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Gapless rolling technology

1. Overview

Liugang’s three-bar main rolling mill is ф610×6+ф430×6+ф380×6 full-continuous bar short-stress line rolling mill, using 165mm×165mm×10000mm continuous casting billet, mainly producing hot rods with a diameter of φ18mm-φ40mm. Rolled ribbed bars. The design maximum line speed of the finished rack is 15m/s, and the annual output is 1 million tons. In order to further increase production and reduce consumption, this article mainly introduces some problems and solutions encountered in the commissioning process of the three-bar zero-interval rolling technology in May 2019, so as to realize the seamless bite of steel billets before and after the rough rolling 1# mill during the rolling process. The downstream stands are rolled smoothly, the flying shears normally cut the head and tail, and the looper between the finishing mills is stable, which shortens the time of the finished stand without steel gap and realizes the increase of machine-hour output.

steel mill

2. System principle

The zero-gap rolling system is in the state of not pulling the steel, using the cascade speed and the amount of displacement between the rolling mills to carry out secondary control, to realize the cascade control of two plates of steel at different speeds on the same rolling line.

(1) Every two steels on the same rolling line are rolled at different cascading speeds respectively, and there are two dynamic cascading relationships in the rolling line.

(2) Using the current signal control, when the first billet tail leaves the 1# rolling mill, the upstream stand and the downstream stand are interrupted and cascaded. After the head of the second billet bites into the 1# rolling mill, the speed is first reduced and then increased, and it is cascaded with the upstream stand, and the two billets are gradually pulled apart by the difference in the linear speed of the front and rear stands, so as to ensure the normal shearing and smoothness of the flying shears. Looper control of the landing sleeve.

(3) When the gapless rolling system is put into operation, the optimal rolling rhythm can be adjusted according to the distance between the two plates of steel, so as to ensure the minimum distance between the two steels, maximize the working efficiency of the rolling mill, and increase the machine-hour output.

(4) The gapless rolling system is to control the passing speed of the two steels to produce

The raw process requires distance, rather than drawing steel to ensure distance.

The three bars use the 1# rolling mill to reduce the speed first and then increase the speed to realize the seamless connection of the head and tail of the first rolling mill. (1# Flying Shear, 2# Flying Shear) Flying shears and loopers are required to achieve the minimum rolling gap to ensure the rolling mill interval, and at the same time to ensure that the uniformity of the head, middle and tail dimensions of the finished product is not affected. Optimize the tapping rhythm. The deceleration principle of 1# rolling mill: A thermal detection probe is installed 10m north of the ground roll in front of the 1# rolling mill to detect the signal at the tail of the billet. Start to decelerate, the deceleration time is 1.8s, the deceleration range of 1# rolling mill is 0.4 (40%), which is 40% of the motor speed of 1# rolling mill (as shown in Figure 1); the principle of 1# rolling mill speed-up: the deceleration is completed in 1.8s Immediately after that, it rises back to the set speed (the speed rises back to the set speed before biting into the 2# rolling mill), so as to realize the speed cascade relationship between the 1# rolling mill and the 2# and subsequent rolling mills (as shown in Figure 2).

3. Problems encountered during debugging

3.1 The 1# rolling mill does not slow down in normal tapping and rolling, and the two steels collide with each other

The 1# stage tapping operator tapped too fast and connected the front and back two billets on the tapping floor roll. When passing through the thermal detection probe on the north face of the tapping floor roll, the probe detected a steel signal, resulting in the 1# rolling mill not slowing down for two billets. Steel rear-end collision; when the length of the billet is greater than 10m, the 1# rolling mill has a steel bite current, but the probe on the north side of the discharged ground roll still detects a steel signal, and the 1# rolling mill does not slow down and two steels collide with each other.

3.2 The tail of the rolled piece is pulled down

When the 1# operator was rolling back and forth on the tapping roller table during the normal rolling of the 1# rolling mill, when the steel passed the thermal inspection probe 10m north of the tapping floor roll, the 1# rolling mill slowed down in advance, and the tail of the rolled piece was pulled down.

3.3 The failure of the B-section of the tapping ground rollers often affects the tapping rhythm

After the zero-gap rolling technology was put into use, the billet was bitten into the 1# rolling mill and the speed was reduced, but the original line speed of the bottom rolls kept faster than the line speed of the 1# rolling mill, which did not match the line speed of the ground rolls. , which affects the tapping rhythm.

3.4 The length of the head and tail of 2# flying shear is unstable, and it bends after shearing

2# flying shear shearing head and tail shearing command source 12# rolling mill has steel signal and 12# rolling mill post thermal detection probe detection signal, after 2# flying shear front thermal detection probe detects steel signal and then cuts, because 2 #Flying shear toughness is too close to the thermal inspection probe of 12# rolling mill, only about 1.65m away. After zero-interval rolling technology is put into use, the rolling rhythm is fast, and the response of flying shears is delayed or too late, resulting in head and tail shears. The cutting length fluctuates greatly, and the head and tail are bent after cutting, which cannot be effectively cut, and even the head is cut for more than 1 meter.

3.5 The length of the first section of the finished product is unstable, and the finishing mill is looped over high sets

When the head of the rolling piece bites into the finishing mill, there is occasionally a high-sleeve phenomenon of the head. After checking the PDA, it is found that after the zero-interval rolling technology is invested, the distance between the front and rear of the two rolling pieces is shortened, and after the looper falls in the finishing rolling area , when the head of the next steel bites into the rolling mill, the sleeve is slow, and the dynamic compensation speed of the rolling mill has not yet reached the set value. The length of the first section is unstable.

