According to the melting theory of plastics, the extruder screw of a plastic film blowing machine is divided into three sections: the feed section, the melting section, and the homogenization section. At the end of the feed section, when entering the melting section, according to the melting theory, the temperature should be the melt flow temperature. The melt flow temperatures of various blowing film resins are as follows:
Temperature Requirements for the Feed Section:
At the inlet of the feed section of the plastic film blowing machine, the temperature should be kept relatively low to prevent the resin from clogging the inlet due to its viscous flow. Additionally, as the resin is continuously compressed in the feed section, air should be expelled from the inlet. Depending on the machine's structure, the feed inlet of the plastic film blowing machine may not be electrically heated, but heat is transferred through the barrel; the temperature at the inlet is around 50-90 degrees Celsius.
This determines the temperature range for the feed section. The inlet temperature is 50-90 degrees Celsius, and the end temperature is equal to the melting point or melt flow temperature; the temperature in this section can be set for linear heating.
Temperature Requirements for the Melting Section:
At the beginning of the melting section, the temperature of the plastic film blowing machine needs to reach the melt flow temperature for the resin to melt. For crystalline resins, the melt flow temperature is equal to the melting point. As the molten layer is continuously compressed and increases in thickness, the temperature needs to be continuously increased to change the length of the resin molecular chains. Polymers with different thermal kinetic energies melt one after another. Therefore, after determining the temperature at the end of the melting zone of the plastic film blowing machine, the temperature profile for the other sections (upper and middle parts) can be determined based on a linear temperature increase.
Temperature Requirements for the Homogenization Zone:
In the homogenization zone, the plastic film blowing machine primarily remelts and homogenizes the molten material under constant pressure and temperature. The temperature in this zone can be kept constant, or slightly higher than the temperature at the end of the melting zone (approximately 2-5 degrees Celsius).
For film blowing, the temperature at the die head of the plastic film blowing machine should be relatively low, but not below the melt flow temperature, to facilitate film formation and normal blowing. The molten material exiting the die should have a certain viscosity to prevent cracking or collapse. Generally, this temperature is 10-30 degrees Celsius lower than the temperature at the end of the homogenization zone; the temperature drop from the homogenization zone to the die head can be considered isothermal.
Temperature Control Points for Plastic Film Blowing Machines:
1. Different resins have different optimal blowing temperatures.
2. Even for the same resin, different grades and melt flow indices will have different optimal blowing temperatures. Higher melt flow indices indicate better flowability and lower required temperatures.
3. For the same resin, different film thicknesses require different blowing temperatures; thicker films can be produced at higher temperatures.
4. A slightly higher temperature at the die opening can reduce viscosity and improve production efficiency.
