and Shigeo MISAWA On the drilling mechanism of rock with long rod, previously reported, it was proved that the drilling efficiency results not from the increase of rod length, but from the decrease of output of rock drill and the cuttings. Later results of the drilling tests with joint rod proved that the reflection energy at joint had an important effect upon the drilling efficiency. So we investigated on the reflection energy with various type of joints. The results obtained are as follows: (1) Even at the jointless rod (5m), energy loss was 10% per cycle of the elastic wave. (2) The total energy loss of taper joint rod (5m) per cycle was 15%, buttress joint was 17 % and upset joint was 37%. (3) The reflection energy of taper joint was 4.0%, buttress joint was 3.0% and upset joint was 2.0%. (4)
The authors analyzed the frictional resistance acting on a cutting tool during rock cutting.The friction coefficient obtained was about 0.55 on the worn part of the clearance face and was in the range of 0-0.19 on the rake face.We showed that the experimental result of the resultant force acting on the rake face agreed well with the theoretical predictions by Nishimatsu,and analyzed theoretically the resultant force on the worn part of the clearance face assuming the stress distribution on the contacting surface between the worn part of the clearance face and rock.According to the results obtained,the resultant force acting on the worn part of clearance face is as important as that on the rake face and cannot be neglected especially when the cutting tool which has a worn part on its clearance face is used,The theory developed here was considered in a plane state.If we make a strict comparison of the experimental results with the predictions,we must carry out the rock cutting test in two dimensional state or develop the theory which can be applied to the rock cutting in three dimensional state.
We have studied the effects of clearance between a bit and rock on percussive fracturing of rock . Since strain wave in a rod has periodecity, the form of strain wave does not change, when the clearane is increased by the amount corresponding to the time of the period. In this case, damping of the strain wave in the rod is neglected.Therefore, it is considered that by carrying out the experiment on the clearance corresponding to the time within first one period, the effect of any futher clearance can be estimated.Over the range of the clearance corresponding to the first one period, single-blow tests were carried out with pendulum-type impact rig. The weight of hammer and striking velocity were changed. As a rock specimen, granite was used.The results obtained are as follows;(1) Depth of crater into rock is approximately constant irrespective to the clearance. (2) For the clearance at zero, depth of penetration is produced only by tne first incident wave, but for the clearance grater than certain value, depth of penetration is procuced by 1st, 2nd, and 3rd incident waves and so on. Moreover, total depth of penetration by one blow of the hammer is approximately constant, being independent of the clearance.(3)Depth of crater has linear relationship with depth of penetration. From the results mentioned above, it is considered that depth of crater is not affected by the clearance, since the depth of penetration is independent of the clearance.
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