In the smelting process of SAF, electrode accidents caused by equipment, raw materials, operation, and other factors mainly include electrode sliding, premature or under the burning of electrode sintering, hard breaking of the electrode, leakage of electrode paste, soft breaking of the electrode, etc. How to reduce electrode accidents, improve operation rate and reduce accidents in production is very important for improving smelting economic indicators.
1. Treatment of SAF Electrode Hard Break
The middle section of the roasted electrode is called the hard break. The causes of hard fracture are as follows:
(1) Impurities are mixed in the electrode paste or the electrode paste has too much oil and too good fluidity during roasting, which makes the coarse and fine particles in the paste layered and reduces the electrode strength.
(2) The components in the electrode paste are mixed unevenly, resulting in the non-compact structure and low strength of the electrode after sintering.
(3) The SAF has a long shutdown time. During the shutdown or power transmission process, the electrode working end generates thermal stress due to the change of electrode surface and internal temperature, resulting in the crack and hard fracture.
Sometimes it is the quality problem of electrode paste after the hard breaking of the electrode, and sometimes it is closely related to smelting operation. For example, uneven three-phase electrode load, high electrode paste column height, re-power transmission after long-time hot shutdown, and unstable increase of electrode load will cause rapid cooling and heating, thermal stress, hard break, etc.
After the electrode is hard broken. The power shall be cut off immediately, the broken end shall be taken out, the electrode shall be placed to the normal length of the working end, and the phase electrode can work normally after roasting for about 6h. Then, the pressure discharge electrode of the submerged arc furnace shall be strengthened to make the working end fully meet the working needs. If the electrode is short, it can also be directly “seated” in the furnace. In the slagging process, if it is difficult to take out the hard-breaking electrode, the hard-breaking electrode can be “seated” in the furnace charge. Try to embed the fracture into the material, then lengthen the electrode, press the fracture, power on the low voltage for “dead phase” roasting, and gradually consume the broken end until it is normal.
In addition to strengthening the management of electrode paste, two measures are mainly taken to prevent electrode hard break accidents: one is to select the best formula for electrode paste, and the other is to reduce the hot stop. During the baking of the electrode paste of the self-baking electrode, the binder after coking tends to shrink, and the filled solid material is stable at this temperature. These differences in physical properties lead to thermal stress inside the material: for example, the solid particles are subject to compressive stress, while the coking binder is subject to tensile stress.
Hard fracture often occurs at the material surface, and the exposed part of the electrode shall be kept warm during SAF shutdown. Another danger area of hard breaking is at the lower end of the copper tile. After the SAF is shut down, put enough electrodes down to reduce the cooling water of the copper tile, which is also a feasible method to avoid hard breaking.
2. Treatment of Electrode Soft Break
The SAF electrode breaks in the unburned part, which is called the soft break. The reason for the electrode soft break is that the electrode is improperly buried when the electrode is burned, or the electrode slides due to the failure of the electrode holding facilities. When the copper tile is in contact with the unburned electrode, the area current through the electrode shell will melt the electrode shell, causing the electrode to fall off and the electrode paste to flow out. After the hard breaking accident of the electrode, the electrode is prone to soft breaking and even paste leakage due to improper treatment.
In case of a soft break of the electrode, the power shall be cut off immediately, the electrode cooling fan shall be turned on to the full air volume, the damage condition of the electrode barrel shall be carefully checked, and the treatment shall be carried out after making the correct judgment. Usually, the fracture can be “set” back within the copper tile, the electrode can be aligned and compacted, and then the copper tile can be clamped, and the power can be transmitted slowly. If the electrode shell at the fracture has been burned, and the position is not within the copper tile at the lower part of the copper tile, the electrode can be lowered, the fracture can be aligned and compacted, and the fracture can be surrounded by “skirt”, and then dead phase roasting can be carried out: or pull out the broken electrode, weld the electrode shell to the bottom again, and lower the electrode to roast the whole electrode.
In case of paste leakage at the unfired part, power off immediately, plug the leakage and pull the electrode back to the sintered part, and then power on. In case of enlarged paste leakage caused by hard breaking accident of electrode, do not clean the paste leakage first, insert the dead phase under the phase electrode, bury the phase electrode with materials, press the phase electrode for about 1m, bake the electrode with low voltage and low current for about 8h, and then move the phase electrode after the electrode is completely red. The control of compliance during this period is the key to roasting the electrode.
If the motor housing is burnt through and has leakage, it can be plugged with the asbestos cloth. If the cross-section of the missing paste is too large, the method of “skirt” shall be adopted, that is, a large electrode shell steel plate shall be used to enclose a cylinder and welded on the electrode shell at the missing paste. It is better to bury it with a SAF charge for dead phase roasting.
The most serious problem is that all motor shells are leaking (all electrode paste flows out). At this time, the electrode paste in the furnace has to be cleaned, the hard head of the electrode is pulled out of the furnace as far as possible, the electrode is welded with an electrode shell bottom, and the wood is used for roasting again, and the dead phase roasting is carried out at the same time.