Influencing Factors And Control Measures Of Hot-rolled Coil Quality

The main process equipment of 1580 hot-rolled strip production line includes: two three-stage regenerative walking furnaces, post-furnace dephosphorization, one four-high reversible roughing mill, coil box, fine phosphorus removal, and seven four-high finishing mills , Layer cooling roller table, three downcoilers with three auxiliary rollers, walking beam transport area.

(1) The shape of the strip itself

From the daily production experience, the influence of the strip shape on the finished coil is fatal. Although the coiler can correct the strip to a certain extent, if the strip itself is irregular in shape, or the Serious deviation from the rolling centerline, the coiling equipment cannot make up for it in a short time, resulting in coil-like defects. The plate-shaped defects are mainly manifested in sickle bending, rolling, edge wave, middle wave and so on.

First, cambering and rolling can seriously affect the short stroke control of the side guides. The short stroke of the side guide is divided into two stages. After the strip head reaches the parallel section, the side guide starts to perform the first short stroke. When the pinch roller bites the steel, the side guide starts to perform the second short stroke. After the second expansion of the mandrel is completed, the side guide plate will continue to close due to the opening degree compensation value until it touches the strip steel. At this time, the transmission side performs pressure control and automatically opens and closes according to the detected pressure. If the strip is cambered or rolled, it will disturb the detection of the edge of the strip by the side guide, so that the side guide will correct the strip incorrectly. In the subsequent coiling process, there will be excessive pressure on one side, and the side guide will be adjusted again, trying to make the strip return to the rolling center line, which will result in a tower shape. Similarly, if there is such a defect in the strip, the side guide will be repeatedly corrected during the coiling process, thereby forming a stacking fault defect.

The wave defect is mainly caused by the shaking phenomenon during the strip coiling process. During the coiling process, the pinch roller is also controlled by pressure. When the strip has an edge or middle wave shape, the pressure detected by the pinch roller will change accordingly. At this time, the pinch roller will Adjusting the roll gap, coupled with the uneven force along the direction of the roll body, so that the strip will be subjected to a certain force in the horizontal direction perpendicular to the rolling center line, which will cause the strip to shake left and right in the horizontal direction, which is very easy cause layer faults. Because the wave shape generally occurs at the end of the strip, the control of the pinch roller is optimized for the new production line of Legang, that is, when the distance from the end of the belt is 9m (this value can be adjusted), the pinch roller is changed from the original pressure control to position control. , thereby reducing the left and right shaking of the strip to a certain extent.

Control measures :

There are many factors that affect the shape of strip steel. 1580 has made improvements in the production process in terms of steel temperature, rolling force distribution, looper control, transition material matching, cooling water use, and rough rolling incoming sheet shape. Good results have been obtained in thinning and rolling.


(2) Accuracy of side guides

The accuracy of the side guide is mainly reflected in three aspects: parallelism, counterweight and liner wear.
The parallelism is relative to the rolling center line. If the parallelism on both sides is poor, the side guide plate and the strip will not be in complete contact, but the inlet or outlet is partially in contact, which greatly reduces the side guide and the strip. Therefore, it can not play a good clamping effect on the strip.

In actual production, the parallelism of the side guide plates cannot be maintained well, which is mainly affected by the design structure of the side guide plates of the 1580 production line and the impact of the strip during production. The 1580 production line has a hydraulic cylinder in the middle of both sides of the parallel section of the side guide plate. The outlet and inlet are designed with rack and pinion, and the hydraulic cylinder is connected with synchronizing shafts on both sides. When the strip head hits one side of the side guide, under the huge impact force, the inlet or outlet of one side of the side guide will be forced to deviate, and finally the single side of the side guide is no longer parallel to the rolling centerline.

Control measures:

Use the jack to adjust the parallelism of the side guide plate during roller change or maintenance, and ensure that there is no relative rotation at the connection of the synchronous shaft.

If the alignment of the side guides is poor, even if the side guides can hold the strip perfectly, because the strip deviates from the rolling centerline during the clamping process, coiling defects of the inner tower or the outer tower will eventually occur.

