Lowering, Maintenance, and Handling of Electrode Accidents in Ferroalloy Electric Furnace

Lowering, Maintenance, and Handling of Electrode Accidents in Ferroalloy Electric Furnace

The electrode operation of a ferroalloy electric furnace includes issues such as electrode shell extension, electrode placement, electrode paste addition, electrode inspection, electrode accidents and their handling.

As production progresses, the electrodes are consumed, resulting in a decrease in the power of the electric furnace. In order to restore power, the electrode needs to be plugged down. Before inserting, check for any debris on the electrode to prevent it from getting stuck or damaging the electrode casing; Check the electrode paste surface. If the paste pressure is too low, the electrode cannot be pressed immediately. Notify the paste adding personnel to add paste.

When pressing and releasing the electrode, the feeding worker must supervise at the electrode edge. The placement, maintenance, and occurrence of electrode accidents all require timely handling. This article has compiled a list of these issues for your reference. If there are any inappropriate aspects, please feel free to correct and modify them, and we can communicate and make progress together.

1. The electrode is a critical component of the ferroalloy electric furnace. Proper use and maintenance of electrodes (especially self baking electrodes) directly affect the normal operation of the electric furnace. Therefore, smelting operators must understand the characteristics of self baking electrodes, use and protect them correctly, reduce and avoid various electrode accidents, which is of positive and important significance for the normal operation of electric furnace equipment, smooth operation of electric furnace conditions, and reduction of energy consumption indicators.

2. Electrode is an important component of electric furnace equipment and a part of the bus bur system. Its main function is to rely on electrodes to input low voltage and high current from the furnace transformer into the furnace, and convert electrical energy into heat energy for high-temperature smelting through the arc at the electrode end, furnace material resistance, and furnace melt. Therefore, maintaining the integrity and normal state of the electrodes is an important guarantee for the normal operation of the electric furnace.

3. Generally, carbon electrodes are divided into three types based on their processing and manufacturing techniques: carbon electrodes, graphite electrodes, and self baking electrodes. Generally, self baking electrode is widely used in Submerged Arc Furnace due to its fewer processes and low cost. The production of ferroalloy products such as ferrosilicon, high carbon ferrochrome, high carbon ferromanganese, silicon manganese alloy, and silicon calcium alloy all use self baking electrodes.

4. The self baking electrode consists of an electrode shell and an electrode paste. The so-called self baking electrode refers to the electrode paste made from smokeless coal, coke, asphalt, and tar as raw materials at a certain temperature, which is added to the electrode shell already installed on the relevant equipment of the electric furnace, and then sintered and coked to form the electrode. During the smelting process, as the electrodes are continuously consumed and lowered, it is necessary to regularly extend the electrode shell at the upper part of the electric furnace and add electrode paste in order to obtain electrodes with good sintering conditions and good density.

5. The Heat Source for Sintering Self Baking Electrodes Comes From:

(1) The resistance heat generated when current passes through the electrode itself is the main heat source for electrode sintering, and it can also be said that the sintering process of self baking electrodes is determined by the current passing through the electrode;

(2) The upward conduction of heat at the hot end of the electrode heats the electrode paste moving from top to bottom;

(3) Radiant heat from the furnace mouth and convective heat from the airflow. The sintering process of self baking electrodes is actually a process in which the binder in the electrode paste gradually decomposes and releases volatile substances as the temperature increases.

When the distance between the lower end of the bottom ring and the material surface (the height of the material surface under normal furnace conditions) is less than 500mm, it is allowed to press the electrode. The electrode firing condition is good, and the pressing amount per phase during normal sintering does not exceed 20mm. Generally, the electrode pressing and discharging work should be carried out after each furnace has been ironed. During normal smelting, electrode discharge is not allowed. During the electrode pressing period, the smelting inspection worker and the instrument worker should closely cooperate, follow the command, and require the smelting inspection worker to observe the electrode pressing situation at the hydraulic station.

7. Under normal circumstances, it is not allowed to stop the voltage discharge of the electrode. When the sintering of the electrode is normal, the load should be reduced by about 30% according to the operating requirements before the operation can be carried out. Quickly use up all phase loads within 10-15 minutes after pressing and releasing the electrodes. When the electrode sintering is abnormal or abnormal situations occur, it is allowed to stop the voltage and discharge the electrode.

