Basic process operation rules of Consteel electric arc furnace

Production preparation:

1. Raw and auxiliary materials:

1.1. Scrap:

• The classification, technical requirements, inspection methods, acceptance rules, transportation, and quality specifications of scrap steel meet the requirements of GB/T4223 scrap steel;
• The size of scrap steel meets the requirements of “Technical Operating Regulations for Raw and Auxiliary Materials of Consteel Electric Furnace”;
• The chemical composition of scrap steel meets the requirements of special steel grades for harmful trace elements.
• Lime, fluorite, ferroalloy, etc. meet the requirements of national standards or technical agreements.
• All materials are fixed and stacked in place. High-level material storage materials are sufficient.

 

2. Equipment status

2.1. Confirm that the Consteel electric furnace machinery and hydraulic equipment are normal; the supply of water, gas, and other media is normal; the inspection and confirmation of electrical appliances, computers, and other automation systems are normal.

• Electric furnace equipment cooling water pressure ≥ 0.3MPa, compressed air pressure ≥ 0.4MPa;
• The cooling water pressure of the electric furnace transformer is normal (0.01～0.02 MPa), and the oil-water cooler is put into operation;
• The dust removal fan is put into operation, and the cooling fan of the mechanical air cooler is put into operation.

 

3. Preparation before the furnace

3.1. Confirm that the electrode water-cooled spray ring is working normally, and deal with the fouling or blockage in time.

3.2. After each furnace is tapped and before electrifying, carefully observe the upper furnace shell and furnace lining: pay attention to whether there is water leakage in the upper furnace shell, carefully observe the working condition of each furnace wall carbon-oxygen gun, and deal with clogging or water leakage in time; For the furnace lining in the middle and late stages, special attention should be paid to observe the erosion of magnesia-carbon bricks in the eccentric area, 2# electrode hot area, both sides and lower parts of the furnace door, and promptly notify the outsourced construction team to use gunning material for gunning; After each tapping, the furnace door should be cleaned in time and the furnace door should be repaired with charging materials.

3.3. Clean and fill EBT.

• Clean up the residual steel and residue of the EBT, and confirm that the EBT is unobstructed.
• Turn off the EBT, and fill the EBT. The filling material of the tap hole should be properly higher than the sleeve brick, and the shape should be in the shape of a steamed bun.
• After filling the EBT, the Shaker goes back to +2. , insert the electric furnace buffer, shake the furnace to a horizontal position, and arrange the furnace door to prepare for a new furnace steelmaking operation. ● Connect the oxygen tube for drainage. ● Observe the furnace condition.

3.4. Connect, change, and adjust electrodes.

 

 ingredients, loading

1. The addition of scrap steel

• The water-cooled trolley exits the furnace shell and stops at the “OUT” position.
• The first furnace of the new furnace and the first furnace of the clean molten steel repair furnace are the furnace slope and furnace bottom of the newly laid ramming material. Before charging, a thin iron plate should be laid on the furnace slope and furnace bottom and 1~2 tons of iron should be added. Lime base. The scrap steel material used in the material tank is mainly sheared material, and the material tank is parked under the electric furnace platform.

2. Determination of scrap amount

• New furnace and repair furnace: The total loading capacity is about 105 tons, all of which use scrap steel, do not use pig iron and medium and heavy scrap steel materials, mainly shear scrap steel; the tapping capacity is about 70 tons. For the charging of the new furnace, scrap steel is added in batches from the material tank. When the loading capacity reaches 70 tons, the charging of Consteel will be started. About 35 tons of scrap steel will be added from Consteel toppings.
• Cold empty furnace: The total loading capacity is about 110 tons, the proportion of steel materials: is about 80% of scrap steel, about 20% of pig iron, and the amount of tapping is 70-80 tons. First, add 30~40 tons of scrap steel, and then start Consteel feeding after dissolving. The feeding height in the Consteel trough is controlled to be about 500mm, and the maximum should be less than 700mm.

