Reasons and preventive measures of graphite electrode breakage

Reasons for graphite electrode breakage

The reason for the fracture of the graphite electrode lies in the operation and control, but the quality of the electrode itself is also the decisive factor for the fracture of the electrode.

1. Reasons for the intrinsic quality of the electrode

1.1 Reasons for broken joints Joints play a key role in connecting electrodes in steelmaking, and the quality of joints is directly related to the use of electrodes in electric furnace steelmaking. The connection area formed by the graphite electrode and the joint is a part with large and complex electrical, thermal and mechanical loads, and it is also a common fracture part. According to relevant information, in electric furnace steelmaking, more than 80% of the electrode use accidents are caused by broken joints or loose and tripping. As far as the quality of the joint itself is concerned, the main reasons for breaking are as follows: the bulk density of the joint is low, the strength is generally low, and it is easy to break during use; The resistivity is too high, and the temperature of the joint part rises quickly when the power is turned on, which will cause the thermal stress of the joint part at the electrode connection to be large and the probability of breakage to increase; The flexural strength of the joint is not enough; The internal split joint is mixed into the finished joint to form a major hidden danger; The machining accuracy index of the joint and the electrode is not reasonably matched, and it is also prone to breakage.

1.2 Usually, the probability of electrode breakage is low. The main reasons for electrode breakage are as follows: the electrode screw hole has quality defects; the bulk density and strength of the electrode are not enough; the electrode and the joint index and machining accuracy do not match ; The deep crack at the end of the electrode is caused by the poor thermal shock resistance of the electrode; in addition, the electrode with internal transverse crack is mixed into the finished product and is not detected, and there is a great risk of breaking.

2. Preventive measures for graphite electrode breakage

2.1 Breaking prevention measures in smelting operation

2.1.1 The layout of the charge structure is reasonable: the layout of various scrap steels in the material basket and the conditions of adding them into the furnace should be reasonably configured to avoid the light and thin steel materials forming a ball at the top of the furnace and difficult to descend, and to avoid large pieces of scrap steel to break the electrode.

2.1.2 Carefully observe the distribution of unmelted charge during smelting, especially when it is close to melting. If a bridging structure has been formed, oxygen blowing or physical swinging or shaking should be used first to let the charge collapse under the condition of a power failure and the electrode has been raised to a high position, so as to prevent the collapsed material from breaking the electrode.

2.1.3 The strength of the electrode should be suitable for the process requirements. The connection electrode should use a nut of suitable strength, clean it up, and use a special holding device. Before replacing the electrode and lifting it, the lifting ring must be fastened to ensure that the lifting ring is in close contact with the electrode. To keep the interface clean, it is required to keep the end caps of the new electrodes until the lifting ring is installed.

2.1.4 The electrode holder should not hold the area between white line near to the electrode connections. The electrode connection must not be above the electrode holder. The electrode holder cannot be clamped on an open tip or a tip with a loop.

2.2 Preventive measures in the control process

2.2.1 After the high-voltage power transmission, it is necessary to observe whether the three phases of the no-load voltage of the secondary short network are balanced (determined by the insulation resistance of the three-phase short network to ground, and the unbalanced voltage should be within 10%).

2.2.2 Before the electrode is automatically lowered, make sure that there is no non-conductive object in the scrap layer directly under the electrode.

2.2.3 After the first phase electrode descends and touches the scrap, observe whether the secondary voltage of the phase electrode drops immediately.

2.2.4 When an arc occurs in a certain phase electrode, whether the secondary current display of the phase electrode can be seen (the pointer of the ammeter swings greatly).

2.2.5 Regularly check whether the braking force of the electrode hydraulic drive mechanism and the system delay coefficient change.

In terms of the intrinsic quality of the electrode, the key technical indicators of the electrode (joint) in the smelting process will eventually affect the electrode breakage. Many scholars have carried out detailed research on this. However, there is a certain one-sidedness in judging the quality of the electrode (joint) only by the physical and chemical indicators of the electrode (joint), and the matching of comprehensive factors such as the smelting process, furnace structure and smelting steel grade of our products and different customers should be fully considered.

3. Conclusion

3.1 Material collapse, resonance effect, irregular clamping operation, abnormal condition of the electrode regulator, the hydraulic drive mechanism of the electrode regulator, and improper control measures for the internal quality of the electrode can all cause the electric furnace electrode to break.

3.2 By taking corresponding technical and management measures for such factors as fabric structure, electrode clamping, secondary short-circuit no-load voltage, non-conductive objects, secondary current, braking force of electrode hydraulic drive mechanism and system delay coefficient, the electrode breakage phenomenon can be significantly improved.

3.3 There is a certain one-sidedness in judging the quality of electrodes (joints) based on the physical and chemical indicators of electrodes (joints). The compatibility of our products and the comprehensive factors of different customers' smelting process, furnace structure and smelting steel should be fully considered.