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    Three key control points in blown film production

    release time:2020-03-03  viewed:1045次
     Key control points in film blowing process: temperature, rotating speed of main engine, traction ratio and blowing expansion ratio.
     
     
     
    In the process of film blowing, several key control points are very important, which directly determines the quality of the film produced and whether the production can be carried out smoothly. Now let's talk about some problems that need to be noticed in film blowing production.
     
     
     
    Influence of temperature on quality in blown film production
     
     
     
     
    Whether the plasticization is complete and uniform, whether the foam shape is stable, and whether the temperature is one of the main process conditions.
     
     
     
     
    In the production of polyethylene blown film, different temperatures should be selected according to the melt index (MI) of raw materials and different product specifications. The larger the melt index is, the lower the temperature used in processing is, and vice versa.
     
     
     
     
    For example, if the extruder temperature is low, the plastic viscosity is large, the film transparency is poor, the unplasticized crystal point and cloud are easy to appear, the film is easy to break, and the elongation at break of the film is reduced.
     
     
     
     
    If the temperature of the extruder is too high, the viscosity of the plastic will be reduced, the fluidity will be great, and the opening of the film will be poor, which is easy to cause production instability, but the transparency will be improved.
     
     
     
     
    If the temperature continues to rise, the material will overheat and decompose, the film will turn yellow and have a yellow black focus. Therefore, the temperature instability will make the bubble shape incorrect, affect product quality, and even cause defective products. This article comes from Zhimeng
     
     
     
     
     
     
     
    Thickness control of blown film
     
     
     
     
    Film thickness is one of the main quality inspection indexes, and the factors affecting the thickness are as follows:
     
     
     
     
    ① Head design cavity structure is smooth, no dead angle, so that the material flow rate is uniform.
     
     
     
     
    ② The die gap is even, not deviated, and can be adjusted easily to control the uniformity of the discharge. Good dream weaving, good dream weaving
     
     
     
     
    ③ The blowing flow and velocity of the cooling air ring should also be stable, otherwise, the part with poor film cooling should be extended and thinned, on the contrary, it should be thickened, and the thickness should be adjusted by the wind force. Good dream weaving, good dream weaving
     
     
     
     
    ④ Head heating device: the head heating shall be evenly distributed to ensure equal resin flow at the die mouth. Otherwise, the high temperature part of the film extends, expands and thins, and vice versa. This article comes from Zhimeng
     
     
     
     
    ⑤ The main engine operates normally to ensure even discharge and even traction speed.
     
     
     
     
    ⑥ For the influence of external air flow, the air flow interference caused by the fluctuation of external wind force is not allowed under the cooling line of film blowing pipe, and the curtain can be set with plastic film.
     
     
     
     
     
    Good dream weaving, good dream weaving
     
     
     
    The effect of screw speed on film production quality
     
     
     
     
    If the rotational speed of the rod increases, the plastic will stay in the barrel for a short time, and the plastic will not be well plasticized, and the film will have incomplete crystallized points, or the film will have poor appearance quality due to the increase of the extrusion amount and the mismatch of the cooling part.
     
     
     
     
    There are also special cases in production. With the increase of screw speed, the discharge volume will increase. However, the temperature of heater does not continue to rise, and the production is still normal, which is caused by shear heat. However, the product quality can only be stable if it is always matched with the traction ratio. Good dream weaving, good dream weaving
     
     
     
     
    The decrease of screw speed is beneficial to the cooling of membrane tube. In the case of incomplete plasticization, reducing the screw speed is conducive to improving the product quality, but the rotation speed is low, the plastic stays in the barrel for a long time, and it is easy to decompose. In a word, the rotating speed of the screw should match the processing conditions of raw materials, finished product specifications and temperature to ensure the product quality.

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