Durable rock bit for blast hole drilling
A rock bit for blast hole drilling includes: a bit body having a coupling formed at an upper end thereof, a plurality of lower legs, a dome formed between the legs, and a bore formed through the coupling and the dome; a plurality of skirts, each skirt covering a gap formed between adjacent legs and each skirt mounted to edges of adjacent legs; a plurality of roller cones, each rotary cone rotatably mounted to a respective bearing shaft of a respective leg; a row of gage cutters mounted to each roller cone; a row of inner cutters mounted to each roller cone; one or more nose cutters mounted to each roller cone; and a center jet secured in the bore. Each cutter is an insert.
1. A rock bit for blast hole drilling, comprising:
a bit body having a coupling formed at an upper end thereof, a plurality of lower legs, a dome formed between the legs, and a bore formed through the coupling and the dome;
a plurality of skirts, each skirt covering a gap formed between adjacent legs and each skirt mounted to edges of adjacent legs;
a plurality of roller cones, each rotary cone rotatably mounted to a respective bearing shaft of a respective leg;
a row of gage cutters mounted to each roller cone;
a row of inner cutters mounted to each roller cone;
one or more nose cutters mounted to each roller cone; and
a center jet secured in the bore and comprising:
an orifice plate having a plurality of ports or a single port with a plurality of branches, each port or branch aimed at an interface between adjacent roller cones; and
a back flow valve operable to open in response to injection of drilling fluid down the bore and to close for blocking upward flow through the bore,
wherein:
each cutter is an insert, and
inner and outer surfaces of each skirt extend straight across the respective gap.
2. The bit of claim 1 , wherein:
the bit further comprises a plurality of sets of roller bearings, each set disposed between a respective cone and a respective bearing shaft, and
each leg has a passage extending from the bore to the respective set of bearings.
3. The bit of claim 2 , wherein:
the center jet comprises a tube having a plurality of sets of slots aligned with inlets of the passages, and
each set of slots is oriented to face a respective passage.
4. The bit of claim 1 , wherein the orifice plate has the plurality of ports.
5. The bit of claim 4 , wherein the orifice plate further has a center port aimed downward.
6. The bit of claim 4 , wherein the orifice plate further has a plenum formed therein.
7. The bit of claim 1 , wherein the orifice plate has the single port with a center portion aimed downward and the plurality of branch portions.
8. The bit of claim 1 , further comprising a set of interstitial protectors mounted on each roller cone.
9. The bit of claim 8 , wherein the interstitial protectors are located between adjacent nose cutters.
10. The bit of claim 1 , wherein at least a portion of each cone is treated to resist erosion.
11. The bit of claim 10 , wherein the treatment is case hardening.
12. The bit of claim 10 , wherein the treatment is hardfacing.
13. The bit of claim 10 , wherein the treated portion is located between the inner cutters and the nose cutters and at a mouth of each cone.
14. The bit of claim 1 , wherein the coupling is a threaded pin.
15. The bit of claim 1 , wherein the center jet is the only nozzle or port of the drill bit for discharging fluid to remove cuttings.
16. A rock bit for blast hole drilling, comprising:
a bit body having a coupling formed at an upper end thereof, a plurality of lower legs, a dome formed between the legs, and a bore formed through the coupling and the dome;
a plurality of skirts, each skirt covering a gap formed between adjacent legs and each skirt mounted to edges of adjacent legs;
a plurality of roller cones, each rotary cone rotatably mounted to a respective bearing shaft of a respective leg;
a row of gage cutters mounted to each roller cone;
a row of inner cutters mounted to each roller cone;
one or more nose cutters mounted to each roller cone; and
a center jet secured in the bore and comprising:
an orifice plate having a plurality of ports or a single port with a plurality of branches, each port or branch aimed at an interface between adjacent roller cones; and
a back flow valve operable to open in response to injection of drilling fluid down the bore and to close for blocking upward flow through the bore,
wherein:
each cutter is an insert, and
each skirt is arcuate and extends along a curved path across the respective gap, such that when the rock bit is viewed from a bottom thereof, a foot print of the skirts and gage lands of the cones resembles a circle.