outer diameter. The second portion has a shoulder extending therefrom that facilitates the centering of the carrier element with respect to the inner diameter and an outer diameter of the core bit tubular body. 
         [0007]    In a third embodiment, there is a core bit that comprises a core bit tip comprising a ring-shaped carrier element having a first portion with a plurality of abrasive segments secured thereto and a second portion comprising a shoulder extending therefrom. The core bit further comprises a core bit tubular body having an inner diameter and an outer diameter that accommodates the core bit tip at one end thereof. The shoulder facilitates centering of the core bit tip with respect to the inner diameter and an outer diameter of the core bit tubular body. 
         [0008]    In a fourth embodiment, there is a method of forming a core bit tip. In this embodiment, the method comprises: providing a carrier element having first portion and a second portion opposite from the first portion, the second portion having a shoulder extending therefrom that facilitates centering of the carrier element with respect to an inner diameter and an outer diameter of a core bit tubular body; and attaching a plurality of diamond segments to the first portion. 
         [0009]    In a fifth embodiment, there is a method of forming a core bit. In this embodiment, the method comprises: providing a core bit tip comprising a ring-shaped carrier element having a first portion with a plurality of abrasive segments secured thereto and a second portion opposite from the first portion comprising a shoulder extending therefrom; providing a core bit tubular body having an inner diameter and an outer diameter that accommodates the core bit tip at one end thereof; centering the shoulder of the second portion of the core bit tip with respect to the inner diameter and outer diameter of the core bit tubular body; and attaching the core bit tip to the core bit tubular body following the centering of the shoulder of the second portion of the core bit tip with respect to the inner diameter and outer diameter of the core bit tubular body. 
         [0010]    In a sixth embodiment, there is a method of re-tipping a core bit. In this embodiment, the method comprises: removing a worn core bit tip from a core bit tubular body having an inner diameter and an outer diameter that accommodates the core bit tip at one end thereof; providing an unworn core bit tip comprising a ring-shaped carrier element having a first portion with a plurality of abrasive segments secured thereto and a second portion opposite from the first portion comprising a shoulder extending therefrom; centering the shoulder of the second portion of the unworn core bit tip with respect to the inner diameter and outer diameter of the core bit tubular body; and attaching the unworn core bit tip to the core bit tubular body following the centering of the shoulder of the second portion of the core bit tip with respect to the inner diameter and outer diameter of the core bit tubular body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a perspective view of a carrier element used in a core bit tip according to one embodiment; 
           [0012]      FIG. 2  is top view of the carrier element shown in  FIG. 1  according to one embodiment; 
           [0013]      FIG. 3  is top view of the carrier element shown in  FIG. 2  with abrasive segments secured thereto according to one embodiment; 
           [0014]      FIG. 4  is a perspective view of the carrier element and abrasive segments shown in  FIG. 3  according to one embodiment; 
           [0015]      FIG. 5  is top view of the carrier element shown in  FIG. 1  according to a second embodiment; 
           [0016]      FIG. 6  is top view of the carrier element shown in  FIG. 5  with abrasive segments secured thereto according to one embodiment; 
           [0017]      FIG. 7  is a perspective view of the carrier element and abrasive segments shown in  FIG. 6  according to one embodiment; 
           [0018]      FIG. 8  is a perspective view of a carrier element used in a core bit tip according to a second embodiment; 
           [0019]      FIG. 9  is top view of the carrier element shown in  FIG. 8  according to one embodiment; 
           [0020]      FIG. 10  shows a core bit with a core bit tip accommodated by a core bit tubular body according to one embodiment; 
           [0021]      FIG. 11  shows a cross-sectional view of a core bit tip with a carrier element depicted in  FIG. 1  that is accommodated by the core bit tubular body depicted in  FIG. 10  according to one embodiment; 
           [0022]      FIG. 12  shows a core bit with a core bit tip accommodated by a core bit tubular body according to a second embodiment; and 
           [0023]      FIG. 13  shows a cross-sectional view of a core bit tip with a carrier element depicted in  FIG. 8  that is accommodated by the core bit tubular body depicted in  FIG. 12  according to one embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0024]    Referring to the drawings,  FIGS. 1-2  illustrate a carrier element  10  used as part of a tip for an abrasive tool according to one embodiment. In one embodiment, carrier element  10  may be used as part of a core bit tip for use with a core bit in a drilling tool. As shown in  FIGS. 1-2 , carrier element  10  is a ring-shaped carrier that can be a solid metal disk, a ring, a ring section, or a plate. Although carrier element  10  is illustrated as being ring-shaped, those skilled in the art will recognize that the carrier can have a variety of shapes and that the principles of the present invention are not limited to any particular shaped carrier. Carrier element  10  can include heat treatable steel alloys, such as 30CrNiMo8, 25CrMo4, 75Cr1, C60, or simple construction steel like St 60. Carrier element  10  as described herein can have a tensile strength of at least about 600 N/mm 2 . Carrier element  10  can be formed to its final geometry and dimensions by a variety of metallurgical techniques known in the art. 
