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Siemens PLC Applications in the Paper Industry: Optimizing Production Processes

Hello to all my friends in the paper mills, today we will discuss how to use Siemens PLC to enhance the efficiency and quality of the paper production line. Paper making is not simple; from wood pulp to finished paper, there are more than a dozen processes in between, and each step requires precise control. The PLC acts like the “brain” of the entire production line, coordinating the various equipment to ensure stable paper quality.

Why Choose Siemens PLC?

When it comes to PLC, Siemens can be considered the “big brother” of the industry. It is like the “positioning roller” on the paper machine, stable and reliable, standing the test of time. Siemens PLC not only has robust hardware with strong anti-interference capabilities, but also flexible software programming that can meet the demands of various complex processes.

Main Applications of PLC in Paper Production

1. Pulp Preparation Control

In the first step of paper making, we use PLC. It controls the speed of the chip refiner and automatically adjusts the refining concentration based on paper quality requirements. This is similar to controlling the water-to-rice ratio while cooking; if you master it well, you can cook delicious rice.

Code Example:

// Refiner speed PID controlIF "Start Refining" THEN    "PID_Compact_1"(        Setpoint := "Set Concentration",        Input := "Actual Concentration",        Output => "Motor Frequency"    );    "Refiner".running := TRUE;ELSE    "Refiner".running := FALSE;END_IF;

2. Delivery System Control

Once the pulp is prepared, it needs to be transported to the paper machine through pipelines. In this process, the PLC mainly controls the start/stop and speed of each pump to ensure stable pulp flow. This is like the human blood circulation system; the heart (pump) must maintain a stable rhythm for the blood (pulp) to flow smoothly.

Note: Sudden changes in flow can easily cause paper sheets to break, so the PLC program should include slow acceleration and deceleration as well as anti-water hammer functions.

3. Dewatering Control at the Wire Section

At the wire section of the paper machine, the task of the PLC is to control the negative pressure of the vacuum dewatering box. This process is like using a straw to drink juice; the suction must be moderate; if it is too weak, the moisture cannot be removed, and if it is too strong, it will suck away the fibers.

Example Ladder Diagram:

|--[ ]--|   |   |  "Start Vacuum Pump"   |  [TON]   |  T1   |  PT = 5s   |  ( )   |  "Open Vacuum Valve"

4. Pressing Section Control

After dewatering at the wire section, the paper sheet is still wet, and pressing is required. The PLC mainly controls the pressure and speed of the pressing rollers. The pressure must be uniform; otherwise, the paper thickness will be inconsistent; the speed must be coordinated; otherwise, the paper sheets may wrinkle.

Hardware Wiring Diagram:

Pressure Sensor -----> PLC Analog Input Module               |               |---> PLC CPU               |Inverter     <---- PLC Analog Output Module  |  |Pressing Roller Motor

5. Dryer Section Temperature Control

After pressing, the moisture content of the paper sheet has dropped to about 50%, and the next step is drying. The main task of the PLC at this stage is to accurately control the steam pressure and adjust the drying cylinder temperature. This is like baking bread; the temperature and time will affect the final taste, and paper making is no different.

Code Example:

// Drying cylinder temperature PID control"PID_Compact_2"(    Setpoint := "Set Temperature",    Input := "Actual Temperature",    Output => "Steam Valve Opening");IF "Actual Temperature" > "Alarm Temperature" THEN    "Main Steam Valve".close := TRUE;    "Alarm Light".light := TRUE;END_IF;

Note: Excessively high drying temperatures can make the paper brittle, while excessively low temperatures can affect production efficiency. The PLC program should set a reasonable temperature curve that automatically adjusts according to the type of paper.

6. Rewinding Control

After the paper is dried, the last step is rewinding. The PLC is responsible for controlling the rewinding tension to ensure that the paper roll is firm and uniform. If the tension is too low, the paper roll will be loose; if too high, the paper may break. This is like fishing; the force used to reel in must be just right.

Practical Application Case: A certain paper mill used to rely on manual experience to control the rewinding tension, resulting in unstable paper roll quality. After upgrading to Siemens PLC control, the tension sensor provides real-time feedback, and the PID algorithm automatically adjusts the rewinding motor speed, significantly improving paper roll quality and reducing customer complaints by 30%.

Common Problems and Solutions

1. Problem: Occasionally, communication interruptions occur during PLC program operation. Solution: Check the site wiring and strengthen signal line shielding; add a communication watchdog to the program to detect and handle anomalies in a timely manner.

2. Problem: Fluctuations in paper moisture content. Solution: Optimize PID parameters and consider adding feedforward control; check if the sensors are accurate and calibrate or replace them if necessary.

3. Problem: Long adjustment time when switching paper types during production. Solution: Utilize the PLC’s recipe management function to preset process parameters for different paper types for one-click switching.

Practical Suggestions

1. Regularly back up the PLC program to prevent unexpected situations.
2. Set reasonable operating permissions to avoid production accidents caused by misoperations.
3. Use the PLC’s data collection function to establish a production management system for traceability of the production process.
4. Pay attention to preventive maintenance of the PLC; regularly check hardware connections and module status.
5. Continuously optimize the PLC program and adjust control strategies based on actual production conditions.

Paper making is a complex and meticulous process, and Siemens PLC is a powerful tool to enhance production efficiency and quality. Mastering these skills will make you successful in the paper industry! I hope everyone can apply what they have learned, and if you have any questions or want to learn more, feel free to leave a comment for discussion. Get your “positioning roller” ready, and let our paper quality be as stable as a rock!

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