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Abnormal instance analysis

It has been more than ten years since we set up after-sales service in 1997. Based on years of practice, we established "graphite electrode operation instruction" in October 2002, printed and distributed to our users carrying hope to cooperate together to reduce electrode consumption in steel-making. Good effect has been obtained for the past several years. In order to strengthen the impression of the instructions, and to let users better use of electrodes, we inductive analyzed the common abnormal problems that occur in the process of using electrodes for your reference.

Example 1: electrode selection
In Y2000, one factory introduced a second-hand 150 t LF furnace, with 25 MVA, 43 KA transformer, overload 20%. They chose to use UHP φ 350 electrodes. Although with 36 KA current limit, electrodes from home and abroad used to break and craft heating up was difficult. After carefully calculation and comparison, we suggest their technical department to use UHP φ 450 electrodes in March 2001.In October 2002, the plant declared: prepare to use UHP φ 400 electrodes instead. In October 2003, we were invited to a meeting aimed to analysis their LF furnace. During the meeting, we stated our advise:“By changing the UHPφ350 electrodes to UHP φ450 electrodes, the equipment could be matched and heat up and heat preservation purpose would be achieved.”In September 2004, our investigation found that the plant finally decided to change the electrode to UHP φ 450 after a comparative investigation.

Example 2:One company used RP and MP φ 300 mm electrode on a 70 mt LF furnace in 1996, and found the electrodes turns red and thin and can no longer use.
The problem is that the above electrode cannot bear 26 KA current

Example 3: The effect of AC Furnace phase sequence to electrode loose.
AC Furnace phase sequence has a great effect on electrode loose, which is happened on users from home and abroad.Among the15 units of domestic electric furnace that we measured: 10 of them need to change the phase sequence. 5 of them no longer get loose after take our advise to change their phase sequence. 1 of them don’t want to change, and 1 of them doesn’t change because the operator can not read English, and the electrode loose situation still the same; 3 of them is going to change. Recently, there are another plant who also face such problem. After our introduction, they are going to measure the sequence.

Example 4: In May 2000, one factory reflected electrode loose. According to our investigation: in addition to the phase sequence should change, only 4 teeth inside of the electrode upper hole are in good condition, other teeth have different degree of damage.There was one T3 iron lifting plug found mix-used to carry T4 electrodes on the spot. After corrected phase sequence and removed the T3 lifting plug, no loose were found till now.

Example 5: in 1996, one plant’s electrodes always got broken, result from the large blocks of steel slag collapse or non-conductive factors. According to the statistics from their engineering department, 78% of electrodes breakage are caused by above reasons.

Example 6: In 1998, due to electrode hole wall on furnace cover slagging, electrodes were broken for 8 times handled by one team on LF furnace. After slag removal and keep the distance between electrode and wall of hole, no such breakage happened again.

Example 7: In 2000, one factory used TOKAI φ 700 electrodes and happened more than 20 times of breakage. The manufacture came and checked their operation and found they connected the electrodes so tight that over the triangle mark. After justified, the breakage phenomenon eliminated.

Example 8: In 2003, every team of one factory has breakages on LF furnace. The reasons are: 1) one foot screw of the column was broken and one loosen among the four screws;2) The column verticality is 14 times larger than required. After adjustment, no more breakage.

Example 9: In 2003, 16 pcs of nipples were broken in a factory. After check, we found they all broke at the point of pin. Pin hole φ 28mm, and deep( 30 ~ 50mm )× 2. We suggest them not to use pin.

Example 10: In January 2002, one plant reflect electrode breakage. We found that was caused by molten steel ladle-to-ladle, large temperature drop, and slag layer hardness increase, which not only often forced electrodes to breakage but also destroyed clamps causes electrode consumption increase.

Example 11: In July 2002, electrode consumption increased when used in one plant’s LF furnace. After we compared the data of before and after April, we found the electrode consumption rose 77.9%, power consumption rose by 15.8%, and 17.5% growth on production cycle. Then through calculation, there would be 170MT electrodes consumption increasing amount and their lost is about 5 million RMB. Through field investigation,we knew that in order to improve the environmental protection, the factory increased the height of small furnace cover about 1 meter; At the same time, suction dust removing valve from opening 45 ° to 90 °, that caused electrodes oxidation and heat dissipation increased. We wrote a report according to our findings and sent to the relevant leader of that factory and they approved.

Example 12: In September 2000, one factory reflected that their electrodes consumption has increased from 0.42kg /t to 0.52kg /t on LF furnace . The reason is VD ratio grew from 42.76% to 73%.
According to the memory of the leader in that factory in August 2004, what they knew was same as our analysis.

Example 13: in May 1998, there was a factory used our φ 300mm RP electrodes on 3 sets of 8MT electric furnace. During April-May, the consumption rose from 4.6 ~ 4 .8kg /t to over 5kg /t.
We investigated and found their big electric furnace works, and small electric furnace decreased hot metal supply. The truth has become a consensus. However, it cannot be understand by competent leadership at the time.

Example 14: In 2004, a plant said their electrodes have tripping phenomenon. Through on-the-spot investigation, we found that they used electrodes from several manufactures, and no loose will happen when they use separately but join two electrodes from different manufactures. This is mainly due to different manufacturers have different electrode machining tolerance and we recommend the user to reduce the changing times of electrodes from different manufactures to avoid mixing.

The above are some excerpts of electrode using problems we encountered and put forward suggestions of improvement through years of experience. Because the continuous and discontinuous consumption of electrodes involves the design of the electrode manufacture and design, equipment, raw materials, process, operation, and many other aspects, both sides and internal shall work together to find out the real reason as soon as possible when an exception occurs. The above instances are examples of honest fellowship solves practical problems. We are very appreciate the great help, cooperation and support from our customers during our investigation.We have a professional after-sales service team, and once you encounter electrodes use question, we will provide you with solutions in the first time.