         [0025]    As shown in  FIGS. 1-2 , carrier element  10  has a first portion  12  that accommodates the plurality of abrasive segments (not illustrated in these figures) and a second portion  14  opposite from first portion  12  that attaches to a rotatable body (e.g., a core bit tubular body) having an outer diameter and an inner diameter (not illustrated in these figures). Second portion  14  comprises a shoulder  16  that extends therefrom at an outer edge  17  of second portion  14 . Shoulder  16  facilitates the centering of carrier element  10  with the rotatable body. As is known in the art, a shoulder is generally an area adjacent to or along the edge of a higher, more prominent part. In this embodiment, shoulder  16  assures centering of carrier element  10  on the outer diameter of the rotatable body. This permits a face of second portion  14  that is substantially perpendicular to shoulder  16  to rest at one end of the rotatable body on a front face that is between the outer diameter and inner diameter and shoulder  16  to rest on the outer diameter of the rotatable body. These features are described below and illustrated in  FIG. 11 . With the face of second portion  14  resting on this front face of the rotatable body and shoulder  16  resting on the outer diameter of the rotatable body at this same end thereof, carrier element  10  can then be solidly attached to the rotatable body in various well-known processes which are described below. 
         [0026]    In one embodiment, as shown in  FIGS. 2-4 , first portion  12  of carrier element  10  comprises a groove  18  formed therein that accommodates a plurality of abrasive segments  20  (see  FIGS. 3 and 4 ). Although groove  18  is shown in  FIGS. 2-4  as having a V-shape, those skilled in the art will recognize that other shaped grooves (e.g., U-shaped) can be formed utilizing well-known metallurgical techniques and that embodiments of the present invention are not limited to any particular shape. Generally, whatever shaped groove is used, it is desirable that a bottom portion of abrasive segments  20  have the same profile in order to mate to groove  18 . 
         [0027]    In another embodiment, as shown in  FIGS. 5-7 , first portion  12  of carrier element  10  comprises a flat face  22  that accommodates abrasive segments  20  (see  FIGS. 3 and 4 ). In this embodiment, the bottom portion of abrasive segments  20  will have the same profile to mate with flat face  22 . 
         [0028]    Another feature of carrier element  10  that is shown in  FIGS. 1-7 , is a slot  24  that extends through first portion  12  and second portion  14  including shoulder  16 . Slot  24  allows carrier element  10  to fit easily on a range of rotatable bodies that may have varying outer diameters. 
         [0029]    Another element of carrier element  10  that is shown in  FIGS. 1-2  and  4 - 5  is a number of holes  26  located across the profile of carrier element  10 . Holes  26  are located across the profile of carrier element  10  in a radial direction in order to ease the penetration by capillary action of silver solder into the interface between carrier element  10  and the rotatable body for embodiments where the two are brazed together with silver solder. The holes will permit the brazing process to provide a very strong bonding between carrier element  10  and the rotatable body. In a preferred embodiment, carrier element  10  will have three holes  26  located across its profile, however, those skilled in the art will recognize that one or more holes  26  may be used. 
