Gold Levitation with induction melting

Application: Special Induction Heating Applications

Application Objectives: An academic research customer, who already operated a levitation system and coil for aluminum, required a new coil, designed for levitation melting of 1 g of gold. They approached UltraFlex Power Technologies to create a simulation model for this kind of levitation melting before committing to a new coil. Main goal was to study the effects of frequency and electrical conductivity (skin depth) and the effects of different shapes of the load.

The challenge: To prove software simulations are as close as possible to reality

Equipment: UltraHeat S2 Series – SMT-2/200 + Levitation custom coil

Materials:

Gold Sphere
- Diameter – 4.66 mm
- Volume – 5.29*10-8 [m3]
Cylindrical part
- Diameter – 2 mm
- Height – 16.3 mm

Process:

The tests revealed that a spherical gold piece performed better in the simulations. Across the coil currents tested, the sphere reached steady state more quickly and coupled better with the coil. This resulted in higher dissipated power, a greater temperature rise, and more efficient heating.

On the other hand, a cylindrical gold piece with a diameter of 2 mm and a height of 16.3 mm showed insufficient coupling to the coil. This led to low power and made it difficult for the cylinder to levitate. In addition, the strong temperature dependence of gold’s electrical conductivity reduced levitation stability.

Based on these findings, the gold piece should be as close to spherical as possible for better levitation and heating efficiency. Higher frequencies are also suggested for better control of the levitation process. Moreover, special attention should be given to the thermo-physical properties of the material, as they can significantly impact the simulation results.

Results and Conclusions:

The geometric shape of the gold piece is critical for successful levitation. Spherical shapes perform better, while “electromagnetically” thin bodies have worse coupling to the coil. The electrical conductivity of gold changes significantly with temperature, affecting levitation stability. It is recommended that the gold piece be as close to a sphere as possible.

The effects of melting were not simulated due to geometric changes. Higher frequencies are recommended for better control, and the Lorentz force can be regulated by the coil current.

The practical tests done by the customer with the new coil proved that the simulations were over 90% consistent with the real behavior of the gold samples.

Reference Info: AR 3464-9220

Pictures