PCD Percussion Drill Bit

Abstract

An insert for a percussion drill bit for drilling a hole in rock comprises a cylindrical portion and domed cutting surface. The domed cutting surface that comprises polycrystalline diamond has a tip radius that is between 0.3 and 0.4 times that of the diameter of the cylindrical portion. The diameter of the cylindrical portion is preferably greater than the gauge diameter of hole multiplied by 0.2.

1 . An insert for a percussion drill bit comprising:
 a cylindrical portion that extends along an axis, the cylindrical portion having a diameter about the axis;   a domed cutting surface that forms an axial end of the insert, the cutting surface comprising polycrystalline diamond, the cutting surface having a tip radius where the axis intersects the cutting surface, the tip radius and the diameter defining a tip radius-to-diameter ratio, the tip radius-to-diameter ratio being between 0.3 and 0.4.   
     
     
         2 . An insert in accordance with  claim 1  wherein the cutting surface comprises a first surface portion having a constant radius equal to the tip radius, a second surface portion having a shape defined by a constant radius arc revolved about the axis, and a third surface portion that is frustoconical in shape, the constant radius arc that defines the shape of the second surface portion has a radius that is greater than the tip radius, and the third surface portion extends from the cylindrical portion to the second surface portion. 
     
     
         3 . An insert in accordance with  claim 1  wherein the diameter of the cylindrical portion is greater than 0.40 inches and less than 0.48 inches. 
     
     
         4 . An insert in accordance with  claim 3  wherein the tip radius is greater than 0.1 inches and less than 0.2 inches. 
     
     
         5 . An insert in accordance with  claim 4  wherein the tip radius is greater than 0.14 inches and less than 0.16 inches. 
     
     
         6 . An insert in accordance with  claim 1  wherein the tip radius-to-diameter ratio is between 0.33 and 0.35. 
     
     
         7 . A percussion drill bit configured and adapted to drill a hole in rock, the hole having a diameter, the drill bit comprising:
 a body having shaft and head portions;   at least one insert, the insert comprising a domed cutting surface that comprises polycrystalline diamond, the insert being rigidly attached to the head portion, the insert comprising a cylindrical portion having a diameter, the diameter of the cylindrical portion being greater than the diameter of hole multiplied by 0.2.   
     
     
         8 . A percussion drill bit in accordance with  claim 7  wherein the head portion comprises two wings and a central portion, the two wings protrude in radially opposite directions from the central portion, the drill bit comprises six of the inserts, each wing has two of the inserts protruding therefrom, and the central portion has two of the inserts protruding therefrom. 
     
     
         9 . A percussion drill bit in accordance with  claim 8  wherein the inserts protrude from the head portion by at least 0.30 inches. 
     
     
         10 . A percussion drill bit in accordance with  claim 8  wherein each of the inserts that protrude from the wings also protrudes overlap the central portion of the head portion and also protrude from the central portion. 
     
     
         11 . A percussion drill bit in accordance with  claim 7  wherein the diameter of the cylindrical portion defines an axis, the cutting surface has a tip radius where the axis intersects the cutting surface, the tip radius and the diameter of the cylindrical portion define a tip radius-to-diameter ratio, and the tip radius-to-diameter ratio is between 0.3 and 0.4. 
     
     
         12 . A percussion drill bit in accordance with  claim 11  wherein the tip radius is greater than 0.14 inches and less than 0.16 inches. 
     
     
         13 . A percussion drill bit in accordance with  claim 11  wherein the tip radius-to-diameter ratio is between 0.33 and 0.35. 
     
     
         14 . A percussion drill bit in accordance with  claim 11  wherein the cutting surface comprises a first surface portion having a constant radius equal to the tip radius, a second surface portion having a shape defined by a constant radius arc revolved about the axis, and a third surface portion that is frustoconical in shape, the constant radius arc that defines the shape of the second surface portion has a radius that is greater than the tip radius, and the third surface extends from the cylindrical portion to the second surface portion. 
     
     
         15 . A percussion drill bit in accordance with  claim 11  wherein the diameter of the cylindrical portion is greater than 0.40 inches and less than 0.48 inches. 
     
     
         16 . A percussion drill bit in accordance with  claim 15  wherein the tip radius is greater than 0.1 inches and less than 0.2 inches. 
     
     
         17 . A percussion drill bit configured and adapted to drill a hole in rock, the percussion drill bit comprising:
 an insert, the insert having a cylindrical portion that extends along an axis, the cylindrical portion having a diameter about the axis, the insert also having a domed cutting surface that forms an axial end of the insert, the cutting surface comprising polycrystalline diamond, the cutting surface having a tip radius where the axis intersects the cutting surface, the tip radius and the diameter defining a tip radius-to-diameter ratio, the tip radius-to-diameter ratio being between 0.3 and 0.4.   
     
     
         18 . A method of drilling a hole in rock using the percussion drill bit of  claim 17 , the hole having a bore diameter in the range of 1.75 inches to 2.5 inches, the method comprising maintaining a thrust pressure on the drill bit below 363 psi while drilling. 
     
     
         19 . A method of drilling a hole in rock using the percussion drill bit of  claim 17 , the hole having a bore diameter in the range of 1.375 inches to 1.625 inches, the method comprising maintaining a thrust pressure on the drill bit below 291 psi while drilling.