Internal Air Pressure vs. Vacuum Sizing for Ovality Issues?
To achieve more consistent ovality in an application like medical tubing extrusion, consider vacuum sizing.
Q. We’re extruding some medical tubing with 0.060-in. or smaller O.D. We have been using internal air pressure for sizing but have had intermittent problems with ovality. Would vacuum sizing offer any advantage? —West Coast tubing processor
A. If ovality is your major concern, then the answer is yes. Using either contact or non-contact vacuum sizing greatly enhances the potential to improve ovality. You still need to be sure to center the die bushing so that the wall of the tube is concentric. If there is a thin spot in the wall, even with non-contact sizing, the thin spot will push out, leading to ovality.
With vacuum, once the tooling and associated drawdown are worked out, the repeatability is excellent and setup can be repeated in just 10-15 min. That’s because the differential pressure is created by the vacuum over the defined length of the chamber, and in-line cutting or coiling can cause only minimal tolerance variation. The other advantage of vacuum is that the weight of the water is actually removed from the tube as vacuum level is increased. With the internal air method, the operator must adjust the water level to improve ovality.
Bob Bessemer, sales manager, medical extrusion
Conair, Cranberry Township, PA
(724) 584-5500 • conairgroup.com
Related Content
-
Foam-Core Multilayer Blow Molding: How It’s Done
Learn here how to take advantage of new lightweighting and recycle utilization opportunities in consumer packaging, thanks to a collaboration of leaders in microcellular foaming and multilayer head design.
-
First Water Bottles With Ultrathin Glass Coating
Long used for sensitive juices and carbonated soft drinks, KHS Freshsafe PET Plasmax vapor-deposited glass coating is now providing freshness and flavor protection for PET mineral water bottles.
-
Impacts of Auto’s Switch to Sustainability
Of all the trends you can see at NPE2024, this one is BIG. Not only is the auto industry transitioning to electrification but there are concerted efforts to modify the materials used, especially polymers, for interior applications.
