Method and apparatus for uniform induction heating of an elongated

Abstract

Method and apparatus for uniformly heating a workpiece such as a sucker rod or the like having a uniform cross-section over a major portion of its length and an enlargement adjacent each end thereof. A multi-turn inductor is coaxially disposed around a portion of an elongated workpath with the rod being longitudinally moved at some preselected rate of travel along the workpath toward the inductor entrance end. The inductor is normally at a first level of energization adapted to inductively heat the rod major portion to some predetermined temperature as it passes through the inductor. Sensing a preselected power absorption level by the rod as the enlargement adjacent the leading end is inductively coupled with the inductor causes the inductor to be automatically placed at a second, higher level of energization for heating the enlargement to the predetermined temperature. The inductor then automatically returns to the normal level of energization after some predetermined time interval for inductively heating the rod major portion. As the enlargement adjacent the rod trailing end is placed in an inductively coupled relationship with the inductor, the predetermined power absorption level increase is again sensed and the inductor is automatically switched to the higher level of energization. The inductor energization levels and the power absorption level sensing capabilities are adjustable to accommodate different rod and feed characteristics.