Full instrumentation is made on a medium size boring machine to speed up the experiments and to get more precise data. Penetration rate, torque, thrust and pressure of water supply can be recorded automatically on four channel pen-writing oscillograph. All results are of laboratory studies bored into the rock specimens ranging from hard to soft formations. Diamond bit used is a surface setting core bit, 46mm in size, having 12 carat setting. Rotation speed and volume of water supply are variable as parameter. Main results obtained from these experiments are as follows:1) Penetration rate is almost proportional to thrust and rotation speed of bit 2) Relation between thrust and torque is almost constant for all rocks and this relation does not change by rotation speed.3) Max. penetration rate is proportional to volume of water supply in the case of the rotation speed i constant.4) Max. penetration rate is proportional to square root of rotation speed and the max. thrust corresponding to max. penetration rate is inversely proportional to square root of rotation speed. 5) Penetration rate and max. thrust for each rock can be presumed from the shore hardness, indentation depth and compressive strength of the rock.
The metal core bit is widely applied for boring of the softer rocks.This study was made on such important problems for boring as bit shape,cutting mechanism of cutting edge of bit,interrelation between thrust,rotation speed,penetration rate,torque and bit wear and relations between boring conditions and bit wear.The main results obtained are as follows: 1) max.penetration rate was increased about 3 times compare with ordinary bit by improving the bit shape.2) in the case of rotation speed of bit and water supply is constant,relations between thrust(W), penetration rate(V)and torque(T)is W=a Vn,W=a'Tn' in grinding stage and W=w,+mV, W=w'+m'T in cutting stage,and each coefficient of these formula is almost proportional to wearing width of cutting edge of bit.3) in the case of thrust is constant,the penetration rate is proportional to rotation speed of bit,but torque does not change by rotation speed. 4) if consider the bit wear,the effective boring would be done in lower rotation speed and in higher thrust.Also,it was proved that the relation between thrust,torque and penetration rate would be calculated from the data of the cutting resistance,exactly.
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