Induction Furnace

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• Article Title: Induction Furnace

Main > Digital Fabrication > RepLab Tools > Induction furnace

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Overview

An induction furnace is composed of an induction coil, alternating current power supply, and electrically conductive workpiece.

The 'primary' coil induces current in the 'secondary' workpiece through electromagnetism.

This current is converted to heat at a rate of VI=I²R.

The magnetic field does not induce a uniform current in a solid rod, but reduces and lags in phase towards the center. A parameter called reference depth d is used to determine the length at which the field strength is reduced to 1/e (37% compared to the surface).

Copper is often chosen as a material for the coil due to being a common metal with the lowest resistance.

Requirements

• Meets OSE Specifications
• Modular in power units of 5 or 10 kW
• Microcontroller-driven - ideally an Arduino brain with power elements

Details

The advantage of the induction furnace is a clean, energy-efficient and well-controllable melting process compared to most other means of metal melting. Most modern foundries use this type of furnace and now also more iron foundries are replacing cupolas with induction furnaces to melt cast iron, as the former emit lots of dust and other pollutants. Induction furnace capacities range from less than one kilogram to one hundred tonnes capacity and are used to melt iron and steel, copper, aluminium and precious metals. Since no arc or combustion is used, the temperature of the material is no higher than required to melt it; this can prevent loss of valuable alloying elements.[1] The one major drawback to induction furnace usage in a foundry is the lack of refining capacity; charge materials must be clean of oxidation products and of a known composition and some alloying elements may be lost due to oxidation (and must be re-added to the melt).

Operating frequencies range from utility frequency (50 or 60 Hz) to 400 kHz or higher, usually depending on the material being melted, the capacity (volume) of the furnace and the melting speed required. Generally, the smaller the volume of the melts, the higher the frequency of the furnace used; this is due to the skin depth which is a measure of the distance an alternating current can penetrate beneath the surface of a conductor. For the same conductivity, the higher frequencies have a shallow skin depth - that is less penetration into the melt. Lower frequencies can generate stirring or turbulence in the metal. A preheated, 1-tonne furnace melting iron can melt cold charge to tapping readiness within an hour. Power supplies range from 10 kW to 15 MW, with melt sizes of 20 kg to 30 tonne of metal respectively.

An operating induction furnace usually emits a hum or whine (due to magnetostriction), the pitch of which can be used by operators to identify whether the furnace is operating correctly or at what power level.

Development Notes

Read a commercial description of an induction furnace from Voltamptransformers

Read about 3-phase electrical power at its wikipage

Read about 3-phase electrical standards in north America at control.com forums

Product Ecology

Uses

• Universal Power Supply - Power

Creates

• Steel - GVCS (pretty much every machine depends on this)

See Product Ecologies for more information.

Components

• Induction Furnace Circuit
• Heat Dissipation System
• Coil
• Melt Chamber
• Feeder
• Crucible

Status

The Induction Furnace is currently in the research phase of product development.

Internal Links

• Spectrometer
• Foundry

External Links

• Wikipedia: Induction Furnace
• Wikipedia: Investment Casting
• Molten Oxide Electrolysis - carbon free process that goes directly from ore to pure metal with pure oxygen as a byproduct
• NASA's page on MOE
• Youtube: Better Metal from Bill Gates youtube channel
• Youtube: Donald Sadoway at EmTech MENA 2019: Steel Production without Co2 Emissions
• An Open Source Design for a 3kw Induction Heater

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