Industrial electric heating furnaces – Arc furnace device – Electrode
Patent
1996-02-28
1998-07-07
Hoang, Tu B.
Industrial electric heating furnaces
Arc furnace device
Electrode
373 97, 204286, 204294, H05B 706
Patent
active
057780218
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCE TO RELATED APPLICATIONS
This application was filed pursuant to 35 USC 371 based on International Application No. PCT/NO95/00123 filed Jul. 7, 1995 which claimed the priority of Norwegian Application No. 942724 filed Jul. 21, 1994.
TECHNICAL FIELD
The present invention relates to a self-baking electrode for use in electrical smelting furnaces.
BACKGROUND ART
Conventional self-baking electrodes comprise a vertically arranged electrode casing 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 soften 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.
The conventional electrode of this type is equipped with inner, vertical metallic ribs affixed to the inner surface of the electrode casing which ribs extend radially towards the center 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 of 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 electrical 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.
Already in the 1920's it was proposed to conduct heat into self-baking electrodes through inserts of prebaked carbon bodies in the unbaked electrode paste. Thus in Norwegian patent No. 45408 it is disclosed a method for production of self-baking electrodes where prebaked carbon bodies are placed in the periphery of the electrodes and kept in place by the unbaked carbon paste. The carbon inserts are not affixed to the electrode casing, but are only kept in place by the unbaked electrode paste, and when the electrode is baked, by the baked electrode paste. In order to keep the carbon inserts in place before, during and after baking of the electrode paste, it is a necessary that each casing is completely filled with hot liquid electrode paste when a new length of casing is installed at the top of the electrode column, as it is only the electrode paste that keep the carbon inserts in place against the inside wall of the casing. Such a method for adding electrode paste is unwanted as gases hazardous to health which evolve from the tar/pitch binder in the electrode paste, will vaporize from the top of the electrode column and will then be an unacceptable health hazard to the operators. The carbon inserts shown in the Norwegian patent have a ratio between radial length and thickness of less than 1:2. The carbon inserts will therefore conduct heat only a short length inwardly into the electrode paste and thereby make it difficult to obtain complete baking in the central part of the electrode. As the carbon inserts according to Norwegian patent no. 45408 are not affixed to the casing or to one another in vertical direction and in addition have a ratio between radial length and thickness of less than 1:2, these carbon inser
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patent: 4692929 (1987-09-01), Cavigli et al.
patent: 4756813 (1988-07-01), Stanley
Elkem ASA
Hoang Tu B.
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