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。
The problems encountered in extrusion process of PVC foamed sheet can basically be classified into 4 categories, one is stability, two is melt strength, three is lubrication, and four is dispersion. These four kinds of problems, especially the first three types of problems, will be mutually restricted and cross influence.
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。
From the surface phenomenon, sometimes the stability is insufficient, which will affect the whole surface of the plate, the surface of the plate is yellow, and the foamed sheet is brittle.
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. 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.