在PVC发泡板材挤出过程中，碰到的问题基本可以归为4类，一是稳定性问题；二是熔体强度问题；三是润滑问题；四是分散问题。这四类问题特别是前三类问题会相互制约，交叉影响。
In the extrusion process of PVC foamed sheet, the problems encountered can be basically classified into 4 types, one is the stability problem, the two is the melt strength problem, the three is the lubrication problem, and the four is the problem of dispersion. These four problems, especially the first three kinds of problems, will restrict each other and influence each other.
从表面现象看有时稳定性不足，会影响整个板面，板面发黄，发泡板材脆性大。
Judging from the surface phenomenon, sometimes the stability is not enough, it will affect the entire panel, the yellow on the surface and the brittleness of the foamed sheet.
熔体强度不足会导致发泡板泡孔大，纵切面泡很长。判断熔体强度是否不足，最直接的办法是到三辊后面用手指按压包在中辊上的板材，熔体强度好按压时能感觉到弹性。若按压后很难弹起，说明熔体强度较差。因为螺杆结构和冷却方式差别较大，很难判断温度是否合理，一般来说，在挤出机允许的负荷内，3—5区温度以低为好。
Melt strength deficiency will lead to foam foaming plate, longitudinal long pimple. To judge whether the strength of the melt is insufficient, the most direct way is to press the plate on the middle roll with the finger on the back of the three roll and feel the elasticity when the melt strength is good. If it is hard to press after pressing, it indicates that the melt strength is poor. Because of the difference between the screw structure and the cooling method, it is difficult to judge whether the temperature is reasonable or not. Generally, the temperature of the 3 - 5 zone is low in the permissible load of the extruder.