Selection of the drilling cuttings up-hole velocity
The effective of cleaning hole is very important when hammer is drilling. It is better that the annular air velocity is between in 1220 m/min to 2135 m/min.The annular air velocity for cleaning hole is up to the output volume of compressor, drill bit diameter and drill pipe diameter. When the annular air velocity is less than 1220 m/min, it will cause:
1. Shorten the service life of drill bit
Large diameter is drilling, the drilling cuttings fall back to the bottom hole. drill bit reground and even be submerged. That would cause premature wear.
2. Reduce the drilling speed
Before the next hammer impact, the debris could not be moved since there is no enough air speed from the bottom of bit air hole. So the bit will drill the debris again.
3. Bit buried
Sometimes, the bit air hole could be blocked by the debris and nothing will be expelled, ultimately the drill bit will be buried in the hole.
When the up-hole velocity is higher than2135 m/min, the hammer, drill bit, and drill pipe could be excessive abrasive.