Drill bit with curved sludge grooves

Abstract

A percussive drill bit includes a head and an axially rearward skirt. A plurality of ribs project radially outward at the skirt and define lengthwise extending channels. The ribs and channels, in the lengthwise direction are curved or angled to deviate from a longitudinal axis of the drill bit to facilitate rearward transport of fines and flushing fluid.

1 . A drill bit comprising:
 a head having cutting elements arranged to abrade rock by rotation of the drill bit about its longitudinal axis;   a skirt extending axially rearward from the head; and   a plurality of ribs projecting radially outward and extending axially along the skirt to define axially extending channels, the rib and channels each having a length extending axially in a lengthwise direction between the head and an axially rearward end of the skirt, wherein in the lengthwise direction at least a part of the ribs and channels are bent or curved such that a lengthwise part of the ribs or channels is oblique to the longitudinal axis.   
     
     
         2 . The drill bit as claimed in  claim 1 , wherein the lengthwise part of the ribs and channels that are oblique to the longitudinal axis are positioned at an axially rearward part of the skirt. 
     
     
         3 . The drill bit as claimed in  claim 2 , wherein an axially forward part of the ribs and channels is aligned generally parallel to the longitudinal axis. 
     
     
         4 . The drill bit as claimed in  claim 2 , wherein said axially rearward part extends up to 20%, 30%, 40%, 50%, 60%, 70%, 80% or 90% of the length of the skirt between an axially rearwardmost region of the head and the axially rearward end of the skirt. 
     
     
         5 . The drill bit as claimed in  claim 1 , wherein the lengthwise part of the ribs and channels extend at least partly helical around the axis. 
     
     
         6 . The drill bit as claimed in  claim 1 , wherein each rib includes a leading face and a trailing face separated by a radially outward facing land face, the leading and trailing faces at least partial defining the channels. 
     
     
         7 . The drill bit as claimed in  claim 6 , wherein in the lengthwise direction both the leading and trailing faces of the ribs are bent or curved in the same circumferential direction around the axis so as to be aligned oblique to the axis. 
     
     
         8 . The drill bit as claimed in  claim 6 , wherein in the lengthwise direction, at least a part of a leading edge and a trailing edge of the ribs at a junction between the land face and the respective leading face and trailing face is bent or curved so as to be aligned oblique to the axis. 
     
     
         9 . The drill bit as claimed in  claim 8 , wherein the part of the leading edge and the trailing edge that are oblique to the axis are positioned at an axially rearward part of the skirt. 
     
     
         10 . The drill bit as claimed in  claim 6 , wherein at a cross sectional plane perpendicular to the longitudinal axis, the leading face is aligned generally normal to the rotational direction of the bit about the axis. 
     
     
         11 . The drill bit as claimed in  claim 10 , wherein in the cross sectional plane perpendicular to the axis, the trailing face is aligned transverse to the rotational direction of the bit and/or oblique to the leading face. 
     
     
         12 . The drill bit as claimed in  claim 1  wherein an angle by which the ribs are bent or curved such that their length deviates in a circumferential direction is in the range of 1 to 20° relative to the axis. 
     
     
         13 . The drill bit as claimed in  claim 12  wherein the range is 3 to 10°, 3 to 8° or 4 to 6°. 
     
     
         14 . The drill bit as claimed in  claim 1 , further comprising an internal bore and passageways extending axially from a forward end of the bore arranged to emerge as openings at a forward cutting face of the head, at least some of the channels extending axially along the head in communication with the openings. 
     
     
         15 . The drill bit as claimed in  claim 1 , wherein the cutting elements include cutting buttons embedded into the head.