• Normal continuous operation: The total loading capacity is 80±5 tons, and the ratio of iron and steel materials: is 70~80% of scrap steel, and 20~30% of pig iron. The tapping volume is 70~80 tons.
• The amount of steel left in the furnace should be kept at 25~35 tons during normal production, which can be adjusted according to the age of the electric furnace and the actual production situation. When the amount of steel remaining is less than 10 tons, it is necessary to use a material tank or Consteel to add scrap steel to make the furnace load more than 25 tons before it can be smelted by electricity. After the electric furnace returns to the horizontal position, the connecting trolley reaches the “EAF” position, and the connecting feeding trolley and the Consteel feeding channel are started to directly add iron and steel materials into the furnace.

 

3. The addition of pig iron

• Time for adding pig iron: 1/3 of the pig iron is added after the charging capacity of the furnace is 85 tons, and 2/3 of the pig iron is added from the Consteel trough after the electric furnace is energized, and the charging is completed before the charging capacity reaches 60 tons.
• The addition amount of pig iron: The amount of pig iron added is generally 15~30 tons/furnace, and the amount of pig iron added can be adjusted according to the difference between smelting steel grades and scrap mechanical pig iron content and the special requirements for harmful elements.
• Ways of adding pig iron: Mainly add the south Consteel truck into the Consteel trough, and use the North Consteel truck to add it when the south Consteel truck fails.

 

4. Addition of slag

• The addition amount of lime and dolomite: under normal conditions, the total amount of lime added is 3000~4000Kg/furnace, and the amount of dolomite added is 1000Kg/furnace. Adjust according to the content of P and S in molten steel. In the first furnace of the new furnace and the middle repair furnace: the amount of lime added is about 4000Kg, and fluorite and dolomite are not used. Add 1000~2000Kg lime before the feeding tank; add about 2000~3000Kg lime when Consteel feeds.
• Normal continuous operation: the addition amount of lime is 3200Kg, and the addition amount of dolomite is 1000Kg, which are added to the Consteel hopper through the lime feeding system. Add in 4~5 times, 800~1000Kg each time, respectively, at the beginning of power-on, 45 tons in the furnace, 60 tons in the furnace, 75 tons in the furnace, and 90 tons in the furnace. If the content is high, lime can be added to the high-level silo.
• Addition of fluorite: fluorite is used as a slag-adjusting material, and its amount should be determined according to the viscosity of the slag to ensure that the slag has good fluidity, and excessive use is prohibited.

 

Smelting operation

• 1.Power supply

1.1 Electric furnace transformer voltage classification power:

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1.2 The first furnace of the new furnace and repair furnace

Load the first batch of materials, manually supply power with 8~10 level voltage, stop for 15~20 minutes after melting and add the second batch of materials, and then manually supply power with 8~10 level voltage, stop after about 15~20 minutes after melting Add the third batch of materials, and manually supply power with 8~10 level voltage; after the basic melting is stopped for about 30 minutes, start the Consteel feeding, and manually supply power with 10~13 level voltage. If the material tank is small and the number of feedings is large, the shutdown time after melting and cleaning can be appropriately reduced. The smelting time of the first furnace of the new furnace is more than 210 minutes; the smelting time of the first furnace of the repaired furnace is more than 150 minutes.

1.3 The first furnace of the cold furnace

Load the first batch of materials and supply power with 8~10 level voltage. After melting, add the second batch of materials and supply power with 10~13 level voltage. After basic melting, start Condy to feed with 15~17 level voltage to supply power.

1.4 Normal smelting

When the electric furnace returns to the horizontal position, start the Consteel feeding, and control the appropriate feeding speed and power supply curve according to the smelting progress, furnace temperature, and foam slag conditions, generally supply power with 15~17 levels of voltage. In the smelting process, the foamed slag is made, the submerged arc operation is realized, the oxygen supply intensity is controlled, and the large boiling phenomenon is avoided. Note: Try to avoid on-load voltage regulation during the production process of the electric furnace! When adjusting the voltage, lift the electrode until the current returns to zero, and then adjust the voltage.

