In the production process of PVC pipes, uneven wall thickness is a common issue, especially evident during the pipe extrusion process. Specifically, it manifests as uneven wall thickness around the central axis of the pipe outlet, where the thickness may vary between the upper and lower parts, or between the left and right sides of the pipe. This phenomenon is often attributed to two main issues:

  1.Mold Issues

A key factor contributing to uneven wall thickness in PVC pipes is the mold. Variations in mold gap or mold channel shape can cause uneven flow of PVC material during the molding process, resulting in inconsistent pipe wall thickness. Particularly, deficiencies in mold design standards or manufacturing precision can obstruct material flow during the pipe forming process, leading to variations in wall thickness at different positions.

Specific manifestations include:

• Uneven mold gap: Asymmetry in the gap between the upper and lower or left and right sides of the mold can cause the material to flow faster in these areas, resulting in thinner wall thickness in those parts of the pipe.

• Mold design defects: Unreasonable channel design in the mold can affect the flow of molten PVC, leading to thicker or thinner wall thickness in certain areas.

• Mold channel blockage: Any minor blockage can hinder the smooth flow of molten PVC, thereby affecting the uniformity of pipe wall thickness.

Finally, proper mold cleaning is an important step to ensure the normal operation of the mold, and any inadequate cleaning can lead to uneven wall thickness of PVC pipes.

    2.Uneven Plasticization and Insufficient Pressure

During production, uneven plasticization or insufficient pressure can also cause uneven wall thickness. Uneven plasticization means that the PVC material has not melted uniformly during the heating process, resulting in poor flowability of some parts of the material and affecting the pipe wall thickness. Insufficient pressure means that the molten PVC material in the mold has not been fully squeezed into every corner of the mold, leading to incomplete forming.

Specific manifestations include:

• Uneven plasticization: If the temperature control of the plasticizing equipment is unstable, or the screw speed is not appropriate, it may lead to differences in the physical properties of the molten PVC material during flow, resulting in thinner wall thickness in certain parts of the pipe.

• Insufficient pressure: If the output pressure of the extruder is too low during production, it cannot deliver enough molten PVC into the mold, which can also cause uneven pipe forming, especially in the distal or corner parts of the mold.

The causes of uneven wall thickness in PVC pipes may involve multiple factors such as mold design, mold blockage, uneven plasticization, and insufficient pressure. Rallychem has shown outstanding performance in solving production issues in the PVC, CPVC, and engineering plastics industries. Particularly for the issue of uneven wall thickness in PVC pipes, Rallychem provides multi-dimensional solutions covering formula optimization, process improvement, and equipment upgrading, achieving effective cost control and significant efficiency improvement from the source.