The Advantages of DC Electric Arc Furnace

Do you know what an electric arc furnace is? In fact, electric arc furnaces come from tools used to make steel. There are many types of electric arc furnaces. Different types of electric arc furnace steelmaking methods are different. A DC electric arc furnace is a steel-making electric arc furnace that is powered by a DC power source. So what are the advantages of DC electric arc furnace? Today I will introduce the advantages of DC electric arc furnace.

It is the same as AC electric arc furnace, which uses the arc generated between the electrode and the charge (or molten pool) to generate heat, so as to achieve the purpose of melting, and can be used to melt steel or alloy.

Compared with the traditional AC electric arc furnace, the main advantages of the DC arc furnace are:

(1) The arc is stable and concentrated, the molten pool is well stirred, the temperature distribution in the furnace is uniform, and the erosion of the furnace lining is small;

(2) The current and voltage fluctuations are small, the impact on the power grid is reduced, and the cable life is extended accordingly;

(3) Less electrode loss, 50% less electrode consumption per ton of steel than AC arc furnace. The performance of the DC arc furnace is better than that of the AC arc furnace, but it has been suffering from the failure to obtain a high-power DC power supply, which has prevented it from developing for a long time.

With the application of thyristor technology, the manufacturing technology of high-power DC power supply equipment has been solved, so in the late 1970s, the metallurgical industry re-launched the research of DC arc furnaces, and the technical problems of construction and use of DC arc furnaces in the early 1980s have been solved one by one. The world's first DC electric arc furnace was built and put into production at the Bush Steel Plant in Germany in 1982. In the next six or seven years, the United States, France, Italy, Japan and other countries have successively rebuilt or built their own DC electric arc furnaces from 30t to 60t.

In 1989, Tokyo Steel Corporation of Japan built the largest DC arc furnace with a capacity of 130 tons. In recent years, many DC arc furnaces have been built and put into production in various countries around the world, with capacities ranging from 60t to 180t. In 1989, China Taiyuan Machinery Foundry developed China's first small DC electric arc furnace and put it into production. In the same year, a 2000kVA submerged arc DC electric arc furnace in Xuanhua Ferroalloy Plant was put into production, used to produce ferrosilicon, ferromanganese, calcium silicon and other ferroalloys. Since the beginning of the 1990s, DC arc furnaces have received more and more attention. Shanghai No. 3 Steel Plant, Great Wall Steel Plant, Qiqihar Steel Plant, Jiangyin Yanshan Steel Plant, Shanghai No. 1 Steel Plant have introduced large-scale DC arc furnaces with a capacity of 80 ~ 100t. Baoshan Iron and Steel (Group) Company introduced a set of 150t DC electric arc furnace equipment with double furnace shells (one power supply) from France.

There is only one electrode above the DC electric arc furnace, which is the negative electrode and the bottom electrode is the positive electrode. Its power supply system is different from that of AC arc furnace. It is equipped with rectifier and reactor. A contact is installed on the furnace bottom to form a current circuit. The maintenance and service life of the contact are the key problems in the operation of the DC arc furnace. Generally, the copper plate is placed on the furnace bottom steel plate to facilitate conduction. Three layers of magnesia carbon bricks are built on the copper plate, and then refractory materials are knotted on it.

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The Effective Ways to Reduce Roll Consumption

1. Overview

The roller directly contacts the strip rolled product, which is an important tool for hot rolling production. Reducing roller consumption can effectively reduce production costs and increase benefits. At the same time, it can effectively improve the operation rate of the rolling mill and ensure the surface quality of hot rolled products. In the production of hot-rolled strip steel, the consumption of rolls is particularly huge. Therefore, it is of great significance to find out measures to reduce the roll consumption and increase the life of the rolls.

2. Optimize the roll change period

2.1 Rough rolling work roll
The original rough rolling roll changing period is 2.5wt ～ 3.8wt, on this basis, gradually extend the roll changing period, and compare the roll wear, strip shape and surface quality. The roll changing period is now stable at 3.8wt ~ 4.5wt. It does not affect the shape and surface quality of the strip, and extends the service life of the roll.

