GOPEX

Factors causing line marks in glass fiber composite extruded products:
Factors that may cause line marks include: die, perforated plate, screw, die lip hanging material, downstream equipment, such as caliper, cooling water tank, tractor, etc. The immediately visible line marks at the die outlet must be formed at the die outlet (such as the line marks caused by die drips), in the die (poor surface conditions in the die, or hanging materials in the die), and upstream (in the perforated plate, filter screen, or screw). A single line mark is often formed in a right angle die. When the line mark is caused by the straight through die, the number of line marks will match the number of support ribs. The perforated plate can cause a large number of line marks in the products. The line marks may also come from the downstream of the die, caused by the articles in contact with the extruded products, or caused by local cold or hot areas. These problems can be easily diagnosed by observing the position where the line marks occur during extrusion.
Weld lines in glass fiber composite extruded products
Weld line: The line mark in the extruded product may come from the weld line. These weld lines are formed when the polymer melt is separated and re fused in the die or even before the die. The weld line is also called the confluence line; These line marks may be formed in the hose and hard pipe nozzle die, and the place where the die core is supported by the ribs of the bracket is the place where they occur. The polymer melt is separated at the beginning of the support rib and flows together again after the support. Due to the limited mobility of polymer macromolecules, it will take some time for these molecules to re entangle. This rewinding process 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 likely to produce weld lines 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; The time of polymer melt recovery. If the dwell time is longer than the recovery time, the weld line will disappear in the die and there will be no problems on the extruded products. However, if the dwell 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 products. By increasing the residence time in the die or reducing the recovery time of polymer melt, the problem of weld lines can be reduced or eliminated.
How to Produce and Avoid Line Marks in Extruded Glass Fiber Composites
How to avoid line marks in glass fiber composite extruded products
The residence time in the die can be increased by reducing the flow rate (extruder output) or changing the die geometry. The flow divider structure must be as far away from the die outlet as possible. Some die structures can reduce the problem of weld lines. For example, the spiral mandrel die head that can be used for hard pipe, flexible pipe and film blowing, when the melt flows through the spiral die core part, the weld line is expanded; This method can eliminate the problem of weld lines to a large extent. The soft and hard pipe die heads with rotary mandrels or rotary dies can also effectively expand the weld lines and eliminate the problem of weld lines. Some dies have a relaxation zone for strengthening the recovery process. The relaxation region is the main local region in the die runner, where the cross-sectional area of the runner is increased. The recovery time depends on the molecular weight of the polymer and the melt temperature. Decreasing the molecular weight of the polymer will accelerate the re winding process. Higher melt temperature will also increase the mobility of polymer molecules and reduce the recovery time. Molecular structure will also play an important role. The molecules of linear polymers are easier to arrange.