Patent Publication Number: US-7594703-B2

Title: Pick with a reentrant

Description:
BACKGROUND OF THE INVENTION 
     Efficient degradation of materials is important to a variety of industries including the pavement, mining, and excavation industries. In the pavement industry, pavement may be degraded using attack tools, and in the mining industry, attack tools may be used to break minerals and rocks. Attack tools may also be used when excavating large amounts of hard materials. In pavement milling, often, a drum supporting an array of picks may rotate such that the picks engage a paved surface causing it to break up. 
     U.S. Pat. No. 6,733,087 to Hall et al., which is herein incorporated by reference for all that it contains, discloses an attack tool for working natural and man-made materials that is made up of one or more segments, including a steel alloy base segment, an intermediate carbide wear protector segment, and a penetrator segment comprising a carbide substrate that is coated with a superhard material. The segments are joined at continuously curved interfacial surfaces that may be interrupted by grooves, ridges, protrusions, and posts. At least a portion of the curved surfaces vary from one another at about their apex in order to accommodate ease of manufacturing and to concentrate the bonding material in a region of greatest variance. The carbide used for the penetrator and the wear protector may have a cobalt binder, or it may be binderless. It may also be produced by the rapid omnidirectional compaction method as a means of controlling grain growth of the fine cobalt particles. The pats are brazed together in such a manner that the grain size of the carbide is not substantially altered. The superhard coating may consist of diamond, polycrystalline diamond, cubic boron nitride, binderless carbide, or combinations thereof. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect of the invention, a pick adapted to degrade man-made or natural formations has a steel body comprising a shank adapted for attachment to a driving mechanism. The pick also has a leading edge opposite the shank which has an inside edge. A bore is disposed in the steel body proximate the inside edge. A cemented metal carbide core is press fit into the bore. A reentrant is at least partially formed in the bore. In some embodiments, the reentrant joins the leading edge and the bore. In other embodiments, the reentrant is formed in proximate a base of the bore. 
     The cemented metal carbide may be press fit into the steel body with an interference of between 0.0005 and 0.004 inch. In some embodiments, the leading edge may comprise a surface with a hardness of at least 58 HRc. The surface may comprise a material selected from the group consisting of chromium, tungsten, tantalum, niobium, titanium, molybdenum, carbide, natural diamond, polycrystalline diamond, vapor deposited diamond, cubic boron nitride, TiN, AlNi, AlTiNi, TiAlN, CrN/CrC/(Mo, W)S2 TiN/TiCN, AlTiN/MoS2, TiAlN, ZrN, diamond impregnated carbide, diamond impregnated matrix, silicon bounded diamond, and/or combinations thereof In other embodiments, a carbide ring may be fixed to the leading edge. 
     A distance from the leading edge to an end of the reentrant may be 0.05 to 0.20 inch. A superhard material, selected from the group consisting of diamond, cubic boron nitride, or combinations thereof, is bonded to the cemented metal carbide. The diamond may be infiltrated diamond. Metallic binder from the cemented metal carbide may diffuse into the superhard material. The distance from the leading edge to the end of the reentrant may be 25 to 100% of a thickness of the diamond. 
     In another aspect of the invention, the cemented metal carbide has first and second regions comprising different metal concentrations. A superhard tip bonded to the first region has a hardness over 4,000 HV. The second region is attached to the steel body. The metal concentration of the first region may be lower than the second region. The second carbide region may be brazed to the steel body or may be press fit into the steel body. The cemented metal carbide may be tungsten carbide, titanium carbide, niobium carbide, vanadium carbide, hafnium carbide, zirconium carbide, molybdenum carbide, tantalum carbide, chromium carbide or combinations thereof. The cemented metal carbide may also comprise a metallic binder selected from the group consisting of cobalt, tantalum, nickel, vanadium, chromium, niobium, or combinations thereof. The first region may comprise 2 to 12 weight percent of metallic binder whereas the second region comprises 5 to 25 weight percent of metallic binder. It is believed that the region with the lower metallic binder composition may have a greater wear resistance than the region with the higher metallic binder composition. The region with the higher metallic binder composition may better withstand impact than the region with the lower metallic binder composition. The first region may be 1 to 5 mm thick. The two regions may comprise two cemented metal carbide segments. The two cemented metal carbide segments may be brazed together. A chamfer or a reentrant may be disposed in the steel body proximate a leading edge opposite the shank. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional diagram of an embodiment of a plurality of picks on a rotating drum attached to a motor vehicle. 
         FIG. 2  is an orthogonal diagram of an embodiment of a pick. 
