Abstract: An induction furnace includes an induction coil, an electrically non-conductive crucible having an inner diameter disposed within the induction coil, and an electrically conductive member disposed below the crucible and having an outer diameter which is further from the induction coil than is the inner diameter of the crucible. Due to the non-conductive nature of material disposed within the crucible at lower temperatures, the induction coil initially inductively heats the conductive member, which transfers heat to the material to melt a portion of the material. Once the material is susceptible to inductive heating (usually upon melting) the susceptible material is inductively heated by the induction coil. During the process, inductive heating of the material greatly increases as inductive heating of the conductive member greatly decreases due to low resistivity of the molten material and due to the molten material being closer to the coil than is the conductive member.

Abstract: An induction furnace includes an induction coil, an electrically non-conductive crucible having an inner diameter disposed within the induction coil, and an electrically conductive member disposed below the crucible and having an outer diameter which is further from the induction coil than is the inner diameter of the crucible. Due to the non-conductive nature of material disposed within the crucible at lower temperatures, the induction coil initially inductively heats the conductive member, which transfers heat to the material to melt a portion of the material. Once the material is susceptible to inductive heating (usually upon melting) the susceptible material is inductively heated by the induction coil. During the process, inductive heating of the material greatly increases as inductive heating of the conductive member greatly decreases due to low resistivity of the molten material and due to the molten material being closer to the coil than is the conductive member.

Abstract: An induction furnace having a voltage source series inverter, a load circuit having a combination of an induction coil and a resonating capacitor bank, and control circuitry to phase lock the inverter frequency to the natural resonant frequency of the load. The capacitor bank can be divided into two groups, one across the output of the inverter and the other in series with the load. This arrangement allows for the division of the inverter voltage across the furnace coil according to the ratio of the two capacitances. The inverter uses pulse width modulation and is buffered from the load circuit by means of a small series connected inductor. Additionally, the system can have a common power supply system that supplies power in any desired proportion to a plurality of induction furnaces.

Abstract: A system for melting metal and holding molten metal, comprises a rectifier unit receiving AC electric power and outputting DC electric power, a plurality of inverter units, each receiving the DC electric power output by the rectifier unit and outputting AC electric power; and a plurality of induction furnaces each receiving the electric power output by a respective inverter unit. Each inverter unit comprises a plurality of inverter modules connected in parallel, each module independently being connectable to and disconnectable from the rectifier unit and the furnace. The rectifier unit comprises a plurality of rectifier modules connected in parallel, each module independently being connectable to and disconnectable from the AC supply and the inverter units.

Abstract: In a process for the operation of coreless induction melting and/or holding furnaces--in which there results in the melting operation at a relatively high induction frequency (as compared to the mains frequency) a slight stirring motion in the melt, but a high degree of effectiveness for the melting process, and in the melting and holding operation at a correspondingly lower induction frequency there results a greater stirring motion in the melt, but a lower degree of effectiveness for the melting process--it is provided that at least one capacitor switched in parallel to the induction coil(s) is provided, which capacitor(s), together with the induction coil(s), form a resonant circuit; and that in the transition from the melting operation with slight stirring motion in the melt to the melting or holding operation with greater stirring motion, or in the reverse transition, the capacitor capacitance and/or the inductance present in the resonant circuit is increased, or as the case may be, decreased.

Abstract: A multi-furnace control system selectively delivers preselected percentages of available power to furnaces of the system, preferably designated as either a melt furnace or a hold furnace. The power supply delivers power to both furnaces. A capacitor station in parallel connection to the power supply and the furnaces is tuned to form a tank circuit therewith. Switches control the selected power delivered to the furnaces respectively and control the delivery of a first portion of the power for holding molten product in the hold furnace as the master control. A remaining portion of the power is then delivered for melting product in the melt furnace. The capacitor station acts as a reactive tank for both furnaces.

Abstract: Nuclear fuel rod tubes of zirconium alloy are heat treated in an induction furnace to produce a protective oxide coating two to fifteen microns in thickness. The furnace is only slightly larger than the tubes and receives the endmost eight inches of the tube. The furnace is controllable in zones along the tube. To calibrate the furnace to produce the desired temperature profile, typically a flat profile at a temperature between 650.degree. and 750.degree. C..+-.1.5.degree. C., a temperature calibration probe is provided with spaced thermocouples for sensing the temperature developed in the probe at each of the zones when heated. The probe is made of inconel 600 stainless or the like, and is dimensioned and shaped to correspond closely to the dimensions of the fuel rod tubes, including having a closed chamfered end. At the opposite end the probe protrudes from the furnace, where the thermocouple leads are terminated. The leads pass through a potting compound in the probe, such as magnesium oxide.

Abstract: Improved and simplified measurement of the level of molten metal in a crucible heated by an induction coil utilizes a variable frequency power supply for the induction coil. Power supply frequency is changed to maintain the power provided to the coil substantially constant, independent of variations of power factor in the coil circuit. Detection of the frequency of power supplied to the induction coil provides an indication of the changes in power factor of the coil due to changes in the level of molten metal surrounded by the coil, and thus of the level of the molten metal.

Abstract: Disclosed is a method for measuring the extent of slag deposit buildup in the channel of a channel induction furnace during operation. The method comprises measuring an initial temperature rise factor in the furnace at a time when no slag deposits are present, measuring a subsequent temperature rise factor in the furnace after the furnace has been in operation for a period of time, correcting the subsequent temperature rise factor for any changes in the operating temperature and power levels applied to the furnace which may have taken place between the time of the measurement of the initial temperature rise factor and the time of the measurement of the subsequent temperature rise factor, and determining a quantity which is indicative of the extent of slag deposit buildup in the channel from the difference between the initial and subsequent temperature rise factors.