What do the works of Dutch graphic artist MC Escher and plenum retrofits for existing blown film lines have in common? They make the impossible possible.
That's just what equipment manufacturer for blown film cooling equipment Addex Inc. has done with its NPE debut.
Historically, single-inlet plenums have featured only one blower hose, which facilitates an easier installation and creates space around the die. However, they have the reputation of being unable to deliver an even-gauge profile. As a result, multi-inlet air rings have typically outperformed single-inlet plenums because they divide air flow into multiple, closely spaced inlets with corresponding improvements in gauge control.
In response to customer demand, Addex has designed a single-inlet plenum with the performance of a multi-inlet plenum. The company's new patent-pending aerodynamic design employs dual counterflow channels that direct air flow in two opposing directions inside the plenum.
These two counterflows of air join inwardly together to create a combined uniform flow of air to the lip set. The measured overall profile performance is better than with a conventional multi-inlet air ring and inlet effects aren't seen in the film, which was thought impossible in the industry.
"MC Escher had a type of graphic artwork called regular division of the plane, where figures are perfectly interlocked, there's no intervening spaces. We actually took that idea and applied it to airflow," Addex's President Bob Cree told Sustainable Plastics, a sister publication of Plastics News.
"What we have here is a shape which regularly divides, meaning if you mirror image it, there's no intervening spaces between it," he said. "So that when you take the flow from one and you add it circumferentially with the flow from the other, you end up with a combined flow that is perfectly uniform.
"We eliminated the inlet effects by multiplying them by two — by making it twice as bad — but ended up with just the opposite. That's what's special about this," he said.
Addex has tested the new single-inlet plenum against its own multi-inlet plenum, running the two simultaneously. It has found exactly the same profiles.
Other advantages of a single-inlet plenum include a reduction in hoses from eight or more down to a single hose. This saves space on the plant floor, providing easier access around the die for maintenance and operation, and completely eliminates the common problem of multiple hoses having variable lengths and bends leading to negative effects on the finished thickness profile.