How to control haul-off speed of 3-layer co-extrusion film blower

The haul-off speed of a 3-layer co-extrusion film blower refers to the linear speed at which nip rolls pull the bubble away from the die. Together with extrusion output, it determines film thickness and width. A higher haul-off speed stretches the bubble and thins the film; a lower haul-off speed causes material accumulation and thickens the film. The key to haul-off speed control is matching haul-off capacity with extrusion output to stabilize bubble dimensions. Haul-off speed shall also be set in coordination with cooling capacity, frost line height and melt viscosity of each layer, instead of being increased or reduced independently. In practical production, the haul-off speed of most 3-layer co-extrusion film blowers is interlocked with extruder rotating speed and continuously regulated via frequency converters, so that the bubble forms under a stable draw ratio.

Set the haul-off speed range based on target thickness. The target film thickness is the starting point for haul-off speed setting. Calculate the overall basis weight first, then determine the basic haul-off speed according to die gap and blow-up ratio. On the same production line, with fixed extrusion output, faster haul-off produces thinner film while slower haul-off produces thicker film. In daily operation, set the extruder speed first, then adjust haul-off speed gradually and measure film thickness continuously until it falls within the allowable range. Recalibrate the correlation when changing formulations or product specifications; parameters from previous batches shall not be reused directly.

Coordinate cooling capacity and frost line height. Haul-off speed is restricted by cooling conditions. After exiting the die, the bubble is cooled and shaped by the air ring. Raising haul-off speed increases the travel distance of the bubble per unit time and shortens cooling duration, which moves the frost line downward. An excessively low frost line leads to unstable film orientation and transverse wrinkles; an excessively high frost line indicates insufficient cooling, resulting in sticky film surface and thickness fluctuation. While adjusting haul-off speed, observe the frost line synchronously and adjust air ring airflow or cooling water temperature if necessary. Workshop temperature varies with seasons, so the matching relationship between haul-off speed and cooling conditions for the same product needs fine seasonal tuning.

Balance haul-off speed with the three-layer materials and extrusion output. The inner, middle and outer layers of the 3-layer co-extrusion film blower differ in melt viscosity and melt strength, so haul-off speed affects their thickness unevenly. If the middle layer is soft while the outer layer is rigid, excessive haul-off speed easily triggers interlayer thickness offset. Before adjusting haul-off speed, check whether the rotating speed of each extruder is balanced to stabilize the flow ratio of three melts inside the die, then adjust the overall haul-off speed. The haul-off speed shall have a linear correlation with total extrusion output. When extrusion output fluctuates, haul-off speed shall be corrected accordingly to avoid alternating thick and thin film.

Link haul-off with winding and downstream processes. Haul-off speed also affects winding quality. Mismatch between haul-off and winding tension causes uneven edges and ridged rolls. After adjusting the haul-off speed of the 3-layer co-extrusion film blower, calibrate winding tension and spreader roll speed synchronously to feed flat film into the winder. Downstream processes such as slitting and printing require stable film thickness uniformity; haul-off speed fluctuation causes transverse thickness deviation of the roll and register errors in printing. Maintain steady haul-off speed during normal production. Frequent start-stop, rapid acceleration or deceleration swing bubble diameter and form thickness bands.

Commissioning and routine control methods. When starting production for new specifications, begin at a low haul-off speed to stabilize bubble formation, then raise speed step by step to reach the target. Pause after each speed shift, wait for bubble stabilization, check thickness and frost line, and proceed only when no fluctuation occurs. An on-line thickness gauge can be adopted for thickness monitoring, and thickness feedback can be connected to haul-off speed regulation for automatic fine adjustment. Before shutdown, reduce haul-off speed first and then stop the extruder to prevent bubble breakage. During routine inspection, check nip roll wear and haul-off roll pressure; slipping nip rolls create a discrepancy between set haul-off speed and actual film travel speed. Recheck the correlation between haul-off speed and thickness and make timely corrections under drastic ambient temperature changes.

In summary, haul-off speed control for the 3-layer co-extrusion film blower shall be based on target thickness, coordinated with cooling, frost line and three-layer melt status, and synchronized with extrusion and winding rhythm. Stepwise commissioning and on-line thickness monitoring keep haul-off speed within a stable range for uniform film thickness and flat film surface.

Dalian Longyao Plastic Machinery specializes in R&D and manufacturing of film blowers. Its equipment is supplied across Shandong Province, serving plastic processing factories in Qingdao, Yantai, Weifang, Linyi, Zibo and other cities. It provides complete film blowing lines, auxiliary parts and technical commissioning services for Shandong customers.

Shandong boasts numerous plastic packaging manufacturers with diverse requirements for film specifications and production capacity. We supply multiple models including ABA 3-layer co-extrusion film blowers, two-layer high-low pressure film blowers and biodegradable film blowing lines, suitable for producing plastic bags, packaging films and biodegradable films.