Shrink wrap defects are evidence, not diagnoses. Their location, the first process stage where they appear, whether they repeat in the same place, and what changed since the last accepted pack determine the correct investigation path. The same visible symptom can result from film presentation, package geometry, sealing, tunnel exposure or an equipment fault.
Inspect and retain samples at four points: before sealing, after sealing, after the tunnel and after cooling. Route the problem to the first stage that fails instead of changing several settings at once.
First Decide Which Process Owns the Investigation
| First failed observation | Investigation owner |
|---|---|
| Film is wrinkled, short or misaligned before sealing | Film format, width, threading, tension or product presentation |
| Seal is open, displaced or damaged before tunnel entry | Seal-process qualification |
| Pre-tunnel package passes; appearance changes in tunnel | Thermal-exposure recipe or product suitability |
| Packs vary while recipe and inputs appear unchanged | Machine, control, conveyor or maintenance troubleshooting |
| Package passes after cooling but fails downstream | Package specification and handling validation |
Use the sealing temperature, dwell and pressure guide for a pre-tunnel seal failure. Use the tunnel recipe guide when the accepted pre-tunnel package changes during thermal exposure. Alarms, unstable motion, abnormal heat behavior and hardware symptoms belong in shrink wrap machine troubleshooting.
Record a Defect Signature
For every retained sample, record:
- Product, orientation and position in the run.
- Film manufacturer, grade, gauge, width, lot and roll position.
- Machine and recipe reference.
- First stage where the defect is visible.
- Exact location, direction, size and repeatability.
- Whether it follows one product side, tunnel side, roll edge or SKU.
- Recent film, product, recipe, changeover or maintenance change.
This signature prevents a plausible cause from being reported as a confirmed cause.
Wrinkles
Wrinkles present before the tunnel support hypotheses involving film folds, tracking, tension, product alignment or too much film for the package geometry. Wrinkles that first form during shrinking support hypotheses involving uneven exposure, film amount, product shape or blocked air access.
Look for a repeatable direction. A pattern tied to one roll edge suggests a different investigation from a pattern tied to one product corner or one side of the tunnel. Confirm the pattern before routing the issue; do not respond to every wrinkle by increasing tunnel temperature.
Dog Ears
Dog ears are triangular projections of film near package corners. Their size and repeatability can support hypotheses involving film amount, corner geometry, product orientation or local thermal exposure.
Compare the failed pack with the approved width, cut length, orientation and retained sample. If the projection changes with package geometry, return the issue to film fit or package design. If the same package changes by tunnel position or load pattern, investigate the qualified tunnel recipe. Extreme heat is not an acceptable shortcut for excess film or unsuitable geometry.
Burn Holes
First determine whether the film was already punctured before the tunnel. Retain the sample and inspect whether the hole follows a product edge, seal area, repeatable contact point, film defect or tunnel position. These observations create hypotheses; they do not prove excessive temperature by themselves.
Stop production and escalate under the site’s safety procedure if there is smoke, abnormal odor, uncontrolled heat, exposed heater damage, conveyor damage or another equipment safety symptom. Do not continue a trial to reproduce a hazardous failure.
Loose or Incomplete Shrink
Separate an all-over loose package from one local loose panel. All-over looseness can support hypotheses involving film identity, overall exposure, conveyor speed, loading or excess film. A one-sided or repeatable local panel can support hypotheses involving air access, orientation, tunnel loading, product shadowing or geometry.
Confirm the film and recipe identities, product gap and last approved sample before routing the issue. A displayed temperature that matches the recipe does not establish that actual thermal exposure remained unchanged.
Open Seals and Product Distortion
An open seal visible before tunnel entry is a sealing-process failure. A seal that passes before the tunnel but opens during shrinking creates hypotheses around initial seal margin, cooling, film tension or shrink load; hand the evidence to the seal-process owner.
Product distortion creates a suitability and exposure question. Record whether the product, label, adhesive, cap, tray or primary package changed. Do not keep adjusting the tunnel if the proposed package cannot meet the product’s validated heat or compression boundary.
Close the Triage Record
The defect record should end with one of four dispositions:
- Returned to the approved setup and verified with consecutive accepted packs.
- Routed to film or package specification review.
- Routed to seal or tunnel recipe requalification.
- Stopped and escalated for machine or safety investigation.
Record the evidence, authorized change, verification result and approver. Do not close the issue with “temperature adjusted” or “film problem” when neither statement identifies the verified cause.
The shrink wrapping process overview helps teams name the four inspection stages consistently. This page remains a finished-package triage tool; it does not replace equipment diagnostics or model-specific repair procedures.
