Submerged Arc Furnace (SAF) Electrode Accident Analysis

Electrode safety accidents are common safety accidents of nonferrous metals and calcium carbide companies in submerged arc furnace(SAF) smelters. The specific analysis of the causes of electrode accidents is accurate, and purposeful preventive measures can be taken to reduce the occurrence of electrode safety accidents. However, because the analysis of electrode safety accidents is affected by various factors of electrode paste supply manufacturers and electrode paste application manufacturers, in order to accurately judge the cause of electrode safety accidents, we must agree with each other on the objective direct evidence, and the submerged arc furnace electrode section is a good objective direct evidence, so the analysis of electrode section is of great practical significance.

1. The Electrode Paste Shrinks and Loosens, Resulting in Layered Stone and Granular Materials

Cross section: the cross-section of the electrode has an obvious granular matter layer-by-layer shrinkage phenomenon. According to the size section of the pyrogen of the electrode burning radiation source, there are two situations: one is the deposition of granular materials along the outer ring of the electrode, and the other is the deposition of granular materials in the middle of the electrode.

Other phenomena: the fluidity index of electrode paste exceeds 2.0, and the elongation exceeds 40.

Root cause: the popularity of electrode paste is too strong, which causes the shrinkage of particles. The strength of some electrodes with more stones is slightly lower, which is easy to be broken by external forces. The more particles are easy to be broken by the thermal stress of the electrode itself. Two different accumulations of stone are caused by different sintering methods.

2. There Are Too Many and Too Long Bars in the Electrode Cylinder, Which Are Often Found in the New Ignition Furnace

Section condition: the section opens in segments along the rib.

Other phenomena: the electrode paste inspection index value is normal, and there are many phenomena such as valve falling, bifurcation, and turning around after ignition.

Root cause: For the new ignition of the submerged arc furnace(SAF), it is generally the problem of the electrode tube ribs. 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 be reduced. In addition, the electrode will fall off and crack if the drilling form on the ribs is incorrect or the drilling is too small.

3. Electrode Paste Has No Fluidity or Its Fluidity Is too Low. The Resolution Basis Is That the Plasticity Value of Electrode Paste Is Less Than 5%

Section condition: the section has obvious cracks, vaguely showing the electrode paste.

Other phenomena: the fluidity index of electrode paste is less than 1.0, and the plasticity value is less than 2.0.

Root cause: the fluidity index of the electrode paste is not good, which can not fill all the indoor space of the electrode cylinder, resulting in cracks and hanging paste, reducing the overall strength of the electrode.

4. Melting of the Top Layer of the Paste Column

Section condition: the section is loose and cracked, and some sections are leveled.

Other phenomena: through observation, the top layer of the pasted column melted into viscosity, and the actual operation of boiler pipe blowing occurred from the top to the paste adding time before the electrode breaking time. The difference between the shrinkage and looseness of such electrode breaks and electrode paste depends on the normal circulation of the electrode paste itself.

Fundamental cause: the heat transfer coefficient of the commonly used raw materials for electrode paste of large and medium-sized submerged arc furnace(SAF) is high, and the top layer of the pasted column is easy to melt. When the furnace is shut down for a long time, the electrode paste melted at the top layer will coagulate for the second time. If the electrode paste is not added immediately, the whole electrode sintering process will end. After the secondary temperature rise, the popularity of the electrode paste here will decline, and the electrode strength will be slightly low, causing the electrode to break hard.

5. Poor Thermal Shock Resistance of Electrode Paste

Section condition: the section is leveled.

Other phenomena: the electric flow changes greatly before electrode cutting, and everything else is normal.

Root cause: The change in current amount will cause the resistor of each part of the electrode to be heated differently, which will lead to a certain thermal stress inside the electrode. When the thermal shock resistance of the electrode paste is weak, it will cause cracks. In the whole process of electrode sintering, too fast a sintering rate will also expand the temperature difference between the inside and outside of the electrode. When the electrode section has vertical cracks and there is no bifurcation at the bottom, it can generally be distinguished that the thermal shock resistance of the electrode paste is weak.

6. Foreign Object Protection

Cross-section condition: it is leveled and dirty things can be seen.

Other phenomena: there is dirt in the electrode paste during operation, the electrode cylinder has no cover, and the production workshop has a large amount of smoke and dust.

Root cause: the decoration of dirty things blocks the conventional fluidity of electrode paste so that the left and right electrodes of dirty things cannot be sintered into a whole, and the reduction of electrode strength will cause cracks

7. Soft Break of Black Core

Section condition: the area near the electrode section shall be leveled, and the middle ring shall be raised or lowered.

Others: electrode sintering is slow, and everything else is normal.

Root cause: the electrode sintering is too slow, and the sintered core around the electrode of the kneader is not sintered, while the sintered electrode has low strength, and it is easy to break when the impact of external force is relatively large.

8. What Are the Problems with the Preparation of Waste Materials from the Furnace? The Carbon Content Is Low and the Slag Alkalinity Is Low

Cross section: the electrode is severely corroded and bifurcated during operation, and the electrode narrows significantly from top to bottom.

Other phenomena: the electrode paste inspection is normal, the temperature of the heating furnace is low, the production is small, and the electrode is inserted too deeply.

Root cause: carbon deficiency of the waste materials from the submerged arc furnace(SAF), serious corrosion of the dissolved materials on the electrodes, reduced overall strength of the narrowed electrodes, and easy fracture when the impact of external forces is relatively large.

9. Poor Oxidation Resistance of Electrode Paste

Section condition: the electrode is significantly narrowed, and the side air oxidation is relatively serious.

Other phenomena: the actual operation of the submerged arc furnace(SAF) is normal without water seepage, and the application of the centrifugal fan is not changed without power failure.

Root cause: the oxidation resistance of electrode paste is poor. Too much air oxidation will narrow the electrode and reduce its overall strength of the electrode. It is easy to break when the impact of external force is relatively large. The judgment of weak oxidation resistance of electrode paste and corrosion of electrode due to carbon deficiency is that the factors of carbon deficiency are generally larger when the electrode paste is narrower under the material surface, and the electrode paste is poor in oxidation resistance when the material surface is narrower.

There are many soft and hard-breaking accidents of submerged arc furnace electrodes, which are also very complicated. It is impossible to analyze the cause of the accident from the cross-section alone. Therefore, before an in-depth analysis of the cause, it is necessary to ensure that the inspection index value of the electrode paste is in line with the standard, especially the strength. Only the electrode paste with strength up to the standard is necessary to analyze the electrode cross-section. The amount of data given by the electrode cross-section can objectively reflect what happens to the electrode during the whole sintering process, Furthermore, it provides a way to analyze electrode safety accidents.