Control measures:

After the side guide plate is replaced, it should be carefully calibrated, and the parallelism value should be strictly controlled within the standard. In the production process, the wear of the side guide plate liner is inevitable, but excessive wear will affect the pressure control of the side guide plate, because in the program, in order to prevent the side guide plate from being closed due to abnormal pressure detection under pressure control. phenomenon, the side guide will set itself a maximum closing amount after pressure control, that is, the side guide will automatically realize position control after the closing amount under pressure control exceeds a certain set value.

Due to the excessive wear of the side guide liner, the actual closing amount of the side guide may exceed the set value, and the side guide will remain in its current position. At this time, the side guide plate has a great hidden danger to the coiling process, because the slight fluctuation of the strip width will cause the steel to be clamped at the side guide plate, which may cause steel piles in severe cases. As an operator, the abnormal condition of the side guide plate must be detected in time, and the opening function of the side guide plate must be immediately intervened. However, the rear side guide plate cannot have the original clamping effect on the strip, and the strip may sway from side to side. Eventually a stacking fault occurs.

Control measures:

Carefully check the wear of the side guide plate by using the roller change time. If the wear amount is more than 5mm, it should be replaced in time. In the new production line of Legang, in order to solve the problem of rapid wear of the side guide plate, the side guide plate is specially designed with a water cooling structure, which will greatly improve the hardness of the contact part between the side guide plate and the strip steel, thereby reducing the impact of the edge of the strip steel on it. wear.

(3) Accuracy of pinch rollers

The pinch roll itself plays the role of bending and guiding the strip head, and provides a certain tension for the strip coiling through the lead rate and the lag rate during the coiling process. The accuracy of the pinch roller is mainly reflected in two aspects, one is the wear amount in the length direction of the roller body, and the other is its levelness.

During the long-term contact with the strip steel, the surface of the pinch roller will be worn to a certain extent. In addition to the usual grinding of the roller surface of the pinch roller, the wear amount of the pinch roller along the length of the roller body is often uneven. This will cause itself to not be in good contact with the strip steel, and it is likely to generate a lateral force in the horizontal direction perpendicular to the rolling center line, so that the strip steel can not be stable in the horizontal direction, but sway left and right .

Control measures:

Periodically replace the pinch rollers according to design standards.

The standard for the levelness of the pinch roll is 0.1mm/m. If it exceeds the standard, then one side of the pinch roll means that the reduction is higher than the other side, resulting in uneven pressure on both sides, so that the strip rolls in the coil. The lateral force during the pick-up process will also accelerate the wear of one side of the pinch roller.

Control measures:

On the premise of ensuring the levelness of the lower pinch roll, use a feeler gauge to measure the roll gap on both sides of the pinch roll regularly, and notify the mechanic to make adjustments if necessary. At present, the design of the pinch roll of Legang production line has added the function of “leveling”, that is, the leveling function can be jogged within the range of 2.5mm/m, which provides a considerable amount of adjustment for the levelness of the upper pinch roll. convenient.

(4) The use of pinch rollers

The pinch roll is a follow-up roll located in front of the pinch roll. When the head of the strip passes through the pinch roll and reaches the pinch roll, the pinch roll starts to press down and maintains a certain distance from the strip. Its main function is to During the coiling process, the up and down fluctuation of the strip steel can be slowed down, so that the strip steel can reach a relatively stable state before entering the pinch roll, so that the pinch roll can have a good control of the strip steel, and finally form a Better roll shape.

The 1580 production line was designed with pinch rollers, but for various reasons, the pinch rollers were not used effectively. According to the investigation and analysis, the pinch roller has a certain positive effect on the roll shape control of thin specifications with poor plate shape and thick specifications of ≥ 7mm.

Control measures:

It is recommended to use pinch rollers for thin and thick products with poor shape and ≥ 7mm in the production process, and regularly check the surface of the pinch rollers, and grind or replace them if necessary.

(5) The precision of the rollers of the unloading car

The phenomenon of the outer tower caused by the idler of the unloading car mainly exists within 3 or 3 turns of the outer ring of the steel coil. Locked, when the unloading car is in contact with the outer ring of the steel coil, the idler has a lateral squeeze on the strip, causing the outer ring of the steel coil to gradually overflow.

Control measures:

Regularly check the parallelism of the idler and the locking pin, and deal with any abnormality in time.


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