メインニップル部分でのブローフィルム気泡の空気漏れ
When a blown-film bubble gradually becomes smaller, first check whether air is escaping through the main nip. A small gap beside a folded edge, a damaged roller surface, or uneven contact between the two rollers can allow air to escape while the film continues moving.
Start by locating the leak. If air is escaping at the nip, its position and timing will help narrow the cause. A leak beside a fold requires a different check from one that returns with each roller revolution.
If no leak is found at the nip, check the film for other openings and have the production team review the inflation and cooling system.
Find Where the Bubble Is Losing Air
The main nip pulls the flattened film upward and helps retain air inside the bubble. On a conventional non-IBC line, a small opening at this contact can gradually reduce the trapped air and cause the bubble to shrink.
On an IBC-equipped line, the internal air supply and exhaust also affect bubble size. A fluctuating bubble therefore needs to be checked against the air system’s operation.
Look for an identifiable escape path through safe observation. Air may leave through a hole in the film tube, a damaged area near the die, or the main nip itself.
Once a leak is confirmed at the nip, its pattern gives the next direction.
Where the Leak Points
Air escapes beside a folded edge.
Check the fold thickness and local contact. A raised section may be holding the nip slightly open.
The leak repeats with roller rotation.
Identify the matching roller. Inspect the suspected surface for cuts, attached debris, or roundness problems.
A gap remains at the same position across the roller width.
Check for uneven cover wear or roller deflection. The contact may be weaker in that area.
No leak can be identified at the nip.
Look for other openings in the film. If the bubble is fluctuating without a confirmed leak, return to the air and cooling systems.
How Folded Edges Can Open the Nip
The main nip must maintain continuous sealing contact as the flattened film passes between the rollers.
A common arrangement uses a rubber-covered roller against a harder mating roller. The rubber cover deforms slightly to accommodate the film while maintaining contact. Actual roller construction varies by machine.
The central area of a flattened tube normally consists of two film layers. Near the folded edges, the film turns back on itself, creating a different local profile. Gusseted film introduces additional folds and can produce more pronounced thickness steps.
A raised fold can hold the rollers slightly apart. Most of the contact remains closed, but a narrow air path may form beside the thicker section.
Consider a line that runs plain tubing without leakage but develops the problem after changing to gusseted film. Compare the previous and current fold arrangements. If the leak appears beside the additional folds, the thickness change is worth investigating before replacing the roller.
The condition of the rubber cover also affects this contact. A cover that has hardened with age may accommodate the folded area less effectively. Uneven wear can make the contact less consistent.
Increasing nip pressure may close a small opening, but excessive pressure can crush the folded edges and leave permanent creases.
この ピンチローラー must maintain a seal while allowing the folded film to pass without unacceptable damage.
For a leak concentrated beside a fold, examine the fold arrangement, local contact, and existing roller condition together. If the rubber cover is sound and the leak started with a change in film construction, the film profile deserves attention before a replacement is specified.
When Air Leaks Once per Roller Revolution
A small cut in the rubber cover can interrupt the seal each time it passes through the nip. Tape, dirt, or other material attached to either roller surface can produce the same effect.
As the affected area passes through the contact, a small amount of air may be carried beyond the nip. If this happens repeatedly, the bubble can gradually lose air, particularly on a conventional non-IBC line.
The first useful observation is whether the leak returns at the same point in the roller’s rotation.
Identify which roller matches the timing. The two rollers may have different diameters, so their rotation periods can differ.
After the equipment has been safely stopped, inspect the suspected area for cuts, missing rubber, embedded particles, or attached debris.
A visible cut that coincides with the leak provides a clear reason to examine that roller more closely. If the problem follows a contaminated spot and proper cleaning restores the seal, replacement may be unnecessary.
If the surface looks intact, check roundness.
An out-of-round roller can change the contact as it turns. A small opening may appear when the affected section reaches the nip and close again as it passes.
The harder mating roller also deserves attention if its rotation matches the leak. A damaged surface on that roller can interrupt the seal even when the rubber-covered roller is in good condition.
When the leak clearly follows roller rotation but no damage is visible, qualified maintenance personnel should confirm roundness and contact before a replacement is specified.
Why a Gap May Stay in the Same Place
Some leaks remain at the same position across the roller width throughout rotation.
A common example is heavier wear in the center of a rubber-covered roller. When the middle section becomes smaller in diameter than the ends, it may no longer contact the mating roller as intended.
The opening can remain in the same widthwise position even as the roller turns.
Mechanical deflection can produce a similar contact pattern. Under load, the roller shafts and bodies may bend slightly, reducing contact in the middle while the ends remain closed.
The distinction matters for repair.
Center wear changes the rubber cover’s diameter profile. The worn covering may require correction or replacement.
Deflection involves the roller assembly and its behavior under load. Replacing the covering alone may leave the gap unchanged.
A contact impression across the nip can help maintenance personnel identify where contact is weak. Checking the old roller’s diameter profile can then help distinguish cover wear from other mechanical causes.
When the gap stays in one area throughout rotation, the contact pattern provides more useful evidence than searching for a single surface cut.
When the Rubber-Covered Roller Needs Replacing
Once the leak has been traced to the rubber-covered roller, inspect the old cover before deciding how to replace it.
A localized cut, missing rubber, or uneven wear can affect the sealing contact. The existing roller’s condition helps establish whether the covering can be repaired or a replacement is required.
If the original roller worked well and the operating conditions remain unchanged, its drawing, dimensions, and confirmed specifications provide a straightforward basis for manufacturing a replacement.
A recurring leak after replacement deserves a closer check. Compare the old and new roller dimensions and surface condition. Confirm whether the mating roller, folded film profile, or operating conditions have changed.
For a roller-related problem, Wolorin can support custom manufacturing and replacement based on the actual roller requirements. Drawings or existing specifications can be used directly for quotation and production confirmation. Where repeated damage raises questions about the original specification, the old roller condition and contact requirements can guide a more detailed manufacturing discussion.
If the leak points to the rubber-covered main nip roller, send Wolorin your drawings, dimensions, or existing specifications for quotation or manufacturing confirmation. With incomplete details, start with old-roller photos, its position, contact film, and the observed roller issue.