Short-coil furnaces come in 2 quite different versions. In version A, a “lower furnace with an integrated low induction coil” is flange-fitted below a “cylindrical upper furnace” without cooling equipment. The iron piles are fitted only in the area of the furnace coil. Version B consists of a crucible furnace with a low induction coil and a cooling coil made of V2A material installed directly in the coil extension. The iron piles are fitted with electro-plate in the area of the coil, and in the area of the cooling coil, only the extended side plates with their welded bridges serve to support the cooling coil against the furnace body. Die losses with Type B are approx. 15% lower than with Type A, due to the coil lengthened by the cooling coil.
Shrinkage dimension is expressed as a percentage shrinkage between the model and the casting. This
is the linear contraction of a casting when cooling down from the solidification
temperature to room temperature.
Short-circuit rings are used in magnetic applications in order to keep the scatter fields away from certain components. In crucible induction furnace design, short-circuit rings are
required for furnaces with a high specific output, so that the components mainly in
the upper furnace area are not heated excessively by the scatter field. In the bottom
area, the electrically conductive parts are further away from the coil than those in
the upper area. The short-circuit ring is made of coil copper in a water-cooled
design. The ring is usually fitted above and behind the iron piles, in order to generate an opposing field to the scatter field. By reason of the induction law, the magnetic field generated is arranged in opposition to the generating magnetic field.
In furnaces with high specific outputs, the loss performance in the short-circuit
ring can amount to approx.10 kW. The amount of water required to dissipate this
energy is approx. 35 l/h and kW, and therefore approx. 350 l/h at 10 kW. The
short-circuit ring must be installed electrically insulated from the supporting
construction. Casting into the upper concrete ring without any possibility of
escape for loss water is not recommended.
Scrap drying is essential for induction furnaces if the charge material is stored in the open
instead of indoors. When operating induction furnaces, care must be taken to
ensure that no fluids get into the melt. 1 cm3 of fluid getting into the bath will
expand suddenly in volume to around 1,600 cm3 (ratio of steam to water at
100 °C and atmospheric pressure), with even greater expansion at melt
temperature. This is referred to as a water vapour
explosion. With medium-frequency furnaces, scrap drying can be dispensed
with provided that the scrap is handled accordingly. The operator must at all
times ensure that material is not charged into the sump, but that there is always
enough solid material on top of the melt so that it will be dried before coming
into contact with the melt.
The former practice of heating scrap up to temperatures of approx. 200 °C is no
longer viable nowadays because of increased energy costs. The material made up
60% and the container the remaining 40%. The achievable melting performance
increase is significantly lower than that indicated by the theoretical calculations.
Saveway is a system that works as follows: it is based on the highly non-linear change in the electrical resistance of the fireproof material. As the crucible wall thickness is reduced, the melt penetrates further forward in the direction of the installed electrode plates. This causes the temperature of the fireproof material in front to rise, while its electrical resistance falls. For the measurement current, this means that it flows from one electrode to the melt, and from there back to the other electrode. A certain proportion of the measurement current flows directly from electrode to electrode. This proportion tends toward zero with reducing wall thickness, while the measurement current through the melt increases sharply. This alteration in the condition of the fireproof lining is assessed by the complex measurement system, and the wear to each electrode plate is calculated and displayed.
The Roebel conductor, or drill conductor, 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 cooling 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.
A robot is a designation for a human-like mechanical device or machine, which comes
from the Czech language. Modern industrial robots are highly mechanised, and
are now indispensable in the foundry industry. In die-casting foundries in particular, and in view of the low piece weights involved, robots started to be used
as soon as they had been developed.
