Bubbles and pores are critical defects that severely reduce the pressure resistance and service life of PVC pipes, leading directly to high scrap rates. Main manifestations include surface blisters, internal voids, and a spongy, porous cross-section.
Root Cause Analysis: Three Primary Culprits
Material & Moisture: PVC dry blend, especially with hygroscopic fillers (e.g., calcium carbonate) or reprocessed material, readily absorbs moisture. This water instantly vaporizes in the hot barrel, creating bubbles.
Equipment Limitations: Improper screw design (insufficient compression ratio or excessive shear heating) leads to poor melt homogenization, failing to effectively remove air and volatiles.
Process & Vacuum Calibration: Incorrect temperature profiles, or insufficient/uneven vacuum in the calibration tank, prevent the removal and collapse of bubbles before the melt solidifies.
The Solution: Midtech’s Integrated Engineering Approach
Midtech’s solution prevents and eliminates bubbles at the systemic design level, ensuring stable, high-quality production.
1. Precision Material Pre-Treatment
We provide integrated high-efficiency dehumidifying drying systems that ensure material reaches optimal dryness before entering the extruder, eliminating moisture at the source.
2. Professional PVC Screw and Barrel Design
For PVC’s specific characteristics, Midtech employs dedicated two-stage vented screws. The first metering zone builds stable pressure, allowing the melt to fully decompress in the vent zone (under vacuum) to efficiently remove moisture and volatiles. This is paired with bimetallic barrels for precise temperature control.
3. High-Efficiency Vacuum Calibration & Cooling System
Our multi-zone, independently controlled vacuum calibration tanks are equipped with high-power vacuum pumps and precision water/spray systems. They deliver strong, uniform suction to immediately conform the soft pipe to the sizing sleeves, eliminating both surface and sub-surface bubbles.
We provide customers with a proven baseline process parameter set and train operational teams, focusing on establishing rational temperature profiles and synchronizing vacuum with haul-off speed.
Proven Result:
A client in the Middle East, after implementing our complete solution, reduced bubble-related scrap rates from over 15% to less than 0.5%, with products fully compliant with international standards such as ISO 4427.
Get a technical solution tailored to your specific problem.
Contact Midtech for stable and reliable production:
Email: info@midtech-mc.com
WhatsApp/Phone: +86 13962227556