During electric furnace maintenance or prolonged power outages, in order to prevent electrode heat loss and electrode condensation, the electrode should be lifted up appropriately, with some coke added, and then the electrode inserted downwards. The furnace material around the electrode should be pushed towards the electrode, and as much as possible, the exposed electrode below the copper tile should be buried in the furnace material. Attention should be paid to moving the electrode to prevent electrode adhesion. During major or medium repairs or prolonged power outages of electric furnaces, the electrode cover should be sealed to prevent dust from accumulating and causing electrode accidents.

9. According to the consumption of electrodes, electrode paste must be added in a timely manner for each phase and every day. It is not allowed to add electrode paste every one (or more) days, and the amount added for each phase is determined based on the height of the paste column. After adding paste, the surroundings of the platform should be cleaned up to prevent electrode paste from causing short circuits between the platform and electrode shell, resulting in personal and equipment accidents. If there is a special need for electrode paste, it shall be specified separately.

10. The height of the electrode paste column is usually calculated from above the bottom ring, and a relatively stable paste column height must be maintained.

Generally, the height of the paste column is required to be 4.5-5.0 meters. It is not allowed for the paste column to be too high or too low, and it is not allowed for a large amount of yellow smoke (paste loss) to occur inside the electrode shell.

11. In case of electrode slippage, oil leakage, paste leakage, soft break, hard break, or severe arcing between electrodes, the power should be immediately cut off (without reducing the load, the power should be cut off directly).

12. Electrode Suspension (suspension) and its Processing Method:

The so-called hanging paste refers to the phenomenon where the electrode paste is suspended inside the electrode shell, causing the paste column to have large voids without electrode paste, which is called hanging paste or suspension material.

Reason for Occurrence:

(1) The temperature at the upper part of the paste column is too low, which prevents the electrode paste from melting and sinking.

(2) When adding paste, the electrode paste block is too large and stuck between two ribs. Generally, hanging accidents occur more frequently in winter or during furnace start-up, and more frequently in closed furnaces or when the paste column is too high.

Handling Method:

(1) Use a wooden stick to strike the electrode in a closed furnace to make the suspended material fall. If necessary, cut off the electrode shell of the suspended material part, poke it down or burn it with an oilcloth to melt and fall the suspended material.

(2) An open or semi closed furnace can stop air supply to melt and drop the suspended material, or a heavy hammer can be used to smash the suspended material from inside the electrode shell.

13. Oil leakage, paste leakage and their treatment methods:

The leakage of liquid or semi liquid electrode paste from the damaged electrode shell is called leakage paste.

Reason for Occurrence:

(1) Poor contact between the electrode shell and the copper tile, resulting in arcing and breakdown of the electrode shell;

(2) The electrode sintering is not good, the one-time pressure release is large, and at the same time, the load is used too quickly, resulting in excessive current density on the electrode shell, which turns red and burns through the electrode shell.

(3) When the electrode shell is extended, the weld seam cracks or is not welded properly.

(4) Poor insulation of the electrode locator or other conductive substances causing arcing and breakdown of the electrode shell between phases.

Handling Method:

(1) Small oil flow and leakage can directly reduce the load, and sintering at low load for a period of time is sufficient.

(2) When the leakage situation is severe, the power should be immediately cut off to handle the load slowly after power transmission, and the baking electrode should be operated carefully.

(3) When the leakage of paste is severe, the electrode paste leaked in the furnace mouth must be cleaned out of the furnace first. Then, iron plates should be used to weld the holes on the original electrode shell, and the electrode paste should be added in a timely manner. Then, the electrode should be baked with wood or carbon blocks until its surface hardens before dead phase baking or low load baking can be carried out.

14. Electrode Hard Break and Its Treatment Method:

The electrode fracture at the already sintered part is called hard fracture.

Reason for Occurrence:

(1) The quality of the electrode paste is problematic, with high ash content, low volatile matter, and poor adhesion, resulting in insufficient strength of the electrode itself.

(2) During the electrode sintering process, the residence time in the volatilization stage is short, and the porosity in the electrode is high, resulting in a decrease in strength.

(3) The electrode paste contains soil and debris, or there is too much dust on the surface of the paste column.