2.2 Back-up roll of finishing rolling mill
The rotation speed of F1-F7 roll is different and the difference is large, so the wear degree of back-up roll is also different. The one-cut roll change period that originally used 10wt-15wt is unreasonable, and the segmented roll change is now used.

Since the adoption of sectional roll change, not only the rolling capacity of the roll has been increased by about 14.94%. Moreover, according to the statistical data, the wave shape of the roller when rolling the thin gauge at the end of use is also reduced.

3. Correct treatment method of rolling accident

Serious rolling accident directly increases the numerical value of roll consumption, and whether the accident roll can be handled correctly after the accident is the key to reduce the roll consumption.

3.1 Stuck steel accident
In case of steel jamming, the cooling water shall be stopped immediately and the upper roll shall be lifted to avoid the upper roll contacting the strip steel; after the strip steel is removed, the roll shall be changed and cooled slowly. If the roll cannot be changed immediately and the crack is not serious, the working roll can enter into normal rolling only after the cooling water is not opened and idling for 5-10 minutes to make the temperature spread evenly.

3.2 Steel sticking accident
First remove the sticking steel. After that, the steel sticking area shall be inspected in detail, including hardness, crack, flaw detection, etc. the affected area of steel sticking must be removed to ensure that the hardness of the roll surface is uniform and free of crack.

4. Treatment method of common accident roll:

4.1 Hot cracks
Most of the hot cracks are caused by the cold and exciting heat of the roll after the accident of steel jamming or steel piling.

Treatment method: R1 and F1-F4 rolls can be rolled with hot cracks on the premise of ensuring smooth rolling, and the cracks are closed (closed cracks do not extend, but with the use of time), and the cracks will be gradually eliminated.

4.2 Roll bonding
Steel sticking on the roll, tail flicking or steel piling accidents cause the steel sticking on the roll.

Treatment method: when the thickness of the roll is more than 3mm, the adhered strip needs to be turned off first. Check the surface of the roll body after the attached sheet metal is removed. If there is any crack or peeling (peeling off), the cutting depth shall be determined according to the damage degree, so as to eliminate the defect without increasing the roll consumption.

4.3 Edge peeling of working roll
The edge of the working roll is peeling off, and the stress concentration of the shoulder of the roll is caused.

Treatment method: because the shoulder of the roll does not contact the steel plate directly, the part of the crack peeling off can be removed, the chamfer can be grinded, and the chamfer way and angle of the contact supporting roll can be adjusted to improve the stress distribution of the roll body.

4.4 Back up roll defects

The back-up roll is not in direct contact with the strip steel and its hardness is lower than that of the working roll, but its price is expensive, so it is not suitable to adopt the conventional grinding method.

Treatment method: when the damage is at the edge of the roller, increase the length of the end chamfer properly during grinding. The residual defects shall be treated with an angle grinder and the periphery shall be too smooth to prevent further spread of peeling defects. When the damage is in the middle of the roller, it should be grinded as usual and then treated with an angle grinder to make the defect too smooth.

5. Adjustment of roll shape

According to the actual production situation, the F1-F4 roll is changed from concave roll to HVC roll. Moreover, the negative crown of f5-f7 roll is increased to improve the stress distribution on the roll surface. The utility model can achieve the purpose of better controlling the plate shape and reducing roller consumption.

6. Other ways to reduce roll consumption

① Organize to drill the treatment methods of various rolling accidents, improve the emergency response speed, and minimize the damage to the roll caused by the accident;

② Set up reasonable detection standard of roller to ensure the quality of roller and reduce unnecessary loss;

③ Select excellent roll manufacturers, and customize high-quality rolls with materials and hardness in line with the production characteristics of Chongqing Iron and Steel Co., Ltd;

④ After the production is stable, the high-speed steel roll is selected for the working roll in the front section of finishing rolling to further reduce the roll consumption.

7. Conclusion

① The adjusted HVC profile and negative crown roll not only improve the stress distribution on the roll surface, but also strengthen the crown control ability of the strip steel, which is conducive to the guarantee of product quality.

② Adjusting the roll changing period, responding to the rolling accident and correctly handling the accident roll can ensure the product quality, increase the rolling amount of a single roll and extend the service life of the roll.

