Loose film and burn holes can appear on the same line for different reasons. A useful investigation starts with the last accepted pack and asks what changed: film batch, product geometry, loading pattern, sealing or tunnel settings. Avoid treating the temperature controller as the only cause of every wrapping defect.
What should you record before adjusting settings?
Keep defective and acceptable samples labelled by time and product. Record the film supplier, grade, thickness, pack dimensions and orientation. Compare the actual setup with the approved recipe for the shrink tunnel machine. Check whether the film has been stored and handled according to its supplier's instructions.
Inspect the seal before shrinking. A weak or incomplete seal entering the tunnel can open during exposure and resemble a shrinking problem. Film quantity matters too: excess material around a small pack can leave folds that a temperature change alone will not resolve.
How should you run a controlled comparison?
Use one product and film batch, allow the equipment to stabilize and change only one approved operating parameter at a time. Keep pack spacing consistent and inspect the finished pack after cooling. Record both the improvement and any new defect so the preferred setting reflects the whole pack.
Work within the equipment and material suppliers' operating limits. If the product warps, labels move or film contacts heated surfaces unexpectedly, stop and ask for application support. Do not reach into the tunnel or remove guarding to observe a moving pack.
Which observations help the service team?
- Whether defects occur at the same corner, seam or conveyor position.
- Whether the first packs differ from steady production.
- Photographs of the wrap before and after shrinking.
- Changes in film, loading interval or product temperature.
When should the setup be re-approved?
A new film specification or substantially different product deserves a fresh documented trial. Ask after-sales support to review persistent defects and update the approved recipe after the cause is confirmed. The tunnel sizing guide helps identify when the application needs a different configuration.