Vacuum induction melting was originally developed for processing of specialised and exotic alloys and is consequently becoming more commonplace as these advanced materials are increasingly employed. While it was developed for materials such as superalloys, it can also be used for stainless steels and other metals.
The Vacuum Induction Melting Process
As the name suggests, the process involves melting of a metal under vacuum conditions. Electromagnetic induction is used as the energy source for melting the metal.
Induction melting works by inducing electrical eddy currents in the metal. The source is the induction coil which carries an alternating current. The eddy currents heat and eventually melt the charge.
Vacuum Induction Melting Furnaces Furnace
The furnace consists of an air-tight water-cooled steel jacket, capable of withstanding the required vacuum for processing. The Metal is melted in a crucible housed in a water-cooled induction coil and the furnace is typically lined with suitable refractories.
The molten metal may be poured/cast either under vacuum or inert gas environments.
Other features found in some furnaces (depending on size) may include:
• Tilt and pour mechanisms
• Casting chambers
• Sampling ports
• Mould handling facilities for automated and semi-automated processing, sometimes incorporating vacuum interlock systems.
What Materials are Processed in Vacuum Induction Furnaces?
Metals and alloys that have a high affinity for gases, in particular nitrogen and oxygen are often melted/refined in vacuum induction furnaces to prevent contamination/reaction with these gases. Thus, the process is generally used for processing of high purity materials or materials with tight tolerances on chemical composition.
How Can Impurities be Removed?
Melt chemistry can be controlled and manipulated by removing impurities. These can be removed using processes such as chemical reaction, dissociation or floatation.
What is Vacuum Induction Melting Used For?
Some applications of vacuum induction melting are:
• Refining of high purity metal and alloys
• Electrodes for remelting
• Master alloy stick for processes such as investment casting
• Casting of aircraft engine components