③ The treatment measures for the accident roll reduce the unnecessary grinding of the roll, thus reducing the labor intensity of the staff.

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30, 000 Ton Tpy Wire Rod Mill Production Line

The finished product of this production line is hot rolled 5.5 wire rod. The main technological process is: 70 × 70 square continuous casting billet smelted by intermediate frequency furnace and continuous casting machine is sent to the full continuous rolling unit through the conveying roller table to be directly rolled into shape; then after pressure feeding, spinning and cooling, it is rolled by the turning machine and push the small coil to the winder. N small rolls are merged and bundled into a large roll on the winder; then list, weigh, and store.

Parameters:
1. Designing one production line of 6tons/hour

2. Raw materials: steel scrap
3. Produced billet size:70*70*2300mm
4. Finished product: 5.5wire rod
5. Total power consumption:8700kw

Process flow:

Intermediate Frequency Furnace Smelting——Continuous Casting Mold——Rough Rolling Unit—Cut the Head and Tail—Middle Rolling Unit—Broken Tail—Prefinishing Rolling Unit—Finishing Rolling Unit—Pinch Roll—Spinning—Loose Cold Cooling-Rolling-Collecting-Packing-Listing-Lifting and Weighing-Storage

Equipment composition:

• Φ320 roughing rolling mill     1set

• Φ250 one drive two rolling mill     7set

• Accessory Equipment:

        1. coil upender   1set
        2. scatter-cold chain     1set
        3. Head cutting shear    1set
        4. Tail cutting shear     3sets
        5. Roller bed before breakdown     1set
        6. Lifting platform      1set
        7. Hanging arm roll     1set
        8. Roller bed before continuous rolling      1set
        9. Collection machine    1set
        10. Laying head (include pinch roll set)      1set

•  Melting equipment:

1. 2 tons medium frequency induction furnace   3sets
2. R4000-70 single-strand casting machine    1set

• Heating furnace:

1. Furnace body    1set
2. Pushing device    1set 
3. Discharge machine    1set 
4. Chimney     1set 
5. Burner      1set 
6. Fan     1set 
7. Heat exchanger      1set

If you are interested in the wire rod production line, please mail at marketing2@hanrm.com.

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Common Accidents on the Site of High-speed Steel Rolling and Measures (4)

15. What are the reasons for stacking steel between the stands of the finishing mill?

(1) The rolling guide sticks the steel;

(2) The guide wheel does not turn or the bearing burns out;

(3) The rolled piece split;

(4) The guide or the roll ring is installed incorrectly;

(5) The roll gap is not set properly or the incoming material size is not reasonable;

(6) The guide is not fastened.

16. What are the reasons for the poor wire loop of the laying head outlet?

(1) The tension between the rolling mills is too large;

(2) the alignment deviation of the water cooling section, the nozzle duct wear and corrosion cause the rolling operation to be unstable;

(3) The clamping force of the pinch roller is not appropriate due to the wear of the pinch roller ring or the failure of the cylinder link mechanism;

(4) The deviation of the bending line of the spinning tube, the spinning tube is seriously worn, and the spinning tube is sticky connected, the unbalance of the spinning tube causes the loop formation difference;

(5) Improper speed configuration of the finishing mill, pinch roll, and laying head, serious speed fluctuation of the rolling mill, causing the rolling speed to be faster or slower, resulting in uneven coil size;

(6) When the temperature of the rolled piece is high, the coil is too soft, and the coil falls on the receiving platform, and it will become an ellipse or a random circle.

17. What are the common types of damage to rolling guides in finish rolling? What are the causes? How to prevent it?

1) The guide roller bearing is broken, so the guide roller cannot rotate;

2) The guide roller is short of oil, and the bearing is locked;

3) The guide roller lacks water, causing the guide roller to not rotate or burst;

4) The guide roller shaft is broken;

5) The guide roller moves, the screw of the pin is loose;

6) The guide arm is loose.

Solutions:

1) Strictly control the size of the red billet, ensure the same size as the guide, and prevent the thickness of the material from impacting the guide roller.

