Start with the process stage, not the visible symptom alone
A sleeve-wrapped bundle is produced by a chain of dependent stages: product collation, film presentation, sealing, tunnel heating, cooling and discharge. A poor result at the end of the line may have started much earlier. For example, a skewed collation can pull film unevenly, place the seal off centre and then create apparently inconsistent tunnel shrink. Record the exact point at which the pack first departs from the approved condition before changing settings.
Use one representative product format and one approved film roll while investigating. Confirm that guides, film tracking, seal faces, conveyor transfers and cooling arrangements are in their known production positions. Change one controlled variable at a time, produce enough packs to show a repeatable result, and record what changed. Never defeat guards or reach into moving or hot equipment to observe a fault.
| Observed symptom | Areas to inspect first | Useful evidence |
|---|---|---|
| Seal opens, peels or contains unsealed areas | Film compatibility and cleanliness; seal-face condition; film tension and overlap; sealing time, temperature or pressure where adjustable; pack interference at the jaw. | Photographs of the full seal, film supplier data, approved settings and whether the defect appears in the same position. |
| Film splits or develops holes | Sharp product or tray edges; damaged film; excessive local heat; tight film path; snag points; insufficient cooling before handling. | Location of every split, product-edge photographs, roll identification and comparison before and after the tunnel. |
| Loose areas or incomplete shrink | Tunnel warm-up; airflow path; dwell and conveyor speed; pack spacing; cold air entry; film shrink behaviour and pack loading. | Tunnel settings, start-up time, spacing photographs and whether the fault changes across the tunnel width. |
| Wrinkles or asymmetric shrink | Film centring, seal position, product alignment, tunnel airflow balance, uneven pack geometry and inconsistent gaps between packs. | Front, rear, side and overhead photographs plus the pack position on the tunnel conveyor. |
| Tray or product distortion | Heat exposure, dwell, airflow concentration, unsupported areas, heat-sensitive labels or containers and hot discharge accumulation. | Production-weight samples, material information and product temperatures or condition before and after the tunnel where measured safely. |
| Bundle moves or collapses after discharge | Collation stability, film strength, shrink recovery, side openings, cooling time, discharge support and the point at which the pack is lifted or accumulated. | Video of discharge and handling, bundle weight and the agreed lifting or palletising method. |
Separate material, machine and line causes
Material causes include a changed film grade, thickness, roll width, winding condition, storage history or supplier. Machine causes include contamination, wear, damaged seal insulation, film tracking, airflow obstruction or a setting that is no longer matched to the format. Line causes include inconsistent collation, product gaps, abrupt transfers, upstream surges, downstream blockages and packs being handled before the film has stabilised.
If a fault begins after a change of product, tray, film supplier, roll batch, maintenance activity or line layout, start with that change. When no change is obvious, compare the current condition with the approved trial record and planned-maintenance checks. Stop and escalate faults involving guarding, emergency stops, unexpected movement, damaged electrical equipment, persistent overheating, smoke or inability to isolate energy safely.