Induction Melting: Stirring Molten Metal Bath in 1000lb Furnace

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Discussion Overview

The discussion revolves around the phenomenon of not experiencing electric shock while stirring the molten metal bath in a 1000lb induction furnace, specifically focusing on the electrical properties and behavior of the molten metal and the equipment used.

Discussion Character

  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions why they do not feel shocked when stirring the molten metal bath, noting the use of an alumina crucible.
  • Another participant inquires about the potential difference (voltage) between the stirrer and ground.
  • A participant mentions using a metal stick to stir but is uncertain about the voltage involved.
  • It is proposed that stirring the melt only connects to one part of the circuit, and without a return path through the person, there is no shock. The voltage difference is suggested to be minimal due to the high conductivity of the melt.
  • The concept of skin effect at the induction oscillator frequency is introduced, explaining that eddy currents flow only on the surface of the melt, with the center remaining cooler. Stirring is described as a method to mix the hotter surface with the cooler interior to enhance melting efficiency and reduce heat loss.

Areas of Agreement / Disagreement

Participants present various viewpoints on the electrical behavior of the molten metal and the effects of stirring, but there is no consensus on the exact reasons for the lack of shock or the specifics of the voltage involved.

Contextual Notes

There are unresolved aspects regarding the exact voltage measurements and the implications of the skin effect on the heating of the melt, as well as the assumptions about the electrical circuit involved.

Bladestein
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Why am I not shocked when I stir the molten metal bath of a 1000lb induction furnace? Alumina crucible used.
 
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What is the potential difference (Voltage) between your stirrer and ground?
 
Not sure. I am physically using a metal stick to stir.
 
Bladestein said:
Why am I not shocked when I stir the molten metal bath of a 1000lb induction furnace? Alumina crucible used.
An induction furnace heats the conductive melt by inducing eddy currents. Those eddy currents circulate within the melt. When you stir the melt you are only making one connection to the fully contained circuit. There is no return path through you. If you used two metal stirrers, one in each hand, you would be subjected to a voltage difference. That voltage would only be a couple of volts because the melt is highly conductive.
Skin effect at the induction oscillator frequency will result in the eddy currents only flowing in the surfaces of the melt. The central part will only be heated by the hot surface. You stir it to get the hot surface inside and the cold centre outside which speeds up the melting while reducing heat loss.
 

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