(4) The height of the paste column is too high, resulting in clear electrode gelatinization and particle stratification.

(5) The furnace condition is abnormal, the electrode position is high, the lifting is frequent, the lifting amplitude is large, and it is damaged by external forces.

(6) Insufficient verticality of electrodes and poor insulation can cause partial burning and external injuries.

(7) Electrode overheating.

(8) The frequent hot shutdowns and short intervals result in frequent electrode rapid cooling and heating.

(7) Improper handling after hot shutdown, excessive load after power transmission, or prolonged shutdown due to stress caused by rapid cooling and heating.

Handling Method:

(1) When the broken end does not exceed 500mm and is difficult to remove, press the broken end into the furnace material, and add some chromium ore or reduce the proportion of coke in the batch to consume the broken end as soon as possible in the furnace. Depending on the actual situation, increase the number of electrode pressing cycles and the amount of pressing each time appropriately.

(2) When the severed head is too long, it must be removed and the electrode pressed down. It can be directly subjected to dead phase roasting or roasted with wood or carbon blocks before sending electricity for roasting. However, caution must be taken during operation to prevent soft breakage accidents from occurring and expanding the accident.

15. Electrode Soft Break and Its Treatment Method:

The electrode breaking at the unsintered part is called soft break.

Reason for Occurrence:

(1) The quality of the electrode paste is problematic, with high volatile matter and softening point.

(2) Caused by a suspension accident.

(3) The electrode shell iron sheet is too thin or the welding quality is poor.

(4) Untimely handling of leaked paste.

(5) The poor sintering of the electrode can be caused by excessive pressure release or failure to power off in a timely manner when the electrode slides down.

(6) After pressing and releasing the electrode, the load is too fast and the current is too high, causing it to break.

Handling Method:

(1) Quickly release the copper tile and press it down to the original position, clamp the leaked area in the copper tile, clamp the original hard head and lift the electrode, adjust the cooling water and air volume, and reasonably distribute the load to roast the electrode.

(2) Quickly release the copper tile and press it down to the original position. If the leakage is trapped in the copper tile and the electrode cannot be lifted up, the broken end should be firmly seated, and the other two electrodes should be lifted up to perform dead phase firing on that electrode.

(3) After the above method, if the broken end cannot be connected, it can be removed and treated according to the electrode hard break treatment method. In severe cases, weld the bottom of the electrode, add electrode paste again, and treat it according to the new electrode baking method.

16. Electrode Overburning and Its Treatment Methods:

The phenomenon of premature sintering of electrodes above the bottom ring is called electrode overburning.

Reason for Occurrence:

(1) The cooling water volume of the bottom ring is too small.

(2) Poor contact between the bottom ring and the electrode.

(3) The softening point of the electrode paste is too low. (4) The furnace condition is abnormal.

(5) The electrode placement time interval is too long, causing the electrode to overheat.

(6) Poor insulation.

Handling Method:

(1) Reduce the load on the phase electrode and increase the cooling water or air volume.

(2) Artificially accelerating the consumption rate of electrodes.

(3) Adjust the electrode paste formula.

(4) If necessary, break the excessively long electrode terminals.

(5) Timely maintenance of equipment and adjustment of furnace conditions.

17. Electrode Condensation and Its Treatment Methods:

The phenomenon of electrode condensation or electrode adhesion, which occurs when the electrode and the molten material in the furnace cannot move due to delayed movement of the active electrode or other reasons after hot shutdown, is called electrode condensation or electrode adhesion.

Handling Method:

(1) If only one electrode is condensing, adjust the secondary voltage appropriately, lift up the other two electrodes to supply power, and naturally lift them up after the furnace material melts.

(2) If the three-phase electrodes are stuck together, the voltage level of the transformer can be adjusted to the lowest voltage or switched to a star shaped connection for power transmission until the adhesive around the three-phase electrodes melts, and then the electrodes can be lifted up.

18. Precautions for Adding Electrode Paste:

(1) The addition of electrode paste is the responsibility of a designated person in the production department, who is responsible for the paste addition of three-phase electrodes, ensuring the safety of the three-phase electrodes and the normal operation of the electric furnace.

