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Temperature loss is given in K/h for a completely filled crucible and with the electrical output switched off. Smaller furnaces have higher temperature losses than large furnaces. In a 1-t furnace at 1,450 °C, this will produce a figure of approx. 50 K/h and for 12 t approx. 30 K/h. These figures apply for a fully heated crucible and completely closed furnace cover, with the exhaust gas extraction switched off.

Synthetic iron is a term for cast iron produced from steel scrap with the addition of carbon and silicon.

Sump melting is as a rule practiced in mains frequency induction furnaces, The optimum sump height corresponds to approx. 2/3 of the filling level, since in this case the whole coil is filled with molten metal, and the maximum electrical / inductive coupling is available. Medium-frequency furnaces are operated with a sump of approx. 15% of the total capacity. After tapping a medium-frequency furnace, the sump is still at a relatively high temperature. When switching on the output again after charging, the remaining sump would be very well coupled, and would be over-heated for a short time. This produces an “elephant’s foot” as is normal in mains frequency furnace operation. To avoid this, approx. 30% of the sump weight charged into the sump should consist of compact cooling scrap (risers, sprues and approx. 100 mm large pieces). In larger furnaces (from approx. 5 t), a “starter block” with a weight of approx. 30% of the sump weight can also be charged in. This simultaneously lowers the temperature, raises the bath level and reduces the wear to the crucible wall.

A sump is the technical term for molten metal in a melting furnace or a ladle which is not emptied, but is reused.

Storage is the term for the “storage” of a melt in a storage or holding furnace, which can take the form of a channel or crucible storage furnace. When storing GGG, special attention must be paid to the magnesium melting loss, so that the cooling of the magnesium content does not get out of control.

A stopper ladle is a casting ladle with bottom emptying, which can be emptied by raising the stopper rod. Alternatively, a swivelling stopper can also be used.

Stoppers are used for sealing off the tapping hole of cupola furnaces. The material used is graphite clay. For sealing off a stopper ladle, a stopper is screwed to the stopper rod that seals off the outlet hole.

Steel crucible furnaces are crucible furnaces that work with a crucible made of welded or cast steel. Steel crucibles are used for non-ferrous metals and as a rule for special applications. The most common application is the melting of recycled magnesium.

Starter rings can be used as a substitute for starter blocks. The outer diameter is approx. 100 mm less than the crucible diameter, and the inner diameter of the rings is approx. 200 mm less than the outer diameter. The use of such rings was recommended in the 1970’s for mains frequency furnaces with crucible diameters > 1,000 mm for sinter charging. The first ring was placed on the crucible cone; distance pieces 50 mm thick and about 100 mm long and wide were then placed at three places around the circumference of the ring. The next ring was then placed on top of these parts. This procedure was repeated up to the upper edge of the induction coil. Compact scrap can also be filled in inside the rings right up to the top. Due to the good coupling, this ensures very even heating of the rings, and thus also of the ramming template and ramming mix. Dry mixes were heated at approx. 100 K/h. When semi-plastic mixes with up to 4% moisture were used, the temperature increase was reduced to 50 K/h. This allowed even drying by means of the ramming template on the crucible wall. This process was however discontinued at the end of the 1970’s for cost reasons. The starter rings were made from approx. 80/100 mm thick steel plates. One customer in Finland cast the rings from scrap iron.

Spinel is an aluminous mineral with the chemical formula MgO·Al₂O₃ for genuine spinel.