1.5 Common faults of power supply:

• Trip: During the smelting process, if the current fluctuates too much (such as material collapse, etc.), a trip will occur. The high-voltage switch of the trip furnace can continue to close and production as long as it is released by pressing the “reset” button in the main control room; If jumps 33KV or 220KV, you must notify the electrician to deal with it.
• Allow closing indicator light off: Check whether the “F7” power supply conditions are met.

 

2. carbon-oxygen gun operation:

The setting range of carbon powder injection amount is 20~50 kg/min, so as to ensure that the foamed slag in the furnace is good. Oxygen flow setting: small flow – 1500~2000Nm3/h; large flow – 3500~4000Nm3/h,

2.1 The first furnace of the new furnace

Oxygen is not blown during the melting of the first, second, and third batches. After the third batch is melted, oxygen is blown at a small flow rate with a carbon-oxygen lance, and a small amount of carbon powder is sprayed to form foam slag as appropriate. After starting Consteel, increase the amount of toner, control the oxygen flow at a small flow, and control the toner injection flow at about 20Kg/min.

2.2 Feeding stage

First, start the water-cooled carbon-oxygen gun to blow oxygen and spray carbon at a small flow rate in the furnace to form foamy slag, and then power on for normal smelting operation. Determine the oxygen flow rate according to the molten steel volume in the furnace; use a small flow rate to supply oxygen before the loading volume reaches 35 tons, and use a large flow rate to supply oxygen after 35 tons. The principle of energizing after the advanced gun is established. The large flow of oxygen should not be used for oxygen supply before the scrap steel enters the furnace; when the temperature of the molten pool is low, the carbon-oxygen gun mainly produces foamed slag, and after the foamed slag is made, the carbon-oxygen gun mainly cuts scrap.

2.3 Warming up the stage

When the content of molten steel [C] is high, blow oxygen with a large flow of oxygen lance to heat up. When the content of molten steel [C] is low, carbon can be injected into the furnace to heat up. Control the amount of slag in the furnace, flow slag in an appropriate amount on time, create foamy slag, and heat up the submerged arc. Note: According to the amount of carbon, scrap steel, and real-time furnace conditions, the oxygen flow and the gun position are reasonably controlled to prevent the molten steel from over oxidizing and boiling.

 

3. Control of bath temperature and composition

3.1 Composition control:

3.1.1 When the loading amount is close to and reaches the target value, it will enter the heating stage. When the temperature of the molten pool reaches about 1550 °C, take the first sample for full analysis. (If there is cold steel in the furnace, wait for the cold steel to basically melt. Re-sampling); decide whether to take a second sample according to the analysis results. If the composition of the first sample meets the process requirements, take the end-point sample when the temperature of the molten pool reaches about 1580 °C; if the first sample [C] is high, take oxygen to remove [C] and then take the second sample for analysis; if [ When P] is high, add lime and an appropriate amount of fluorite to make slag to remove [P] after slag flow, and then take a second sample for analysis.

3.1.2 Control of trace harmful elements is a basic requirement in the production of low-alloy steel, generally including Cu, Ni, As, Sb, Sn, Pb, Bi, etc., mostly from scrap steel, In order to control the content of trace harmful elements and minimize the loss, it is required to do:

• If trace harmful elements are found to exceed the standard during electric furnace melting, immediately contact the storage and transportation dispatcher, notify the situation, and ask for the storage and transportation to replace the scrap steel.
• The scrap that has been sent to the Consteel stockyard must be matched with the scrap sent after storage and transportation before it can be put into the furnace.
• For the situation that the trace harmful elements in the electric furnace exceed the standard, the molten steel in the furnace must be poured out as much as possible when the electric furnace is tapping, and the leader should be asked to deal with it.
• Exceeding the standard of trace harmful elements on duty must be clearly reflected in the duty record to avoid the recurrence of accidents.

