Frekvenčné meniče

Transformation Application of SB70 Inverters in Winding of Stainless Steel Sheets

Nitrogen bright annealing furnace – Put the stainless steel sheets into the nitrogen bright annealing furnace for high-temperature treatment to soften the sheets before subsequent processing series to form finished product. This procedure is of crucial importance in its impact on quality of the products, and therefore has high requirement. It generally consists of several components: unwinding motor, before the pressure roller motor, S club motor, winding motor, etc. The unwinding motor, front roller motor, S roller motor has power of 5.5 kW and the winding motor has power of 30 kW. Operation process of system – A roll of stainless steel sheet is led by the unwinding motor into the annealing furnace through the front roller; after high-temperature heating treatment, and then led by S roller motor, and wound by winding motor. During the work process, the constant linear speed of each part is constant, which has important effect on the subsequent processing of the products. It is shown as follows:

Fig. 1 Schematic Wiring Diagram of Winding Stainless Steel Sheets

Before the transformation, traditional inverter synchronization method is previously used for control. However, frequency conversion control can only guarantee synchronization of S roller motor and winding motor in speed. For the winding motor part, with the increase of winding turns, the outer diameter is gradually enlarged, and its linear speed is required to be unchanged; therefore, it is actually constant tension between the two. To maintain a constant speed, the operator must always measure the linear speeds of S roller motor and winding motor, and according to the difference of the measured speeds, manually change the frequency of S roller inverter and winding inverter to adjust the linear speeds of the two in order to achieve consistent linear speeds. As it is difficult for manual operation, which cannot achieve constant tension control or constant linear speed control for winding stainless steel sheets, and thus cannot maintain a constant tension, the excessive large tension and tautly deformed steel sheets or excessive small tension and loosely deformed steel sheets are often the results, affecting the quality of the products. Moreover, the previous winding system has the following drawbacks: 1. As each power point receives non-uniform force, the system can not run in the same linear speed; 2. S roller motor is liable to slip at low speeds; 3. Overload and stalling often occur to the winding motor; 4. In material feeding and discharge, it is difficult to control.

Under the existing conditions, for the winding motor, with the increase in volume diameter, as long as the S roller motor and winding motor can always maintain constant linear speed (i.e., constant tension), the technological requirements of the winding system is satisfied. For this, in the original system, frequency-conversion speed regulation is adopted for transformation. As the unwinding motor is at the front stage, the requirement in tension control is not high; therefore, transformation will only be made on the S roller motor and the winding motor. The S roller motor of the system will adopt SB70G5.5 kW. Between the S roller motor and winding motor, there is a flexible connection for stainless steel sheets. If the winding motor has linear speed higher than that of S roller motor, the S roller motor will be in power generation state, and therefore, the inverter needs to be provided with external braking resistor. Winding motor adopts SB70G30KW, while the inverter adopts vector control without PG and uses the rich arithmetic logic unit of SB70, and through connection of internal computing unit, to increase torque limitation on the basis of the speed control. Torque limitation value is given directly by the internal arithmetic unit, based on 100% of the 2.5 times of the motor rated torque.

The analog output frequency of S roller SB70G5.5 kW is used as the given value of the linear speed to supply the winding motor, and by regulating the gain and offsetting of corresponding input signals of the inverter as linear speed signal, to carry out the calculation, limitation of the torque, in order to achieve constant linear speeds of the S roller motor and winding motor. The schematic wiring diagram of the inverter is shown in Figure 2:

Fig. 2 Schematic Wiring Diagram of Tension Control Inverter

For S roller inverter, the setting is relatively simple. For frequency setting, the potentiometer setting and external control starting is configured. Emergency stop button that has combined movement with the winding motor is provided in case of emergency stop. In just starting the winding motor, inching function is needed, and therefore, inching function is provided. In inching, torque limitation is switched by the analog switch in the inverter to make the torque limitation to be 100% in inching.

The scheme has been used to make transformation for winding of the four nitrogen bright annealing furnace and has been successfully applied. After transformation, with the constant-tension winding, the precision of processing is high, and the product quality is greatly improved. It is safe, reliable and of stable performance, and improves production efficiency. The system is not provided with tension sensor. The speed encoder realizes the control of linear speeds and constant tension of S roller and winding motors, which has won favorable praise from the users who have expressed high recognition and satisfaction of the excellent and powerful function of SB70 inverters.