DE2904516A1 - ARRANGEMENT ON INDUCTION FURNACE - Google Patents

Description

A. S E A AB V ä s t e ras / Sweden arrangement at Induction crucible furnaces

The invention relates to an arrangement on induction crucible furnaces according to the preamble of claim 1.

Modern ovens have a high concentration of power. For example, at 1000 kW / t charge, molten steel is overheated ^{by 100 ° C. in a little more than 2 minutes.} Not least in the case of crucible furnaces, it is important that the personnel handling the melt receive information in the control room and / or that measures are taken when the batch or partial batch used has been completely melted, since the furnace lining cannot tolerate high excess temperatures.

A solution to this and other related problems has been proposed in high frequency crucible induction furnaces fed by so-called load controlled static converters. According to this solution, the working frequency is changed in accordance with the changing resonance frequency of the oscillating circuit, which is formed from the furnace coil and the parallel capacitor of the furnace. The mentioned resonance frequency f _R is

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carries —-—-, where L is the inductance of the coil and C the

Capacity of the capacitor is.

The capacity C remains unchanged during the entire melting process. The inductance L, on the other hand, is high at the beginning of the melting process and decreases during the melting process, since the The amount of molten metal in the furnace increases. This means that the frequency increases during the melting process. When a A certain, best adjustable working frequency is reached, this is detected by measurement, whereupon a signal is emitted will. This indicates that all of the charched material has melted. This method is already in Swedish Patent application 7704116-8.

The above method cannot be used with induction crucible furnaces, which are fed with a current of constant frequency. This is the case, for example, when the feed by means of a rotating agitator, a network or a converter with a fixed frequency.

The invention is based on the object of solving the above-mentioned problem in an induction crucible furnace, the coil of which a is fed at a fixed frequency.

To solve this problem, an arrangement according to the preamble of the claim, which has the features mentioned in the characterizing part of the claim.

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The operating personnel responsible for the melting process can be informed of this with the aid of the signals mentioned be sure that all charged material has melted completely and the overheating process has started. The invention uses hence the fact that the power factor and the impedance of the furnace, both normally occur during the melting process decrease continuously, stop at the reached values when the fully melted state is reached and so on remain unchanged for a certain period of time. So you can set a certain period of time, and when the power factor or the impedance has remained essentially unchanged during this period, a signal is emitted, which indicates that the batch is finished. melted. Alternatively, you can proceed in such a way that you have a certain adjustable value for the power factor or the Impedance specifies and provides that a signal is emitted when the power factor or the impedance on the given value has decreased. Possibly both courses can be measured and two different signals for information and warning of the operating personnel are given. So this is a parallel solution to the above solution High frequency induction furnaces with static converters.

The signal transmitter can be supplemented with an additional arrangement, which automatically reduces the supplied power to an adjustable, lower value, e.g. the holding power, when one or both of the aforementioned signals are given.

So you go from melting to keeping warm and prevent

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from overheating and damage to the furnace.

The above-mentioned arrangement of induction crucible furnaces can be used in multiple ways within the scope of the general inventive concept disclosed Way can be varied.

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Claims (1)

Claim Arrangement of induction crucible furnaces which are fed with a current of fixed frequency, characterized in that measuring devices are provided which measure the power factor or the impedance of the furnace during operation of the furnace, that the measuring devices are coupled to signal transmitters which emit a signal when the power factor is reached or the impedance remains essentially unchanged during the melting process for a predetermined, preferably adjustable time at a certain value and / or has fallen to a certain, adjustable value, and that the signal generator may be equipped with an additional arrangement to reduce the power after a the signals mentioned is provided. 90983 4/0675