Secondary cutting element for drill bit

Abstract

A rotary drag bit comprises a bit body and a plurality of blades extending radially away from the bit body, each blade including a cutting assembly. Each cutting assembly has a plurality of primary cutters orientated in the direction of rotation of the drill bit for drilling or boring into a subterranean rock formation, and a plurality of secondary or brute cutters located behind the primary cutters in relation to the direction of rotation of the drag bit. The invention is concerned primarily with the secondary cutters, which comprise a layer of superabrasive material, such as PCD, PCBN or CVD diamond, bonded to a support substrate. The interface between the superabrasive layer and the substrate has a stepped region that provides the cutter with a skirt or hoop of superabrasive extending into the substrate. The secondary cutter is orientated in use to present a bearing surface to the rock formation and a secondary cutting edge in the direction of rotation of the rotary bit.

1 . A rotary drag bit comprising: 
 a bit body;    a plurality of blades extending radially away from the bit body, each blade including a cutting assembly;    each cutting assembly having a plurality of primary cutters orientated in the direction of rotation of the drill bit for drilling or boring into a subterranean rock formation, and a plurality of secondary cutters located behind the primary cutters in relation to the direction of rotation of the drag bit; and    one or more of the secondary cutters comprising a layer of superabrasive material bonded to a support substrate:    the superabrasive layer having a major bearing surface on one side thereof and a major interface with the substrate on an opposite side thereof,    the interface defining a stepped region in the peripheral zone of the cutter providing the cutter with a skirt or hoop of superabrasive extending into the substrate,    the or each secondary cutter being orientated in use to present the bearing surface to the rock formation and the secondary cutting edge in the direction of rotation of the rotary bit.    
   
   
       2 . A bit according to  claim 1 , wherein the interface has a central table or surface which is profiled.  
   
   
       3 . A bit according to  claim 2 , wherein the profile of the table or surface is a series of concentric rings, a plurality of dimples, or a cross-hatch structure.  
   
   
       4 . A bit according to  claim 1  wherein the table defines a periphery and base that are each generally rounded such that the interface in the region of the hoop or skirt is one which generally has no discontinuities.  
   
   
       5 . A bit according to  claim 1 , wherein the superabrasive material is PCD, PCBN or CVD diamond.  
   
   
       6 . A bit according to  claim 5 , wherein the superabrasive material is PCD, the PCD comprising at least 25 percent by mass of ultra-hard abrasive particles having an average particle size in the range 10 to 100 microns and consisting of particles having at least three different average particle sizes and at least 4 percent by mass ultra-hard abrasive particles having an average particle size of less than 10 microns.  
   
   
       7 . A tool component in the form of a secondary cutter as defined in  claim 1  for a drill bit.  
   
   
       8 . (canceled)  
   
   
       9 . (canceled)