The Effects of Clearance between a Bit and Rock on Percussive Fracturing

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  • フィードクリヤランスが岩石破砕におよぼす影響について
  • フィードクリヤランス ガ ガンセキ ハサイ ニ オヨボス エイキョウ ニ ツイテ

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We have studied the effects of clearance between a bit and rock on percussive fracturing of rock.<BR>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.<BR>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.<BR>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.<BR>The results obtained are as follows;<BR>(1) Depth of crater into rock is approximately constant irrespective to the clearance.<BR>(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.<BR>(3) Depth of crater has linear relationship with depth of penetration.<BR>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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