         [0030]      FIGS. 8-9  illustrate a second embodiment of a carrier element. In this embodiment, carrier element  30  is similar to carrier element  10 , however, the location of shoulder  16  with respect to second portion  14  is different. In particular, shoulder  16  in the embodiment shown in  FIGS. 8-9  is located about an inner edge  32  of second portion  14 , while shoulder  16  in the embodiment of  FIGS. 1-7  is located about its outer edge. In this embodiment, shoulder  16  assures centering of carrier element  30  on the inner diameter of the rotatable body. This permits the face of second portion  14  that is substantially perpendicular to shoulder  16  to rest on the front face between the outer diameter and inner diameter of the rotatable body and shoulder  16  to rest on the inner diameter of the rotatable body. These features are described below and illustrated in  FIG. 13 . With the face of second portion  14  resting on this front face of the rotatable body and shoulder  16  resting on the inner diameter of the rotatable body at this same end thereof, carrier element  30  can then be solidly attached to the rotatable body in various well-known processes which are described below. 
         [0031]    Although not illustrated in  FIGS. 8-9 , carrier element  30  may have similar features to the ones shown in  FIGS. 1-7  for carrier element  10 . In particular, first portion  12  of carrier element  30  can have groove  18  formed therein that accommodates abrasive segments  20 . As mentioned above, groove  18  can be V-shaped, U-shaped, etc., to accommodate similarly shaped bottom portions of abrasive segments  20 . Alternatively, first portion  12  of carrier element  30  can comprise flat face  22  to accommodate bottom portions of abrasive segments  20  having the same profile. Another feature that carrier element  30  may include, is slot  24  extending through first portion  12  and second portion  14  including shoulder  16 . Carrier element  30  may also have a number of holes  26  located across its profile in a radial direction. As mentioned above, three holes is the preferred number, however, those skilled in the art will recognize that one or more holes  26  may be used. 
         [0032]      FIG. 10  shows carrier element  10  used in a core bit as part of a core bit tip  34  accommodated by a core bit tubular body  36  according to one embodiment. Core bit tip  34  and core bit tubular body  36  collectively form a core bit  38 . Core bit tubular body which may be a steel tube receives core bit tip  34  at a front end  40  and at a back end  42  opposite thereof there is a fastening element  44  such as for example a nut with a threaded opening for detachably securing to a drilling tool. Those skilled in the art will recognize that fastening element  44  may include other well known elements besides a threaded nut and embodiments of the present invention are not limited to any particular one. 
         [0033]      FIG. 11  shows a cross-sectional view of the coupling of core bit tip  34  with carrier element  10  depicted in  FIGS. 1-7  to core bit tubular body  36  according to one embodiment. In particular,  FIG. 11  shows a face  46  of second portion  14  that is substantially perpendicular to shoulder  16  resting on a front face  48  formed between the outer diameter  50  and inner diameter  52  at front end  40  of core bit tubular body  36  and shoulder  16  resting on outer diameter  50  of core bit tubular body  36 . With face  46  of second portion  14  resting on front face  48  of core bit tubular body  36  and shoulder  16  resting on outer diameter  50  of core bit tubular body  36 , core tip  34  can then be solidly attached to core bit tubular body  36  in various well-known processes which are described below. 
         [0034]      FIG. 12  shows a core bit  50  in which carrier element  30  is used as the part of core bit tip  34  that couples to core bit tubular body  36  according to one embodiment. Core bit  50  is similar to core bit  38  shown in  FIG. 10 , except that carrier element  30  is used and the shape of abrasive segments  20  are different. The difference in the shape of abrasive segment  20  is illustrated in  FIG. 13 . In particular, abrasive segment  20  in  FIG. 13  has a flat-shaped bottom and pointed top section, whereas abrasive segment  20  in  FIG. 11  has a V-shaped bottom portion and flat-shaped top section. 
         [0035]      FIG. 13  also shows a cross-sectional view of the coupling of core bit tip  34  with carrier element  30  depicted in  FIGS. 8-9  to core bit tubular body  36  according to another embodiment. In particular,  FIG. 13  shows face  46  of second portion  14  that is substantially perpendicular to shoulder  16  resting on front face  48  formed between outer diameter  50  and inner diameter  52  at front end  40  of core bit tubular body  36  and shoulder  16  resting on inner diameter  52  of core bit tubular body  36 . With face  46  of second portion  14  resting on front face  48  of core bit tubular body  36  and shoulder  16  resting on inner diameter  52  of core bit tubular body  36 , then core tip  34  can be solidly attached to core bit tubular body  36 . 
