Blown film industrial process
In the process of forming a blown film, depending on the direction of extrusion and traction, it can be divided into three types: flat blow, upper blow, and lower blow.
The type process also has a special blow molding method, as described above.
The method uses a right angle machine head, that is, the discharge direction of the machine head is perpendicular to the extruder, the extrusion tube is broken upward, and after being pulled to a certain distance, it is clamped by the herringbone board.
The extruded tubular air is inflated into a bubble tube by the compressed air introduced at the bottom, and its transverse dimension is controlled by the amount of compressed air gas, and the longitudinal dimension is controlled by the traction speed, and the blown film can be obtained by cooling and setting the bubble tube.
The main plastics suitable for the upper blowing method are PVC, PE, PS, HDPE.
The method uses a right angle handpiece, and the process of drawing the bubble tube from under the machine head is called a flat extrusion method. This method is particularly suitable for raw materials with low viscosity and plastic films requiring high transparency. Such as PP, PA, PVDC (vinylidene chloride).
The method uses a straight head that is concentric with the extruder screw. The process of the bubble tube and the center line of the head is on the same level. The method is only suitable for blowing small-diameter films, such as LDPE. PVC, PS film, flat blowing method is also suitable for the production of blown heat shrinkable film.
The above three processes have their own advantages and disadvantages. Compared with the advantages and disadvantages of the process, the blowpipe is hung on the cooling pipe, the traction is stable, the floor space is small, the operation is convenient, and the film with large diameter and thick thickness is required. The high-rise plant and high cost are not suitable for processing plastics with high fluidity, which is not conducive to film cooling. The production efficiency is low. The extrusion is favorable for film cooling, and the production efficiency is high. The plastic extruder with high fluidity can be processed from the ground. Inconvenient and unsuitable for the production of a thin film flat-spinning head, which is center-type, simple in structure, uniform in film thickness, easy to operate, and easy to blow up the film. It is not suitable for processing film with large relative density and large diameter. Large area of bubble tube cooling is slow, it is not suitable for processing plastic with large fluidity