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Positive mixers are always used when compounds need to be mixed and prepared in small quantities and in a relatively short time (up to approx. 3 min). For larger quantities, mixing times of approx. 5 min. will be required.

Plunger cylinders are “single-acting” cylinders, which are arranged vertically, and are operated by hydraulic, or more rarely pneumatic power. Lowering takes place under the weight of the lifted load. The piston rod is simultaneously the piston itself. The maximum stroke is limited by means of a turned ring at the lower end of the piston rod and a stop bush in the upper area of the cylinder sleeve. The sealing elements are installed in the cylinder sleeve.

A pellet is a ball made of fine-grained materials using bonding agents, rolled on a disc or in a drum to a diameter of 8 to 16 mm^[1]. A briquette, by contrast, is a pressed block.

References

1. de Lima, J. R. B.; Ribeiro, T. R.: Iron Ore Pelletizing Process: An Overview. In: Iron Ores and Iron Oxide Materials, IntechOpen 2018, DOI 10.5772/intechopen.73164, Balling Process section. Accessed 27 August 2026.

Heat recovery can only be practiced successfully with crucible furnaces to a limited extent, and only with great effort, depending on the system configuration.
As a rule, the temperature range of the cooling water lies between 30 and 65 °C. In practice, a temperature difference of about 27 K is common, independent of these range limits. Heating pumps work efficiently at approx. 80 °C. Above 72 °C, the limescale precipitates out of the cooling water, the water lines become clogged, and the water has to be treated accordingly. Practical applications include:

Treatment of washing water and heating of rooms in winter. With a 5-t furnace with 3,000 kW, approx. 810 kW of heat energy is absorbed by the cooling water (empirical value; coil and crucible wall losses, excluding the converter^[1]), which can only be used economically to a very small extent. There is a large number of engineering companies involved in the field of heat recovery. The furnace’s cooling water reaches 65 °C; the return temperature is limited to 72 °C because of limescale precipitation. Heat pumps only work economically at around 80 °C. A direct increase to a usable temperature is therefore not possible.

References

1. Herbert H. Netzel: Induktionsofenhandbuch. 3rd edition, Eigenverlag IES, Witten 2003, p. 222. Empirical value, not a manufacturer specification. In the section on cooling water quantities (p. 118), the same handbook gives 810 kW or 1,050 kW for the same example furnace, with different scope stated. We standardise on 810 kW (coil and crucible wall).

Optipour system is the optical casting system of the firm ABB, which measures the surface of a casting sump in the inlet funnel of a mould to be cast with an electronic camera, and then regulates the casting process in relation to the molten metal surface as determined by the camera. The casting process is stopped on reaching the specified filling level.

Ni hard cast iron is a martensitic, white cast iron alloyed with nickel and chromium for heavy-duty pump housings, pump pulleys, grinding components, rollers etc.

Multi-frequency is a designation of the firm of Junker referring to frequency switching during melting and carburisation.

Mould machines are devices for the production of sand moulds. They are divided into the following groups, according to the type of sand compression: (look next page)

a) Manual mould machines b) Vibrating mould machines c) Press mould machines
d) Stamp mould machines
e) Blast mould machines
f) Injection mould machines g) Slinger mould machines

Mould gases are released when casting the molten metal into the mould, and due to the oxygen in the air within the mould, are usually combustible and are seen as a gas flame.

Shell moulds consists of least 2 mould halves or shells, which are stabilised with filling sand and used in mould boxes. The shell moulds are machine-manufactered, and are used for casting materials that tend to penetration.