This invention concerns a cooling system for electrodes in D.C. electric arc furnaces.
The invention is applied to cool electrodes in D.C. electric arc furnaces used to melt metal alloys.
Although the cooling system can be applied both to the electrodes associated with the crown of the furnace (cathodes) and to the electrodes at the bottom of the furnace (anodes), in the following description, for reasons of practicality, we shall refer to the application of the system to an electrode functioning as a cathode.
At present, electrodes in electric arc furnaces, when they are functioning as a cathode, are generally composed of two main parts: a lower part made of graphite and an upper part made of metallic material, which also has a bearing function, associated with the electrode-bearing arm of the furnace.
When the electrode is functioning as an anode, the graphite part is replaced by a copper part, but the following description can be applied in the same way, with the appropriate transpositions and adaptations.
The two parts of the cathode are constrained together by an intermediate joint, normally threaded, made of an electricity-conducting material so as to allow the passage of electric current.
During the melting cycle the graphite part reaches very high temperatures and is progressively consumed so from time to time new segments of graphite are added. These temperatures cause a flow of heat from the graphite part to the metallic part of the electrode which can cause damage to its structure, apart from causing dispersion of the heat which is useful in the melting process being carried out.
Moreover, excessive over-heating of the intermediate joint can compromise the mechanical stability of the connection between the two parts of the electrode.
For this reason, the electrode needs a cooling system which acts in correspondence with the metallic part and which is able to remove a great part of the heat which migrates from the graphite part towards the metallic part.
This cooling system however must be achieved in such a way that the following three results are obtained concurrently:
uniformity and control of the temperature of the metallic connection, so as not to subject it to mechanical stresses which make it unstable; PA1 a good electrical contact which reduces the Joule effect to a minimum; PA1 an increase in the heat resistence in order to diminish energy losses and to reduce the temperature of the mechanical connection.
These results are obtained all together if the cooling system in its entirety, either because of the material used or because of the structure or because of the dynamics of its functioning, makes it possible to obtain a low heat conductivity and at the same time a high electric conductivity.