Application of Liquid Ring Vacuum Pumps in the Plastics Industry

Liquid Ring Vacuum Pumps are essential equipment in the plastics industry, providing reliable vacuum solutions for various critical processes. Their ability to handle wet gases and vapors makes them particularly well-suited for this sector.

1. Plastic Pellet Production and Devolatilization

In the production of engineering plastics or compounding of recycled materials, the polymer melt often contains undesirable volatile components such as moisture, residual monomers, solvents, or low-molecular-weight oligomers. Liquid ring vacuum pumps are used in devolatilization extruders to create a high vacuum that forcibly removes these volatiles. This process is crucial for enhancing product purity, improving mechanical properties, and ensuring final product quality by preventing defects like bubbles and streaks.

2. Injection and Compression Molding - Mold Degassing

When molten plastic is injected into a mold, trapped air and gases released from the material itself can cause defects. Liquid ring vacuum pumps are connected to vents in the mold cavity to evacuate air immediately before injection. This application is vital for eliminating surface defects such as burn marks, short shots, and flow lines, resulting in high-gloss, flawless surfaces, especially for critical components like optical lenses or automotive parts.

3. Extrusion Processes - Melt Degassing

Similar to pellet production, vacuum degassing is employed during sheet, film, pipe, or cable extrusion. Liquid ring pumps are used in conjunction with vacuum sizing tanks or calibration units. They remove entrapped air and volatiles from the melt, ensuring precise product dimensions, excellent surface finish, and improved mechanical strength by achieving a dense, bubble-free structure.

4. Vacuum Thermoforming

This process involves heating a plastic sheet until pliable and then using vacuum force to draw it onto a mold. Liquid ring vacuum pumps provide the rapid and powerful suction required to accurately form the sheet into complex shapes, capturing intricate mold details. This is essential for manufacturing products like food packaging, refrigerator liners, and automotive interior panels.

Why Liquid Ring Vacuum Pumps are Ideal for the Plastics Industry:

Tolerance for Water Vapor and Moisture: This is their primary advantage. Plastic degassing generates significant water vapor and condensable gases. The pump's sealing liquid (typically water) can directly condense and absorb these contaminants without risk of pump damage, a common issue for dry pumps.

Robustness and High Reliability: Their simple design, with only one rotating impeller and no metal-to-metal contact inside the pumping chamber, ensures minimal wear and tear, allowing for continuous 24/7 operation.

Smooth and Quiet Operation: The compression process within the liquid ring is gentle, resulting in low vibration and noise levels, which improves the working environment.

Handling of Challenging Streams: While not for dusty environments, they tolerate gas streams that may carry traces of plastic condensates or oligomers better than pumps with precise internal clearances.

Relatively Low Maintenance Costs: Simple construction translates to easy maintenance, primarily involving routine sealing liquid changes and occasional checks on mechanical seals, leading to lower spare parts costs.

In summary, Liquid Ring Vacuum Pumps are indispensable in the plastics industry for ensuring product quality, enabling complex processes, and boosting production efficiency from raw material preparation to final shaping. Their reliability in handling wet processes makes them a cost-effective and practical choice for creating the necessary vacuum environment.