Category: Uncategorized

Racking off is the removal of slag from the surface of the bath. Racking off is also used to refer to the removal of auxiliary casting materials from bunkers with the aid of mechanical devices.

Material condition specifies the condition of a material – solid, liquid or gaseous.

A cover extraction hood is a combination of an internal cover, fitted with an extraction hood enclosing the cover. This type of extraction has proven itself well in practice, and is used almost exclusively for high-output furnaces. The hood can be adapted to meet the corresponding requirements by means of set opening angles, and can for example remove all the smoke during charging. Another option is the fitting of this extraction system with automatically opening slots in the frontal area for smoke extraction directly in front of the crucible furnace during the production of nodular graphite iron.

Cover drives for crucible induction furnaces are available in a wide range of versions. Flap covers or sliding covers are normally operated by means of differential cylinders and chains. If cover hoods are being used, the drive takes the form of 2 differential cylinders. Swivel covers are driven via a curved roller and guide cylinder by means of a vertically acting plunger cylinder. The lowering takes place under the own weight of the cover and the piston rod. In case of certain special requirements, a small differential cylinder can also be used.

Oscillating conveyors are continuous conveyors in channel form for the transport of bulk materials, and are used in foundries for the charging of crucible furnaces. They can also be used for the separation of old sand. Depending on their cladding, they can also be used for the transport of pre-warned scrap or still hot castings.

Pinching is the expression for the breaking of the stream in the channel and thus also the secondary inductor current due to too high an output, in relation to the static pressure of the melt from the vessel above the inductor. Pinching can also occur at static pressures adequate for normal operation due to the accumulation of deposits and the associated restriction of the channel. In order to avoid damage to the inductor, the output must be reduced when pinching occurs.

Shrinkage cavities are created when a melt solidifies due to volume contraction. With suitable mould design, the shrinkage should occur in the ingate or riser, and not in the casting itself. Exothermal supply heating can be provided with the aid of shrinkage powder.

Balancing is required when connecting a 1-phase crucible induction furnace to a 3-phase power supply. Through the use of Steinmetz switching, the 1-phase load is converted into 3-phase of the same size. The power suppliers allow an imbalance of 10% of the highest phase current, depending on the stability of the network. In case of the failure of a balancing choke, a crucible induction furnace can also be operated without balancing devices. It may be necessary to obtain the permission of the power supply company for this imbalanced load at 60% of the nominal current with 2 phases.

The important factor in this method of operation is that the nominal current of the transformer is not exceeded. an example is given below for a 12.5-t furnace with 2,000 V and 2,600 kW nominal output.

1. the balanced phase must be disconnected from the network.
2. the choke must be completely removed.
3. the maximum phase current is determined from the rating plate of the transformer.

4. by slowly increasing the output at 70% of the crucible filling level, the maximum voltage in practice can be determined. If for example at 1,700 V the phase current is over 1,000 A, the next lower step at 1,400 V must be defined as the maximum voltage step, in order not to overload the transformer. The output will then be 1,275 kW and 49% of the nominal output.

1. This current is given for the lowest melting stage for constant output. As a rule, the top 5 steps are designed for this purpose, which in this case means at 1,700 V and Step 6 with 930 A.
2. at 1,700 V and 930 A, this gives an output of 1,580 kW, or 60% of the nominal output.

Templating refers to the production of sand moulds of larger sizes for the production of rotationally symmetrical castings, using rotating templates in place of models, for example for the casting of bells.

Bunkers are supply containers for the storage of bulk materials. In foundries, bunkers are used for holding mould materials, fuels and materials for making up the charge.