System and method for induction heating a helical rotor using a coil
Embodiments of the invention provide a system and method for induction heating a helical rotor of a progressing cavity pump in order to reduce the surface roughness of the rotor. In order to heat the rotor most evenly, it is desired to space the coil as closely around the rotor as possible. The invention provides a mechanism for threading the helical rotor through an induction coil having an interior diameter which is less than the major diameter of the rotor. The induction coil may include one loop and overlapping ends. The rotor to be heated is rotated about its longitudinal axis and advanced axially through the coil as it rotates. The axial speed and rotational speed are synchronized so that the rotor moves one pitch through the coil for each complete rotation.
1. A method for induction heating, the method comprising the steps of:
radiating a magnetic field from a helical induction coil onto a helical rotor having a minor diameter, a major diameter and a pitch length, the helical coil having at least one loop with overlapping, adjacent ends, the loop having an inner diameter which is greater than the minor diameter of the helical rotor and smaller than the major diameter of the helical rotor;
placing the helical rotor within the loop and maintaining a gap between the helical rotor and the coil;
rotating the helical rotor about its longitudinal axis within an inner circumference of the induction coil at a speed of rotation;
advancing the helical rotor axially through the induction coil at a speed of advance; and
synchronizing the speed of advance with the speed of rotation such that the helical rotor advances one pitch length for each complete rotation.
2. The method of claim 1 , further comprising the step of providing an axial spacing between the overlapping ends such that an inner surface of the coil substantially matches an exterior shape of the helical rotor.
3. The method of claim 1 , further comprising adjusting the placing of the helical rotor within the inner circumference of the coil, by adjusting the gap of the helical rotor from the overlapping ends in relation to the pitch length.
4. The method of claim 3 , wherein the step of adjusting comprises progressively decreasing the gap between the rotor and the overlapping ends for rotors of increasing pitch length, and progressively increasing the gap between the rotor and the overlapping ends for rotors of decreasing pitch length.
5. The method of claim 4 , further comprising the step of providing an induction coil with a circular waveguide for shorter pitch rotors and with a rectangular waveguide for longer pitch rotors.