Troubleshooting guide
A practical guide to shrink-wrap seal quality, including failures in the tunnel, fine film strands, contamination, inspection and safe intervention.
Seal-quality framework
Seal quality depends on the exact film, clean and aligned sealing surfaces, the approved sealing condition, film tension, product clearance and the amount of material in the joint. Tunnel heat can expose a weak seal but should not be used to disguise one.
| Observed symptom | First evidence to check | Why it matters |
|---|---|---|
| Seal opens in the tunnel | Film identity, contamination, full seal width, product clearance and pre-tunnel handling | Shrink force and heat can expose a joint that was incomplete before entering the tunnel |
| Untidy trim or film strands | Film presentation, seal/cut surfaces, alignment, tension and approved machine condition | The film may not be held or separated consistently across the whole joint |
| Seal varies across its width | Cleanliness, pressure distribution, component condition and film folds | Local differences can create strong and weak sections in one seal |
| Seal holds cold but fails after heat | Film compatibility, joint construction, tunnel exposure and load on the seal | A joint can appear closed but lack the margin needed during shrinking and handling |
Common seal questions
Diagnose the seal at the point where it is created, then confirm that it survives the approved shrink and handling process.
The joint may be incomplete, contaminated, uneven, overstressed by a tight film envelope or unsuitable for the exact film. Tunnel heat and film contraction can reveal that weakness. Product movement or a seal placed against a sharp edge can add further load.
Inspect the film and full seal before heat. Do not compensate for a weak joint by changing tunnel settings without finding the sealing cause.
Fine strands can occur when the film is not cut and separated cleanly across the whole seal. Possible contributors include film presentation, contamination, component condition, alignment or a sealing/cutting condition that does not match the approved film.
Only authorised personnel should inspect hot or moving sealing parts, following the machine instructions and isolation procedure.
No. The tunnel can shrink film around the product, but it is not a reliable repair stage for an incomplete or contaminated seal. Extra heat may increase stress on the joint and create new film or product defects.
Correct the seal at the sealing stage, then confirm it through the approved tunnel recipe and downstream handling.
A joint can look closed before heat yet lack enough uniform strength for the shrink force, film softening and handling load that follow. Variations in film folds, contamination, pressure or seal width may only become visible in the tunnel.
Test the complete joint and retain a known accepted sample so early deterioration can be identified.
Inspect the entire seal for continuous closure, consistent appearance, contamination, folds, thinning, gaps and product contact. Check it before the tunnel and again after shrinking and cooling. The accepted method should reflect the real pack duty rather than one isolated pull.
Where a formal seal test is required, define the method and acceptance limit for the specific film and application.
Extra layers, creases, dust, oil, product residue or labels in the joint can prevent uniform heat and pressure from reaching the intended film surfaces. The result may vary across one seal even when the controller setting is unchanged.
Control the film path and product position so the seal area arrives flat and clean.
Stop and follow the site procedure when the defect could allow the pack to open, release a product group, damage equipment, create unsafe film accumulation or fall outside the agreed acceptance standard. Repeated adjustment without identifying the cause can make the process less stable.
Any inspection or clearing near hot, moving or energised parts must use the approved safe intervention method.
Seal review
Provide the film identity, full-seal photographs, product orientation, current recipe, defect location and a known accepted pack so Lancing can help identify the process stage.