The formation of cracks on graphite electrodes is related to the quality and improper operation, 80% of the breaks are caused by nipples.
The cost will increase by inappropriate methods of using graphite electrodes, and prolong the smelting time. If broken graphite electrodes fall into the furnace, it will add the carbon content. What is worse, will lead to shutdown of furnace. So, steel mills usually have high requirements on graphite electrode quality, they won’t buy products from manufacturers whose products have frequent accidents.
The factors which caused the fracture of graphite electrodes
- Preparations break the graphite electrodes
When smelting, after the bottom of preparations gradually melt, it is like a main shaft, the space under it is empty, the un-melted scrap steel on furnace wall will fall down to the electrodes, causing cracks. Generally, the broken part is the electrode holder.
- Vibration break
Electrodes generate magnetic force through connecting electricity, the greater the current, the stronger the magnetic field force, causing severe vibration. Under severe vibration, the probability of the electrode breaking due to loosen connections and trips increases. The electrode is subjected to electromagnetic force during smelting, and it will definitely vibrate, which will easily cause the electrode to fatigue and break. These breaks have no disciplines, mostly occurs near the middle of the electrode nipples and nipples.
- Inappropriate operation of electrode holder
It is not allowed to have foreign matter between the electrode and holder, both should be always vertical, holder cannot be held out of the safety line of the electrode. These irregular operations will cause the electrode to break.
The solutions of breaking electrodes
- The breaks caused by the quality of electrodes and nipples, requires to improve the physical and technical indexes of electrodes, must meet the International IEC 60239-2005 standards and the national industry standards. Different power EAFs adopt graphite electrodes of different power level.
- Use technology and management measures to optimize the electrode holder, water-cooling system and feeding structure. Avoid light and thin scrap steel forming a lump on the top of the furnace that is difficult to fall down, and avoid big scrap steel from collapsing and breaking the electrodes.
- Adjust the preparations collapse, resonance and electrode lift. Regulate the irregular operation of the holder that can cause the electrode to break. If a bridging structure has been formed during the melting of preparations, it needs to blow oxygen or physically swing to make the preparations fall in situation of power failure and the electrode is lifted to avoid breaking the electrodes.
- The nut of the electrode holder contacts closely with the electrodes, keep the electrode nipple protective cap until it is lifted and installed. The holder cannot be clamped in the warning line, nor can it. The electrode connection cannot be above the holder.
- Pay attention to the voltage balance during discharge process, and there are no non-conductive objects in the scrap steel layer under the electrode. When the electrodes go down and contact the scrap steel, the secondary voltage will drop immediately. When an arc occurs, observe that the pointer of the secondary ammeter cannot swing greatly.
According to the statistics, the electrode nipple technology during smelting have a great influence to electrode breaks. The Carbon industry association conducts product quality spot checks on most companies and compares them with the corporate standards of well-known carbon companies such as SGL, UCAR, TOKAI, DAN CARBON etc. Most indicators comply to the standards even exceed them. Therefore, to solve the graphite electrode break problem, need to consider the comprehensive factors of different smelting processes, furnace structures, smelting steel grades, forming a set of scientific and reasonable graphite electrode manufacturing and technical using plans.