Earth shorting is an insulation fault between construction elements carrying voltage and those connected to earth or the melting bath earthed by means of the bottom electrodes.
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Differential cylinders
Differential cylinders are “dual-acting” cylinders, i.e. both ends can be subjected to pressure in order to carry out movements. Unlike a synchronizing cylinder, the piston rod sits on only one side. This creates two working areas of different size: the full piston area and the smaller annulus area on the rod side. The ratio of the two areas is called the area ratio Φ. Because of this, the cylinder retracts faster than it extends, with correspondingly lower force. These cylinders can also be installed in the horizontal position.
References
- Herbert H. Netzel: Induktionsofenhandbuch. 3rd edition, Eigenverlag IES, Witten 2003, p. 35.
Desulphurisation
Desulphurisation is partial or more thorough removal of sulphur from metal melts, e.g. with the aid of calcium carbide, lime or soda for cast iron. Good desulphurisation is a primary requirement in the production of cast iron from nodular graphite.
Deoxidisation
Deoxidisation refers, in foundry technology, to the removal of dissolved oxygen from molten metals in order to prevent quality defects in castings.[1] Agents such as aluminium, silicon, manganese or calcium are added to the melt, reacting with the oxygen to form oxides that settle out as slag. Without sufficient deoxidisation, porosity and oxide inclusions result.
What does deoxidisation mean in foundry technology?
Deoxidisation means the targeted reduction of the oxygen content in molten metals, in particular in steel and iron alloys. Oxygen normally enters the melt through contact with the atmosphere or through oxides present in the raw materials used. A high oxygen content can cause casting defects during solidification, in the form of porosity and oxidic inclusions. The aim of deoxidisation is to ensure a homogeneous melt quality and to markedly improve the mechanical properties of the final product.
Deoxidisation methods
To remove oxygen effectively, deoxidising agents are added to the melt. Commonly used agents are aluminium, silicon, manganese and calcium, either individually or combined as alloys. These elements have a higher affinity for oxygen and react with it quickly to form stable oxides, such as manganese oxide (MnO), silicon dioxide (SiO2) and aluminium oxide (Al2O3). These oxides either settle out as slag on the surface or are removed from the melt by other process routes. The choice and amount of deoxidising agent used depend on the base material and the requirements placed on the casting.
Importance of deoxidisation for casting quality
Successful deoxidisation substantially raises the quality of the final product, especially in the industrial production of high-value components such as automotive parts, machine housings or plant components. Pores and oxide inclusions reduce the strength and service life of a workpiece and increase the scrap rate at the same time. Deoxidisation is therefore an essential step in modern foundry technology, needed to meet demanding requirements for quality, safety and cost-effectiveness.
Practical use: what the foundry engineer needs deoxidisation for
In day-to-day melting operations, deoxidisation decides whether a casting comes out of the mould free of porosity or ends up as scrap. Too little deoxidisation lets the dissolved oxygen react with carbon during solidification to form carbon monoxide, which becomes trapped as a gas bubble in the part, visible as pinholes just below the casting surface. Too much deoxidisation, or the wrong agent, produces non-metallic oxide inclusions, which act as hard particles that impair machinability and as notches that lower fatigue strength. In practice, the amount of deoxidising agent is therefore not judged by feel, but dosed according to an analysis of the base material, the target steel grade and the intended degree of deoxidisation (killed or unkilled/rimming steel). Before casting, the technician often checks with a quick test or an oxygen probe whether the target level has been reached before releasing the heat.
Deoxidising agents at a glance
| Agent | Oxygen affinity | Typical addition range | Particularity |
|---|---|---|---|
| Aluminium | very high | approx. 0.02–0.05% | standard for fully killed steel, gives a fine-grained microstructure |
| Silicon | high | approx. 0.15–0.30% | forms SiO₂ slag, common with cast iron and cast steel |
| Manganese | moderate | mostly as a ferro-silicon master alloy | also has a desulphurising effect |
| Calcium | high, but hard to dose | ppm range (Ca treatment) | modifies oxide inclusions into a globular rather than angular shape |
These are guideline values for steel melts and vary noticeably with steel grade, starting analysis and furnace type.[4] A binding dosage is set only by the plant’s own melt-control practice.
Frequently asked questions about deoxidisation
What is the difference between killed and unkilled steel?
Killed steel is fully deoxidised, so no gas reaction occurs during solidification and the melt solidifies “quietly”. Unkilled (rimming) steel is only partially deoxidised, so carbon monoxide still escapes during solidification.
How is insufficient deoxidisation recognised in the finished casting?
Typical signs are pinholes near the surface, visible on X-ray or ultrasonic inspection, and an increased scrap rate during machining caused by hard oxide inclusions.
Why is deoxidisation not always taken to the maximum?
Because every deoxidising agent leaves residues of its own. Too much aluminium, for example, increases the number of fine alumina inclusions, which can clog nozzles during continuous casting. Dosage is therefore always a trade-off between removing oxygen and limiting the amount of inclusions.
Standard reference
The designation system for steels under DIN EN 10027-1[2] can indicate the deoxidation practice as an additional symbol, for example a note on killed casting. The classification of steel grades itself is set out in DIN EN 10020[3]. Both standards matter to the technician whenever an ordered steel grade requires a specific degree of deoxidisation.
References
- Metalltechnik-Lexikon: Desoxidation, Stahl (German only, no English edition available). Specialist glossary, accessed 27 August 2026.
- DIN EN 10027-1:2017-01, Designation systems for steels – Part 1: Steel names.
