1.What are the factors that affect the consumption of electrode in EAF steelmaking ?
Factors affecting the consumption of electrode mainly include: 1) charge amount and the feeding way, 2) feeding time and outage time, 3) Tap-to-tap time, 4) emissions and dust removal system, 5) electrode adjustment, 6) high current, large amount of slag, 7) improper oxygen injection, 8) electrode connection and joint,9) body quality and the processing precision of electrode, 10) nipple strength.
2.What matters need to be paid attention in electrodes storage in steel factory?
Before use electrode, warehouse should pay attention to waterproof, moisture proof. It’s better to store in a dry and clean place, and to prevent from mechanical damage. Nipples should keep away from damp.
3. How to avoid the electrode from breakage and tripping in the process of steelmaking?
Taking the following measures can effectively avoid electrode from breakage and tripping in steelmaking process: 1) the phase sequence is correct, that is anticlockwise. 2) steel scrap uniform distributed in the furnace and try to put large pieces of steel scrap at the bottom of the furnace. 3) avoid non-conductive material in scrap. 4) electrode column and the top hole alignment, and parallel to the electrode column. The top hole wall should clean up frequently to avoid accumulation of residual steel slag to force electrode to break. 5) to keep the electric furnace tilting system in good condition, and keep the electric furnace tilting steady. 6) the electrode holder should not be placed in the joint and sockets. 7)choose to use high strength, high machining accuracy and high quality nipples. 8)torque should be appropriate for electrode connection. 9) to prevent the mechanical damage of electrode socket thread and nipple thread in and before the process of jointing. 10) steel slag or foreign material shall prevent from embedding the socket and nipple which may affect screwing.
4. What shall be noted when steel mills lifting electrodes by crane.
No matter use a forklift or crane to transport electrodes requires for elaborate operation. In the process of electrode lifting, any electrode end or thread damage can cause serious problems for the use of the electrode, especially to protect the threaded hole and the nipple thread. Pads should be used when ascending electrodes , so as not to damage the electrode end face and the nipple thread.
5. How to join electrode correctly?
When joining electrodes, compressed air should be used to blow off the socket, electrode surface and nipple. Dust and foreign objects embed should be prevented. Joint should keep clean and smooth. When electrode is screwed to a certain extent (1-2 cm gap between the two electrodes), compressed air should be used again to blow off the dust and then use a torque wrench to tight the electrode in proper torque.
6 About the correct clamping position of electrode holder.
Electrode holder can’t clip in the joint of electrode and thread parts, but between the two safe lines. Meanwhile, the electrode surface and holder should be blew off by compressed air before clamp a electrode to ensure that current and heat flow between the electrodes and gripper conduction is good, and prevent holder damaged by electric arc, so as to extend the use of the holder.
7. What are the measures to reduce the consumption of electrode oxidation in EAF furnace steelmaking process?
Reducing measures mainly include: 1) to reduce the oxidation consumption of electrode perimeter, strengthen the sealing of the furnace, and reduce air intrude into the furnace; to minimize the exposure time of overheated electrodes outside the furnace, and standardize oxygen blowing operation. 2) if conditions permit, adopting spray cooling technology to effectively reduce the electrode side oxygen consumption in EAF furnace. 3) steel mills could spray antioxidant substances on electrode surface, or the electrode manufacture can take antioxidants impregnation treatment technology before delivery to improve the oxidation resistance of electrode ontology.
8. What are the impacts of electrode phase sequence on the use of electrode?
In EAF furnace steelmaking process, the phase sequence of the electrode has a great influence on electrode loosen and breakage. If the sequence is clockwise, electrode will get loose after powered on and used for a period of time, which will easily cause electrode loose or nipple breakage. The correct phase sequence is anti-clockwise. In that way, electrode joint will be more and more tight in use. For the sequence of the electrode measurement, Hp graphite (Beijing)co., LTD can provide free measurement if required by the users.