3.6 3# fixed-length flying shear signal confusion

After the gapless rolling technology is put into use, the interval time of K1 is shortened from 4.0-4.5s to 1.8-2.3s, the gap between incoming steel is small, and the thermal inspection before K1 exit and 3# fixed-length flying shear cannot correctly identify the head and tail of the front and rear steel. The signal and the length measurement signal overlap, causing disorder of the measured LPP value, inaccurate feedback of the double-length length information, and the operator of the main console cannot accurately judge the reference value of the multiple-length length of each section in time.

4. Optimization and improvement measures

For the many problems encountered during the commissioning of the zero-interval rolling technology, the following improvements have been made according to the actual working conditions on site:

4.1 Optimize the monitoring method of zero-interval rolling technology, and timely find the phenomenon of 1# rolling mill not slowing down and rear-end collision

By adding thermal detection probes between the 1# and 2# rolling mills, the interval time difference between the last steel tail and the next steelhead between the 1# and 2# rolling mills is detected (this time difference is the optimized rolling process in our normal production process. Control rhythm), when it is less than the time interval value set by us, an alarm signal will be issued, which is convenient for the operator of the main console to take emergency measures to break the part at the 1# flying shear to prevent the rear-end collision and cause the steel pile accident.

Add a rolling time overtime alarm function on the main console computer, such as we set the rolling time to 50s, when the rolling time exceeds 50s, the system will send an alarm signal to make the emergency response in time.

4.2 Realize the cascading relationship between the bite reduction speed of 1# rolling mill and the speed of section B of the discharge roller table

By optimizing the control program of the ground roller in the B section of the tapping roller table, the cascading relationship between the speed of the roller table and the speed reduction of the 1# rolling mill is realized, so that the speed of the B section of the tapping roller table matches the actual linear speed of the 1# rolling mill, thus effectively solving the problem. It is imagined that the ground roller motor trips due to the increased load of the ground roller motor and the serious wear of the ground roller.

4.3 Optimize 2# flying shear cutting program

Re-modified the 2# flying shear T400 control program, the cutting head and tail program was changed from the original 12# mill with steel signal and the 12# mill back thermal detection probe detection signal to the 12# mill virtual bite steel signal, cancel the 12# mill post thermal detection probe The signal is a necessary condition for the 2# flying shear. According to the ratio of the distance from the 12# rolling mill to the 2# flying shear and the linear speed of the 12# rolling mill when there is steel current, the time for the 2# flying shear to start shearing is obtained, and from 12# The motor code disc of the rolling mill and all the signals are sent to the T400 module, and the speed data is directly obtained. The data is accurate and high-precision and the response is fast; after the optimization program, it is found that the length of the shearing head and tail is stable and the length of the shearing head and tail is stable by comparing the actual samples of the flying shear shearing head and tail. production process requirements. After modifying the 2# flying shear cutting program, reset the leading coefficient, lag coefficient, forward sliding coefficient and backward sliding coefficient on the computer screen of the main console. The operator adjusts the parameters according to the on-site cutting situation, which solves the problem of cutting The phenomenon that the head and tail are bent after cutting.

4.4 Optimize the looper lifting and lowering procedure, and add the lifting and lowering delay function

On the basis of the current signal in the front and rear frames of the original finishing mill and the steel signal detected by the looper scanner as the looper, the looper lifting program was optimized, and the looper lifting was added to the computer screen of the main console. , Latching delay function, the operator can flexibly adjust the delay time of the looper up and down according to the steel bite and throwing conditions of the finishing rolling piece, so as to realize the stable bite of the rolling piece and the stable dropout, and the length of the first section of the finished product is double the foot. Stablize.

4.5 Optimize the dynamic compensation signal of steel bite in the finishing mill, and add the function of dynamic compensation time for steel bite

By constantly trying to modify the dynamic compensation percentage of steel bite, the phenomenon of high looping has not been significantly improved; optimize the dynamic compensation signal of steel bite in the finishing mill, add the function of dynamic compensation time for steel bite, and after modifying the dynamic compensation and compensation time, the head bite is stable , the phenomenon of high sets dropped significantly.

4.6 Optimize the signal acquisition method of 3# fixed-length flying shears

In order to ensure the stability of the detection signal of the 3# fixed-length flying shears, the 7# thermal detection (at the exit of K1) and 8# thermal detection (before the 3# fixed-length flying shears) of the original program all use a longer delay shutdown control Signal, now due to the short interval between rolling pieces, the longer delay makes the length measurement of the last steel not completed when the flying shear starts the high-speed counting signal, and the length measurement signals overlap, causing the measured LPP value to be chaotic; after optimization 3# The high-speed calculation method of fixed-length flying shears shortens the long-count delay shutdown time of thermal detection, and the accuracy of LPP value is significantly improved.

5. Conclusion

(1) During the debugging of the zero-interval rolling technology in the three-bar workshop of Liugang Bar, Wire and Profile Plant, the existing problems were solved one by one, and the parameters conducive to production during the debugging process were collected and optimized to form a standardized operation guidance document. (2) It provides a lot of strong guiding basis for the adaptability improvement of zero-interval rolling, debugging, and improvement of other specifications and varieties. (3) With the investment in zero-gap rolling technology, the interval time between finished product stands has been shortened from the original 4.0-4.5S to 1.8-2.3S, and the hourly output of the hot-rolled ribbed steel bar with a diameter of φ25 has been increased from the previous 142 tons to the current 148 ton, the average shift output has increased by about 48 tons, and the daily output per shift has repeatedly hit new highs, achieving a cost reduction of 6.68 yuan per ton of steel.

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