螺旋钻杆：冷拉一次成型叶片，不退火，韧性好，耐用。
Spiral drill pipe: Cold-drawn forming a blade, anneal, good toughness, and durability.
滚丝轮螺纹和钻杆螺纹的螺旋角有误差。
Secondly there is error between the thread roll angles of thread rolling die and drill rod.
通过分析长螺旋钻机在切削各类土质时，钻具的角速度与土块运动机理关系，提出确定钻具临界的方法，而工程施工中钻杆的实际转速应大于临界转速，以提高钻机的工作效率。
An analysis related to various kinds of soil cutting by earth auger, this paper puts forward that running speed of frill should be faster than critical speed so as to increase the efficiency of drill.
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