         [0036]    It can be appreciated that carrier elements  10  and  30  enable quick and easy attachment of core bit tip  34  to core bit tubular body  36 . In particular, using either the outside or inside portion of shoulder  16  to rest on the inner diameter  52  or outer diameter  50  of core bit tubular body  36  assures concentric and solid attaching of core bit tip  34  to core bit tubular body  36 . 
         [0037]    Once the core tip  34  has been secured to the core bit tubular body  36  in one of the aforementioned embodiments, then core tip  34  and core bit tubular body  36  may be attached to each other using one of the following methodologies. In one embodiment, a brazing process may be used to attach core tip  34  to core bit tubular body  36 . In this embodiment, the brazing process may use an induction or torch brazing principle to attach core tip  34  to core bit tubular body  36 . In this embodiment, low temperature silver brazing alloys such as BrazeTec 4900 or the like can be used. As mentioned above, holes  26  in carrier elements  10  or  30  allow for easy flow of the braze alloy by capillary action into the interface during the brazing process to provide a very strong bond between core tip  34  to core bit tubular body  36 . In another embodiment, core tip  34  can be attached to core bit tubular body  36  by using an adhesive such as a high strength glue that has a relatively high level of temperature resistance. Illustrative but not limiting examples of a high strength glue may include cyanoacrylate adhesives. In another embodiment, core tip  34  can be attached to core bit tubular body  36  by fastening the two together using a mechanical locking device. Illustrative but not limiting examples of a mechanical locking device may include a bayonet lock, rivets or clips. 
         [0038]    Abrasive segments  20  that may be used with carrier elements  10  or  30  may include an abrasive component that includes abrasive particles embedded in a metal matrix having a network of interconnected pores that are partially or substantially fully filled with an infiltrant. The abrasive particles can be a superabrasive such as diamond or cubic boron nitride. The abrasive particles can have a particle size of not less than about 400 US mesh, such as not less than about 100 US mesh, such as between about 25 and 80 US mesh. Depending on the application, the size can be between about 30 and 60 US mesh. The abrasive particles can be present in an amount between about 2 vol % to about 50 vol %. Additionally, the amount of abrasive particles may depend on the application. For example, an abrasive component for a grinding or polishing tool can include between about 3.75 and about 50 vol % abrasive particles. Alternatively, an abrasive component for a cutting-off tool can include between about 2 vol % and 6.25 vol % abrasive particles. Further, an abrasive component for core drilling can include between about 6.25 vol % and 20 vol % abrasive particles. 
         [0039]    The metal matrix can include iron, iron alloy, tungsten, cobalt, nickel, chromium, titanium, silver, and any combination thereof. In an example, the metal matrix can include a rare earth element such as cerium, lanthanum, and neodymium. In another example, the metal matrix can include a wear resistant component such as tungsten carbide. The metal matrix can include particles of individual components or pre-alloyed particles. The particles can be between about 1.0 microns and about 250 microns. 
         [0040]    There may be a bonding region between abrasive segments  20  and top portion  12  of carrier elements  10  and  30  that can contain a bonding metal. The bonding metal in the bonding region can be continuous with the infiltrant filling the network of interconnected pores. In an exemplary embodiment, the bonding metal composition can include copper, a copper-tin bronze, a copper-tin-zinc alloy, or any combination thereof. The copper-tin bronze may include a tin content not greater than about 20 wt %, such as not greater than about 15 wt %. Similarly, the copper-tin-zinc alloy may include a tin content not greater than about 20 wt %, such as not greater than about 15 wt %, and a zinc content not greater than about 10 wt %. 
         [0041]    According to embodiments herein, the bonding region can form an identifiable interfacial layer that has a distinct phase from both the underlying carrier and the abrasive component. The bonding metal composition is related to the infiltrant composition in having a certain degree of commonality of elemental species. Quantitatively, an elemental weight percent difference between the bonding metal composition and the infiltrant composition does not exceed 20 weight percent. Elemental weight percent difference is defined as the absolute value of the difference in weight content of each element contained in the bonding metal composition relative to the infiltrant composition. 
