Industrial electric heating furnaces – Arc furnace device – Electrode
Patent
1997-08-26
1999-11-02
Hoang, Tu Ba
Industrial electric heating furnaces
Arc furnace device
Electrode
373 92, H05B 7107
Patent
active
059784105
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to method for production of carbon electrodes for the use in electric smelting furnaces.
BACKGROUND ART
In electric smelting furnaces for production of ferro alloys, ferro phosphorus, pig iron, and other products it is to day mainly used self-baking carbon electrodes. Conventional self-baking electrodes comprise a vertical arranged electrode casing normally made from steel, extending through an opening in the furnace roof or hood. The upper end of the electrode casing is open in order to allow addition of unbaked carbonaceous electrode paste which upon heating softens and melts and is thereafter baked into a solid carbon electrode due to heat evolved in the paste in the area of supply of electric operating current to the electrode. As the electrode is consumed in the furnace the electrode is lowered and new sections of casing are installed on the top of the electrode column and further unbaked electrode paste is added.
Conventional electrodes of this type are equipped with inner, vertical metallic ribs affixed to the inner surface of the electrode casing which ribs extend radially towards the centre of the electrode. When a new section of electrode casing is installed at the top of the electrode column, the ribs are welded to the ribs in the casing below in order to obtain continuous ribs in vertical direction. The ribs serve as a reinforcement for the baked electrode and to conduct electric current and heat radially into the electrode paste during the baking process. To compensate for the consumption of the electrode, the electrode is lowered downwardly into the furnace by means of electrode holding and slipping means.
When conventional electrodes of this type are used, the electrode casing and the inner ribs melt when the electrode is being consumed in the furnace. The metal content of the casing and the ribs is thus transferred to the product produced in the smelting furnace. As the electrode casing and the inner ribs usually are made from steel, such conventional self-baking electrodes can not be used for electric smelting furnaces for the production of silicon or for the production of ferro-silicon having a high silicon content, as the iron content in the produced product will become unacceptably high.
For processes where iron contaminates the product to be produced it has conventionally been used prebaked carbon electrodes which are produced in suitable lengths outside the smelting furnace and added to the top of the electrode column by means of threads or threaded nipples. It is also known to use modifications of conventional self-baking electrodes where contamination of the product in the furnaces with iron from the casing and the ribs are avoided or reduced.
Pre-baked electrodes are normally produced by forming sections of electrodes from a carbonaceous electrode paste, whereafter the formed complete electrode sections are subjected to heat treatment in order to bake the electrode paste into a solid carbon electrode. Such a method of production requires a long period of heat treatment and the temperature has to be closely regulated during heating and during cooling in order to prevent crack formation in the finished electrode length. Further, the baked electrode has to be machined in order to obtain an acceptable surface finish and to make threads in the ends of each electrode length. Prebaked electrodes produced in this way are therefore very costly.
In Norwegian patent No. 154860 it is disclosed a method for continuous production of elongated carbon bodies which bodies are cut into suitable lengths and which are used in the same way as prebaked electrodes after machining and threading. In this method electrode paste supplied to a casing is baked by lowering the casing containing unbaked electrode paste continuously or substantially continuously through a baking furnace which is heated to a temperature of between 700 and 1300.degree. C. by external supply of heat and by combustion of gases which evolve during the baking. Also this kind of electrod
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Johansen Johan Arnold
Ugland Reidar
Elkem ASA
Hoang Tu Ba
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