The quality of PVC mix preparation directly affects the extruder's extrusion speed, process parameters and the quality of the profile product, so this process should be strictly controlled. The kneading of the mixture is completed in the high-speed or low-speed kneading machine.
What are the factors affecting the preparation of pvc mixture
1)Temperature control High-speed kneading machine speed is usually between 900-2000r/min, materials in the machine at high speed friction heat, in the mixing process, the temperature control is very important, general temperature control need to do the following points:
① Must ensure that the cooling water temperature below 15 ℃; ② PVC resin and additives.
② PVC resin and additives into the mixer, immediately after the mixing, the use of friction heating, when the temperature reaches about 120 ℃ can be discharged to the cold mixer; ③ hot material in the cold mixer.
③ hot material mixed in the cold mixer for a certain period of time, when the material temperature is lower than 45 ℃ before you can open the cold mixer gate discharge.
2) mixing time materials in the mixing process experienced density changes, homogenization and part of the process of gelatinization, all need a certain amount of time to complete. Mixing time is too short, the extrusion process will become difficult, the material melting time becomes longer, the quality of the product deterioration. But too long, the temperature will rise too high, easy to cause the decomposition of the material discoloration, and more energy consumption, low production efficiency.
3) charging order Hard PVC formula has more components, choose a reasonable charging order is very important. Selected charging order should be conducive to the role of additives to play, to avoid undesirable synergistic effects of additives, but also conducive to improving the speed of dispersion.
If the addition of external lubricants too early, it will cover the outer layer of PVC particles, hindering the recombination of PVC particles, thereby reducing the degree of densification, homogenization and gelation speed, so the external lubricant is usually added in the late mixing; there are also processing aids ACR easy to adsorb stabilizers and liquid additives, affecting its stabilizing effect and plasticizing effect, it should also be added after the stabilizer.
Typical hot and cold mixing process is as follows:
a. The PVC resin in the high-speed kneader first stirring temperature to 60 ℃;;.
b. Into the stabilizer, continue to stir the temperature rise to 90 ° C;; and
c. Into the internal lubricants, processing aids, impact agents, fillers, coloring agents.
d. Into the external lubricant;
e. Continue to stir, warming to 115-120 ℃.
f. At low speed, the material will be discharged into the rotating cooling water through the cold mixer.
g. Cold mix to 40-45 ℃ below the discharge, sieve, bagging.
