Temperature index control scheme of plastic film blowing machine

According to plastic melting theory, the extruder screw of blown film is divided into three sections: feeding section, melting section, and homogenizing section. At the end of the feeding section, when entering the beginning of the melting section, according to the melting theory, its temperature should be the viscous flow temperature. The viscous flow temperature of various blown film resins is distinguished as PP: 164-175 degrees Celsius, PE: 105-135 degrees Celsius, PA: 195-210 degrees Celsius.

    At the inlet of the feeding section of the film blowing machine, I hope the temperature is lower to avoid the resin viscous flow blocking the feeding port. In addition, the resin shrinks from time to time in the feeding section, and the air must be discharged backwards from the feeding port. According to the structure of the equipment, although the feeding port is not electrically heated, heat is transferred through the barrel, and the temperature of the feeding port is about 50-90 degrees. In this way, the temperature of the feeding section is determined. The entrance is 50-90 degrees, and the end is equal to the melting point or the viscous flow temperature, and the temperature can be set as a linear heating in this section.

    At the beginning of the melting section, the temperature reaches the viscous flow temperature before melting. For crystalline resin, the viscous flow temperature is equal to the melting point temperature. Then tighten and add the melting layer from time to time, and the temperature needs to be improved from time to time, so that the resin molecular chain length is different, and the polymers with different thermal activity energy are melted one after another. Therefore, after the temperature at the end of the melting section is established, it can be set in this section. The other parts of the upper part are heating up linearly.

In the homogenization section, the first thing is to remelt the homogenization and output the melt at a constant pressure and constant temperature. The temperature in this section can be kept constant, or the temperature at the end of the melting section will increase slightly (about 2-5 degrees).

    Regarding the blown film, it is required that the temperature of the die section be lower, but it cannot be lower than the viscous flow temperature, which is convenient for film lifting and normal film blowing. The melt must have a certain viscosity when it comes out of the die, so that it will not break or collapse. Under normal conditions, it is about 10-30 degrees lower than the end of the homogenization section, and the temperature from the homogenization section to the touch point can also be regarded as an equal temperature drop.

The key points about the control of extrusion temperature are:

Different types of resins, different blown film process temperatures;

The same resin, the model and the melting index are different, the process temperature of the blown film is different, the activity with a large index is good, and the temperature is low.

   With the same resin, blown films with different thicknesses, the process temperature is also different. For thick films, the process temperature can be higher, and the temperature of the die can be higher, which is conducive to reducing the viscosity and improving the yield.

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