The temperature control in the system is managed by the CTSC-200 series 8-channel thermocouple module, specifically the CTSC 231-7TF32. This intelligent controller uses a PID algorithm to regulate the temperature of the controlled area, heating or cooling as needed and providing real-time feedback to the CPU.
Hollow Blow Molding Machine
Process Overview and Control Principle
1. The Process:
1) Plastic Extrusion
The raw plastic material is heated and melted into a uniform fluid, then extruded through the die at a specific pressure and flow rate.
2) Parison Formation
Under gravity and extrusion pressure, the molten plastic forms a parison, which is the pre-shaped structure for the final product.
3) Parison Blowing
Once the parison reaches the desired length, it is placed into the mold. The mold cuts the parison, and compressed air is introduced to inflate it, ensuring contact with the mold walls.
4) Cooling
After inflation, the product is cooled within the mold until it solidifies and takes its final shape.
5) Ejection
Once cooled, the finished product is removed from the mold. The formation and blowing of the parison are the most critical steps in the process, and precise wall thickness control is essential for both quality and cost efficiency.
2. Principles of Blow Molding
One major challenge in extrusion blow molding is achieving consistent wall thickness, especially for large or complex products. Due to the parison’s weight, thinning and necking can occur, leading to uneven thickness. To ensure product quality, the parison must often be made thicker than necessary, increasing material costs. Thus, controlling the parison’s wall thickness is a key factor in improving product quality and reducing material usage. By precisely managing the thickness variation, the final product can achieve even wall thickness while using less material.
Second, PLC Control Program
(1) The system utilizes the CTSC-200 PLC for motion control and includes a 50-point parison wall thickness control system.
(2) Temperature measurement is done using industrial armored thermocouples. The CTSC-200 series 8-channel thermocouple module CTSC 231-7TF32 handles temperature control. This module features an integrated PID algorithm, allowing for precise heating or cooling of the target area and real-time temperature feedback to the CPU.
(3) For wall thickness control, the 231-7HC32 high-speed input module collects data from the electronic scale regarding the parison length and core gap. It then controls the actuator via the 4-channel analog output module 232-0HF32.
(4) A touch screen interface allows users to set, modify, and view various parameters such as parison temperature, extrusion pressure, wall thickness, and cooling time. The system is menu-driven, making it user-friendly and reliable.
Temperature control is achieved using thermocouples, electric heaters, and fans. The PID function is handled by the module, offering both analog and digital outputs, with a single bidirectional control mode. It achieves a control accuracy of ±1°C. Wall thickness control involves an electro-hydraulic servo valve, an actuator, and an electronic scale for position feedback. The wall thickness profile is set digitally, with the 50-point control system adjustable via the operation panel. The Y-axis represents wall thickness, while the X-axis shows the number of points along the parison.
Third, Main Interface
ã€System Features】
1. High-precision 16-bit analog acquisition module CTS7 231-7HC32, fully capable of capturing signals from the electronic scale.
2. Excellent cost-performance ratio—smaller machines can achieve the performance of medium-sized systems, significantly reducing overall system costs.
3. Temperature acquisition modules use isolation technology, offering stronger anti-interference capabilities.
4. The temperature module integrates an intelligent PID algorithm, simplifying programming and enhancing temperature control accuracy.
Fourth, Summary
Currently, large-scale blow molding machine buyers often rely on competitive bidding to purchase equipment, placing high demands on suppliers to deliver high-performance, low-cost solutions. The most critical aspect of "high performance" is precise wall thickness control. However, adding advanced wall thickness controllers can significantly increase costs. The CO-TRUST PLC offers a complete control solution for blow molding machines, including wall thickness control. Its stable performance, low price, and comprehensive support have earned the trust of customers across the industry.
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