1, the stability is insufficient, it will affect the whole plate surface, the surface of the plate is yellow, and the foamed sheet is brittle. The solution is to reduce the processing temperature. If there is no improvement, the prescription can be adjusted, and the amount of stabilizers and lubricants can be increased properly. It can be changed one by one, so it is easy to find out the problem quickly and solve the problem at the fastest speed.
2, the melt strength deficiency will lead to foam sheet bubble, blister long slit.
The most direct way to judge whether or not the melt strength is enough is to press the fingers on the middle rolls after pressing the three rolls, which can feel the elasticity when the melt is strong and press. It is difficult to start if pressed, indicating that the strength of the melt is poor. Because the screw structure and cooling way are quite different, it is difficult to determine whether the temperature is reasonable. Generally speaking, in the allowable load of the extruder, the temperature in zone 3 to 5 is low. In order to obtain the foaming even products in the foamed sheet, it is necessary to ensure the good melting strength of the PVC material.
So the quality and model of the foaming agent are very important, of course, the dosage of yellow white hair agent should also be well matched.
3, the lubricants are divided into external lubricants and internal lubricants.
The outer slide to release, is good for the smooth surface of the plate, the outer slide is too small, the extruder 5 zone temperature is not easy to control, easy to heat up, it will lead to the confluence of the core temperature is high, the middle plate out on yellow, bullae, and other issues, the plate surface is not smooth; the outer slide, precipitation become serious, precipitation structure and plate surface in the mold performance smooth, also showed some individual phenomenon on the surface of back and forth in the irregular movement.
The internal sliding is favorable for plasticization and melt flow. The inner slide is not enough to control the thickness of the plate. It is shown that the thickness of the plate is thick and thin on both sides, and the inner sliding is much, which is easy to appear the phenomenon of high temperature of the confluent core.
4, the poor dispersion will bring the surface of the plate unsmooth.
The problem of process temperature control: the four problems mentioned above belong to the fundamental problem, the foundation and the deep problem. Compared to the above four problems, the process temperature control is much more intuitive, is a surface problem, but the temperature control is not good, it will induce the emergence of fundamental problems. To improve the processing temperature, the material will reduce the stability time, stability problem; lubrication balance of the original will be broken, the general performance is lack of lubrication, especially at the late stage of lubrication, need to improve the amount of external lubrication; temperature increase will lead to lower melt strength, foam sheet bubble bubble increases, reducing the number of. Sheet brittle fracture; the temperature decreased with increasing melt strength will reduce melt viscosity, viscosity reducing shear dispersing ability, strong ability of screw is not dispersed, sometimes uneven dispersion.