What problems will be encountered in the extrusion process of PVC foam board

   The problems encountered in the extrusion process of PVC foam board can be basically divided into four categories, one is stability; The second is intensity; Three is slippery; Fourth, dispersion. These four categories, especially the  three, will restrict and influence each other. On the face of it, it can sometimes be hard to distinguish immediately. Only through observation and analysis can the root causes be fundamentally solved.

   1、Lack of stability will affect the entire board, the board will turn yellow, and the foam board will become brittle.

   2、The lack of strength will lead to large bubble holes in the foam sheet and long bubble holes in the longitudinal section.

   The way to determine whether the strength is not direct enough is to press the sheet against the middle roll behind the three rolls with your fingers. You can feel the elasticity on good days. If it is difficult to bounce back after pressing, it is poor. Due to the large differences in screw structure and cooling methods, it is difficult to judge whether it is reasonable. In general, under the allowable load of the extruder, the lower the 3-5 zone, the better. In order to obtain uniform foam products in the foam tube, it is also necessary to ensure that the PVC foam board has good quality. Foaming additives are developed to solve the existence of foaming products and can effectively improve the quality of foaming pipes.

   3、lubricant

   Divided into outward sliding and internal sliding. Outward sliding is conducive to demoulding and cleaning of the plate surface. The outer slip is too little, the extruder 5 zone is difficult to control, easy to heat up, resulting in high temperature of the confluence core, large bubble, string bubble, yellowing and other phenomena. In the middle of sheet, sheet is not smooth; Get serious. The mold structure and the precipitation of the plate outward slip also show some individual phenomena of the plate moving back and forth irregularly. Internal sliding is conducive to plasticizing and fluidity. Internal slip is insufficient, the thickness of the board is difficult to control, thick in the middle, thin on both sides; Too much internal slip, easy to appear high confluence core.

   4、Poor material dispersion results in rough surface of the sheet.

   The above four are basic and deep-seated. Process control is much more intuitive, but poor control leads to fundamental. Improve processing, reduce material stability time, resulting in stability problems; Breaking the original balance, generally manifested as external deficiencies, especially in the late external period, the need to increase the external volume; The increase also reduces the melt, increases the bubble hole, reduces the bubble hole, becomes brittle and easy to break; Increasing reduces viscosity, reduces shear dispersion, and sometimes disperses unevenly.

   Mixing includes two steps: cold mixing and hot mixing. The PVC foam board resin and various auxiliary materials are weighed and stirred evenly in the hot mixing pot, and then automatically stirred and cooled in the cold mixing pot. After cold mixing, the material is screened by the screening machine and stored. After the powder material enters the extruder from the hopper on the extrusion line, with the continuous forward movement and the temperature change occurring during the extrusion process, the material slowly transforms from a solid state to a viscous flow state, and the blowing agent begins to break down. Because the pressure in the extruder and the mold is very high, the gas released by the blowing agent decomposition is dissolved into the PVC melt under high pressure, when it is extruded from the mold, due to the sudden loss of pressure, dissolved in the gas rapidly expanding foam, then immediately enter the set cooling set, and then enter the water tank for further cooling, after the drawing machine cut into a certain length of the product.