         FIG. 3  is an exploded diagram of an embodiment of a pick. 
         FIG. 4  is a cross-sectional diagram of another embodiment of a pick. 
         FIG. 5  is a cross-sectional diagram of another embodiment of a pick. 
         FIG. 6  is a cross-sectional diagram of another embodiment of a pick. 
         FIG. 7  is a cross-sectional diagram of another embodiment of a pick. 
         FIG. 8  is a cross-sectional diagram of an embodiment of a reentrant disposed in a pick. 
         FIG. 9  is a cross-sectional diagram of another embodiment of a reentrant disposed in a pick. 
         FIG. 10  is a cross-sectional diagram of another embodiment of a reentrant disposed in a pick. 
         FIG. 11  is an exploded perspective diagram of another embodiment of a pick. 
         FIG. 12  is a perspective diagram of an embodiment of a trencher. 
         FIG. 13  is an orthogonal diagram of another embodiment of a trencher. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENT 
       FIG. 1  is a cross-sectional diagram of an embodiment of a plurality of picks  100  attached to a rotating drum  101  connected to the underside of a pavement milling machine  102 . The milling machine  102  may be a cold planar used to degrade man-made formations such as pavement  103  prior to the placement of a new layer of pavement. Picks  100  may be attached to the drum  101  bringing the picks  100  into engagement with the formation. A holder  104  is attached to the rotating drum  101 , and the pick  100  is inserted into the holder  104 . The holder  104  may hold the pick  100  at an angle offset from the direction of rotation, such that the pick  100  engages the pavement at a preferential angle. 
       FIG. 2  is an orthogonal diagram of an embodiment of a pick  100 . The pick  100  may have a steel body  200  comprising a shank  201  adapted for attachment to a driving mechanism. In the preferred embodiment, cemented metal carbide  202  may have a first region  203  and a second region  204 . The two regions  203 ,  204 , may comprise different metal concentrations. A superhard tip  205  may be bonded to the first region  203  and the second region may be attached to the steel body  200 . The metal concentration of the first region may be lower than the metal concentration of the second region. This may be beneficial in that the first region may be more wear resistant than the second region and the second region may withstand impact better than the first region. The superhard tip  205  may comprise a hardness over 4,000 HV. The superhard tip  205  may comprise a material selected from the group consisting of diamond, cubic boron nitride, or combinations thereof. The diamond may be infiltrated diamond. Metallic binder from the first cemented metal carbide  202  may diffuse into the diamond. 
     In the preferred embodiment, the first and second regions  203 ,  204 , may comprise two cemented metal carbide segments. The two segments may be brazed together. The steel body  200  may also comprise a washer  206  such that when the pick  100  is inserted into a holder, the washer  206  protects an upper surface of the holder and in some cases facilitates rotation of the pick  100 . The pick may also be disposed in a protective sleeve  207  such that the protective sleeve  207  protects the pick while it is being press fit into the holder and allowing the pick to rotate. 
     An exploded diagram of an embodiment of a pick  100  is shown in  FIG. 3 . In the preferred embodiment, a leading edge  300  opposite the shank  201  may comprise a reentrant  301  disposed in a bore  302  of the steel body  200 . The second region  204  of the cemented metal carbide  202  may be press fit into the bore  302  of the steel body  200 . In other embodiments, the second region may be brazed to the steel body. The cemented metal carbide  202  may be press fit into the steel body  200  with an interference of between 0.0005 and 0.004 inch In this embodiment, the regions  203 ,  204 , of the cemented metal carbide  202  are two segments that may be brazed together at a surface  305 . 
     Referring now to  FIG. 4 , a pick  100  comprises cemented metal carbide first region  203  and a second region  204 , the second region  204  being press fit into a steel body  200 . In the preferred embodiment, a reentrant  301  may be disposed in the steel body  200  from the bore  302  to the leading edge  300  opposite the shank  201 . A surprising result of the present invention shows that when the tip of the pick  100  is weakened by placing a reentrant  301  in the steel body  200 , cracking may be prevented during operation The leading edge  300  may comprise a surface  400  with a hardness of at least 58 HRc. The surface  400  may comprise a material selected from the group consisting of chromium, tungsten, tantalum, niobium, titanium, molybdenum, carbide, natural diamond, polycrystalline diamond, vapor deposited diamond, cubic boron nitride, TiN, AlNi, AlTiNi, TiAlN, CrN/CrC/(Mo, W)S2, TiN/TiCN, AlTiN/MoS2, TiAlN, ZrN, diamond impregnated carbide, diamond impregnated matrix, silicon bonded diamond, and/or combinations thereof In this embodiment, the two cemented metal carbide regions  203 ,  204 , are two separate segments. The two regions may be brazed together. The first region  203  may comprise an axial length  401  of 1 to 5 mm. A distance  402  from the leading edge  300  to an end  403  of the reentrant  301  may be 0.02 to 0.20 inch. The distance  402  may be 25% to 100% of a thickness  404  of the superhard tip  205 . In some embodiments, another reentrant  450  may be formed may be formed proximate a base  451  of the bore  302 . 
