Cutting structure for earth-boring bit to reduce tracking

Abstract

An earth boring bit has cutting elements arranged to avoid tracking. The bit has a bit body having a bit axis of rotation. First, second and third cones are rotatably mounted to the bit body, each of the cones having a plurality of rows of cutting elements including a heel row and an adjacent row. The heel row of the first cone has at least equal the number of cutting elements as the heel rows of the other cones. The adjacent row of the second cone has at least 90 percent as many cutting elements as the heel row of the first cone. The heel row of the third cone has a pitch that is in the range from 20-50% greater than the heel rows of the first cone.

1. An earth boring bit, comprising:
 a bit body having a bit axis of rotation; 
 first, second and third cones rotatably mounted to the bit body, each of the cones having a plurality of rows of cutting elements, each of the cutting elements comprising an insert having a barrel pressed into a mating hole in one of the cones, the rows of cutting elements including a heel row and an adjacent row; 
 the heel row of the first cone having at least equal the number of cutting elements as the heel row of the second cone and 20-50% more cutting elements than the heel row of the third cone; and 
 the adjacent row of the second cone having at least 90 percent as many cutting elements as the heel row of the first cone.; 
 wherein the heel row and the adjacent row of the second cone are staggered relative to each other such that an outermost portion of the barrel of each of the cutting elements of the adjacent row of the second cone is substantially as far from the bit axis as an innermost portion of the barrel of each of the cutting elements of the heel row of the second cone; and 
 wherein the heel row and the adjacent row of the third cone are staggered relative to each other such that an outermost portion of the barrel of each of the cutting elements of the adjacent row of the third cone is substantially as far from the bit axis as an innermost portion of the barrel each of the cutting elements of the heel row of the third cone.  
 
     
     
       2. The bit according to  claim 1 , wherein the number of cutting elements of the heel row of the first cone is substantially the same as the number of cutting elements of the heel row of the second cone. 
     
     
       3. The bit according to  claim 1 , wherein the heel row and the adjacent row of the second cone are staggered relative to each other such that an outermost portion of the barrel of each of the cutting elements of the adjacent row of the second cone is substantially as far from the bit axis as an innermost portion of the barrel of each of the cutting elements of the heel row of the second cone. 
     
     
       4. The bit according to  claim 1 , wherein the heel row and the adjacent row of the third cone are staggered relative to each other such that an outermost portion of the barrel of each of the cutting elements of the adjacent row of the third cone is substantially as far from the bit axis as an innermost portion of the barrel each of the cutting elements of the heel row of the third cone. 
     
     
       5. The bit according to  claim 1 , wherein the cutting elements of the adjacent row of the second cone protrude from supporting metal of the second cone substantially as much as the adjacent rows of the first and third cones. 
     
     
       6. The bit according to  claim 1 , wherein the cutting elements of the adjacent row of the first cone protrude from supporting metal of the first cone more than the amount the heel row of the first cone protrudes. 
     
     
       7. An earth boring bit, comprising:
 a bit body having a bit axis of rotation; 
 first, second and third cones rotatably mounted to the bit body, each of the cones having a plurality of rows of cutting elements, each being an insert having a barrel pressed into a mating hole in supporting metal of the cone, each of the cones having a heel row and an adjacent row of cutting elements, the heel rows of the cones being located substantially the same distance from the bit axis; 
 the heel row of the first cone having at least equal the number of cutting elements as the heel row of the second cone and 20-50% more cutting elements that the heel row of the third cone; 
 the adjacent row of the second cone having at least 90 percent as many cutting elements as the heel row of the first cone, each of the cutting elements of the adjacent row of the second cone having a barrel diameter that is substantially the same as a barrel diameter of each of the cutting elements of the heel row of the first cone; and 
 the adjacent row of the third cone being staggered with the heel row of the third cone, such that an outermost portion of the barrel of each of the cutting elements of the adjacent row of the third cone is at least as far from the bit axis as an innermost portion of the barrel of each of the cutting elements of the heel row of the third cone. 
 
     
     
       8. The bit according to  claim 7 , wherein each of the cutting elements of the adjacent row of the first cone has a barrel diameter at least equal to the barrel diameter of the cutting elements of the heel row of the first cone. 
     
     
       9. The bit according to  claim 7 , wherein each of the cutting elements of the adjacent row of the first cone has a barrel diameter greater than the barrel diameter of the cutting elements of the heel row of the first cone. 
     
     
       10. The bit according to  claim 7 , wherein the barrel diameter of each of the cutting elements of the heel row of the first cone is at least equal to the barrel diameter of each of the cutting elements of the heel row of the second cone. 
     
     
       11. The bit according to  claim 7 , wherein the barrel diameter of each of the cutting elements of the heel row of the first cone is at least equal to the barrel diameter of each of the cutting elements of the heel row of the third cone. 
     
     
       12. The bit according to  claim 7 , wherein a barrel diameter of each of the cutting elements of the adjacent row of each of the cones is at least equal to a barrel diameter of each of the cutting elements of the heel row on the same cone. 
     
     
       13. The bit according to  claim 7 , wherein each of the cutting elements of the adjacent row of each of the cones protrudes from the supporting metal at least as far as each of the cutting elements of the heel row of the same cone. 
     
     
       14. An earth boring bit, comprising:
 a bit body having a bit axis of rotation; 
 first, second and third cones rotatably mounted to the bit body, each of the cones having a heel row, an adjacent row, and an inner row of cutting elements, each of the cutting elements being an insert having a barrel pressed into a mating hole in support metal of the cone; 
 the first cone heel row having at least equal the number of cutting elements as the second cone heel row and 20-50% more cutting elements than the cutting elements of the third cone heel row; 
 the second cone adjacent row having at least 90 percent as many cutting elements as the first cone heel row; 
 the third cone adjacent row cutting elements being staggered with the third cone heel row cutting elements; and 
 each of the cutting elements of the adjacent heel row of each of the second cone having a barrel diameter smaller than a barrel diameter of each of the adjacent row cutting elements of each of the other cones. 
 
     
     
       15. The bit according to  claim 14 , wherein the second cone heel row has substantially the same number of cutting elements as the first cone heel row. 
     
     
       16. The bit according to  claim 14 , wherein each of the adjacent row cutting elements of each of cones protrudes from the supporting metal of its cone at least as far as each of the heel row cutting elements of the heel row of the each of the cones. 
     
     
       17. The bit according to  claim 14 , wherein a distance between the first cone heel row and adjacent row is greater than a distance between the second cone heel row and adjacent row and between the third cone heel row and adjacent row. 
     
     
       18. The bit according to  claim 14 , wherein the second cone adjacent row and heel row are staggered such that an outermost portion of the barrel of each of the cutting elements of the second cone adjacent row is at least as far from the bit axis as an innermost portion of the barrel of each of the cutting elements of the third cone heel row. 
     
     
       19. The bit according to  claim 14 , wherein the number of cutting elements in the third cone adjacent row is less than the number of cutting elements in the second cone adjacent row. 
     
     
       20. The bit according to  claim 14 , wherein the cutting elements of the second cone adjacent row protrude from supporting metal of the second cone substantially as much as the cutting elements of the adjacent rows of the first and second cones.