9. Why the electrodes columns need to be parallel and align with the top hole of furnace cover?
Electrode column shall be centered with the top hole of furnace cover and electrode column should avoid friction with the furnace cover. Otherwise, the lifting and lowering friction can make the furnace cover force to break electrodes. For AC furnace, three phase electrode columns should try to keep parallel.
10. How to exert torque when screwing electrode?
Torque should be proper when screwing electrode and operation should be spoiled. Too small torque will cause nipple heat loose and too big torque will result in socket cracks. Special screw electrode tool shall be used in screwing and please do not twist too tight or too loose.
11. Why we say graphite lifting appliance is better than metal one?
Though metal hook is durable and not easy to be damaged, thermal expansion of the metal hook could easily burst electrode socket when heated. Meanwhile, it is easy to damage the electrode thread when carrying and cause massive scraping which makes electrodes easy to loose. On the contrary, graphite lifting appliance have same thermal expansion property and hardness as the electrode, which will not happen the above poor situations. But the use of graphite lifting appliance period is short, and easy to be damaged. If found serious damage, it should be changed in time.
12. How to correctly choose electrode for arc furnace steelmaking?
According to the design characteristics of electric arc furnace to choose proper and most cost-effective electrode which is suitable for arc furnace production. It is very necessary to choose proper electrodes for each furnace. The special properties of the steel furnace, charging mode, maximum current intensity, the length of the electrode column under the holder, and the distance between the electrode circle and so on are the factors which must be considered in choosing electrodes for arc furnace.
13. What are the effects of specific resistance of the graphite electrode to electrode usage in steelmaking.
The specific resistance of graphite electrode is a sign of physical and chemical index of electrode conductivity state which is related to its manufacturing process. Generally, when steel mills choose a certain specifications of electrodes, they must choose those whose resistance is within the national metallurgical standard range. High resistance will make electrodes red and hot after energized, that will increase electrode oxidation consumption.
14. What are the effects of bulk density of the graphite electrode to electrode usage in steelmaking?
Graphite electrode bulk density reflects the solid state of electrode, which is related to the manufacturing process of the electrode. Our country has different specified value for different specifications of graphite electrode. The low bulk density products shows that the overall structure of porosity is higher, which will make electrode oxidation speed faster under high temperature. Then it will easily cause electrode consumption increase. In general, steel mills shall choose larger bulk density electrodes but within the specified value. However, it does not mean the higher of bulk density the better. Because some electrodes with too high bulk density are sometimes not good at thermal shock resistance, which easily lead to electrode surface spalling, butt loss and crack that affects steel making. The bulk density of electrode is closely related to the manufacturing process.
15. Why domestic UHP electrode production must use imported needle coke?
UHP graphite electrode production must choose high quality needle coke. Due to domestic research and development of needle coke is so slow that the production of needle coke quality cannot achieve the quality requirement of producing high quality UHP electrode, and most of them are only used to product normal electrodes or HP electrodes. Therefore, raw materials of UHP electrode production have to rely on imports of needle coke.
16. What are the features of the needle coke used for UHP electrode production?
Needle coke is a high-quality carbon raw material, which mainly come through thermal cracking residue of petroleum refining. It’s surface have obvious strip lines and form elongated needle fragments if crushed, and fibrous structure could be observed under the microscope lens, so it is called needle coke. Needle coke is easy to be graphitized above 2000 degrees of high temperature. If we use needle coke to produce graphite electrodes, the electrodes will have low resistance, high bulk density, and small thermal expansion coefficient. So, it’s a must material in producing UHP electrode. Needle coke is more expensive than ordinary coke.
17. What is the distribution and price of the needle coke in current world?
Currently, there are mainly 7 enterprises around the world who produce needle coke (one company in America shut down in 2005). The needle coke annual output decreased from 900000 tons in Y2004 to 800000 tons which is far from enough to meet the needs of carbon industry in the world. In recent years, the world needle coke prices are rising rapidly from $540 per ton in 2004 up to now the $920 per ton (rose 70%), It is expected in 2006 that it will rise 200-250 dollars/ton and resources will be in great tense. It will make a great impact on domestic production of the UHP electrode, and the total production amount of UHP electrode will not improve under the influence.
