General Principles for Selecting Drill Bits:
Grade 5-7 complete and homogeneous rock strata. Example: For shale, limestone and sandstone, HRC35-45 electroplated drill bit is generally selected for matrix hardness.
Grade 7-9 medium abrasiveness, relatively complete rock strata. For marble, siliceous limestone and common granite, HRC35-40 flat-bottomed drill bit is generally selected.
Grade 9 or above medium abrasiveness, relatively complete rock strata. Example: For Shi Ying sandstone, diamond electroplating and hot pressing drill bits with HRC25 or so should be selected.
Hard and weak abrasive strata (commonly known as "slipping" strata).
Example: Quartzite feels smooth from the point of view of coring. It is appropriate to select HRC15-20 high and low serrated electroplated diamond bits or 5-10 degree hot-pressed gear bits.
For drilling fractured rock formations with developed fractures and complex structures, diamond bits with HRC45 matrix should be selected.
Reaming shell impaired
Features of reaming shell impaired products: Dimensional difference between diameter of diamond bit and outer diameter of core tube.