Key technologies of drilling process with raise boring method
2015-8-1 · In the downward reaming method, the pilot hole is the passage of the drill string and cuttings, thus the falling down of the cuttings can damage the drill string. In the upward reaming method, however, the pilot hole only serves as the passage of the drill string which needs small-diameter hole, so the drilling speed of the pilot hole is fast. (3)
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