If a hole is drilled, the pressure can be reduced in the hole and thereby in the rock section adjacent to the hole . 如果一个井孔钻成,井内压力就要下降,井孔附近岩体内的压力也跟着下降。
Safety protection and control of deep well drilling 深孔钻的安全保护与控制技术
Detachable pilots for counterbores and countersinks 扩孔钻和沉头钻用可拆卸导杆
Tool inspection methods part 11 : core drills 刀具产品检测方法.第11部分:扩孔钻
Root canal files and reamers , type k for hand use 手持k型牙根管锉和扩孔钻