Studies on the Boring with Metal Core-bit

Abstract

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.