Differential heating of upset ends of oil country tubing by induction heating.

摘要

The induction preheating means and methods of the present invention include a furnace for selectively preheating certain portions of irregularly shaped work objects prior to heating to a final uniform temperature in another furnace. The method includes selectively controlling the intensity of the induction magnetic field to provide magnetic field portions of higher intensity adjacent those portions of work objects tending to absorb less energy and magnetic field portions of lower intensity adjacent those portions of the work object tending to absorb energy at a higher rate. The method and means of the present invention are used to achieve substantially uniform temperatures in irregularly shaped work objects after final heating in a main heating furnace.