18. How to avoid electrode consumption increase in steel making?
The following items should be noted to avoid electrode consumption increasing: 1) maintain good state of power supply, and energize within the current range according to the requirements of electric furnace design. 2) prevent the arc starting point immerse in the molten pool. 3) prevent electrode immerse into molten steel to refrain from add carbon. 4) If conditions permit,spray cooling technology shall be used. 4)set up the correct exhaust system. 5)adopt right oxygen blowing system.
19. What are the procedures of UHP graphite electrode production? How long does it take for the whole production cycle?
A batch of UHP graphite electrode production process and corresponding time is as follows: extrusion (3 days) – baking (25 days) – impregnation (4 days) – re-baking (15 days) – graphitization (15 days), machining, quality inspection (2 days), finished product packaging (1 day). Thus from feeding materials to end-product requires 65 days without stop. Normally, the production cycle is about 90 days. Because the nipple production requires three more procedures, its production cycle is much longer.
20. What aspect of LWG furnace products is better than Acheson furnace?
The development direction of graphitization furnace is LWG, and the reason is its products quality is better than that of Acheson furnace in homogeneity. It’s more suitable for the electric arc furnace steelmaking production requirements.
21. Why the quality of nipples is very important in EAF steelmaking?
Nipple plays a key role in electrode connection and it is directly related to the electrode usage in electric furnace steelmaking. No matter how good quality the electrodes have, problems will happen without reasonable collocation of good nipples during steelmaking. According to relevant data which shows that in electric furnace steelmaking, more than 80% of the electrode using accident is caused by nipple fracture and tripping. Therefore, high quality nipples are the guarantee of EAF steelmaking normal use.
22. Which properties of graphite electrode(nipple) have influence on electric furnace steelmaking?
1)electrode bulk density, specific resistance, strength, elastic modulus and coefficient of thermal expansion etc. 2)nipple bulk density, specific resistance, strength, elastic modulus and coefficient of thermal expansion etc. 3)machining precision of electrodes and nipples. Without good machining precision, the using effects will not be good even with high quality of electrodes and nipples. 4)the quality of internal structure of electrode and nipple. No cracks is allowed inside electrode and nipple which may cause problems.
23. What will happen if the electrode surface at the top of the holder were severe oxidized in EAF steelmaking? How to prevent?
When making steel in EAF, blowing oxygen into furnace will make the flame higher than the electrode end surface at the top of holder during combustion scrap steel. Sever oxidation may turn the electrode end surface from flat to slope. If connect a new electrode on its top end, the deformation of end surface could not well matched with the new electrode. A big electrode gap will easily cause the inner nipple oxidation and broken. Under the condition of no changing condition of steelmaking, the best preventive measure is to add a shield on the surface of the electrode end face at the top of the holder, to protect electrode end face by blocking fire and air.
24. Whether the dust collection system on EAF will influence the electrode consumption?
When the fan of dust collection system is working, it forms negative pressure, which will speed up the air flowing around the hot electrodes during making steel. In that case, it increases electrode oxidation consumption. In steelmaking, a good dust collection system adjustment could not only maintain a good working environment, but also stabilize electrode consumption.
25. Why should steel mills prevent a mixture use of electrodes from different manufactures?
Steel mills always purchase graphite electrodes from several manufacturers and mix uses their electrodes. It not only makes them difficult to make one company’s electrode consumption statistics, but also easily cause electrode loose and break accidents due to the fit tolerance. It is because different carbon enterprises have different machining tolerance. The correct way is to use electrodes from one manufacture alone, and carry on another manufacture’s electrode after they finished. We shall reduce the changing times of different manufacture’s electrode. To use the nipples to fit electrodes of same manufacture and prevent mixing.