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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.
is the term for an open or closed cavity in the structure of a material.
was a special conductor guide used in generator technology. The BBC engineer Ludwig Roebel was awarded a patent for these interwoven or drilled copper strips on 19th March 1912. The special feature of this conductor is the fact that every individual conductor within a specified length range is present in every layer of all the individual conductors. The individual conductors are insulated from one another, and therefore reduce the considerable eddy currents that cause losses. In induction furnace technology, advantage has been taken of this knowledge in the design and construction of air-cooled inductors of up to approx. 500 kW per inductor coil. This form of conductor cannot be used for crucible induction furnaces. Due to the dimensions of the channel, the iron core, the diameter of the coil, the number of windings, the length and the cooling air ducts necessary for the construction of inductors, the use of air-cooled inductors is necessarily restricted. From the physical and energy-technology point of view, their use can be highly recommended, since the losses are lower than with normal conductors formed in parallel and water-cooled hollow copper conductors. For comparison, the copper loss figures for the 3 most common conductor types at 500 kW nominal output are:
water-cooled hollow copper conductors approx. 90 kW
12-way flat individual conductors, undrilled approx. 75 kW
12-way flat individual conductors, drilled approx. 64 kW
However, since it is comparatively expensive to provide the relatively clean cool- ing air required, the water-cooled inductor has become the type more commonly used in practice. Air-cooled inductors are constructed with an output of up to approx. 150 kW and generally have 1-way flat conductors, or from approx. 120 kW also 2-way flat undrilled conductors.
Raw iron is the first smelt produced in the blast furnace, and consists of the untreated iron obtained from iron ore. Raw iron is used as the charge material for the production of cast iron and for steel production. Hematite raw iron is used exclusively for foundry production. The standard material has the following chemical analysis:
Foundry raw iron is also used in foundries, and differs from hematite manly with regard to the phosphorous content, which at 0.50 to 0.70% is 4 to 6 times higher. Specular pig-iron is a special raw iron with a significantly higher manganese content of from 6 to 30%. The normal analysis is:
Low-carbon or high-carbon raw iron, Siegerland special raw irons, special raw iron for the production of cast iron with nodular graphite and charcoal raw iron. Raw iron is generally used in the form of pigs or ingots of approx. 20 kg in weight, or more rarely as 60 kg joined ingots consisting of 3 20 kg pigs.
Magnetic separators are used for sorting and separating magnetic materials out from other materials. These devices are sometimes also constructed as belt separators.
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 pri- mary requirement in the production of cast iron from nodular graphite.
are in principle designed in the same way as crucible melting furnaces. Depending on their particular application however, they are equipped with sig- nificantly better heat insulation and sometimes also an induction coil, split into sections. In the case of a 50% division, both coils will for example have an out- put of 3,000 kW. When both coils are switched in series, the total output is only 1,500 kW. Crucible storage furnaces have the advantage that in the event of prob- lems, stoppages or other interruptions, they can be completely emptied. Due to the low specific output, it is advisable to sinter crucible storage furnaces with molten iron.
is a device for removing the wear crucible from the crucible furnace. Due to the contraction of the crucible in the cold condition and the conicity of approx. 0.8%, this can be done with hydraulic cylinders with different pressure surfaces and strokes. In order to prevent possible difficulties, the crucible should be “loosened by hand” in the area of the casting spout. If the crucible cannot be removed due to too little contraction, the crucible must be slit from bottom to top to a width of about 100 mm. Slitting from bottom to top has 2 advantages over working from top to bottom: 1. when starting in the lower cone area, the work is not carried out directly against the coil, and 2. during further caulking toward the top the work is carried out against the existing hole and later against the slit. This minimises the risk of damage to the coil. The position is opposite to the casting spout. The crucible is started out at a force of up to 200 kp/cm2 and the further removal at 30 – 60 kp/cm2, depending on the crucible size, without damage to the coil.
refers in general to the checking and monitoring of certain processes. Some of the main types of control include quantity, cost and quality control.
Bridge formation is a phenomenon that cannot entirely be avoided in induction furnaces. If there is no proper heat-conducting contact between the liquid melt and the material above, the crucible is said to have a bridge. This phenomenon can occur for example due to material becoming jammed above the melt or a ceramic cover over the melt due to superheating and break-up of the ramming mix. To avoid this happening, the furnace should only be recharged with so much material so that a smooth surface can still be seen in the crucible. If a bridge has nevertheless formed, the furnace should be tilted, and the bridge broken up with extreme care. In MF furnaces, the bridge can sometimes be melted at low power. Serious damage and injury to personnel has in the past been caused by the uncontrolled melting and breaking up of the bridge in the basic position.