         [0042]    By way of example only, in an embodiment having a (i) bonding metal composition containing 85 weight percent Cu, 10 weight percent Sn and 5 weight percent Zn, and (ii) an infiltrant composition containing 82 weight percent Cu, 17 weight percent Sn, and 1 weight percent Zn, the elemental weight percent difference between the bonding metal composition and the infiltrant composition for Cu is 5 weight percent, for Sn is 7 weight percent and for Zn is 4 weight percent. The maximum elemental weight percent difference between the bonding metal composition and the infiltrant composition is, accordingly, 7 weight percent. 
         [0043]    Other embodiments have closer compositional relationships between the bonding metal composition and the composition of the infiltrant. The elemental weight percent difference between the bonding metal composition and the infiltrant composition may, for example, not exceed 15 weight percent, 10 weight percent, 5 weight percent, or may not exceed 2 weight percent. An elemental weight percent difference of about zero represents the same composition making up the bonding region and the infiltrant. The foregoing elemental values may be measured by any suitable analytical means, including microprobe elemental analysis, and ignores alloying that might take place along areas in which the infiltrant contacts the metal matrix. 
         [0044]    Abrasive segments  20  are preferably attached to top portion  12  of carrier elements  10  and  30  via the “infiltration attachment” of the segments with the interconnected pores through the bonding region between the segments and the top portion of the carrier elements. Those skilled in the art will recognize that other alternative methodologies may be used. In one embodiment, a brazing process may be used to attach abrasive segments to carrier elements  10  and  30 . In this embodiment, the brazing process may use a preferably higher temperature braze alloy such as BrazeTec 2500 or the like to avoid segment detaching when the entire carrier element is attached to core bit tubular body  36  in a brazing process using a lower temperature braze alloy. In another embodiment, abrasive segments  20  can be attached to carrier elements  10  or  30  by using laser welding. In still another embodiment, abrasive segments  20  can be attached to carrier elements  10  or  30  by using direct sintering. With these alternative methodologies, it is likely that abrasive segments  20  may have a different structure than the “infiltrated” segments“. For example, it is likely that abrasive segments  20  that are attached to carrier elements  10  and  30  are produced by “hot pressing” or “free sintering” principles will have bond structures that are greater than 96% dense and have bond compositions such as pure cobalt or cobalt bronze. The diamond content on the other end may be identical to those described above for the “infiltrated segments”. 
         [0045]    Not only do carrier elements  10  and  30  facilitate easy and quick attachment of core bit tip  34  to core bit tubular body  36  at the factory level in which core bits are manufactured, it is readily apparent that the configurations of carrier elements  10  and  30  make it well suited for easy and quick re-tipping of the core bits at a job site or craftsman workshop once the abrasive segments  20  on the core tip  34  become worn and needs replacement thereof. In accordance with one embodiment of the present invention, once it is determined that the abrasive segments  20  on core tip  34  are worn or need replacement, an operator of core bit  38  or  50  removes the worn core bit tip  34  from core bit tubular body  36 . The operator then takes an unworn core bit tip that can comprise carrier element  10  or  30  and centers shoulder  16  of second portion  14  of core bit tip  34  with respect to either inner diameter  52  or outer diameter  50  of core bit tubular body  36  depending on which carrier element  10  or  30  is used. The unworn core bit tip is attached to core bit tubular body  36  following the centering of shoulder  16  of second portion  14  of core bit tip  34  with respect to either inner diameter  52  or outer diameter  50  of core bit tubular body  36 . Then the unworn core bit tip is secured to the core bit tubular body  36  using well-known processes that may include brazing, adhering with an adhesive material, or fastening the unworn core bit tip to the core bit tubular body with a mechanical locking device. 
         [0046]    Although a preferred embodiment for carrier elements  10  and  30  is as a core bit tip for use in a core bit with a drilling tool, the carrier elements are suitable for use with other abrasive tools. For example, the principles of carrier elements  10  and  30  can be applied to cup wheels, face grinding wheels or saw blades. 
         [0047]    While the disclosure has been particularly shown and described in conjunction with a preferred embodiment thereof, it will be appreciated that variations and modifications will occur to those skilled in the art. Therefore, it is to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the disclosure.

Technology Classification (CPC): 8