Abnormal Electrode Usage Cases Analysis

In 2006, a 70t LF (electric arc furnace) furnace was equipped with RP graphite electrode and impregnated graphite electrode φ 300mm by a factory, resulting in redness and thinning of the electrode, which can not be reused.

Upon investigation: the reason was that the above electrode could not bear 26KA current. 

The phase sequence of AC electric arc furnace has a great effect on the electrode loosening, which occurs in users at home and abroad. Among the 15 domestic electric furnaces measured by us, 10 needed to change the phase sequence, and 5 of them were no longer loose after changing the phase sequence according to our suggestion; One was not willing to change, and one electric furnace was not changed because the installers didn’t understand the foreign language and the electrode was still loose; Three users were ready to change. Recently, there was another factory. Recently, the electrode of another factory has been always loosened after starting up. After listening to the introduction, they also prepared to measure the phases sequence. 

In May 2008, a factory reflected the electrode loosening. Upon investigation: in addition to changing the phase sequence, all teeth in the upper hole of electrode had different degrees of damage, except that four teeth were intact. We found on the site that, it was caused by mixing one T3 iron hanging head in the lifting of T4 products. After the phase sequence was changed and T3 hanging head was removed, the electrode has not loosened again.

In 2006, since a factory had large lumpiness of slag steel, the electrodes were frequently broken due to material collapse or failure to conduct. According to the statistics of the factory Technology Section, this phenomenon accounted for 78% of broken electrodes.

In 2008, the electrodes of LF furnace in a shift of a factory was broken for eight times. Upon investigation: the electrode wall was scraped and broken due to slagging on the electrode hole wall of the furnace cover. After slag cleaning and keeping a certain distance between the electrode and the hole wall, the electrodes had not been broken again.

In 2000, a factory used φ700 electrodes of Tokai Carbon were broken more than 20 times in one moth. The manufacturer came to see the operation: the cause was that the triangular mark was too tight when connecting the electrode. There was no fracture after change as required.

In 2003, the electrodes of LF furnace in a factory were broken in every shift. Upon investigation: ① in the screws of four feet of column, one broken and one loose; ② the verticality of the column was 14 times larger than the requirement. After alignment, there had no break.

In 2003, the nipple of a factory was broken. Upon investigation, 16 broken nipples were located at the pinholes of the nipples. The depth that the pinhole φ28mm was hit into the nipple was (30~50mm) ×2. We required that the pinhole was not hit into the nipple. 

In January 2002, a factory reflected the electrode was broken. Upon investigation: we found the molten steel reladling, fast temperature drop and increase in hardness of slag cover, causing the break of electrode, damage of holder, as well as increase of electrode consumption.

In July 2002, a factory reflected that the electrode consumption of LF furnace increased. Upon investigation: the electrode consumption increased by 77.9%, the power consumption increased by 15.8%, and the period prolonged by 17.5%, compared with that before and after April. Through calculation, 170t electrode would be additionally consumed, with a loss of RMB 5,000,000. Through the field investigation, this factory heightened the small furnace cover of one meter to improve the environmental protection; and meanwhile, the air suction and dedusting valves were opened from 45° to 90°, which was caused by the increase in electrode oxidation and heat dissipation. We made the findings into a report, and sent it to the relevant leaders of this factory. Its leader agreed with our findings.

In September 2000, a factory reflected that, the electrode consumption of LF furnace was raised from 0.42kg/t to 0.52kg/t. Upon investigation: it was caused by increasing of VD ratio from 42.76% to 73%. In August 2004, when its leader recalled, he fully agreed with our analysis at that time.

In May 2002, φ300mm RP electrodes were used on three sets of 8ton electric furnaces of a factory, and from April to May, the electrode consumption was raised  from 4.6~4.8kg/t to above 5kg/t. Upon investigation: it was caused by start-up of its large electric furnace and drop in hot metal supply of small electric furnace. We have reached a consensus regarding this truth. But, at that time, it could not be understood by the leader in charge. 

In 2012, a factory reflected the electrode tripping. Through our field investigation, this factory used the products among many manufacturers, and there was no tripping when these products were used separately. The tripping only occurred while the connection of the two manufacturers' electrodes, which was mainly caused by the difference in machining tolerances of electrodes of different manufacturers. We suggested the users to reduce the frequency of change when using different manufacturers' electrodes to prevent mix.