Induction Skull Melting

Rapid and cost effective melting and processing of reactive metals (e.g. Titanium, Zirconium and their alloys), super clean superalloys and other metals requiring low inclusion content can be provided by Consarc with the Induction Skull melting furnace system.

ISM: The Process

ISM is a method of melting metals in a segmented, water-cooled copper vessel, under vacuum or controlled atmosphere in an induction coil. This is done metal-to-metal, without a refractory lining. The copper crucible is made up of water-cooled segments or "fingers". The magnetic field produced by the coil, in effect, passes through the crucible to induce heat in the metal charge causing it to melt. The field also intensively stirs the liquid metal pool. A thin layer of metal remains frozen against the bottom of the crucible forming a skull. The low velocity boundary layer in the liquid adjacent to the skull, together with the skull itself and the interface (joint) between the skull and the crucible all serve as thermal resistances, reducing the heat conducted from the hot liquid into the cold crucible.

When the crucible, the coil, the frequency and the power level are all properly designed and matched, the sides of the liquid metal pool are pushed inwards, away from the interior side walls of the crucible. In effect, the sides of the pool are supported magnetically. The absence of physical contact with the side walls prevents the crucible segments from electrical shorting and further reduces the heat loss into the crucible. The process is most often used in casting with top or bottom pouring but it can also be used in ingot production. In this case, open-bottomed crucibles with a drawn down starter plug are used to slowly form an ingot from top fed charge material.

ISM: Advantages

For reactive metals which cannot be melted in a refractory crucible due to metal/crucible reactions, ISM offers a water cooled metal container which does not react with the melt. Unlike the alternative Vacuum Arc Skull Melting process which requires the charge to be in the form of an electrode, ISM can be charged with chunks, plates, turnings, high purity sponge or mixtures of these material forms. This greatly reduces the cost of the charge material
For super clean superalloys and other metals that are required to have a very low inclusion content, ISM eliminates the problem of inclusion pickup from the crucible
For degassing of the metal charge, volatilising of low vapour pressure impurities and pouring of gas-free castings, ISM can be operated in vacuum
For melting alloys with high vapour pressure alloying elements, ISM can be operated in an inert atmosphere at a pressure that eliminates or minimises alloy loss
A wide variety of alloys can be melted successively in the same crucible with no fear of chemical cross contamination
The intense stirring generated by the magnetic field fuses any high melting temperature charge components and homogenises the melt in both chemical composition and temperature. This translates into faster melt down, better mould filling (for castings) and a higher quality product
The elimination of the ceramic crucible eliminates the need for downtime due to crucible replacement, thereby increasing furnace productivity.

Configurations

Consarc can supply economical single chamber batch systems, twin chamber batch systems for higher productivity or multi-chamber designs with automated materials for high production and / or unique material handling constraints.

Induction Power Equipment

Power is supplied from a solid state Inductotherm induction power supply specifically designed to the correct supply the correct power and frequency for the ISM process. It is taken through the vacuum chamber by means of a sealed water-cooled coaxial rotary power feedthrough or power port assembly to the melting coil.

Static or Centrifugal Casting

Tilt pouring of the metal from the ISM crucible is a rapid process and moulds can be pouredin a static or centrifugal casting configuration. Centrifugal casting turntable systems are designed by Consarc to integrate into the chamber design for ease of mould handling.

Controls

All Consarc ISM installations are supplied with a fully integrated PLC and the option for PC SCADA based control systems for safe and efficient operation of the furnace. Remote control operation is also recommended for reactive metal melting and casting.