Vacuum induction melting

Vacuum induction melting (VIM) uses an electric current to melt metal in a vacuum.The first prototype was developed in 1920. Induction heating induces eddy currents in the conductor.The eddy currents create a thermal effect to melt the metal.Vacuum induction melting has been used in the aerospace and nuclear industries.

Program

VIM involves placing a coreless induction furnace in a vacuum chamber.Melting and casting operations are performed at low pressures to control the overall alloy chemistry.

Uses 

VIM is particularly useful in the production of alloys with melting points in excess of those practical for other smelts.Nickel, nickel-iron and superalloys are often produced using this process.The VIM process is typically used for small batch production and allows a high degree of control over the alloy composition.Environmental contamination (dust, etc.) and oxidation are low, while normally unwanted elements such as hydrogen or nitrogen can be removed from the process.

Aluminium smelting

Aluminum smelting is the process of extracting aluminum from alumina, usually using the Hall-Héroult process.Alumina is extracted from the ore bauxite by the Bayer process at alumina refineries.It is an electrolytic process, so aluminum smelters consume a lot of electricity; smelters tend to be located close to large power stations, usually hydroelectric, to keep costs down and reduce the overall carbon footprint.Smelters are usually located near ports as many use imported alumina.

Layout of an aluminium smelter

The Hall-Héroult electrolysis process is the main production process for primary aluminum.The electrolytic cell is made of a steel shell with a series of refractory insulating linings.The battery is contained and supported by a brick-lined outer steel case.Inside the casing, the cathode blocks are bonded together by tamping.The top liner is in contact with the molten metal and acts as a cathode.The molten electrolyte remains hot inside the battery.Prebaked anodes are also made of carbon in the form of large agglomerates suspended in the electrolyte.A single Soderberg electrode or multiple prebaked carbon blocks are used as the anode, while the main recipe and the basic reactions that take place on its surface are the same.An aluminium smelter consists of a large number of cells (pots) in which the electrolysis takes place.A typical smelter contains anywhere from 300 to 720 pots, each of which produces about a ton of aluminium a day, though the largest proposed smelters are up to five times that capacity.Smelting is run as a batch process, with the aluminium metal deposited at the bottom of the pots and periodically siphoned off.Particularly in Australia these smelters are used to control electrical network demand, and as a result power is supplied to the smelter at a very low price.However power must not be interrupted for more than 4–5 hours, since the pots have to be repaired at significant cost if the liquid metal solidifies.