分析了其中4种孔底换钻头钻具的结构及工作原理；
The esigns and working principles of 4 types of it are analysed.
介绍了小口径换热管堵塞采用柔性钻头疏通的处理方法。
The author introduces a method of dredging stems in small_bore tubes by flexible aiguille.
在分析各国整体切削具不提钻可换式钻头结构及存在主要问题的基础上，提出采用整体旋转切削具可换式钻头。
Based on analyses about the structures and existing problems of integrally retractable alternative cutting element bits, a integrally rotary replacing cutting element bit was proposed.
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