Heat Shrink Defects: Causes and Corrective Actions

Heat shrink defects can originate in tubing selection, installation or heating. Do not correct every failure by increasing temperature; excess energy can hide one symptom while damaging the underlying assembly.

Symptom and cause map

Symptom	Possible causes	First checks
Incomplete recovery	Low energy, short dwell, shadowing, wrong sleeve size	Tubing data and actual heated-zone exposure
Wrinkles or folds	Oversized sleeve, uneven heating, poor positioning	Supplied/recovered dimensions and fixture
Split sleeve	Damage, sharp edge, excessive expansion or heat	Pre-install condition and assembly geometry
Scorching or gloss change	Excess temperature, dwell or airflow concentration	Recorded process settings and surface temperature
Sleeve moves from position	Airflow, insufficient restraint, early adhesive flow	Start position and fixture control
Trapped air	Heating direction or sealed geometry	Shrink progression along the assembly
Uneven adhesive flow	Thermal non-uniformity or unsuitable tubing	Sectioned sample and circumference inspection
Wire or connector damage	Heated zone too large or exposure excessive	Component temperature and post-process function

Isolate material from thermal-process variation

Confirm tubing identity, lot, storage and cut condition. Run an approved sample at the recorded process settings. If the result changes with orientation, investigate airflow, infrared shadowing or fixture position. If it follows the tubing lot, quarantine the material before changing the machine.

This applies to focused stations such as the WM-667ZM, conveyor systems such as the WM-666 and larger infrared systems such as the WM-664.

Controlled correction sequence

1. Preserve failed assemblies, tubing lot and recorded settings.
2. Confirm sleeve size, material and installed position.
3. Identify the first point where recovery becomes non-uniform.
4. Check fixture, heated zone and exposure before changing temperature.
5. Change one variable at a time within the material process window.
6. Re-run at normal production speed and cooling condition.
7. Re-approve dimensions, appearance, sealing and required functional tests.

See the EV harness and control-panel process contexts. Evidence-controlled results belong in the case library. For diagnosis, send failed assemblies, tubing data and recorded settings.