“An In-Depth Analysis of the S7-400 Application in Metallurgical Rolling Mill Renovation Projects by an Experienced Engineer”
Today, I would like to share a metallurgical rolling mill renovation project that I recently completed.
This project is quite interesting. The workshop director approached me with a worried expression and said, “Old Zhang, our old rolling mill line is still operational, but the control system is too outdated. It breaks down every day, and the product quality is unstable. What should we do?”
As a veteran in industrial control with 15 years of experience, I immediately decided: “I will take care of this. We will completely renovate it using Siemens S7-400!”
1. Project Background and Requirement Analysis
This is a medium-sized rolling mill production line built in the 1990s, originally using the Siemens S5 series PLC. The main issues are as follows:
- Low control accuracy, leading to significant fluctuations in product thickness
- Frequent system crashes, affecting production efficiency
- Difficulty in sourcing spare parts, resulting in high maintenance costs
- Inability to meet new process requirements
2. System Hardware Configuration Plan
Considering the on-site working conditions, I selected the following configuration:
- CPU417-5H redundant hot standby system
- Power supply module PS407 10A×2
- Ethernet communication processor CP443-1×2
- 8 distributed I/O stations ET200M, including various analog and digital modules
3. Key Points of Control System Design
The most critical aspect of rolling mill control is achieving AGC (Automatic Gauge Control). I adopted the following strategies:
- Closed-loop control of the pressing position: Implemented a fast PID algorithm using SCL
- Closed-loop control of rolling force: Composite control based on Smith predictor with feedforward-feedback
- Control of work roll bending: Developed adaptive control algorithms for different product specifications
4. Implementation Details of the Program
Let’s focus on the implementation of the AGC control program:
//AGC main control loop executed every 100ms
FUNCTION FC100 : VOID
VAR_TEMP
fActThickness : REAL; //Measured thickness
fSetThickness : REAL; //Set thickness
fControlOutput : REAL; //Control output
END_VAR
BEGIN
//Get real-time data
fActThickness := "DB_Process".Thickness;
fSetThickness := "DB_Recipe".TargetThickness;
//PID calculation
#fControlOutput := PID_Control(
fActValue := fActThickness,
fSetValue := fSetThickness,
fKp := 1.5,
fTi := 0.8,
fTd := 0.1
);
//Output limit
IF #fControlOutput > 100.0 THEN
#fControlOutput := 100.0;
END_IF;
//Update actuator
"DB_Control".RollGapOutput := #fControlOutput;
END_FUNCTION
5. Summary of Debugging Experience
-
Steps for system commissioning:
-
First, perform I/O forced testing
- Debugging of individual closed loops
- Empty load joint debugging
-
Trial run with material
-
Common problem handling:
-
PID parameter tuning techniques
- Communication fault diagnosis methods
- Key points for backup machine switching tests
The project ultimately achieved a product thickness deviation control within ±0.02mm, a 15% increase in capacity, and a 60% reduction in defect rate.
As usual, I leave you with a practice question: How can we optimize the AGC control algorithm to improve dynamic response performance? Feel free to discuss in the comments.
Remember, the most important aspects of automation renovation projects are solidity, stability, and reliability. If you have any technical questions, feel free to discuss with me; I, as an old engineer, am open to sharing!
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