Adjust Film Thickness Uniformity of ABA Blown Film Machine

The ABA blown film machine adopts a three-layer co-extrusion structure. The inner, outer and middle layers use different raw material formulas. Film thickness uniformity directly affects the tensile property, roll flatness and subsequent printing & laminating performance of finished films. During production, adjustments can be made step by step through raw material pretreatment, die head adjustment, air ring cooling, haul-off system, process parameters and on-line monitoring to improve thickness deviation and reduce finished defects caused by thickness fluctuation.

Carry out raw material pretreatment to stabilize extrusion conditions. Fluctuations in raw material moisture content and melt index lead to unstable output and trigger thickness deviation. Dry raw materials in advance to prevent steam from entering the extruder and forming bubbles which disrupt continuous melt flow. Maintain a stable ratio of virgin material and regrind. Crush and screen regrind to remove impurities, as impurities may block die flow channels and cause local uneven discharge. When switching raw material grades, thoroughly clean extruder barrels and die heads to avoid residual old materials altering melt fluidity. Keep consistent feeding speed; feeding fluctuation directly changes extrusion output and causes periodic thickness variation.

Optimize die head structure and die gap adjustment. The die head is the core component for film thickness control. Check the die lip before startup and clean accumulated melt and carbonized particles. Carbon deposits block local discharge and create fixed thick or thin zones. The die head is equipped with adjusting bolts to fine-tune die lip clearance and correct circumferential film thickness. Make small and repeated adjustments. Do not apply large single adjustments. Allow sufficient time for melt stabilization before remeasuring thickness. For the ABA three-layer co-extrusion structure, inspect the flow channels of layer A and layer B respectively to ensure uniform melt distribution of three layers and avoid abnormal local discharge of any single layer. Control zoned heating of the die head and keep balanced temperature across zones; local overheating changes melt viscosity and causes uneven output.

Standardize air ring cooling airflow adjustment. Uniformity of cooling airflow from the air ring directly determines bubble setting and is a major source of thickness fluctuation. Inspect air ring outlets and clean plastic dust and debris inside air ducts to prevent outlet blockage and abnormal local airflow. Adjust air volume of each air ring nozzle: increase cooling airflow at thick film positions to speed up melt setting; reduce airflow at thin positions to delay cooling. Maintain stable fan air pressure. Fluctuating pressure causes bubble oscillation and continuous thickness stripes. Keep a fixed distance between air ring and die head to avoid bubble forming disturbance from height changes.

Control bubble stability and haul-off system parameters. Bubble sway results in circumferential film thickness inconsistency. Inspect bubble cage and stabilizing mechanism to reduce lateral bubble offset. Maintain uniform pressure of haul-off rolls; uneven pressure leads to inconsistent film stretching. Match haul-off speed with extrusion output. Excessively high haul-off speed overstretches the film and reduces overall thickness; low haul-off speed thickens the film. Adjust haul-off speed slightly and monitor film thickness synchronously. Keep haul-off roll surfaces clean to avoid adhered plastic particles which cause surface indentation and abnormal local stretching.

Dynamic correction via on-line thickness measurement system. For machines equipped with on-line film thickness monitors, probes collect real-time circumferential thickness data, identify thickness distribution curves and adjust die lips and air rings accordingly. For machines without on-line monitors, take multi-point samples, measure thickness at multiple transverse positions of the film, mark thick and thin points and locate corresponding die head positions. Conduct first article inspection in production. Mass production can only start after qualified first article thickness. Take regular samples for re-testing during production to track thickness variation trends.

Control temperature parameters of each zone to stabilize melt viscosity. Set zoned temperatures of extruder barrels and die heads according to raw material properties. Excessively high temperature reduces melt viscosity and easily causes local thinness; low temperature degrades melt fluidity and increases discharge resistance. For ABA three-layer extrusion, set temperatures for the three extruders separately to match raw materials of each layer instead of adopting identical temperature settings. Avoid sharp temperature swings in heating zones and calibrate temperature sensors regularly to prevent deviation between displayed temperature and actual melt temperature.

Perform routine maintenance to reduce persistent thickness defects. Clean die heads and screws periodically to remove carbonized deposits, which continuously interfere with melt flow. Check wear of screws and barrels. Increased wear clearance causes unstable extrusion pressure and enlarges thickness deviation. Inspect compressed air pipelines and stabilize pressure of pneumatic components to ensure responsive die lip adjustment. Clean die lips in accordance with specifications at shutdown to prevent high-temperature carbonization of retained materials.

Adjusting film thickness uniformity of ABA blown film machines requires coordinated tuning of raw materials, die head, cooling air ring and haul-off speed, combined with on-line monitoring and periodic sampling tests. Iterate corrections in small increments to stabilize three-layer co-extrusion melt discharge and bubble forming, reduce transverse thickness deviation, improve finished film consistency and mitigate wrinkling and tracking deviation during subsequent rewinding and processing.