Techniques for controlling hot-rolled flatness

The shape and automatic control of the rolling mill is a key link in the field of hot-rolled strip technology and equipment, and is also the fundamental guarantee for the production of high-precision, high-value-added products. Compared with the foreign advanced level, there is still a big gap in our country in terms of automation system hardware, large-scale online detection instruments, and pre-set models of plate shape, thickness, temperature, and pressure.

Flatness control technology and equipment: the bottleneck of the preset model must be broken

In the development process of rolling mill flatness control technology and equipment, a hundred flowers blossomed, and various flatness control methods continued to emerge. However, after years of production practice, the current more effective form control methods are CVC, PC, WRB/WRS, which are in a three-pronged manner. Variable crown support rolls (VC) and overall shape control system (DUGS) are also constantly being improved and gradually popularized and applied.

The principle of the CVC flatness control system is that the diameter of the work roll changes continuously. When the upper and lower work rolls are matched, the shape of the roll gap changes with the length of the work roll body. The work roll gap is obtained by the axial movement of the work roll. The positive and negative crown changes, so as to realize the control of the strip crown. The crown control ability and the axial movement of the work roll have a linear relationship. The crown control ability can reach 1.0 mm.

PC paired cross rolling mill changes the roll gap crown through the cross of the upper and lower rolls. The characteristic of the PC rolling mill is that the crown control range is proportional to the square of the intersection angle. When the intersection angle is 0 to 1.5 degrees (the intersection angle is controlled within 1 degree in actual use), the crown control range is 0 to 1400 Mm. The PC rolling mill has two methods, single cross and double cross. The cross movement of single cross is twice that of double cross. Therefore, the double-cross rolling method is generally used in wide-band steel rolling mills, while the single-cross rolling method is used in narrow-strip steel rolling mills (such as Baosteel's 1580 mm rolling mill). The PC rolling mill adopts an online roll grinding method in the rear stand to eliminate roll wear and realize free rolling.

WRB/WRS system work roll bending and axial movement of the work roll is a wide range of use and a long history of flatness control method, especially before PC and CVC were put into practical application, many manufacturers in the world In this way, companies such as Hitachi of Japan (which it calls HCW), CLECIM of France, UNITED of the United States and other companies. WRB/WRS uses work roll bending (WRB) to control crown and flatness, and work roll axial movement (WRS) reduces work roll wear to achieve free rolling. The crown control ability depends on the bending force. CLECIM's bending force is 240 tons (the company's SollacFOS factory), the crown control capacity can reach 500 mm, and the flatness can reach ±30IU.

DUGS is a kind of WRB/WRS, equipped with work roll thermal crown control system (RTC: along the length of the work roll body through the work roll cooling water nozzles distributed in an arc to control the work roll cooling, so as to ensure the work The stability of the roll thermal crown). In the front frame, a heavy-duty work roll bending system (+200 tons/-120 tons) and RTC are used, and the work roll is equipped with axial movement to control the strip crown.

The VC method has a variable support roller profile, but the methods are not uniform. There are support roller inner cavity hydraulic type, support roller outer lining type, support roller step type, etc., but they are generally less used in the production of hot-rolled strip steel.

In addition to the above devices, the key to flatness control lies in pre-setting and online adjustment of the control model. Among them, the preset model is more complicated. It is the most difficult model setting in the field of hot strip steel. It mainly includes the following technical difficulties: the thermal deformation of the roll system and the mechanism of deflection deformation and online algorithms; Transverse and longitudinal flow mechanism and online algorithm in the process, roll gap change mechanism and online algorithm under the action of rolling pressure and roll bending force, prediction mechanism and online algorithm of shape defects that may exist under different roll gap conditions, roll bending force The incoherent mechanism of rolling pressure during AGC adjustment, related mechanisms of crown and flatness, online adjustment mechanism of crown and flatness, prediction of work roll axial force, prediction of work roll wear, axial movement strategy, etc.