Common Tension Control Issues in Stretch Film Machines – Explained
Release time:
2025-08-13 17:56
Throughout the entire production process of stretch film, tension control is the cornerstone that runs through every stage. From the moment the melt leaves the die head until the final winding and forming, any loss of tension control at any point will directly impact the quality of the film. This article will conduct an in-depth analysis of common issues in stretch film machine tension control systems, helping you identify the root causes of faults and providing effective solutions to ensure your production line operates smoothly and efficiently.
Tension Control System: Why Is It So Critical?
A precise tension control system is the invisible hand that enables cast film extrusion machine to produce high-quality film. It ensures that the film maintains a stable and appropriate tension throughout the entire production process, from the cooling roll to the winding roll. Any issues can lead to quality defects such as uneven thickness, width variations, and excessive internal stress.
Analysis and Solutions for the Three Most Common Issues
We have categorised the common issues with tension control systems in stretch film machines into three main categories and analysed each one in detail.
1. Large Tension Fluctuations, Alternating Between High and Low
This is the most common and most frustrating issue. It causes uneven internal stress in the finished roll, making it prone to breaking during use.
Cause Analysis:
- Mechanical factors: Wear on the bearings of the guide rollers, poor dynamic balance, or contaminants on the surface can cause periodic tension fluctuations during rotation.
- Electrical factors: Decreased sensitivity of the tension sensor (Load Cell) or signal interference; slow response of the actuator (such as a magnetic powder brake or servo motor) that controls tension output.
- PLC program issues: Improper PID parameter settings causing the system to over-respond (overshoot) or lag in response to tension changes.
Solutions:
- Regularly inspect and clean all guide rollers, and replace worn bearings.
- Calibrate the tension sensor, check its wiring for secure connections, and eliminate electromagnetic interference.
- Perform self-tuning of PID parameters to find the most suitable control parameters for the current production speed and material.
2. Overall tension is too high or too low
Cause analysis:
- Improper tension setting: The tension value set by the operator does not meet the requirements for the current production film thickness or material.
- Sensor zero drift: After prolonged use, the tension sensor's zero point may drift, causing systematic deviations between measured and actual values.
- Actuator malfunction: The brake or motor controlling tension has issues, unable to output the correct torque.
Solutions:
- Reset the tension value to a reasonable level according to process requirements. Generally, the thinner the film, the lower the required tension.
- Regularly perform ‘zero calibration’ on the tension sensor.
- Inspect and repair or replace faulty tension actuators.
3. Uneven tension on both sides
This typically causes film misalignment or wrinkling on one side.
Cause Analysis:
- Guide rollers are not parallel: This is the primary cause. If the guide rollers on the production line have angular deviations, it will result in uneven force distribution on both sides of the film.
- Uneven extrusion from the die head: If the film curtain extruded from the die head has significant thickness variations, it will naturally cause uneven tension on both sides.
- Winding shaft issues: Leaking air-expandable winding shafts or uneven expansion at both ends.
Solutions:
- Use a spirit level and laser alignment tool to carefully calibrate the parallelism and levelness of all guide rolls.
- Adjust the die head to ensure even extrusion.
- Inspect or replace faulty winding air-expandable shafts.
Quick Troubleshooting Guide for Tension Control System Issues
| Common Issues | Primary Possible Causes | Troubleshooting Steps |
| Large Tension Fluctuations | 1. Mechanical vibration 2. Electrical interference 3. Improper PID parameters | 1. Inspect guide roller bearings and cleanliness 2. Inspect sensor wiring 3. Perform PID self-tuning |
| Overall high/low tension | 1. Incorrect setpoint 2. Sensor zero drift | 1. Verify process parameters 2. Calibrate the sensor |
| Uneven tension on both sides | 1. Guide rollers not parallel 2. Uneven material output from the die head | 1. Laser-calibrate the guide rollers 2. Adjust the die head |
Conclusion: Systematic maintenance is the key
An analysis of common issues with the tension control system of stretch film machines indicates that the majority of problems stem from improper maintenance or incorrect parameter settings. These issues not only affect the main machine but also directly impact downstream cling film rewinding machine, leading to more significant quality issues. The resulting scrap, even if recyclable via a plastic granulating machine, has already caused irreparable losses.
Establishing a systematic equipment inspection and regular maintenance system is the fundamental solution to prevent these issues. Additionally, enhancing operator training to ensure they understand the basic principles of tension control is equally important. More professional equipment knowledge can be found on the Wintech Machine Knowledge page. As emphasized by the industry authoritative media Converting Quarterly, a deep understanding of process control is the key to achieving high-quality production.
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