The yellowing of PVC profiles is mostly due to the presence of paste at the die. The reason is that the die runner is unreasonable or the local polishing in the runner is not good, and there is a stagnant area. The yellow line of PVC profile is mostly due to the presence of paste in the barrel. The main reason is that there is a dead corner between the sieve plates (or transition sleeves) and the material flow is not smooth. The yellow line is a vertical straight line on the PVC profile, the stagnant material is at the exit of the die; if the yellow line is not straight, it is mainly in the transition sleeve. Yellow lines appear when the formula and raw materials are unchanged, the reason should be found mainly from the mechanical structure, and the starting point of decomposition should be found and eliminated. If the reason cannot be found from the mechanical structure, it should be considered that there is a problem with the formula or process. The measures to avoid degradation include the following aspects:
Strictly control the technical indicators of raw materials and use qualified raw materials;
Formulate reasonable molding process conditions, under which PVC materials are not easy to degrade;
The molding equipment and mold should be well-structured, and the dead corners or gaps that may exist on the contact surface between the equipment and the material should be eliminated; the runner should be streamlined and the length is appropriate;
The heating device should be improved, the sensitivity of the temperature display device and the efficiency of the cooling system should be improved.
The heating device should be improved, the sensitivity of the temperature display device and the efficiency of the cooling system should be improved.
