Selection of hot coil box in hot strip rolling

coil box,hot rolling,hot rolled

1. Advantages of the hot coil box technology

The practical application shows that the hot coil box technology has the following advantages:

(1) Conducive to the transformation of the old production line.

For the production line that is limited by the site during the renovation, the use of hot coil box technology can increase the unit coil weight and improve the production capacity and yield of the rolling line.

(2) Reduce rolling line investment.

First, it can shorten the distance between rough rolling and finishing rolling; second, it can reduce the length of the heat output roller table; third, because the finishing rolling unit can achieve constant speed rolling, the peak load of the motor is small, so the main motor can be reduced. power, thereby reducing investment. Generally speaking, it has great reference value for the transformation of old factories. For the new design project, not only the constant speed rolling in the hot coil box mode but also the speed-up rolling of the finishing mill should be considered in the case of the hot coil box failure. Therefore, it is not necessary to blindly pursue the minimization of investment and reduce the main motor power, but should be fully balanced.

(3) Energy saving and consumption reduction.

First, the hot coil box can play a certain role in heat preservation, delaying the temperature drop of the intermediate billet and reducing the actual power consumption of the finishing mill; The peak load in the accelerated rolling process is reduced, the power of the main motor is reduced, and the power consumption is saved.

(4) Improve product quality.

One is to change the situation that the tail of the intermediate billet stays in the air for a long time when there is no hot coil box, which causes a lot of secondary iron oxide scale; the other is that the temperature difference between the head and tail of the intermediate billet entering the finishing mill is relatively small, and the thickness control ability is not strong. The old rolling mill helps to improve the thickness control effect.

(5) Improve the yield.

The finishing mill and the coiler are the high failure areas of the entire hot tandem rolling line. After the hot coil box is used, if the equipment in this area fails, the hot coil box can play a role in heat preservation for a certain period of time. After the failure is quickly dealt with, the hot coil box is uncoiled, the low-temperature head of the intermediate billet is cut off by flying shears, and the remaining part can be continued to be rolled. This reduces the scrap rate and increases the yield of the rolling line.

2. Insufficiency of the hot coil box technology

2.1 Influence of hot coil box on accelerated rolling function

One of the advantages of the coil box is that accelerated rolling can be avoided without a coil box. Conversely, when accelerated rolling is required, the hot coil box presents deficiencies. In order to ensure that the final rolling temperature fluctuates in a small range, the strip that enters the finishing mill after being coiled by the hot coil box cannot be accelerated but needs to be decelerated. The immediate consequence is a reduction in the capacity of the rolling line. Without the use of a hot coil box, high-speed rolling can be achieved and the production capacity of the rolling line can be increased.

2.2 Influence of hot coil box on finishing temperature

After the intermediate billet passes through the hot coil box, although the temperature in the whole length direction is relatively uniform, the temperature of the rolling stock entering the finishing mill will decrease by about 30-40 °C. This is because after several passes, the temperature of the tail of the intermediate billet is lower than that of the head, and after the head and tail are exchanged in the hot coil box and stay for a long time, the overall temperature of the rolled piece will drop. For example, the intermediate billet of 30 mm × 1250 mm reaches the finish rolling F, and the temperature after it is about 920-930 ° C, and does not reach F through the head of the intermediate billet of the hot coil box. The temperature can reach 970~1000℃.

2.3 The high maintenance requirements of the heat coil box itself

Hot coil boxes reduce scrap rates due to failures in the finishing train or coiler area. However, the structure of the hot coil box equipment is relatively complex, and it is a high failure rate equipment itself, which requires a lot of maintenance work and sufficient spare parts to meet the needs of continuous production.

2.4 Generally not suitable for special steel rolling

High-strength or difficult-to-deform steel grades, such as silicon steel, special alloys, etc., due to the narrow deformation temperature range, the edge is prone to cracks. One of the main points of rolling is how to ensure the edge temperature of the intermediate billet, so it is generally not suitable to use a hot coils box and other devices should be used to meet its requirements.

2.5 The uncoiling of the hot coil box affects the stability of the tension after finishing rolling

With the progress of uncoiling, the coil diameter and weight of the steel coil in the hot coil box continue to decrease. During the coreless moving process, the phenomenon that the finishing mill drags the remaining steel coils in the hot coil box will seriously affect the F1 The stability of the post-tension during the rolling process affects the thickness control effect of the rolled piece.

2.6 The wave shape of the head affects the precision of shearing

Although the wave shape formed during coiling can be improved by pinch rollers and straightening rollers during the uncoiling process of the hot coil box, it is difficult to completely eliminate the wave shape, which will affect the shearing accuracy of the flying shear.

2.7 During the uncoiling process, the roller table will scratch the lower surface of the intermediate blank

With the progress of uncoiling, when the unit coil weight of the steel coil is less than a certain value, it will be passively transferred. At this time, the translation speed of the steel coil is greater than the rotation speed of the steel coil, and the steel coil and the roller table are in a sliding rather than rolling contact state, and the roller table may scratch the lower surface of the intermediate blank, which has a greater impact on the production of high-quality products. big.

2.8 Affect the rolling rhythm

In the active coreless transfer mode, the transfer from the coiling position to the uncoiling position only starts when the weight of the coil is greater than a certain value. The longer the coil stays in the coiling position, the greater the impact on the rhythm of the entire rolling line.

3 Conclusion

Hot coil boxes have both advantages and disadvantages in industrial applications. Whether it is a new project or a renovation project, it is recommended to take the above content as the starting point and conduct a comprehensive evaluation of the selection of thermal coil boxes according to the characteristics of each enterprise, so as to obtain a perfect construction or renovation plan.

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