How to Solve Problem of Bubbles in PVC Pipe Production

In the PVC pipe production process , few defects are as frustrating as the “internal bubble.” Whether they appear as tiny surface blisters or hollow voids within the pipe wall, bubbles compromise both the structural integrity and the aesthetic value of the final product.

Solve Problem of Bubbles in PVC Pipe Production

While many operators mistake bubbles for simple “trapped air,” the root causes are often far more complex, involving the delicate interplay of material volatiles and mechanical degassing. At Kangju Machinery, we have analyzed thousands of production cycles to develop a holistic approach to eliminating these voids.

Moisture and Chemical Off-gassing:

The most common culprit is residual moisture or volatile additives. PVC resin is hygroscopic; if the high-speed mixer does not reach the critical 120℃ threshold, water molecules remain trapped in the powder. During PVC pipe extrusion line, these molecules flash into steam, creating “moisture bubbles.”

  • Kangju’s Solution: We advocate for a synchronized “Hot-Cold” mixing cycle that ensures a minimum of 8 minutes of high-intensity friction, effectively “opening” the resin pores to release trapped humidity before it reaches the hopper.

PVC pipe extrusion line

Vacuum Degassing:

If bubbles appear even with dry material, the issue likely lies in the extruder’s degassing zone. As the PVC melt passes the vent port, a high-performance vacuum must extract any remaining gases.

  • Kangju’s Solution: Kangju’s new SJZ series extruder utilizes a dual-stage liquid ring vacuum pump capable of maintaining a stable pressure of -0.09MPa. Furthermore, our specialized screw flight geometry in the degassing zone increases the melt’s surface area, allowing gases to escape more freely from the viscous polymer.

Lubricant Imbalance and “Low-Boiling” Additives:

Sometimes, the bubble isn’t air or water – it’s vaporized lubricant. Over-lubrication (especially with low-quality waxes) can cause a chemical reaction that releases gas at the high temperatures found near the die head.

  • Kangju’s Solution: We recommend a precise balance of internal and external lubricants. If “silver streaks” accompany the bubbles, it is a clear sign of external lubricant overdose, which requires a formula recalibration to stabilize the melt strength.

FAQ:

Q1: How can I tell if a bubble is caused by moisture or by the vacuum system?

A: A simple “Squeeze Test” provides the clue. Moisture bubbles are typically small, numerous, and distributed throughout the pipe wall. Vacuum-related bubbles (air pockets) are often larger and localized near the top of the pipe cross-section.

Q2: Can the temperature settings in the “Feeding Zone” cause bubbles?

A: Yes. If Zone 1 or Zone 2 temperatures are set too high prematurely, the material “seals” too early, trapping air before it can escape back through the hopper. A “gradual rising” temperature profile is essential for natural venting.

Q3: Does the “Sinking” of the pipe wall relate to bubble issues?

A: Often. Voids inside the pipe wall weaken the structure, causing the outer surface to “sink” inward during the vacuum calibration phase. Eliminating the internal void is usually the first step to fixing surface flatness.

Why choose Kangju Machinery?

Planning a plant is complex, but partnering with Kangju Machinery simplifies the transition from blueprint to production. With over 15 years of specialized experience in plastic extrusion line, Kangju does not just supply machines; we deliver “Turn-key Intelligence”.

  • 15+ Years of Technical Mastery: Proven expertise in pipe / profile / panel / sheet extrusion.
  • Customized Molds: Our in-house mold design team uses flow-simulation software. This ensures your PVC wall panels have uniform thickness and a flawless finish from the first meter.
  • On-Site Commissioning: We provide global on-site installation and technician training, ensuring your local team is fully capable of maintaining peak production efficiency.

Kangju Machinery

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