Industrial electric heating furnaces – Arc furnace device – Power supply system
Reexamination Certificate
2000-09-19
2001-12-11
Hoang, Tu Ba (Department: 3742)
Industrial electric heating furnaces
Arc furnace device
Power supply system
C373S070000, C373S104000
Reexamination Certificate
active
06330270
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a method for weighing consumable electrodes submerged in the charge in electric smelting furnaces.
BACKGROUND ART
From Norwegian patent No. 178739 it is known a method for calculating the length of consumable electrodes which are submerged in the charge of electric smelting furnaces, where the length of the electrode is calculated based on registering the weight of the electrodes. According to the Norwegian patent the weight of an electrode is being registered at constant time intervals of up till 5 minutes and where the average value for a plurality of registered weight values is calculated and plotted versus time. Thereafter a curve running thorugh the average values for a minimum period of 24 hours is calculated and this curve is being used to calculate the weight of the electrode after corrections have been made for added electrode paste and added electrode casing. Based on this, the electrode length below the electrode holder can be calculated taking into consideration the diameter and the density of the electrode.
Each registered weight value is, according to Norwegian patent No. 178739, corrected due to possible movement of the electrode during weighing. The registered weight values are further compared with preset upper and lower limits for registered weight values and registered weight values over and below the upper and lower limits are excluded.
It has been found that the method according to Norwegian patent No. 178739 does not give sufficiently accurate results, as the calculated average electrode weight for some time intervals can give a high deviation even if the registered weight values are corrected as described in the patent. This is particularly the case for deviations due to dynamic and static friction between the electrode and the furnace charge. Further varying pressure in the reaction zone in the furnace can influence the registered electrode weight.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a method for weighing electrodes in electric smelting furnaces which method substantially eliminates the influence of dynamic and static friction between the electrode and the furnace charge and the influence of varying pressure in the reaction zone.
Accordingly, the present invention relates to a method for weighing an electrode submerged in the charge of an electric smelting furnace, which method is characterized in that the electrode is being moved in vertical direction at least once, whereafter the electrode is lifted and that the weight of the electrode is registered shortly after the electrode has been lifted.
According to a preferred embodiment of the method, the electrode is moved in vertical direction at least two times at short time intervals before the electrode is lifted and the weight is registered.
According to another embodiment of the method the weight of the electrode is registered after the electrode has been lifted at least two times at short time intervals.
The weight is preferably registered by registering the oil pressure in the hydraulic cylinders from which the electrode is suspended and which moves the electrode in vertical direction. The oil pressure in the cylinders is registered at a frequency of at least 1 Hz and preferably at a frequency between 10 and 300 Hz.
Alternatively the weight of the electrode can be registered by means of load cells, for instance such as described in Norwegian patent No. 178739.
The electrode weight can either be registered when the electrodes due to the automatic electrode regulation has been lifted or lowered at least once and thereafter has been lifted. Alternatively the electrode can be deliberately moved at least once in vertical direction and thereafter lifted before the weight is registered.
It has surprisingly been found that by the method according to the present invention substantially all influence of dynamic and static friction between the electrode and the furnace charge is eliminated. Also the influence of pressure in the reaction zone is substantially reduced. The reason for this is thought to be that during the first vertical movement of the electrode static friction and pressure in the reaction zone will influence substantially on the registered weight of the electrode. When the electrode is moved in vertical direction the first time, the electrode will be loosened from the charge and when the electrode thereafter is lifted, the static friction will be substantially eliminated. Also the dynamic friction between the electrode and the furnace charge will be substantially lower when the electrode is lifted after first having been moved in vertical direction. When the electrode is moved in vertical direction the first time, also the pressure in the reaction zone will be lowered. By moving the electrode in vertical direction at least two times before the electrode is lifted and the weight is registered, it has been found that dynamic and static friction and pressure in the reaction zone will not substantially influence the weight of the electrode.
Tests have shown that by the method of the present invention a very accurate weighing of the electrode is obtained. For a self-baking electrode of the Sø derberg type with a total electrode weight of about 60 tons it has been found that the accuracy in the registered electrode weight will be in the range of 100-200 kg. By the method of the present invention it is thereby possible to detect weight changes on the electrode as small as 100-200 kg. This makes it possible to detect even small electrode breakages and pealing of small pieces from the electrode tip. Further the weight of the electrode can be used to estimate the position of the electrode tip in the furnace at any time.
By weighing of the electrode one has, as described in Norwegian patent No. 178739, to take into consideration the weight of added electrode casings and added electrode paste for self-baking electrodes and to the weight of added electrode lengths for prebaked electrodes.
REFERENCES:
patent: 3914526 (1975-10-01), Markarian et al.
patent: 4303797 (1981-12-01), Roberts
patent: 4569056 (1986-02-01), Veil, Jr.
patent: 4742528 (1988-05-01), Stenzel
patent: 5274662 (1993-12-01), Krepel
patent: 0475008 (1992-03-01), None
patent: 178739 (1996-02-01), None
Brustad Georg
Haugen Frode
Tveit Halvard
Valderhaug Aasgeir
Bierman, Muserlian and Lucas
Elkem ASA
Hoang Tu Ba
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