How To Solve PVC Pipe Surface Black Lines Problem?
Date:2022-8-01 Author:hcscrew
Conical Twin Screw Barrels and PVC Pipe Profile Black Lines
1. Problems with PVC Profile or Pipe Having Black Lines on Their Surfaces
There is a strong connection between PVC pipe or PVC profile black lines or clouding and conical twin screw barrel extrusion. Here are two common ways black lines appear on PVC pipes or profiles:
1.1 Uncertain Position, Continuous Black Lines, Clouding, or Clouds
The leading causes are:
- 1. PVC materials left behind at the blind angle of the conical screw’s barrel, the transitional section, the perforated plate, or the mold.
- 2. An oil leak on the conical twin screw head or too much oil on the mold.
- 3. In a conical twin screw barrel extruder, too much low molecular content cannot be vented properly.
1.2 Continuous Black Lines or Clouding on the Underside
The leading causes are:
- 1. The increase of calcium powder percentage causes serious wear on the conical twin screw barrels. The screw barrel should be re-polished, and the screws’ mounting gap should be re-adjusted. If necessary, replace with a higher quality conical twin screw barrel.
- 2. Imbalance in the lubrication system on the conical screw extrusion. An external lubricant such as PE can be used, or the lubrication quantity can be increased.
- 3. Increase the stabilizer quantity.
2. Reasons for Black Lines on PVC Pipes or Profiles
An anisotropic rotation of the conical twin screw causes this to happen. The transitional section and the bottom of the barrel meet two directions of material, leading to:
- 1. When the extrusion section of the conical screw barrel wears out, the materials’ running track will change. When the conical screw’s inner wall wears away, it causes heat damage to the material. Low molecular decomposition creates a gray cloudy image on pipes, profiles, or other surfaces.
- 2. High internal lubricant levels and non-uniform gaps between the two conical twin screws result in different material shearing speeds. If one part of the material is overplasticized while the other is not, the final PVC products will have white clouding on their surface.
Suggested Solutions:
- – Avoid using lipid lubricants. If this situation occurs, adjust the heating temperature on the fourth section and transitional section or increase feeding quantity to improve backpressure and reduce white clouding.
- – Variations in PVC resin, especially calcium carbide powder process, will have different effects on production patches. Differences in density, viscosity, and formula weights on each patch can lead to black lines and clouding problems.
3. Solutions for PVC Pipe and Profile Black Lines
To solve the black line problem completely, consider the following factors:
- 1. The gap between conical twin screws must be large enough.
- 2. The heating temperature must be adequate.
- 3. The motor current for the conical twin screw extruder should not be too high.
Effective Solutions:
- 1. Replace the old screw with an upgraded quality conical twin screw.
- 2. Set the correct screw gap.
- 3. Ensure screws do not scrape against the inner barrel wall.
- 4. Use a motor current appropriate for the motor.
About Us
Since 1993, HUACHEN Screw Barrel has been a leading manufacturer of conical twin screw barrels in Zhoushan Jintang. Our comprehensive services include drawing rebuilding, design, modification, and customized screw barrels. Trusted globally, our products ensure top-tier performance and durability. If you have any questions, please feel free to contact us.
To learn more about our company, our history, and the services we offer, please visit our About Us page.
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For more information about PVC pipe extrusion, PVC profile extrusion and to inquire about our screw barrel solutions, please contact us.
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