       FIG. 5  shows another embodiment of a pick  100 . In this embodiment, a reentrant  500  may be disposed in the steel body  200  proximate the leading edge  300  opposite the shank  201 . This embodiment also includes a carbide ring  501  fixed to the leading edge  300 . The carbide ring  501  may help to strengthen the tip. The cemented metal carbide  202  may comprise first and second regions  203 ,  204 , having different metallic binder concentrations. 
       FIGS. 6 and 7  show embodiments of a superhard tip  205  bonded to the first region  203  of the cemented metal carbide  202 . The superhard tip  205  may comprise a hardness over 4,000 HV. In  FIG. 6  the first and second regions  203 ,  204 , comprise one segment, whereas in  FIG. 7  the regions  203 ,  204 , comprise two segments. The first and second regions  203 ,  204 , may comprise different metal concentrations. The metal concentration of the first region  203  may be lower than the metal concentration of the second region  204 . This may be beneficial in that carbide with a lower metal concentration may be more wear resistant whereas carbide with a higher metal concentration is more resistant to impact. It is believed that by varying the concentrations of the two regions  203 ,  204 , the life of the pick may be increased. The cemented metal carbide  202  may be tungsten carbide, titanium carbide, niobium carbide, vanadium carbide, hafnium carbide, zirconium carbide, molybdenum carbide, tantalum carbide, chromium carbide or combinations thereof. The cemented metal carbide  202  may have a metallic binder selected from the group consisting of cobalt, tantalum, nickel, vanadium, chromium, niobium, or combinations thereof. The first region  203  may comprise 2 to 12 weight percent of metallic binder, whereas the second region may comprise 5 to 25 percent of metallic binder. The superhard tip  205  may comprise diamond, cubic boron nitride or combinations thereof. In the preferred embodiment, the diamond may be infiltrated diamond. In such embodiments, metallic binder, such as cobalt, may diffuse from the first region  203  of the cemented metal carbide  202  into the diamond. Thus, the two regions  203 ,  204 , of the cemented metal carbide  202  may initially comprise equal concentrations of metallic binder, but will eventually develop a differential in metallic binder concentration as cobalt or other metallic binder diffuses from the first region  203  into the diamond. In the embodiment of  FIG. 7 , the two regions may be brazed together. In other embodiment, the first region may have an initial lower metallic binder concentration than the second region. 
     A reentrant  301  disposed in the pick  100  from the bore  302  to the leading edge  300  may have different geometries as shown in various pick embodiments in  FIGS. 8-10 . The leading edge  300  may comprise a surface  400  with a hardness of at least 58 HRc. In  FIG. 8 , the pick  100  comprises a reentrant  205  with a large width  800  from the bore  302  to the leading edge  300 .  FIG. 9  shows a pick  100  comprising a reentrant  205  of an intermediate width  800  from the bore  302  to the leading edge  300 .  FIG. 10  is an embodiment of a pick  100  that comprises a reentrant  205  with a convex geometry. It is believed that different reentrant geometries may prevent cracking in different locations and with different efficiencies. In some embodiments, the reentrant may be chamfer, bevel, furrow, groove, cant, or combinations thereof. 
       FIG. 11  is an exploded perspective diagram of an embodiment of a pick  100 . The pick  100  may comprise a steel body  200  with a shank  201  adapted for attachment to a driving mechanism. In this embodiment, the second region  204  of the cemented metal carbide  202  may be brazed to the steel body  200  with a braze  1100 . The two regions  203 ,  204  may comprise two segments and may also be brazed together with a braze  1101 . A superhard tip  205  may be bonded to the first cemented metal carbide  203 . Further, the first and second regions  203 ,  204 , may comprise different metal compositions. 
       FIGS. 12 and 13  show various wear applications that may be incorporated with the present invention. Picks  100  may be disposed on a rock wheel trenching machine  1200  as shown in  FIG. 12 . Also, the picks  100  may be placed on a chain that rotates around an arm  1300  of a chain trenching machine  1200  as shown in  FIG. 13 . 
     Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications apart from those shown or suggested herein, may be made within the scope and spirit of the present invention.