EVFD used in 20-high reversing mill

After the successful operation of Nancal 690V industrial AC drives used for SG-650 4-high reversing mill in a stainless steel plant in Jieyang city, Guangdong province China, Nancal EVFD was successfully applied again in the Sendimir 20-high reversing mill project of another stainless steel plant in Jieyang, with the rated capacity of 6150kW.

The successful application further verified the excellent performance of NC EVFD series industrial AC drives, it can fully meet the stainless steel cold rolling industry applications, breaking the monopoly by ABB, Siemens and other top brands.

This article mainly introduces the application of Nancal EVFD series AC drives used in the 20-high reversing mill project.

The production line is designed to roll the steel plate from 5mm to 0.15mm. The power of the whole system is large, which requires high transmission stability and control accuracy of speed and tension.

Compared with 4-high and 8-high mills, the 20-high mill has better process performance and higher control precision.
During the rolling process, the system can control the output torque of the coiler in real time according to the size of the coil diameter, so as to maintain the stability of the coil tension in the rolling process. The main rolling mill can better control the linear speed of the steel coil. The main mill adjusts the roll thickness by changing the force of the press.

In addition, the 20-high mill also has the rolling process of rewinding, which is applied to the final rolling of the coil unevenly wound. During the rewinding operation, the steel requiring rewinding is placed on one side of the coiler and the stable tension is output at the same time. The coiler on the other side runs until all the steel is dragged around a coiler. The main mill does not participate in the whole process of control and drive, rolling diagram is shown as below:


In this project, Nancal EVFD drives a total of 4 motors: 1* 1900kW main rolling motor, 2 *2000kW winding motors and 1* 250kW unwinding motor. The input voltage of the VFD is 690VAC.The rated frequency of the main rolling motor is 18.2hz, the maximum operating frequency is 56.6hz, the rated frequency of the coiler motor is 12.7hz, the maximum operating frequency is 48.2hz, the tension control accuracy is less than 1%, the maximum rolling linear speed is 600m/min, the rated voltage of the motor is 660V, driven by NANCAL common dc bus multi-drives type EVFD., multi-drive rectifier unit adopts AFE front active rectifier, with low harmonic regeneration function. See figure 4 for the system configuration.

The technical solution of this case is based on high performance industrial microcomputer, programmable logic controller (PLC) and ac drive control system. The industrial field bus is used for the communication between VFD and SCADA system.
PLC is mainly responsible for converting the speed tension into the acceptable speed and torque limit of the VFD, and then transmitting it to the control system through the communication of DP bus. The control system of drive carries out corresponding calculation according to the received speed or torque limit.
2.87*1040mm steel coil was rolled on trial production. After 10 processes, the final product was 0.415*1040mm steel coil. The rolling data records are shown in table 1.
Process No.
Thickness of left roiling (mm)
Thickness of right roiling (mm)
Reduction ratio (%)
Tension of left roiling (kN)
Tension of right roiling (kN)
Roll force (T)
Speed of main rolling mill (r/min)



Speed (m/min)
1 2.87 2.35 18.97 52.8 249 252 59 32.3
2 1.88 2.35 20.0 255 216 286 159 82.8
3 1.88 1.51 19.68 222 246 259 93 52
4 1.22 1.51 19.21 225 210 242 223 121.1
5 1.22 1.0 18.02 189 207 227 280 151.6
6 0.82 1.0 18.0 189 171 231 280 152.2
7 0.82 0.68 17.07 147 162 244 148 80.3
8 0.57 0.68 16.18 135 120 225 93 51.1
9 0.47 0.49 14.04 118 127 200 90 50
10 0.415 0.49 15.31 117 99 199 91 50.5
During the whole rolling process, NC EVFD runs stably, the control performance is excellent from large tension to small tension, from zero speed hover to maximum speed operation control, from small load to large load rolling. Both tension and speed control accuracy are excellent, fully meet the strict requirements of field rolling technology on the drive system.