The presence of white lines on the surface of PVC foam sheets, known as leucorrhea, can be attributed to the direct contact and friction between the blank and the corresponding parts of the die. These lines follow the direction of the sheet metal's extrusion and vary based on the pressure and template used. Additionally, grey areas can indicate when the leucorrhea residue is beginning to degrade, while bright bands are a sign of direct contact and friction between the sheet and the mold. It is important to note that these factors all play a role in the appearance and quality of PVC foam sheets.
The small gap between the die and the blank strip causes a decrease in the flow rate, resulting in a thinner melt when it is extruded. This leads to the formation of a blank strip due to lack of contact and friction with the blank. Additionally, impurities in the material can get trapped in the die, causing a decrease in flow rate and the appearance of leucorrhea in certain areas of the die. This is particularly common when using reclaimed materials with complex components and no stabilizer. If not addressed promptly, the leucorrhea can gradually change in color. Improper temperature control in the extruder and the absence of a screw temperature control device can lead to temperature imbalances in the material during extrusion. This can result in local degradation and sticky material, causing a decrease in flow rate in certain parts of the die, resulting in a whitish belt. It is crucial to address leucorrhea promptly as delaying treatment or allowing it to worsen can hinder effective treatment. It is important to be aware of any screw wear, equipment changes, and process settings adjustments in the extruder during treatment in order to address them effectively.
The presence of foam holes on the surface of PVC foam boards indicates a lack of density in specific areas of the melted material. These foam cells can be classified into two types: strip cells and round cells. Several factors contribute to the formation of these cells, including the type of resin, foaming agent, regulator, calcium carbonate, stabilizer, and other raw materials used. These factors are also influenced by the die design and the manufacturing process.
If there are extensive areas with foam holes on the foam board's surface, the PVC foam board factory can adjust the foam regulator treatment accordingly. On the other hand, if there are occasional individual bubbles on the surface of the foam board, it is likely that the mixing procedure, temperature, and feeding procedure were not followed correctly, resulting in uneven mixing. In such cases, the mixtures should be replaced.
In instances where continuous round bubbles are present, it is advisable to replace the foam board. Likewise, if long foam holes appear on the foam board's surface, a suitable adjustment of the dosage of yellow-white foaming agent is necessary as this indicates a low local density on the board. The reasons behind these foam holes are intricate and require analysis based on factors such as time, location, and probability of occurrence.