1、 Bottom surface became and drilling too slow
Reason: the drill
bit matrix is too hard.
2、Bottom matrix become cone shape
Reason: Drilled into
crush rock.
3、Eccentric abrasion
Reason: Poor
concentricity between core bit and drill tool or water gap specification is
different from water channel
4、Outside diameter of bit abrasive seriously，even grid to cone shape.
Reason: cleaning bottom of hole for a long time
5、Inside diameter of bit abrasive seriously，even grid to horn shape.
Reason: Cleaning core for a long time and the core is jammed.
6、Inside and outside diameter abrasive seriously
even appear steps.
Reason: There are metal
chippings at the bottom of hole. Rock debris and diamond mal-distribution.
7、The matrix abrasive too fast and diamond is
overexposure.
Reason: matrix is too
soft or rock powder over pile.
8、There is groove on bit surface
Reason: insufficient
cooling down for core bit，Rock debris
inside and diamond mal-distribution.
9、There is groove in water gap or bottom surface
Reason: High
sand-carrying capacity of washing fluid，matrix
is too soft and pump volume is too large.
10、The steel and matrix become blue
Reason: insufficient cooling，light burning
11、Matrix crack
Inside and outside channel are too deep
12、Steel crack There is hard smash in the hole
