Vacuum induction melting (VIM) utilizes electric currents to melt metal within a

vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often di ...

. The first prototype was developed in 1920.

Induction heating Induction heating is the process of heating electrically conductive materials, namely metals or semi-conductors, by electromagnetic induction, through heat transfer passing through an induction coil that creates an electromagnetic field within th ...

induces eddy currents within conductors.

Eddy current Eddy currents (also called Foucault's currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction or by the relative motion of a conductor in a magnet ...

s create heating effects to melt the metal. Vacuum induction melting has been used in both the aerospace and nuclear industries.

History

The process was invented in Hanau, Germany in 1917.

Heraeus Vacuumschmelze Heraeus is a German technology group with a focus on precious and special metals, medical technology, quartz glass, sensors and specialty light sources. Founded in Hanau in 1851, the company is one of the largest family-owned companies in German ...

and Dr.

Wilhelm Rohn Wilhelm may refer to: People and fictional characters * William Charles John Pitcher, costume designer known professionally as "Wilhelm" * Wilhelm (name), a list of people and fictional characters with the given name or surname Other uses * Mount ...

applied for a patent on vacuum melting on 12 January 1918 and were granted a German patent DE 345161.Patent DE 345161, Vacuumschmelze and Dr. Wilhelm Rohn, Verfahren zum Vakuumschmelzen und Vergueten von Metallen und Legierungen, priority date 12 January 1918, published 12 June 1921.

Edwin Fitch Northrup Edwin Fitch Northrup (born February 23, 1866 – May 13, 1940) was a professor of physics at Princeton University from 1910 to 1920. He was affiliated with the Leeds & Northrup for about seven years. He studied at Amherst College and the Johns Ho ...

built the first prototype of a vacuum induction furnace in the United States of America in 1920. Medium frequency furnaces were seen soon afterwards in England and Sweden in 1927. The process was initially developed to refine certain special metals such as

cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...

and

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow ...

. As these metals and alloys became more common, the process of VIM became more widely used. VIM now helps to melt a variety of metals for aircraft and nuclear applications.

Procedure

: VIM involves placing a core-less induction furnace into a vacuum chamber.http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=TRD&recid=8512511577MD&q=vacuum+induction+melting&uid=792184177&setcookie=yes The melting and casting operations are carried out at low pressures to control the entire alloy chemistry process.

Uses

VIM is used in particular for producing alloys with melting points beyond those practical for other kinds of melting. Nickel, nickel-iron, and

superalloys A superalloy, or high-performance alloy, is an alloy with the ability to operate at a high fraction of its melting point. Several key characteristics of a superalloy are excellent mechanical strength, resistance to thermal creep deformation, g ...

are frequently produced using this process. The VIM process is often used for small batch sizes and allows for a high level of control over the composition of the alloy. There is low environmental contamination (dust etc) and oxidation, while elements that are often undesired such as hydrogen or nitrogen can be removed from the process.

References

{{Reflist Metallurgical processes