Automated Bagging Film Problems: 8 Checks Before You Change the Film
When an automated bagging line starts producing weak seals, wandering film or inconsistent bags, the film is often blamed first. Sometimes the film specification is responsible—but machine condition, reel presentation, settings and product loading can produce very similar symptoms.
Changing several variables at once makes the cause harder to identify. A better approach is to work through the line in a fixed order, record what changes and compare the result against an approved reference reel.
This guide sets out eight practical checks for single-wound polythene sheeting used on automated bagging and wrapping equipment.
1. Define the fault precisely
“The film is not running” is too broad for useful troubleshooting. Record the visible symptom and where it occurs:
the web moves sideways before the forming section;
the film creases or folds at a roller;
the longitudinal seal opens;
the transverse seal is weak, burnt or distorted;
film sticks to the sealing jaw;
the bag tears close to a seal;
bags vary in length; or
the line runs correctly when slowed down but fails at normal speed.
Photographs, short videos, rejected packs and the reel label help the film supplier and machine engineer distinguish a material issue from a setting or presentation issue.
2. Check the reel before adjusting the machine
Start with the simplest physical checks. Confirm that the reel matches the approved specification for:
film width and thickness;
reel outside diameter;
core inside diameter and core width;
winding direction;
maximum reel weight; and
printed-film orientation, if applicable.
The reel should sit squarely on the unwind shaft or chucks. A damaged core, telescoped reel or uneven reel edge can disturb the web before it reaches the first guide roller. If the reel is not presented consistently, changing sealing temperatures will not correct the underlying problem.
3. Follow the complete web path
Compare the threading route with the machine’s approved setup. Check that every roller turns freely and that the film passes on the correct side of dancer rollers, guides and sensors.
Look for dust, adhesive, ink residue or melted polymer on rollers and guide surfaces. Even a small deposit can pull one side of the film differently from the other. Also confirm that adjustable guides are centred and not pinching the web.
If tracking changes gradually across the reel, inspect reel alignment and winding. If it changes suddenly at one point on the machine, examine the nearest roller, guide or sensor.
4. Separate tension problems from tracking problems
Tracking describes where the film travels; tension describes the force applied as it unwinds and moves through the machine. The two interact, but they should be checked separately.
Too little control can allow a loose, unstable web. Excessive or uneven tension can stretch thin polythene, distort print registration and pull the film away from the intended sealing position.
Observe the film during acceleration, steady running and deceleration. A line that behaves correctly at constant speed but loses control during starts and stops may need the unwind brake, dancer system or acceleration settings reviewed rather than a different film.
5. Treat sealing as temperature, time and pressure
A heat seal is not controlled by temperature alone. The result depends on the combined effect of:
sealing-jaw temperature;
dwell time;
jaw pressure and alignment;
film thickness and material blend;
line speed;
condition of the jaw covering or release surface; and
contamination in the seal area.
A higher displayed temperature does not automatically create a stronger seal. It can overheat the film, increase sticking or narrow the operating window. Record the current settings before making small, controlled changes to one variable at a time.
Where the machine has separate longitudinal and transverse sealing systems, assess them independently. They may require different settings because their contact time, pressure and seal geometry are different.
6. Inspect the seal rather than judging appearance alone
Allow sealed samples to cool before testing them consistently. Compare good and rejected packs using the same simple method.
Does the seal peel apart cleanly, or does the film tear beside it?
Is the weakness across the full seal or only one side?
Is there a repeated mark that matches a damaged jaw surface?
Is product, dust, moisture or excess air trapped in the seal area?
Does the seal fail immediately or only during handling?
A failure down one edge can indicate jaw alignment or uneven pressure. Random contamination points suggest a different cause from a uniform seal that is weak across its full width.
7. Check film treatment, slip and print construction
Printed or surface-treated film needs particular care. Confirm which side is treated or printed, how the web should face in the machine and whether the sealing jaws contact an inked area.
Slip level affects how the film travels over metalwork and opens or forms around the product. A film that is too high-friction for the application may drag; one with excessive slip may be difficult to control. The correct balance depends on the machine and pack format, so an approved production sample is more useful than a generic target in isolation.
If a printed film runs differently from a clear reference film, compare the complete construction—including treatment, ink, coating, film blend and winding—not just the nominal micron.
8. Run a controlled comparison
Before changing the specification, run an approved reference reel using the recorded standard settings. Where safe and practical, compare it with the suspect reel under the same conditions.
reel and batch identification;
machine and line number;
product and pack size;
speed, temperature, dwell and pressure settings;
ambient or product conditions that may matter;
quantity run; and
rejected packs by fault type.
This creates evidence. If both reels show the same fault, attention can move towards the machine or process. If the fault follows one reel or batch, the supplier has a clear starting point for investigation.
When should the film specification change?
A specification review is justified when the current film cannot provide a stable operating window under normal, well-maintained machine conditions. Possible changes might include width, thickness, material blend, slip, treatment, winding or reel geometry.
The aim is not simply to make the film heavier. It is to match the film to the machine, product, sealing system and required line speed while avoiding unnecessary material.
Build a useful bagging-film specification
For a new or transferred line, record more than width and micron. A repeatable specification should include:
film format and dimensions;
nominal thickness and agreed tolerance;
material and performance requirements;
core size, reel diameter and winding direction;
treatment and print orientation;
maximum reel weight;
approved machine settings or operating window; and
agreed sample and trial acceptance criteria.
Automated packaging systems are designed to improve throughput and repeatability, but reliable performance depends on the machinery, film and operating process working together. Machine manufacturers also emphasise application-specific support, training and troubleshooting as part of a successful automated bagging setup.
A practical review without changing everything
Stretchband Packaging supplies bespoke single-wound polythene sheeting for automated bagging, wrapping and converting applications. If a line is producing intermittent faults, send us the film specification, reel label, machine details, settings and examples of the failed pack. We can help structure a like-for-like comparison and determine whether the next step should be a film trial, a machine check or simply confirmation that the current specification is suitable.
