What causes streaks in PVC profile extrusion?
Release time：2020-07-21
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What Do the Lines Look Like and What Problems Do They Indicate?
Different types of lines have different underlying causes. First, see which type you’re encountering:
Yellow or black lines: These are usually caused by the material “burning” at high temperatures or impurities mixed into the raw material. For example, the die head temperature may be too high, or there may be dead spots in the screw where the material lingers too long and turns black.
Bright or dark bands: This indicates that the material is not flowing smoothly—it moves faster in some areas and slower in others. This is usually caused by uneven material discharge from the die or excessive friction in the forming die, which polishes the surface to a shine or darkens it.
Longitudinal stripes or weld lines: These look like gaps left where two streams of material have not fused properly. This is commonly seen when the die head temperature is too low, material flow is poor, or there is a buildup of dead material behind the filter screen.
Cloud-like or wavy patterns: The surface has ripples resembling the surface of water. This is usually caused by inadequate plasticization or excessive lubricant, making the material too slippery to adhere properly.
