But movement mode of screw pump is rotating motion.Bearing force mode of rod has been changed from tensile to torsional.So,the threadless rod is often generated fracture and trip.

• 应用到螺杆泵上以后,主要的运动方式是旋转运动,承力方式也由抗拉变成抗扭,使用以前的平扣抽油杆经常出现断脱现象。