(2) The pasting procedure is as follows: first measure the height of the paste column, determine the amount of paste to be added to each phase electrode, and then measure. Transport the electrode paste from the paste pot to the measuring point, measure it, and then pull it onto the platform. After crushing, it is added to the electrode shell. Accurately and conscientiously measure the height of the paste column and record the amount of paste added each time.

(3) To prevent and avoid suspension accidents, it is required that the particle size of the paste block when adding paste should not exceed 100mm. The fragments and surfaces generated by electrode paste during transportation should be added to the electrode shell together, and no residue is allowed.

(4) The electrode paste must be kept clean and dry. If there is a lot of dust, it can be blown with air and cleaned with water if necessary. However, the cleaned electrode paste must be dried before adding; To prevent dust from falling into the electrode shell, the electrode shell cover must be removed before pasting, and the cover should be immediately closed after pasting. During normal operation, the electrode casing cover must be placed on top of the electrode casing.

(5) When adding paste, it should be added vertically from the center of the electrode shell to minimize the impact of the electrode paste on the ribs. It is not allowed to tilt or drop the ribs; When adding paste, other impurities are not allowed to be mixed in the paste block, and gloves, tools, and other items are not allowed to fall into the electrode shell. If any occur, report and handle it in a timely manner.

(6) Strictly control the height of the paste column according to the regulations. Calculation method for paste column height: H paste=H2+a-H1H paste: paste column height H2: height from the upper edge of the casing to the upper edge of the electrode shell H1: height from the electrode paste surface to the upper edge of the electrode shell a: length of the casing.

(7) The height of the paste column and the surface condition of the paste column are the measurement standards for the paste time interval. When the height of the paste column is lower than the specified requirements or the electrode paste around the electrode shell melts slightly, the electrode paste should be added in a timely manner. It is not allowed to emit a large amount of black smoke or yellow smoke (such as low paste column or insufficient paste) inside the electrode shell. Electrode gelatinization (complete melting of the surface) is absolutely not allowed.

(8) Generally, it is required to paste each electrode once a day.

(9) Pasting personnel (including other personnel) must be careful not to use their bodies or conductive objects to connect or touch between the two electrodes during operation, and it is forbidden for paste fragments or other conductive objects to fall into the casing.

(10) After an electrode accident occurs, the addition of electrode paste should be flexibly controlled and added in a timely manner according to the needs under the guidance of relevant personnel. It is necessary to ensure that the height of the paste column meets the process technology operation regulations and meets the usage requirements.

19. General Requirements for Electrode Shell Production:

(1) The electrode shell of a self baking electrode consists of a metal outer shell and multiple radially distributed ribs inside. The main functions of the electrode shell are as follows:

A、 As a forming mold for electrode paste and to improve the strength of electrodes;

B、 As a conductor, it transmits current to the electrode paste for sintering;

C、 The heating element for baking electrodes bears most of the current when the electrodes are not yet sintered properly;

D、 Bear the weight of the electrode at low temperatures.

(2) Ensure that the steel plate used to make the electrode casing is flat, free from rust and stains.

(3) When making the electrode shell, it should be ensured that it has a perfectly circular shape, and all interfaces should be welded smoothly, without any leaks, sand holes, or air holes.

(4) Weld 12 ribs at equal distances inside the electrode shell, with 4-5 notches required on each rib. Bend the small triangular tongues of each incision in a staggered manner towards both sides at an angle of approximately 30-45 degrees, and ensure that all contact points with the electrode shell are welded smoothly and without any missed welds.

(5) The cold-rolled steel plates and ribs used for making electrode shells should not rust or have other stains. The made electrode shells should be stored in a dry warehouse to prevent collision, deformation, and rusting.

20. Basic Requirements for Electrode Shell Extension:

(1) When extending the electrode shell, the newly installed electrode shell ribs must be aligned vertically with the original electrode shell ribs.

(2) It is necessary to maintain the perpendicularity between the newly installed electrode shell and the original electrode shell.

(3) If the new electrode shell needs to be inserted into the original electrode shell, the insertion length should be about 20mm.

(4) When the interface is difficult to connect, attention should be paid not to smash or forcefully install it. It is necessary to ensure that the interface is flat and free of concave (convex) points. If the weld seam is rough, it should be leveled with a hinge grinder. Oil leakage or paste leakage at the weld seam is not allowed.