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What Problems Must Be Paid Attention To In The Production Process Of PVC Foam Board
- Jan 08, 2019 -

In the PVC foaming sheet extrusion process, the problems encountered can be basically classified into four categories, one is the stability problem; the second is the melt strength problem; the third is the lubrication problem; the fourth is the dispersion problem. These four types of problems, especially the first three types of problems, will restrict each other and cross-impact. From the surface phenomenon, it is sometimes difficult to distinguish them immediately. To observe and analyze the analysis, the root cause of the problem can be solved.


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

Insufficient melt strength results in a large foam cell and a long longitudinal bubble. To judge whether the melt strength is insufficient, the direct method is to press the sheet wrapped on the middle roll with a finger after the three rolls, and the elasticity can be felt when the melt strength is good. If it is difficult to bounce after pressing, the melt strength is poor. Because the screw structure and the cooling method are quite different, it is difficult to judge whether the temperature is reasonable. Generally speaking, in the load allowed by the extruder, the temperature in the 3-5 zone is preferably low.

 

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


The lubricant is divided into external lubricant and internal lubricant. The external slip is beneficial to demoulding, which is good for the smoothness of the surface of the sheet. The outer slip is too small, the temperature of the extruder 5 is difficult to control, and the temperature is easy to rise, which leads to the merging core. The temperature is high, and there are problems such as large bubbles, string bubbles and yellowing in the middle of the plate. The surface of the plate is not smooth; the outer slip is more, the precipitation will become serious, and the structure inside the mold and the surface slip on the surface of the plate will also be expressed. For some individual phenomena, irregular movements on the board surface. Internal slip is beneficial to plasticization and melt fluidity. It is difficult to control the thickness of the inner slippery surface. The thickness of the sheet is thin on both sides; the inner slip is more, and the temperature of the merged core is high.


Poor dispersion will result in a matte surface.

Process temperature control of PVC foam board: The four problems mentioned above are fundamental issues, basic and deep-seated. Compared with the above four problems, the process temperature control is much more intuitive and is a surface problem, but the temperature control is not good, which will induce the emergence of fundamental problems. Increasing the processing temperature, the material stabilization time will be reduced, and the stability problem will occur; the original lubrication balance will be broken, generally showing insufficient external lubrication, especially the later external lubrication, the need to increase the amount of external lubrication; temperature increase will also lead to The melt strength is reduced, the cells of the foamed sheet are enlarged, the number of cells is reduced, the sheet is brittle and easy to break; the temperature is increased, the melt strength is lowered, the melt viscosity is also lowered, the viscosity is reduced, the shear dispersibility is reduced, and the dispersion is dispersed. In the case of a screw that is not strong, uneven dispersion sometimes occurs.