Electrode accident is a common accident of ferroalloy and calcium carbide smelted in a submerged electric arc furnace. The cause analysis and judgment of electrode accidents are accurate, and targeted preventive measures can be taken to reduce the occurrence of electrode accidents. However, since the analysis of electrode accident is disturbed by multiple factors of electrode paste supplier and electrode paste user, objective evidence recognized by both parties is required to accurately determine the cause of electrode accident in the submerged electric arc furnace, the cross-section of the electrode is good objective evidence, so the analysis of the cross-section of the electrode is of great significance.
1. Segregation of Electrode Paste, Resulting in Stratification of Aggregate and Powder
- Section state: there is obvious particle delamination and segregation on the section of the electrode in the submerged arc furnace. According to the size and cross-section of the radiation heat source for electrode baking, there are two situations: one is the accumulation of granular materials along the outer ring of the electrode, and the other is the accumulation of granular materials in the middle of the electrode.
- Other phenomena: the flow coefficient of electrode paste is greater than 2.0, and the elongation is greater than 40.
- Cause analysis: the popularity of electrode paste is too good, resulting in particle segregation. The local strength of the electrode with more aggregate is low, which is easy to be broken by an external force. The electrode with more powder is easy to be broken by its own internal stress. The reason for two different aggregate accumulations is different sintering methods.
2. Too Many Ribs and Too Long Electrode Cylinders Are Common in Newly Opened SAF
- Section state: The section blooms in petals along the rib.
- Other phenomena: There is no abnormality in the test indicators of the electrode paste.
- Reason analysis: For the newly opened furnace, it is generally a problem with the ribs of the electrode cylinder. Too many, too dense and too long ribs will cause the electrode paste to be separated into too many small pieces, and the overall strength of the electrode will change. In addition, the opening method on the rib is incorrect or the opening is too small, and the phenomenon of electrode block drop and cracking will occur.
3. Too Long Section of Rib
The submerged electric arc furnace electrode paste has no fluidity or its fluidity is too low. The judgment basis is that the plasticity value of the electrode paste is lower than 5%
- Section state: there are obvious holes in the section, and the shape of electrode paste is faintly visible.
- Other phenomena: the flow coefficient of electrode paste is lower than 1.0, and the plasticity value is lower than 2.0.
- Cause analysis: the fluidity coefficient of the electrode paste is not good, which can not fill all the space of the electrode cylinder, forming a hole and hanging paste phenomenon, reducing the overall strength of the electrode.
4. Upper-Layer Melting of Paste Column
- Section status: the section is loose with holes, and the local section is flat.
- Other phenomena: it is observed that the upper layer of the pasted column melts into a paste, and the time for adding paste is pushed here before the electrode breaking time, and the furnace is shut down. The difference between the broken electrode and the segregation of the electrode paste is that the fluidity of the electrode paste itself is normal.
- Cause analysis: the thermal conductivity of the raw materials used for the electrode paste of a large submerged arc furnace is high, and the upper layer of the pasted column is easy to melt. In case of a long shutdown time, the melted electrode paste on the upper layer solidifies again. If the electrode paste is not added in time, the electrode sintering process will be interrupted. After the secondary heating, the popularity of the electrode paste here will become worse, and the electrode strength will be low, resulting in the hard break of the electrode.
5. Poor Thermal Shock Resistance of Submerged Electric Arc Furnace Electrode Paste
- Section status: the section is flat.
- Other phenomena: the current changes greatly before electrode disconnection, and others are normal.
- Cause analysis: the current fluctuation will cause the difference of resistance heat in each part of the electrode itself, which will cause certain internal stress in the electrode, and cracks will occur when the thermal shock resistance of the electrode paste is poor. In the process of electrode baking, too fast sintering speed will also increase the temperature difference between the inside and outside of the electrode. When there is no bifurcation under the longitudinal crack on the electrode section, it can generally be judged that the thermal shock resistance of the electrode paste is poor.
6. Isolation of Foreign Objects
- Section status: flat, visible foreign body shape.
- Other phenomena: there are foreign matters in the electrode paste, the electrode cylinder has no cover, and the workshop dust is large.
- Cause analysis: the foreign matters cut off the normal flow of electrode paste, so that the upper and lower electrodes of the foreign matters can not be sintered as a whole, and the electrode strength is reduced, resulting in fracture.
7. Black core soft fracture of Submerged Electric Arc Furnace
- Section state: the periphery of the electrode section is flat, and the middle circle protrudes or drops.
- Others: electrode sintering is slow, others are normal.
- Cause analysis: the electrode sintering is slow, and the sintering center around the electrode out of the holder is not sintered. The sintered electrode has low strength, and it is easy to break when it is impacted by an external force.
8. There Is A Problem with the Burden Ratio, Low Carbon Content, And Low Slag Alkalinity
- Section state: the working end of the submerged electric arc furnace electrode is severely eroded and forked, and the electrode is obviously thinner from top to bottom.
- Other phenomena: electrode paste test is normal, the electric furnace temperature is low, the output is small, and electrode insertion is too deep.
- Cause analysis: the furnace charge is short of carbon, the dissolved material erodes the electrode seriously, the overall strength of the thinner electrode decreases, and it is easy to break when it is impacted by external forces.
9. Poor Oxidation Resistance of Submerged Electric Arc Furnace Electrode Paste
- Section state: the electrode is obviously thinner and the side oxidation is serious.
- Other phenomena: the submerged arc furnace operates normally without water leakage, and there is no change in the use of the fan and no power failure.
- Cause analysis: the oxidation resistance of the electrode paste is poor. Excessive oxidation will make the electrode thinner, and the overall strength of the electrode will be reduced. It is easy to break when it is impacted by external forces. The judgment of poor oxidation resistance of the electrode paste and the erosion of carbon deficiency on the electrode is that the factor of carbon deficiency is larger when the material is thinner under the material surface, and the poor oxidation resistance of the electrode paste when the material is thinner on the material surface.
There are many complex reasons for the soft and hard breaking accidents of the submerged arc furnace electrode. It is impossible to comprehensively analyze the causes of the accident from the section alone. Therefore, before analyzing the causes, it is necessary to ensure that the test indicators of the electrode paste are qualified, especially the strength. Only the electrode paste with qualified strength is necessary to analyze the electrode section. The amount of information provided by the electrode section can also objectively reflect what happens to the electrode during the sintering process, thus, a method for analyzing electrode accidents is provided.