Finish control
Temperature, airflow and dwell time are balanced for the required shrink result.
Heat tunnels
Controlled shrink finish for L-sealers, sleeve sealers and shrink wrapping lines.
Product option
Heat Tunnels
The heat tunnel is responsible for the final pack appearance. It must be matched to the film, pack size, conveyor speed, airflow, temperature setting and the upstream sealing equipment. Correct tunnel selection helps avoid loose film, burn-through, distorted packs and inconsistent presentation.
- Specified around film type, pack size and desired shrink finish.
- Works downstream of L-sealers and sleeve sealers.
- Tunnel length, chamber size and conveyor speed should match output.
- Useful for improving presentation quality and consistency.
Specification guidance
Key checks before quoting
Final machine selection should be matched to real products, film, output, space and available utilities.
| Best fit | L-sealer lines, sleeve sealer lines and presentation shrink packs |
|---|---|
| Main checks | Tunnel aperture, belt speed, heat capacity and airflow |
| Film types | Typically POF, PE or PVC depending on application |
| Quote data | Pack dimensions, film thickness, speed and finish expectations |
Why it matters
How this route is usually selected
Integration point
Tunnel size and conveyor height need to suit the upstream sealing machine.
Quality improvement
Correct tunnel selection improves pack consistency and reduces rework.
Next step
Send your pack details for a practical recommendation
Send product dimensions, weight, pack format, required speed, film preference and available space. Lancing UK can then confirm whether this route or another machine type is the best fit.
Send enquiryTunnel setup guidance
Heat tunnel settings that affect finished pack quality
The tunnel is where the film finish is made visible. Even when the L seal is technically sound, poor tunnel setup can cause wrinkles, dog-ears, pin holes, overheated packs or inconsistent presentation. Temperature, belt speed, airflow direction, aperture size and product spacing should be treated as linked settings.
The correct settings vary by product and film. Lancing should be given the product size, film material and expected finish so the tunnel can be considered alongside the sealing frame, not added as a generic accessory.
| Selection point | What to confirm | Why it matters |
|---|---|---|
| Temperature | Set according to film type, pack size and tunnel design. | Too much heat can distort products or film; too little can leave wrinkles and loose corners. |
| Conveyor speed and dwell | Control how long the pack remains in the heated area. | Dwell time affects shrink recovery and can be more important than temperature alone. |
| Airflow | Check whether airflow reaches the sides, corners and underside of the pack. | Uneven airflow can create one-sided shrink, dog-ears or unstable film recovery. |
| Cooling | Allow space for the film to stabilise after the tunnel. | Finished packs often need cooling before handling, labelling or case packing. |
Information to prepare before a quotation
- Film type and thickness.
- Pack dimensions and product heat sensitivity.
- Required conveyor height and belt width.
- Target pack finish and acceptable wrinkle tolerance.
- Downstream handling distance after the tunnel.
Airflow guide
Understand tunnel airflow and why pack spacing matters.
Temperature problems
Troubleshoot overheated, loose or wrinkled film.
L sealer combination
Specify the tunnel with the L sealer as one system.
Buyer FAQs
Can the same tunnel settings run every film?
No. POF and PE films can require different behaviour, and pack size also changes dwell and airflow needs.
Why do corners sometimes stay loose?
Loose corners can come from film allowance, poor air release, insufficient dwell, uneven airflow or product shape.
Should tunnel aperture be oversized?
It needs clearance, but a very large aperture can reduce control and efficiency for small packs.
Does cooling affect pack quality?
Yes. Handling a warm pack too soon can mark the film or change the final presentation.
What should be checked in a trial?
Check seal strength, wrinkles, dog-ears, barcode visibility, film clarity and pack temperature at discharge.
Related guidance: POF vs PE film · Seal quality guide · Sample testing
Tunnel quality controls
Heat tunnel settings that need evidence, not guesswork
In an L-sealer line, the heat tunnel often decides whether the pack is commercially acceptable. A sealed pack can still fail if the tunnel airflow is uneven, dwell time is too short, cooling is insufficient, the pack holds trapped air or the chosen film does not suit the product geometry.
| Tunnel variable | Practical check | Finished-pack effect |
|---|---|---|
| Temperature | Set against the film and product, then record the run condition used for samples. | Too low can leave loose film; too high can distort, cloud or mark the pack. |
| Dwell time | Check conveyor speed and pack length together rather than only the temperature setting. | Affects how fully the film recovers around corners and edges. |
| Airflow | Look for even shrink on both sides, top surface and corners. | Uneven airflow can leave dog ears, waves or inconsistent presentation. |
| Cooling | Assess the pack only after the film has stabilised. | Warm packs can mark, stick, wrinkle or deform if handled too quickly. |
| Energy and utilities | Confirm supply, duty pattern and tunnel aperture before final layout. | The real operating cost depends on the selected tunnel, film, output and production pattern. |
Heat tunnel evidence for a quote
Useful quote evidence includes pack dimensions, film type, required finish, target output, product heat sensitivity, whether packs are labelled before shrinking and whether the discharge goes directly to boxing, accumulation or another machine.
