Why Does the Film Burn at the Seal?

Problem

The seal area shows yellowing, browning or holes in the film, either continuously or after stoppages. Where it appears only after stops, the film has sat against heated jaws while the machine stood still.

Possible Causes

1. Sealing temperature is set above the film's recommended range.
2. Dwell is effectively too long — speed too low for the current settings.
3. Damaged jaw faces create hot spots that locally overheat the film.
4. Film stands still against heated surfaces during stoppages.
5. The temperature controller reads incorrectly (sensor or calibration issue).

What to Check

• STEP 1Compare the setpoint with the film data sheet.The film supplier's range is the authoritative limit — verify the setpoint sits inside it.
• STEP 2Compare setpoint with actual temperature.Confirm the displayed actual value tracks the setpoint and is stable, without overshoot.
• STEP 3Review speed and dwell together.Burning that appears after a speed reduction points at dwell, not at the temperature itself.
• STEP 4Inspect the jaw faces.Look for scoring or buildup that concentrates heat at one point of the seal.
• STEP 5Correlate with stoppages.Check whether marks follow stop-start cycles rather than continuous running.

Corrective Actions

• Bring the setpoint back inside the film supplier's range in small steps, verifying seals at each step.
• Match dwell and speed as a pair — when speed changes, re-verify the sealing setup.
• Clean or recondition jaw faces to remove hot spots.
• Follow the machine manual's procedure for heat handling during standstills and stoppages.