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Furnace lining is the term for the fireproof cladding of a furnace for the melting of metals.

See also

• Fireproof – the material property a furnace lining must meet
• Lining – special case of refractory lining for the induction furnace

Efficiency describes the relationship between the net and gross output. For 1 t of grey cast iron, approx. 390 kWh of energy are theoretically required (melting and superheating to 1,500 °C). In a well-designed crucible furnace, at the tapping temperatures usual in foundries (approx. 1,450 to 1,500 °C), around 520 kWh/t are required, depending on the construction features and capacity of the furnace.^[1] This corresponds to an overall efficiency of around 0.75. Due to the optimum design of a furnace with regard to its heat losses and economical dimensions, this gives a ratio of 1.13:1 between active induction coil length and coil diameter.

The purely electrical efficiency level depends on the coil length or height. With the same crucible capacity and same electrical output, this can be explained by means of 3 versions of a 13-t crucible furnace. The crucible wall thickness is in this case 140 mm. If one considers the magnetic field and the lines of flux in a completely molten furnace, there is a transverse field at the upper and lower end of the coil, and a longitudinal field in the centre of the coil. At the same electrical output, the sectors of the transverse fields are of equal length, i.e. with a coil length of approx. 1,300 mm there are transverse fields each of approx. 300 mm at top and bottom, and a 700 mm longitudinal field in the centre. These assumptions give an efficiency level of approx. 75%.

If the coil length, for the same crucible capacity within the coil of 10 t, is changed, this gives, in the case of a reduction to approx. 1100 mm coil length, a transverse field at top and bottom of 300 mm each and a longitudinal field of 500 mm, resulting in a theoretical electrical efficiency level of approx. 69%.

In case of the extension of the coil to a height of 1,700 mm, this would give a longitudinal field of approx. 1,100 mm and an electrical efficiency level of approx. 81%.

References

1. Dr. Erwin Dötsch (ABP Induction Systems GmbH): Induktionsofentechnologie und Energieeffizienz (induction furnace technology and energy efficiency). GIESSEREI 06/2011, published on guss.de (Bundesverband der Deutschen Gießerei-Industrie e. V.): specific enthalpy 390 kWh/t for melting and superheating cast iron to 1,500 °C, grid energy demand 520 kWh/t at 75% overall efficiency, practical melting operation 560 to 650 kWh/t. Accessed 27 August 2026.

Erosion is the carrying away of material from the surface of components, due to the action of liquids, vapours or gases flowing past them.

References

1. Herbert H. Netzel: Induktionsofenhandbuch. 3rd edition, Eigenverlag IES, Witten 2003, p. 48.

Mould weights are weights of cast iron, which are placed on top of sand moulds ready for casting, in order to counteract the upward pressure of the casting mould.

Frequency converters are frequency converters which create an oscillating circuit without rotating parts via a combination of a condenser and a choke. In the case of so-called triductors, 3-fold mains frequency, and quinductors, 5-fold mains frequency, the 3-fold or 5-fold mains frequency is generated as the operating frequency direct from the mains frequency with a converter efficiency level of approx. 0.94. Modern converters have an efficiency level of 96%, and generate the required operating frequency of approx. 70 – 10,000 Hz via a rectifier.

These converters are equipped with a rectifier, which generates a DC intermediate circuit from the 3-phase rotary current by means of thyristors or diodes, fed via a controlled rectifier bridge. A direct current smoothing is incorporated between the rectifier and the inverter as an intermediate circuit. After the choke comes the adjustable inverter, which automatically generates the corresponding operating frequency in relation to the inductivity of the furnace, the capacity of the condenser bank and the power consumption. These are referred to as load-controlled converters, which are known as “A” parallel or “B” series oscillating circuit converters, depending on the condenser switching.

A: high current between furnace and condensers only

B: high current in the complete furnace circuit

Charging usually refers to the filling of a casting furnace with the materials to be melted. For small furnaces with a capacity of up to 1 t, charging can be carried out by hand. For larger furnaces, mechanical lifting equipment is used.

Melting loss refers to metal losses which occur during melting mainly as a result of oxidation or vaporisation. The oxides form part of the slag, and are then removed with them from the melting bath. The melting loss is therefore defined as the weight difference between the cold metal charge and the finished melt available in the furnace. In case of charges made up of small pieces, such as chippings and fine stamping waste, the melting loss is higher than for compact scrap. For the same overall weight of the charge, the surface area of the charge material (chippings) is many times that of compact scrap.

Decay refers to the loss of alloy elements. The loss of magnesium content during storage and casting of nodular cast iron in larger containers is the most frequent application of the term decay.

Extraction systems are generally specified for the operation of induction furnaces. In the case of crucible furnaces, so much smoke and dust is created directly in front of the furnace when charging and producing nodular cast iron that extraction systems are essential. For a 5-tone furnace, an integral hood extraction system with cover is required with an extraction capacity of approx. 10,000 Nm3/h. In the case of a separate hood, which is swung over the furnace, approx. 15,000 Nm3/h and corresponding flow speed measures must be taken.

Skimming is generally carried out after reaching the tapping filling level. In most cases, a slag forming agent is applied to the bath, and then removed with manual equipment or pneumatic slag removers.
The tools used must be treated in advance with blackening to facilitate subsequent removal of the slag. Tools must be heated and dried over the bath before immersion in the liquid melt.