2) Prevent misalignment of the roll ring, prevent twisting of the rolled piece, and the rolling guide is damaged. The bottom surface of the roll ring needs to be aligned with copper skin.

3) To prevent the roll ring from moving, due to the roll ring movement, the torsion moment is generated in the rolled piece.

4) The guide guard must be aligned to prevent excessive force on one side of the guide roller.

5) Strictly control the installation quality of the rolling guide, prevent the guide roller from moving, the guide guard arm is loose, and the cap screw is tight.

6) Strictly check whether the oil pipes and water pipes are working properly.

18. What common accidents will occur during the production of 27 high-speed roll rings with misaligned holes? How to solve it?

1) The serious slope of finished product;

2) The rolled parts are twisted, are unstable in the water-cooled channel, and are easy to get out of the waste box;

3) Due to the torsion of the rolled parts, the finished guides are easy to damage, resulting in the quality accident;

4) The guide is not easy to align.

Solution: Add copper skin to the bottom of the roller ring.

19. How to deal with the sudden stoppage of the high-speed wire mill?

1) Immediately start flying shearing machine #1, #2, and #3;

2) Emergency stop finishing and pre-finishing;

3) Notify the dispatch room to find the reason;

4) After stopping, ask an operator to the finishing mill to check the condition inside the machine;

5) Roller ring was all replaced or slowly cooled, it is strictly prohibited to cool the roller ring with water.

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Common Accidents on the Site of High-speed Steel Rolling and Measures (3)

12. How to judge the tension between each rolling mill stand in production?
For the tension between the stands of the rolling mill, the adjuster generally hits the tensional rolled piece with a pipe, and judges the magnitude of the tension based on his experience, and can also observe the load (current magnitude) of each mill stand. If the load of one motor in the adjacent frame is particularly small, and the load of the other motor is too large (the current is too large), it means that there is severe steel drawing between the frames, which is easy to pull off the rolled piece and cause piling-up of steel.

13. How to deal with common faults in loopers?

The most common failure is that the looper cannot detect the rolled piece, the looper cannot afford the loop, the looper raises the high loop, and the looper shakes greatly.

(1) The looper cannot detect the rolled part. The usual reason is that the looper scanner lens is dirty or the looper scanner is not aligned with the steel. The solution is to wipe the looper lens first, and then test looper scanner (calibration loop) with the test rod.

The test method is to put the test rod in the looper table. The brightness of the test rod is similar to that of the red steel. Move the test rod slowly from the bottom of the looper table. If the signal does not arrive or is unstable, move the looper scanner to the left and right until it is aligned with the looper scanner head, unless the steel hits the scanner and is fixed after alignment. The possible reason is that there is too much cooling water in the looper table, and the cooling water needs to be reduced appropriately.

(2) The looper can't afford. There may be two situations: the air valve is leaking; the air valve pressure is not enough; The valve is not energized. The first two reasons are dealt with by overhaul, and the latter is checked by electrical to check whether the cable and wiring are firm.

(3) The looper raises its height. If the operator sets the parameters improperly, it can be solved by the operator modifying the parameters.

(4) The looper shakes greatly. It may be that the water mist is too large, which affects the looper signal. A fan can be placed next to the looper to blow.

14. Reasons and countermeasures for looping tail

① Improper setting of the set-up time will cause the set-up time to be too late, which will directly lead to slipping of the loop.

②Severe out-of-tolerance of the red billet size of the front frame of the looper and the excessive opening or excessive wear of the corresponding rolling guide will cause the looper at the tail of the rolled piece to flick intermittently in the retracted state.

③ The electrical control system is abnormal, and the joint adjustment between the roughing and intermediate rolling units is interrupted. The intermediate rolling speed continues to rise with the loop rising, but the speed of all 6 rolling mills in roughing rolling does not increase with the joint adjustment but always remains the same. The situation caused 4# or 6# tails to be flicked, and in severe cases caused the tail to be held back.

④ The action of the roller wind valve of the rising looper is delayed, resulting in the looper falling time being too late, which will directly cause the looper to flick.

⑤ The main method of controlling the looper tail dumping is as follows: reduce the height of the tail of the rolled piece and set the closing time of the take-up loop roller accurately.

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