How to generate and avoid the line marks in glass fiber composite extruded products?
Factors of line marks in glass fiber composite extruded products:
Factors that may cause line marks are: mouth molds, perforated plates, screws, die lip hanging materials, downstream equipment such as caliper, cooling water tank, tractor, etc. The line marks immediately visible at the outlet of the die must be at the outlet of the die (e.g. line marks caused by die drops), inside the die (poor surface conditions in the die or hanging material in the die mold), upstream (in porous plates, filters or screws). Individual thread marks are often formed in a right-angled mouth mold. When line marks are caused by a straight-through die, the number of line marks will match the number of bracket ribs. Perforated plates can cause a large number of thread marks in the article. Thread marks can also come downstream of the mouth mold, caused by items in contact with the extruded product, or caused by local cold or hot areas. These problems are generally easy to diagnose by observing where the line marks occur during the extrusion process.
Welding marks in glass fiber composite extruded products
Weld marks: Line marks in extruded articles may come from weld lines. These weld marks are formed when the polymer melt separates and re-fuses in the mouth die or even in front of the mouth die. Weld lines are also known as confluence marks; These line marks may form within the hose and tube mouth molds where the mold core is supported by the ribs of the bracket. The polymer melt is separated at the beginning of the bracket ribs and flows together again after the bracket. Due to the limited mobility of polymer macromolecules, it takes time for these molecules to rewind. This process of rewinding is also known as the "recovery" process. The longer the molecule, the longer it takes to rewind. Therefore, high molecular weight (high viscosity) polymers are more prone to weld marks than low molecular weight (low viscosity) polymers.
The factors that determine the severity of the weld line problem are: the length of time (residence time) from the melt streamline to the die outlet; Time to polymer melt recovery. If the residence time is longer than the recovery time, the weld line will disappear in the mouth mold and there will be no problems on the extruded product. However, if the residence time is shorter than the recovery time, the weld line will not disappear in the die and the weld line will cause problems on the extruded product. By increasing the residence time within the mouth mold or reducing the recovery time of the polymer melt, the weld line problem can be reduced or eliminated.
