Download ME 401 (Summer 2012)

Induction Furnace
ME 401 (Summer 2012)
Professor Laura West
By: Brian Medema
Introduction:
There are a great many ways to heat metals to their melting points available to us today. Most,
however, rely on combustion of some form of hydrocarbon. These methods are well understood and
widely adopted throughout industrial and amateur communities. It is curious, however, that the
principle of electromagnetic induction is used in industrial practices, but rarely in amateur applications.
Electromagnetic Induction was first discovered by Michael Faraday in 1831 (Zinn, 1988). At its most
basic, Electromagnetic induction means that when an alternating current is passed through a coil of
wire, a voltage is induced in another coil concentric with the first. It would be many decades before the
industrial applications for melting metal would be developed based on this principle.
History:
During the second half of the 19th century, scientists searched for ways to melt metal using electricity.
Initial efforts led to resistive heating and electric arc furnaces (Mühlbauer, 2008). It wasn’t until 1887
that Sebastian de Ferranti proposed the first design for and induction furnace capable of melting metal
(Mühlbauer, 2008). At the time, the only sources of electricity capable of generating sufficient energy to
melt metal were generators, so research was aimed at the available 50/60 Hz sources.
F.A. Kjellin began improving on existing induction furnace designs in 1891, and in 1899 designed and
built the first useful induction furnace, capable of melting a single charge of 50 kg of steel at a time
(Mühlbauer, 2008). The furnace was built with a single-phase AC transformer, with the steel charge set
in a channel, acting as the secondary coil. Melting energy was 7,000 kWh/ton. Later designs greatly
increased efficiency. Kjellin’s 1903 design had a melting energy of 800 kWh/ton.
Designs for high frequency (HF) induction furnaces began appearing in 1916, partially enabled by
research in to radio transmission equipment (Mühlbauer, 2008). These designs additionally focused on
incorporating a crucible, and were thus called “coreless”.
Germany began broadly adopting induction furnaces in 1929. The first furnace had a 300 kg capacity
(steel) and operated at 150 kVA and 2000Hz. After 7000 runs, the engineers found their average crucible
life expectancy to be 80 runs (Mühlbauer, 2008).
Another important breakthrough was melting metal in a vacuum, something not possible in a
combustion-based furnace. E. F. Northrup built the first vacuum prototype in the USA in 1920
(Mühlbauer, 2008)
In 1959, ASEA became the leading company in the use of large induction channel furnaces with several
important technical advances, for many of which ASEA was awarded world-wide patents. The first
advance was a new channel inductor that could be removed and refurbished without interrupting
furnace operations for long periods of time. Another was an anti-sinter mass for grouting the cap
between the furnace and inductor (Mühlbauer, 2008).
Crucible furnaces also advanced after World War II. In 1964, Brown Boveri & Cie built a massive
induction crucible furnace at General Motors central foundry in Michigan, with a holding capacity of 60
tons and 21 megawatts of maximum power (Mühlbauer, 2008). During this period, car manufacturers
greatly increased their demand for iron, and induction crucible furnaces became the dominant type of
furnace, able to achieve power densities of 300-350 kW/ton (Mühlbauer, 2008). These power densities
were much higher than what Cupola furnaces were capable of at the time, which in turn meant faster
melt times.
Industrial usage
Induction furnaces have the ability to create high heat intensity very quickly at specific locations on a
part (Rudnev, 2003). This allows for high productivity and consistent quality. Induction furnaces also
have very high efficiency on a purely mathematical level, and in themselves do not produce carbon or
pollutants (of course, that says nothing of the source of the electricity). Combining these advantages
with the ability to melt metal in a vacuum and thus avoid oxidizing the metal, induction furnaces present
a very attractive face to industrialists. Further advantages include easy automation, high reliability and
easy maintainability of the equipment (Rudnev, 2003). Today, Induction furnaces are used for (Zinn,
1988):







Preheating prior to metalworking
Heat treating
Melting
Welding, Brazing and soldering
Curing a coating
Adhesive bonding
Sintering
Home-builts
While Induction furnaces are one of the most popular choices for large-scale industrial applications,
hobbyists and home-builders seem to have been avoiding the technology in favor of combustionpowered furnaces. And it’s hard to blame them for doing so. Charcoal, oils and propane are easily
sourced, cheap, and familiar to anyone who has operated a barbecue. Additionally, for all but the most
miniscule amounts of metal, a standard wall outlet simply does not supply adequate power, and many
people have a healthy respect for 220V power sources.
Nonetheless, there are a few brave men who have constructed their own do-it-yourself induction
furnaces and posted about their experiences online.
The first is Tim Williams. Williams started with a proof of concept built from spare parts (the inductor
coil is wrapped around a used solder spool) and a circuit thrown together on a breadboard.
(Williams, 2009)
Later on, Williams proceeds to develop a coil of copper tubing, pumping water through the tubing to coil
the coil.
(Williams, Induction Heating, Part Five, 2009)
Williams also developed and built all his own electronics, including power supply, oscillator and control
circuits, and packaged them in a nice case:
(Williams, Induction Heating, Part Five, 2009)
Another home-built can be found at http://www.instructables.com/id/30-kVA-InductionHeater/?ALLSTEPS, constructed by “bwang”.
Hazards
While induction furnaces have many advantages, as outlined above, they retain all the dangers of
working with molten metal and require careful use by the operator. In addition, induction furnaces carry
an electrical hazard, operating with large currents. In the case of home-builts, extra care must be taken
to ensure current is safely insulated from anything the operator might touch or come in contact with.
Conclusion
Induction furnaces play a very important role in industry, and are unlikely to be replaced any time soon.
There is certainly room for induction furnaces amongst amateurs, but it is very easy to be scared off by
the circuitry and large amounts of electricity required. Most hobbyists would probably rather stick to the
familiarity of charcoal or propane.
Works Cited
Williams, T. (2009). Induction Heating, Part Five. Retrieved July 26, 2012, from Electronics:
http://webpages.charter.net/dawill/tmoranwms/Elec_IndHeat5.html
Mühlbauer, A. (2008). History of Induction Heating and Melting. Vulkan-Verlag GmbH.
Rudnev. (2003). Handbook of Induction Heating. CRC Press.
Williams, T. (2009). Induction Heating. Retrieved July 26, 2012, from Electronics:
http://webpages.charter.net/dawill/tmoranwms/Elec_IndHeat1.html
Zinn, S. a. (1988). Elements of Induction Heating: Design, Control, and Applications. ASM International.