3.2 Temperature control:

3.2.1 In the feeding stage, since the output power and chemical energy of the transformer are relatively stable, the temperature control of the molten pool is mainly determined by the feeding speed of Counsel. Appropriately, the molten steel temperature in the furnace at this time is in the range of 1530~1580℃. When the molten steel volume in the furnace reaches 90~95% of the target value, slow down the feeding speed of Consteel, increase the temperature of the molten pool, and conduct sampling and temperature measurement operations. After the molten steel volume in the furnace reaches the target charging volume, the feeding is stopped.

3.2.2 Tapping temperature in the tapping stage: ● Plain carbon steel and low alloy steel: 1600±20℃; ● The temperature of steel with alloy addition of more than 1.2 tons is increased by 20℃. If the addition of Cr iron and Mo iron is large, Then increase the temperature by 20℃; ● The temperature of the cold furnace, new ladle, and spare ladle should be increased by 30±10℃ according to the situation.

 

4. Tapping

4.1 Tapping conditions

• The temperature and chemical composition meet the process requirements ● When the ladle reaches the tapping position, connect the argon gas pipe and prepare the argon gas. ● Prepare the oxygen tube for drainage. ● The ladle is properly weighed and started to zero.

4.2 Tapping operation:

⑴. Connect the trolley and exit to the “OUT” position, and exit the carbon-oxygen gun at the furnace door; power off and turn the electrode operating handle to the “tapping” position, and transfer the control of the shaking furnace to the tapping console behind the furnace. The following is carried out on the tapping table after the furnace:

(2) Tilt the electric furnace to +2～5℃, and turn on the EBT, if the filler cannot flow out automatically, oxygen can be used for drainage.

(3) When the molten steel in the ladle is 5~10t, add the prepared scouring slag and ferroalloy to the ladle along with the steel flow. The additional amount of ferroalloy is subject to the lower limit of the alloy composition of each steel grade. For the specific addition amount, please refer to the “Key Points of Process Operation” for each steel grade; the additional amount of refining slag is 10Kg/t of steel.

⑷. The tapping volume is 70-80t molten steel according to the control target of the weighing system on the ladle car. If the weighing system fails, it can be controlled from 5°, 9°, and 15° according to the tilting angle, and each position has a set output. At the same time, the amount of molten steel in the ladle is estimated according to the liquid level of the molten steel in the ladle and the ladle age.

⑸. When the tapping amount reaches the target value (the target value should be adjusted at any time with the condition of the ladle), quickly shake the electric furnace to -7°, and start the ladle car to exit at the same time to prevent the oxidation slag from pouring into the ladle.

 

4.3 Pre-deoxygenation system

(1) When smelting ordinary carbon steel such as Q215 and Q235, only 0.5kg/ton steel-aluminum cake is added for pre-deoxidation when tapping;

(2) When smelting high-quality steel and special steel, add 0.5-1.0kg/ton steel and aluminum cake for pre-deoxidation when tapping in the electric furnace;

 

5. Furnace lining repair, furnace change, the blast furnace of steel smelting operation:

5.1 In the early stage of smelting, as in normal operation, reduce the amount of pig iron added and control the charging amount in the furnace at about 70t. In order to facilitate the inspection of Consteel equipment, the scrap material in the Consteel trough should be removed.

5.2 After melting, the slag should be drained as much as possible to minimize the amount of slag in the furnace.

5.3 The tilting angle reaches 20° when pouring steel.

5.4 Tap the steel to 50~60t, and quickly shake the electric furnace.

5.5 The remaining steel slag in the furnace is poured into the spare ladle, the upper oxide slag is poured, and the remaining molten steel is poured into the refining furnace ladle.

5.6 After tapping, check the tapping port and clean up the residue under the nozzle. Turn off the EBT, fill in the tapping hole, shake the electric furnace, and start the next smelting furnace.

 

Note:

• To ensure accurate and representative sampling and temperature measurement;
• Designate a special person to weigh the alloy and supervise the weighing to prevent wrong weighing;
• The special forklift for the furnace door is designated to be driven by a designated person; the power distribution operation is operated by the main operator or the sub-operator.
• During normal tapping, it is not allowed to use a manual shaking furnace to empty position.