Common Problems of PVC Foaming Regulators

2023-10-15 13:17

In the process of PVC foam sheet extrusion, the problems encountered can be basically classified into four categories, one is stability problem; the other is melt strength problem; the third is lubrication problem; the fourth is dispersion problem. These four types of problems, especially the first three types of problems, will restrict each other and affect each other. From the surface phenomenon, it is sometimes difficult to distinguish them immediately. Only by observation and analysis can the root cause of the problem be found.

Insufficient stability will affect the entire board surface, the board surface will turn yellow, and the foamed sheet will be brittle.

Insufficient melt strength will lead to large cells in the foam sheet and long longitudinal section bubbles. The most direct way to judge whether the melt strength is insufficient is to press the sheet wrapped on the middle roller with your fingers behind the three rollers. When the melt strength is good, you can feel the elasticity when pressing. If it is difficult to bounce after pressing, it indicates that the melt strength is poor. Because the screw structure and cooling method are quite different, it is difficult to judge whether the temperature is reasonable or not. Generally speaking, within the allowable load of the extruder, the temperature in zones 3-5 should be lower.

In order to obtain a uniform foamed product in the foamed pipe, it is also necessary to ensure that the PVC material has a good melt strength. The foaming aid developed by the company is developed to solve this problem of foamed products, which can effectively improve the quality of foamed pipes.

If the dispersion is not good, the surface of the sheet will be uneven.

Process temperature control problem: The four problems mentioned above are fundamental problems, basic problems, and deep-seated problems. Compared with the above four problems, the process temperature control is much more intuitive. It is a superficial problem, but poor temperature control will induce the emergence of fundamental problems. If the processing temperature is increased, the stability time of the material will be reduced, and stability problems will occur; the original lubrication balance will be broken, which is generally manifested as insufficient external lubrication, especially in the later period, and the amount of external lubrication needs to be increased; The melt strength decreases, the cells of the foamed sheet increase, the number of cells decreases, and the sheet becomes brittle and easy to break; the increase in temperature reduces the melt strength and also reduces the melt viscosity, and the viscosity decreases, and the shear dispersing ability decreases, which is difficult for dispersion. For a screw with weak capacity, sometimes uneven dispersion occurs.