Related pages: airflow guide · temperature settings · polyolefin tunnel guide · PE tunnel guide
Tunnel quality evidence
Heat tunnel setup checks for L-sealer shrink wrapping
A heat tunnel is not only a heater. It is a controlled airflow and dwell-time stage that turns a loose sealed bag into a finished pack. Good tunnel selection considers product sensitivity, pack height, film type, conveyor support and cooling distance.
For L-sealer projects, the tunnel needs enough opening clearance for the product and enough process control to shrink the film without distorting cartons, soft packaging, printed artwork or barcode areas.
| Point to confirm | What Lancing checks | Why it matters |
|---|---|---|
| Temperature setting | Film response and product sensitivity. | Too little heat leaves wrinkles; too much heat can distort packs or damage presentation. |
| Airflow pattern | Pack corners, underside and trailing edge. | Uneven airflow causes uneven shrink, dog-ears and weak visual finish. |
| Conveyor support | Pack weight, footprint and stability through the tunnel. | Prevents rocking, falling and contact marks. |
| Cooling area | Space after tunnel before packing or handling. | Reduces marking while film stabilises after shrinking. |
Shrink tunnel cooling guide
Reduce distortion and handling marks after shrinking.
Shrink tunnel airflow guide
Understand airflow and dwell behaviour.
Pack quality criteria
Agree visual quality standards before trials.
Final specification FAQs
Is a larger tunnel always better?
Not necessarily. The tunnel should be sized around clearance, dwell time, airflow and line speed.
Why do packs distort in the tunnel?
Distortion can come from excessive heat, poor support, sensitive products, insufficient cooling or unsuitable film tension.
Can the same tunnel run different films?
Possibly, but settings and pack quality must be checked for each film and product combination.
Useful next step: Send product dimensions, photos, film details and target output through the existing enquiry form so Lancing can check the L-sealer route before quotation.
Tunnel behaviour
Questions that separate heat exposure, airflow and cooling problems
A shrink tunnel should be assessed as a controlled heat-and-transfer process. The displayed temperature is only one variable; product geometry, airflow, dwell time, conveyor contact and the discharge environment all influence the finished pack.
Which part of a product usually sees the greatest heat exposure in a shrink tunnel?
Direct answer: There is no universal hottest point because exposure depends on airflow direction, product shape, conveyor contact and the position of the pack in the tunnel.
Corners, raised features and surfaces close to strong air jets can react differently from recessed areas or the underside. Heat-sensitive applications should be checked with representative samples and, where necessary, suitable temperature evidence rather than assumed from the setpoint.
Why can a pack look acceptable when hot but change after cooling?
Direct answer: Shrink film and the packaged product continue to stabilise after leaving the heated zone, so wrinkles, distortion or conveyor marks may become more visible during cooling.
A hot pack can also be soft and easily displaced by guides, accumulation or manual handling. Acceptance should therefore include the cooled pack after the normal discharge and handling sequence, not only its appearance at the tunnel exit.
How can draughts or cold discharge areas affect the finished shrink pack?
Direct answer: Uneven or abrupt cooling can set the film at different rates across the pack and can make a marginal process look inconsistent.
Open doors, strong extraction, fans or cold storage interfaces may alter the discharge condition. The effect is application-specific, so the site trial should observe the real location and the time allowed before packs touch, turn or accumulate.
How can a buyer separate a sealing fault from a tunnel fault?
Direct answer: Inspect the closed film pocket before shrinking, then change one tunnel variable at a time while keeping the seal and film route stable.
If the seam is already weak, contaminated, folded or misplaced before the tunnel, more heat will not correct the cause. If the unshrunk seal is sound but the finished pack is loose, distorted or marked, the tunnel, perforation, film choice or cooling stage should be investigated.
Related guidance: Heat-sensitive products · Tunnel conveyor support · Cooling and distortion
Tunnel finish window
Why the shrink tunnel must be tested with the actual film pocket
Direct answer: A shrink tunnel cannot be selected only from aperture size or temperature. The tunnel finish depends on the sealed film pocket entering the tunnel, the film type, perforation, dwell time, airflow, product heat sensitivity and the cooling route after discharge.
For L-sealer projects, the useful trial is the complete seal-and-shrink process. A pack that seals cleanly may still wrinkle, balloon or distort if air cannot escape or if the tunnel and discharge sequence are unsuitable for the product.
Related guidance: Film and seal-window testing · Cooling and distortion · Tunnel conveyor support
Tunnel result checks
Tunnel settings work best when film air release is correct
Direct answer: A shrink tunnel can only recover the film properly when the pack, seal and trapped-air route are already suitable. Temperature, conveyor speed and airflow can improve a pack, but they may not solve ballooning, seal stress or wrinkles caused by insufficient air evacuation.
When a pack leaves the tunnel with loose corners, wrinkles or distortion, check film width, perforation, seal position, tunnel dwell and cooling as one system. Raising tunnel temperature alone can make heat-sensitive products worse if the root problem is trapped air or poor support.
Related guidance: air evacuation and perforation · tunnel conveyor support · airflow guide