Pressure regulation techniques for three-layer co extrusion blown film machine

Compared to single-layer blown film machines, three-layer co extrusion blown film machines can produce films with a three-layer structure in one go, resulting in higher production efficiency. Materials with different properties can be combined together to fully leverage their advantages, resulting in films with better strength, toughness, barrier properties, water resistance, oil resistance, and other properties.

Select equipment with appropriate extrusion volume and film width based on one's own production needs and output planning. It is usually measured by the hourly output (in kilograms) and the maximum bending diameter of the film (in millimeters). The larger the screw diameter, the greater the extrusion amount; The larger the aspect ratio, the better the plasticizing effect and mixing uniformity of the plastic. Generally speaking, the three-layer co extrusion blown film machine used for producing high-performance films can have a screw aspect ratio between 28:1 and 33:1.

Pressure regulation techniques for three-layer co extrusion blown film machine

Extruder pressure regulation

Pressure in the feeding section

Adjustment principle: The pressure in the feeding section should ensure that the material can enter the screw smoothly and will not melt prematurely or block the feeding port due to excessive pressure.

Adjustment method: The pressure in the feeding section can be controlled by adjusting the feeding speed. If the pressure is too low, the feeding speed can be appropriately increased; If the pressure is too high, reduce the feed rate. At the same time, check if there are any foreign objects blocking the feeding port to ensure smooth material transportation.

Compression section pressure

Adjustment principle: The compression section pressure should be sufficient to compress and plasticize the material, and the pressure should gradually increase to ensure the melting quality of the material.

Adjustment method: Mainly controlled by adjusting the screw speed and heating temperature. Increasing the screw speed will increase the shear and friction forces of the material, leading to an increase in pressure; Appropriately increasing the heating temperature can reduce the viscosity of the material, which helps stabilize the pressure and plasticize the material.

But it should be noted that the temperature should not be too high, otherwise it may cause material decomposition.

Measurement section pressure

Adjustment principle: The pressure in the measuring section should be stable to ensure the uniformity and stability of the extrusion volume.

Adjustment method: Determine whether the pressure in the measuring section is appropriate based on the current or torque of the extruder. If the current or torque fluctuates greatly, it indicates that the pressure is unstable. The screw speed or temperature can be adjusted slightly to make the pressure stable. In addition, check the gap between the screw and the barrel. If the gap is too large, it may cause material reflux and affect pressure stability. Worn parts need to be replaced in a timely manner.

Mold head pressure adjustment

Total pressure control

Adjustment principle: The total pressure of the die determines the extrusion speed and thickness uniformity of the film, which should be adjusted according to the specifications and production requirements of the film.

Adjustment method: Control the total pressure by adjusting the extrusion amount of the extruder and the resistance of the die head. Increasing the extrusion volume will increase the die pressure, otherwise it will decrease. At the same time, check whether the flow channel of the mold head is smooth, whether there is any accumulation or damage of debris, and keep the flow channel of the mold head unobstructed to ensure even pressure distribution.

Balance of pressure in each layer

Adjustment principle: The three-layer co extrusion blown film machine needs to ensure the pressure balance of each layer of material in the mold head to achieve good composite effect and thickness uniformity.

Adjustment method: Adjust the pressure of each extruder layer according to the characteristics and thickness requirements of each layer of material. Generally, pressure balance is achieved by adjusting the screw speed, temperature, or throttle valve of each layer of extruder. Pressure sensors can be installed at the feed ports of each layer of the mold head to monitor the pressure of each layer in real time and make precise adjustments based on the monitoring data.

Traction pressure regulation

Traction roller pressure

Adjustment principle: The pressure of the traction roller should be moderate, which can ensure the smooth traction of the film without causing deformation or damage to the film due to excessive pressure.

Adjustment method: Adjust the pressure of the traction roller according to the thickness and material of the film. For thinner and softer films, the traction roller pressure should be appropriately reduced; For thicker and stronger films, the pressure can be appropriately increased. At the same time, ensure even pressure between the two traction rollers to avoid film deviation or wrinkling.

Winding tension

Adjustment principle: The winding tension directly affects the quality of the film winding. It is necessary to ensure that the film winding is tight, neat, and does not produce tensile deformation.

Adjustment method: Adjust the winding tension according to the thickness, width, and winding speed of the film. Generally speaking, films with larger thickness and wider width require greater winding tension; The faster the winding speed, the higher the winding tension needs to be correspondingly increased. A tension controller can be used to automatically adjust the winding tension, adjusting it in real time according to the tension changes during the winding process to ensure stable tension.

After entering their respective extruder barrels, plastic particles move forward under the rotation of the screw and are heated and melted into a melt with good fluidity. Three extruders respectively extrude plastic melts of different colors or materials into a common die. Inside the mold head, the melt converges and recombines through specific channel designs, forming a three-layer composite melt structure. The composite melt extruded from the die is cylindrical in shape. At this time, compressed air is introduced from the center of the die to blow and expand the cylindrical melt into thin film bubbles. During the rising process of the film bubble, it is cooled and solidified by the cooling air blown out by the wind ring and the internal cooling system of the film bubble. Finally, the cooled film is pulled out by the traction roller, folded and flattened by the zigzag board, and then wound into a roll by the winding device.

The cooling system mainly includes air rings and membrane bubble internal cooling systems (IBCs). The air ring is installed above the mold head, and by blowing out uniform cooling air, it rapidly cools the high-temperature film bubbles extruded from the mold head, allowing them to solidify and form. The membrane bubble internal cooling system introduces a cooling medium, such as cold air or cold water, into the thin film bubble to cool the film from the inside, further improving the cooling effect and quality of the film.