Shrink tunnel temperature is one input to a thermal-exposure process. Conveyor speed sets residence time, airflow moves heat around the package, and product spacing and load pattern affect how that air reaches each surface. Film, package geometry, product sensitivity, conveyor support and cooling complete the recipe.
Qualify the recipe on the actual tunnel and product family. A displayed temperature is neither a universal setting nor proof of uniform exposure.
Define the Recipe Boundary
Before trial work, identify exactly what the operator can control and what remains fixed by the tunnel design. Depending on the model, the recipe can include one or more temperature-zone references, conveyor-speed reference, permitted airflow or damper positions, fan mode and cooling settings.
Record each control in its displayed unit. Do not translate a dial position or percentage into an assumed physical temperature or air velocity. Settings from another tunnel are not transferable evidence.
Lock the Non-Tunnel Inputs
A tunnel recipe cannot be qualified while upstream package conditions are changing. Fix and record:
- Film manufacturer, grade, structure, gauge, width and lot.
- Product, orientation and pack arrangement.
- Film amount and seal acceptance before tunnel entry.
- Conveyor surface and support configuration.
- Product gap and number of packs entering per minute.
- Cooling and downstream handling condition.
If the pre-tunnel package is already inconsistent, correct that process before changing tunnel controls.
Group SKUs by Thermal Challenge
Do not create one recipe per product by default. First group products that share film, comparable geometry, load pattern and validated product tolerance. Then identify the limiting members of each family:
- Highest or widest product that challenges air access.
- Dense or heavy product that changes load behavior.
- Light or empty package that is easier to distort or destabilize.
- Product with the most sensitive label, adhesive, surface or component.
- Multipack most likely to shift before film sets.
One product may represent several limits. Document why each test SKU was selected.
Run a Recipe-Qualification Sequence
Start within the machine manual and film supplier’s approved guidance. Use the following sequence:
- Bring the tunnel to its machine-defined ready condition.
- Confirm the locked film, package and spacing inputs.
- Run the baseline recipe through enough packages to reach a stable result.
- Inspect the complete package and product against written acceptance criteria.
- If adjustment is permitted, change one recipe value by a small authorized step.
- Repeat the same load pattern and record the result.
- Keep the last acceptable state available for controlled restoration.
- Stop and escalate if acceptable results require settings outside approved limits or equipment behavior becomes abnormal.
Do not intentionally drive the product or film to a damage boundary. The target is a repeatable accepted package with margin inside the approved operating range.
Challenge the Recipe with Real Loading
An isolated sample does not represent a loaded tunnel. After a baseline passes, challenge the proposed recipe with the intended product gap, run length and SKU sequence. Include conditions that materially change exposure:
| Challenge | What to confirm |
|---|---|
| Cold production start | Stable result after the prescribed ready condition |
| Steady run | Repeatability at required load and spacing |
| Normal stop and restart | No unacceptable first-pack or heat-soak result |
| Limiting SKU | Product and package remain within criteria |
| Planned SKU transition | Correct recipe selection and first-piece release |
| Cooling and transfer | Film sets before downstream contact or accumulation |
If multiple products share one recipe, test the transition between their limiting load patterns. A stable result with a single pack does not prove stability when the tunnel is continuously loaded.
Inspect Both Package and Product
Acceptance should cover enclosure or opening geometry, shrink uniformity, seam condition after the tunnel, label and barcode readability, product distortion, surface condition, multipack alignment and downstream handling. Retain an approved sample when site practice allows.
When a finished-pack symptom fails, use the shrink wrap defects guide to decide whether the next investigation belongs to film amount, sealing, tunnel exposure or machine troubleshooting. Do not embed a second defect encyclopedia in the tunnel recipe.
Release and Control the Recipe
The released record should state:
- Tunnel and conveyor identification.
- Film specification and approved SKU family.
- Product orientation, gap and loading pattern.
- Temperature-zone, conveyor and permitted airflow references.
- Ready condition, cooling condition and target production state.
- Trial run length and acceptance results.
- Limiting SKU evidence, approval date and approver.
- Changes that trigger requalification.
Requalification triggers can include a film grade or gauge change, product geometry or heat-limit change, tunnel control or airflow work, conveyor change, or a persistent package shift that the approved recipe no longer controls.
Use the film-family compatibility guide before qualifying a different material. The basic shrink wrapping process shows where the tunnel sits in the line. For a new project, confirm opening, heated length, conveyor, airflow controls and recipe capabilities on the proposed shrink wrapping equipment.
