The hot rolled slab is descaled with high pressure water in the rolling line of Angang furnace to remove the oxide sheet produced by the slab in the heating furnace. The stability of high pressure water system seriously affects the descaling effect and directly affects the subsequent rolling process. However, the electrical control of high-pressure water system in the process of use, because of the original system design defects, exposed a lot of problems, seriously affect the normal use of high-pressure water system. In view of the problems in production, the scheme is re-formulated, the control system is perfected from the software and hardware, and the stable operation of the high-pressure water system is finally realized.
1 Overview
Angang's high pressure water system consists of 3 sets of pumps, 2 accumulators and 3 hydraulic stations. The pump group is composed of motor, coupler and water pump. It adopts 1 service, 1 backup and 1 maintenance, and is used for coarse descaling and fine descaling of rolling mill. The lifting speed of the high pressure water system is controlled by the coupler, which has a lifting speed valve, a speed regulating spoon tube and a gear detection switch. The accumulator adopts 1 use and 1 backup, and its pressure is detected by 4-20MA pressure transmitter. There is a magnetic flip plate level meter and 6 level switches on each accumulator. The hydraulic station includes lubrication station, 1# hydraulic station and 2# hydraulic station, which are used for motor coupler, coarse removal and fine removal of scale respectively.
2 Control System
The high pressure water control system is controlled by S7-300 PLC. There are 9 stations, PLC1# station and PLC2# station are connected by MPI communication, and the other stations are connected by DP communication, as shown in Figure 1. Screen monitoring using WINCC software
2.1 High pressure water system speed control
Manual speed up control: the manual speed up signal of the coupler, the limit of the third gear of the coupler is not reached, the speed down valve of the coupler is not working, the highest level switch of the selected accumulator is not reached, the speed up valve is powered and the speed up begins.
Automatic speed up control: the pressure value of the selected accumulator is less than or equal to 17MPA, the highest level switch of the selected accumulator is not reached, the limit of the third gear of the coupler is not reached, the speed down valve of the coupler is not working, the speed up valve is powered and the speed up begins.
2.2 Slow down control of high pressure water system
Manual speed down control: the manual speed down signal of the coupler, the zero gear limit of the coupler is not reached, the speed up valve of the coupler is not working, the speed down valve is powered, and the speed down begins.
Automatic slow down control:
(1) The pressure value of the selected accumulator is greater than or equal to 19MPA, the zero gear limit of the coupler is not reached, the speed up valve of the coupler is not working, the speed down valve is powered, and the speed down begins.
(2) Accumulator level protection deceleration: When the highest level switch of the selected accumulator reaches, the zero gear limit comes, and the speed up valve of the coupler does not work, the deceleration valve gets power and begins to decelerate.
3 Problems that occur during operation
3.1 Damage to the PLC 5# station of the 2# pump group resulted in the breakdown of the entire high-pressure water system
Because the accumulator pressure transmitter signal is sent to the PLC5# station corresponding to the 2# pump group; Once the PLC5# station fails, the 2# pump group is shut down, and the signal of the accumulator pressure transmitter is abnormal, resulting in no normal speed rise and fall, and the 1# and 3# pump groups cannot be used normally. The failure of PLC4# station corresponding to the 1# pump group, or PLC6# station corresponding to the 3# pump group, will not affect the pressure of the accumulator, nor will it affect the use of other standby units.
3.2 The Liquid level control of the Accumulator is abnormal
The liquid level detection of the furnace high pressure water accumulator uses the magnetic flap level meter and the liquid level switch, but after many years of use, it is found that the stability of the magnetic flap and the liquid level switch is very poor, the float ball in the magnetic flap is easy to get stuck, and the liquid level switch is also easy to have no signal or false signal. When the liquid level switch has no signal, the accumulator is prone to empty or full tank phenomenon; When there is a false signal of the highest water level, it is easy to cause abnormal speed rise and fall, which seriously affects the safe and stable operation of high-pressure water: at the same time, the magnetic turnover level meter is on the scene, and the local view is inconvenient, and real-time monitoring cannot be achieved
4 Measures taken and effects
4.1 Optimize the PLC system to solve the problem that the three pumps are mutually standby
Select a standby station in the PLC1# station shared by pumps 1#, 2# and 3#, and add the accumulator tank pressure transmitter signal to the standby station by using the distributor; Then edit the program, in the corresponding 1#, 2#, 3# pump control program, add the accumulator pressure control program in parallel, participate in the lifting speed control; At the same time, the switch button of the pressure point of the standby accumulator and the pressure value display are added on the high-pressure water WINCC screen.
When the PLC5# station corresponding to the 2# pump station fails again, just click the switch button on the HMI to change the pressure orientation of the accumulator, and the pressure value of the accumulator will not be affected, so that the operation of the 1# and 3# standby pumps will not be affected, and finally all 3 pumps can be mutually standby pumps.
4.2 Improve the accumulator level control
After research, add a liquid level gauge to the accumulator, select a remote liquid level gauge, model JC-56L-3316mm, and install it outside the magnetic turnover plate liquid level gauge; Select the standby station in the PLC station, lead the 4-20MA signal to the PLC template, edit the PLC program, convert the signal to the liquid level value 0-3316mm, and parallel the signal with the liquid level value greater than 2250mm and the highest level switch of the accumulator to the signal, and add it to the protection speed reduction program of the coupler. In addition, edit the WINCC screen and add the liquid level value display on the high-pressure water accumulator screen.
The level control of the accumulator is optimized to ensure the stable operation of the high pressure water speed. The accuracy of liquid level judgment is improved, the high risk of liquid level switch signal loss is reduced, and the safe use of the accumulator is ensured.
5 Conclusions
The electrical control transformation of high-pressure water system solves a series of control problems of high-pressure water in furnace roll, improves the reliability and safety of high-pressure water system, and ensures the descaling effect. At the same time, it is convenient to judge and solve the fault, reduce the stopping time of the rolling line, and ensure the stable operation of the rolling line.
