1.
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2. How a rock bit drills Abrasion
This is an illustration of the first phase of rock failure.
This is the result of insufficient weight on the bit.
The inserts are contacting the rock under very low weight and the resulting action is very similar to placing a knife blade against a grinding stone.
The driller can very easily tell when he is in the abrasion phase because the cuttings coming out of thehole will be fine dust.

3. Rock cutting, abrasion - very small cracks, insert grinds surface.

4. Fatigue
Here, more weight has been added to the bit with RPM the same as in the previous illustration.
The additional weight has caused some penetration of the inserts into the formation, but not actual failure of the rock.
This is called the fatigue phase and again, the driller can easily recognize this phase by checking the returns.
Small chips and a high percentage of dust will be coming out of the hole.

5. It should be pointed out that rock failure can be accomplished with this type of loading and insert penetration.
However, it may require many impacts on the formation to cause the rock to fail.
The penetration rate will be considerably less than desired.

6. Rock cutting, deeper abrasion - deeper cracking, but does not connect
Rock cutting, deeper abrasion - deeper cracking, but does not connect. Next cone must crack rock between these teeth

7. Spalling
Here, rotation speed (RPM) is still the same but sufficient weight has been applied to the bit for most effective insert penetration into the formation.
Note that the shell of the bit is not against the formation.

8. Rock cutting, spalling starts - enough weight applied to hard rock deeper. Cracks connect. Chips will come free

9. The inserts are loaded under the proper weight to cause the formation to spall.
Chips are removed by the circulating air, allowing the cutting structure to advance.
Under “load” , the bit will drill at maximum efficiency.
The driller will note a large amount of chips with very little dust or fines in the returns.

10. Rock cutting, deep spalling - cracks connecting at deeper levels
Rock cutting, deep spalling - cracks connecting at deeper levels. Cracks connect bertween teeth and between rows

11. Rock cutting, over penetration - cuttings trapped between cone shell and rock. Cannot be blown out by air blast from nozzles.

13. Principle:
The hammer is situated down the hole in direct contact with the drill bit.
The hammer piston strikes the drill bit, resulting in an efficient transmission of the impact energy and insignificant power losses with the hole depth.
The method is widely used for drilling long holes, not only for blasting, but also for water wells, shallow gas and oil wells, and for geo-thermal wells.
In mining it is also developed for sampling using the reverse circulation technique .

15. Principle:
Rotation is provided by a hydraulic or electric motor driven gearbox, called a rotary head.
It moves up and down the tower via a feed system, generating the pull down required to give sufficient weight on the bit.
Flushing of drill cuttings between the wall of the hole and the drill rods is normally done with compressed air.

16. Rotary drag bit

18. Percussive drilling