The jet position has a important influence on cutting process when water jet assists bit cutting rocks. In this paper the test for the effect of jet position on drag bit cutting process is described. The experimental methods, instrumentation and procedure are conducted. Four different jet positions were investigated in the test. The range of diameter of nozzles used is from 0.5 mm to 1.0 mm. The influence of jet position on rock chips formed ahead of bit is discussed. The effect of cut depth, bit velocity on bit force reductions is analyzed. The effectiveness of jet energy is examined for all kind of jet positions. And some important conclusions are given in the end of this paper. One of the most interesting results is that the water jet has the largest effect on drag bit cutting process when it is directed towards the center beneath the bit.

In this part of the paper, the test that three PDC drag bits with different rake angle were used to make linear cuts in two rock types is conducted. The experimental methods, instrumentations and process are described. In order to investigate the relationship between the wear and damage of PDC inserts and bit forces as well as the influence of moderate pressure water jets on the cutting process is analyzed. Towards the end of this part of the paper, the conclusion is given.

在破煤岩过程中，刀具磨损破坏是一个主要原因。本文对刀具的温升给予了理论分析，并进行了实验测试。定量描述了刀具材质、载荷、切割速度及冷却方式与刀具温度的关系，为避免刀具发生热破坏提供了依据。

描述了汽、液两相流在准直管内高速流动时的相变过程及有趣的物理现象，推导了准直管内高速稀疏介质的有阻运动方程式，讨论了流体介质的密度和温度变化过程。研究表明，准直管在一定长度范围内液体介质密度和速度几乎不变。

本文讨论了用于水介千周的中直径高压机械回转密封的结构和工作原理，试验分析了密封环材质的结构对密封性能的影响。研究表明。MC尼尼龙密封环寿命长。泄漏量小、性能稳定，适用于水介质、大中直径等场合。