Induction furnaces are convenient and safe except for one problem;
If molten metal reaches the coils there is tremendous steam explosion which can result in fatal injuries and great expense.
Electrical detection of metal via the spider and the coil give warning, usually in time to stop an explosion, but usually too late to prevent extensive damage.
The coils are normally encapsulated in high alumina refractory, then a parting layer of millboard or mica paper is placed over them, and a dry spiking refractory rammed firmly into place with a metal former for the inside.
Instead of millboard or mica paper, we offer graphite paper. Graphite paper is electrically conductive, and it must never touch the coils.
It is an excellent parting agent, and since it has a low coefficient of friction it assists compaction of the rammed mass. It is fitted in contact with the spider, but not the coils. The spider can now detectmetal contact before the metal even reaches the coil coating, and the furnace can be shut down before any damage is done. The rammed lining comes out easily and the coil coating is unharmed. Usually the graphite paper can be reused several times.
Graphite paper comes in rolls 1metre wide and 1mm thick. It is very flexible. If you close off the outside of the coils, you can make a former for the graphite paper and pour Keratab Ultrafine between the coils. Keratab Ultrafine is a powder which flows like thick cream when mixed with +16% water. It contains 93% alumina.
Graphite paper may not be used as a continuous sheet next to the coils,as it will heat up by induction. It is therefore supplied in sheets consisting of 100mm strips joined with tape such that the strips of graphite are 10mm apart. The paper must be installed with the graphite strips aligned vertically, to avoid inductive heating.
See also Induction Coil Coating and Keraplas.