Rotary cutting tools

Abstract

A rotary cutting tool having a tool body insertable into a drill string with a plurality of projecting or extendable cutter assemblies at positions distributed azimuthally around the longitudinal axis of the tool body. Each cutter assembly includes a support structure bearing a plurality of cutters with exposed hard cutting surfaces facing in a direction of rotation of the tool. The support structure may have a surface positioned to contact a conduit wall and may be made as a body of particulate material infiltrated with a metal binder, where the particulate material may include material such as tungsten carbide having a Knoop hardness of at least 1000. The support structure may have a functionally graded composition with hard material to contact the wall and steel in a region which will be machined during manufacture.

1 . A rotary cutting tool for incorporation into a drill string to enlarge a conduit underground, the rotary cutting tool comprising:
 a tool body having a longitudinal axis extending between upper and lower ends with connectors at the upper and lower ends for attaching to the drill string; and   a plurality of cutter assemblies attached to the tool body at positions distributed azimuthally around the longitudinal axis;   wherein:
 each cutter assembly includes a support structure bearing a plurality of cutters with exposed hard cutting surfaces providing the cutters' leading surfaces in a direction of rotation of the tool; 
 the support structure has at least one surface positionable to contact the conduit wall; and 
 the support structure comprises a body of particulate material infiltrated with a metal binder and the particulate material comprises material having a Knoop hardness of at least 1000. 
   
     
     
         2 . The rotary cutting tool of  claim 1 , wherein the particulate material has a composition that varies from a first region of the support structure bounded by its surface positionable to contact the conduit wall to a second region of the support structure attached to the body of the tool, and wherein the material having a Knoop hardness of at least 1000 is at a greater concentration in the first region than in the second region. 
     
     
         3 . The rotary cutting tool of  claim 1 , wherein the at least one surface positionable to contact the conduit wall is positionable to face radially outwardly and to align with a radial extremity of an exposed part of at least one cutter, so that the cutter does not project outwardly beyond the outward-facing surface and the outward-facing surface contacts the conduit wall after the cutter. 
     
     
         4 . The rotary cutting tool of  claim 3 , wherein the particulate material has a composition that varies from a radially outward region bounded by the outward-facing surface positionable to contact the conduit wall to a radially inward region attached to the tool body, and wherein the material having a Knoop hardness of at least 1000 is at a greater concentration in the radially outward region than in the radially inward region. 
     
     
         5 . The rotary cutting tool of  claim 1 , wherein the particulate material in a region of the support structure bounded by its surface positionable to contact the conduit wall comprises at least 50 wt % of particulate material having a Knoop hardness of at least 1000. 
     
     
         6 . The rotary cutting tool of  claim 1 , wherein the particulate material in a first region of the support structure bounded by its surface positionable to contact the conduit wall comprises at least 30 wt % of particulate material having a Knoop hardness of at least 1300, and wherein the particulate material in a second region of the support structure attached to the tool body comprises at least 75 wt % of particulate material having a Knoop hardness below 800. 
     
     
         7 . The rotary cutting tool according to  claim 1 , wherein at least 80 wt % of the particulate material has a particle size not exceeding 1 mm, and wherein the particulate material in a region of the support structure bounded by its surface positionable to contact the conduit wall comprises particles having a dimension of at least 5 mm and having a Knoop hardness of at least 1300. 
     
     
         8 . The rotary cutting tool of  claim 1 , wherein the particulate material in a region of the block bounded by its surface positionable to contact the conduit wall comprises:
 between 50 wt % and 95 wt % of particulate material having a Knoop hardness of at least 1000 and a particle size not greater than 1 mm, and   between 5 wt % and 25 wt % of particles having a dimension of at least 5 mm and having a Knoop hardness of at least 1300.   
     
     
         9 . The rotary cutting tool of  claim 1 , wherein each cutter comprises a hard faced body of sintered particulate material having a Knoop hardness at an exposed hard face which is at least 1500. 
     
     
         10 . The rotary cutting tool of  claim 1 , wherein the cutters of each cutter assembly comprise leading cutters partially embedded within the support structure, with their leading faces exposed. 
     
     
         11 . The rotary cutting tool of  claim 10 , further comprising:
 additional cutters positioned rotationally behind the leading cutters and having radial extremities at the same radial distance from the tool axis as radial extremities of the leading cutters.   
     
     
         12 . A rotary cutting tool for enlarging an underground conduit, the rotary cutting tool comprising:
 a plurality of cutter assemblies attached to a structure of the tool at positions distributed azimuthally around a longitudinal axis of the tool;   wherein:
 each cutter assembly includes a support structure bearing a plurality of cutters with exposed hard cutting surfaces providing the cutters' leading surfaces in a direction of rotation of the tool; 
 the support structure is a body of particulate material infiltrated with a metal binder, the composition of the particulate material varying progressively from a first region of the support structure positionable to contact the conduit wall to a second region of the support structure spaced from the first region; and 
 the first region contains particulate material with Knoop hardness of at least 1000 at a greater concentration than the second region. 
   
     
     
         13 . A rotary cutting tool for incorporation into a drill string to enlarge an underground conduit, the rotary cutting tool comprising:
 a tool body having a longitudinal axis extending between upper and lower ends with connectors at the upper and lower ends for attaching to the drill string; and   a plurality of cutter assemblies attached to the tool body at positions distributed azimuthally around the longitudinal axis;   wherein each cutter assembly comprises a support structure bearing a plurality of cutters with exposed hard cutting surfaces providing the cutters' leading surfaces in a direction of rotation of the tool; and   wherein the support structure is a body of particulate material infiltrated with a metal binder and incorporates a plurality of objects secured therein by the infiltrating binder.   
     
     
         14 . The rotary cutting tool according to  claim 13 , wherein the plurality of objects are selected from the cutters, additional cutters positioned circumferentially behind the cutters, pieces of material having varying shape and size and having Knoop hardness greater than 1300 which are partially embedded and partially exposed at a radially outward surface of the body of particulate material, and pieces of material providing smooth lubricious areas in a radially outward surface of the body of particulate material. 
     
     
         15 . A method of making a rotary cutting tool for incorporation into a drill string to enlarge a conduit underground, the rotary cutting tool comprising a tool body having a longitudinal axis extending between upper and lower ends with connectors at the upper and lower ends for attaching to the drill string and further comprising a plurality of cutter assemblies attached to the tool body at positions distributed azimuthally around the longitudinal axis of the tool, the method comprising:
 making a support structure for each cutter assembly, the support structure bearing a plurality of cutters with exposed hard cutting surfaces providing the cutters' leading surfaces in a direction of rotation of the tool and the support structure having at least one surface positionable to contact the conduit wall, by
 depositing particulate material as a succession of layers of particulate material, wherein at least some layers include particulate material having a Knoop hardness of at least 1000; and 
 infiltrating the particulate material with a molten metallic binder.