Heat tunnels
Review tunnel options.
Tunnel finish
Shrink tunnel cooling and pack distortion guide
Cooling after the tunnel is part of pack quality, especially for retail cartons, printed packs and heat-sensitive products.
Cooling stage
Why pack quality continues after the tunnel exit
The film can remain soft immediately after the shrink tunnel. Handling the pack too soon, stacking it hot or transferring it against rough surfaces can mark the film or distort cartons.
Tunnel temperature, dwell time and airflow must therefore be balanced with outfeed cooling distance and downstream handling.
| Check | How to assess it | Acceptance evidence |
|---|---|---|
| Soft film at exit | Observe whether packs mark or deform when handled. | Allow cooling or adjust discharge handling. |
| Carton distortion | Check corners, panels and product sensitivity. | Avoid excessive heat or unsupported transfer. |
| Airflow imbalance | Look for one-sided shrink, dog-ears or wrinkles. | Adjust tunnel setup or pack positioning. |
| Downstream handling | Check boxing, labelling or operator touch points. | Avoid damaging the pack after a good tunnel finish. |
Practical checks
Evidence that helps diagnose distortion
- Photos before sealing, after sealing and after tunnel exit.
- Film type, tunnel settings and conveyor speed.
- Product material and whether the product is heat-sensitive.
- Distance from tunnel exit to first handling point.
- Reject examples showing where distortion appears.
FAQ
Questions about this topic
Why do packs look acceptable in the tunnel but poor later?
Film can be soft at exit and can be marked or distorted by early handling.
Can cooling solve every distortion problem?
No. Heat level, dwell time, product sensitivity and film choice also need checking.
Should outfeed space be included in the layout?
Yes. Cooling and discharge space can be important for finished-pack quality.