The internal quality problems of graphite electrodes, improper smelting operation and the matching between the two are easy to lead to electrode breakage accidents in the smelting process. How to accurately grasp the causes of an accident?
At present, with the development of EAF steelmaking toward large-scale, ultra-high power and direct current, the quality of graphite electrodes is constantly improving, and the specifications are constantly increasing. Its fabrication technology has become one of the key technologies affecting EAF steelmaking. The internal quality problems of graphite electrodes, improper smelting operation and the matching between them are easy to lead to the fracture of graphite electrodes. How to accurately grasp the causes of an accident? In practice, the problems of electrode quality and operation often exist at the same time. It is difficult to distinguish the responsibility for accidents, which is not conducive to the improvement of electrode quality work and the use of electrode operation technology. After many visits to customers, the main factors affecting the breakage of graphite electrodes were investigated and analyzed, and the controllable parts were found out. The corresponding technical and management measures were taken to reduce the consumption of graphite electrodes.
- Effect of graphite electrode fracture on smelting process
Generally speaking, there are five kinds of consumption of graphite electrodes in the smelting process:
- Electrode end volatilization
- Electrode Side Wall Oxidation
- Electrode fracture
- Electrode Residual Loss
- Electrode end peeling
Among them, the loss of electrode breakage, surface peeling and debris can be collectively referred to as abnormal consumption, which is different from the chemical reaction loss dominated by oxidation. Therefore, the consumption factors of graphite electrodes in electric furnaces, for high-quality graphite electrodes, under careful operation conditions, the abnormal consumption of graphite electrodes is not very large, accounting for about 1%-15% of the total consumption. It is a common fault that graphite electrode is broken in the process of electric furnace steelmaking.
In the process of steelmaking, the quality and stability of graphite electrodes have a great impact on their continuous production. In addition to the direct loss of electrodes and the increase of consumption and smelting cost, the breakage of graphite electrodes in steelmaking process will lead to the interruption of production and the loss of production caused by stopping the furnace. Stopping production and stopping furnace due to the quality problem of graphite electrode will produce a lot of indirect costs, so customers are more sensitive to the problem of graphite electrode breakage.
二、Analysis of Breaking Reasons of Graphite Electrode
According to the internal and external influencing factors in the smelting process, the graphite electrode can be broken into the following two kinds:
- Internal factors: quality reasons of graphite electrode products themselves。
(1) Reasons for Breaking of Electrode Nipples
Nipples play a key role in the connection of electrodes in steelmaking. The quality of Nipples is directly related to the use of electrodes in electric furnace steelmaking. As far as Nipples quality itself is concerned, the main reasons for fracture are as follows.:
①When the volume density of Nipples is low, the strength of Nipples is generally low and easy to break when used;
②The higher resistivity, the faster temperature rise at the joint, the higher thermal stress at the electrode joint, the higher probability of fracture.;
③Insufficient flexural strength of Nipples;
④Important potential hazards occur when internal crack joints are mixed into finished Nipples;
⑤Nipples and electrode processing accuracy index do not match reasonably, and it is easy to break.。
(2) Reasons for Breaking of Electrode Body
Generally, the probability of breaking the electrode body is low. There are several main reasons for breaking the electrode body.:
①Quality defect in screw hole of electrode body;
②Insufficient bulk density and strength of the electrode body;
③Mismatch between electrode body and joint index and machining accuracy;
④Deep cracks at the end of the electrode body are caused by the poor thermal shock resistance of the electrode.;
- External factors: reasons for improper operation during installation and use。
(1) Collapse breaks down the electrode
If the steel scrap in the furnace has formed a bridge structure in the smelting process, especially near the melting point, the long time and short arc operation will produce a larger lateral impact force, which will cause the collapse of the material. An important feature of this kind of accident is that the action moment of the electrode clamping point is the largest, and the probability of breaking near the electrode clamping point is the greatest.。
(2) Resonance action breaking electrode
Graphite electrodes are bound to vibrate when they are subjected to electromagnetic force in the process of smelting. If the mechanical vibration frequency of the pole is close to or synchronized with that of the electromagnetic force, the electrodes will resonate and lead to fatigue fracture of the pole.。
(3) Failure of clamping operation leads to breaking of electrodes
If the electrodes and clampers can not keep vertical, there will be additional horizontal force acting on the electrodes; if there are foreign bodies in the clamping surface, the clamping point will easily produce stress concentration; if the electrodes are not connected properly, the mechanical strength of the electrodes in the interface can not meet the stress requirements. These bad operations easily lead to the breakage of electrodes in the smelting process.