- DIN EN 10020:2000-07, Definition and classification of grades of steel.
- Total Materia: Steel Deoxidation. Specialist article, accessed 27 August 2026.
Cyclone
A cyclone is a centrifugal force separator used in dust extraction systems.
Current distribution
Current distribution via parallel conductors requires “bridges” at separating distances or phases of 2 – 3 m in order to reduce the line losses. If the rail length between the condenser bank and the wall-side furnace connection is 3 m, such a phase bridge should be used here in the area of the transition point. Bridging should also be used for longer rail lengths and also current pipes. In the area of switches for switching off or over, the rail guide must run without any branching for at least 1 m in front of and behind the switch. Lateral outlets should be avoided at high-tension switches, since the current takes the path of least resistance. If for example both outlets are to the same side, the poles on the other side will be subjected to less load than those in the area of the current supply and off-take.
Current density
Current density is the physical value for current divided by the cross-sectional surface area. The unit of measure is A/mm2. With mains frequency, air-cooled current rails have a maximum of 2 A/mm2, and with medium frequency up to 500 Hz approx. 1 A/mm2. If the electrical conductor is surrounded by flowing water, as in water-cooled cables, a maximum of 16 A/mm2 will be available in this application. Because of the line losses, the length must also be taken into account in addition to the cross-section. double the length with the same cross-section also means double the losses. A 5 m long cable with 600 mm2 copper cross-section has losses of 13.7 kW at 9,600 A of transmitted current, so the losses in a 10 m cable will be 27.4 kW. If the furnace has 2 cables, the losses will therefore be 27.4 kW at a length of 5 m and 54.8 kW with a 10 m cable length. This application example applies to a furnace with an output of 2,150 kW at 1,000 V. The reduction of the current density, in this case from 16 A/mm2 to 10.67 A/mm2 thus produces losses of 18.2 kW and 36.4 kW.
Current
Current in electrical technology is measured in Amperes, or A for short. As defined by Ohm’s law, 1 Ampere is the current which is caused to flow through an Ohm resistance of 1 Ohm by a voltage of 1 Volt.
Curie point
The curie point, also called the curie temperature, is the temperature at which a ferromagnetic metallic material changes from the ferromagnetic state into the non-magnetic state. Two well-known examples are iron, with a curie point of 770 °C, and nickel, with a curie point of 354 °C.[1]
Physically, this change is a consequence of thermal energy overcoming the magnetic exchange interaction between the atomic magnetic moments inside the material. Below the curie point, these moments stay aligned and give the material its spontaneous magnetization. Above the curie point, thermal agitation randomizes the alignment, the spontaneous magnetization collapses, and the material behaves as a paramagnet instead.
Why the curie point matters in foundry practice
For foundries and metal processing, the curie point is a practical reference temperature in several everyday situations. In scrap sorting, magnetic separators pull iron and steel out of mixed scrap streams because these materials are ferromagnetic; this only works reliably below the curie point, so overheated ferrous scrap can pass a magnetic separator without being captured. In induction heating, the curie point is sometimes used deliberately: the ability of a ferromagnetic workpiece to absorb energy from an alternating magnetic field changes sharply once it passes through its curie point, which is the basis of self-regulating induction and resistance heating elements. In quality control, magnetic particle inspection, a widely used non-destructive testing method for castings and forgings, depends on the ferromagnetic response of the component and therefore only functions while the part stays below its curie point.
Curie points of ferromagnetic metals
| Metal | Curie point |
|---|---|
| Iron | 770 °C |
| Nickel | 354 °C |
| Cobalt | approx. 1,115 °C |
Frequently asked questions
What is the curie point of iron?
Iron has a curie point of 770 °C. Below this temperature iron is ferromagnetic; above it, iron becomes paramagnetic and no longer shows spontaneous magnetization.
Why does magnetism disappear above the curie point?
Above the curie point, thermal energy is high enough to disrupt the alignment of atomic magnetic moments that gives ferromagnetic materials their spontaneous magnetization. Once this alignment breaks down, the material behaves as a paramagnet and no longer retains magnetism on its own.
How is the curie point used in foundries?
In foundries, the curie point serves as a practical reference temperature, for example when sorting ferrous scrap with magnetic separators, when designing self-regulating induction heating processes, or when carrying out magnetic particle inspection on castings, since all of these methods only function while the material remains ferromagnetic.
Related standards
Internationally, the characterization of magnetic materials is covered by the IEC 60404 series of standards, which defines classification and measurement methods for soft and hard magnetic materials.[2]
Sources
- Kittel, C.: Introduction to Solid State Physics. 8th edition, John Wiley & Sons, 2005, Chapter 12 “Ferromagnetism and Antiferromagnetism”, p. 329, Table 1 “Ferromagnetic crystals” (iron 1043 K, nickel 627 K, cobalt 1388 K). Retrieved 2026-08-26.
- IEC 60404-1 et seq., Magnetic materials. International Electrotechnical Commission, series in force.
Related topics
The curie point is closely linked to other temperature-related concepts in foundry practice. See also temperature, temperature gradient, solidification temperature, and raw iron for related metallurgical background.
Cupola furnace
A cupola furnace is a foundry shaft furnace for the melting of cast iron. The metal charge (raw iron, scrap and recycled materials) is melted with the addition of slag-forming additives, limestone and coke as energy transmitters. The combustion air (known as wind) is compressed by a blower, and blown into the furnace shaft through nozzles. These are categorised into cold wind or hot wind cupola furnaces, depending on whether the combustion air is cold or heated.