Super Air Knife Provides Tension with Fine Adjustment for a Lightweight Plastic Film

A company had a small converting machine that was winding a plastic film onto a roll. The width of the plastic film was only 3” across, and the amount of tension required for a consistent roll was small. The maximum amount of tension without damaging the plastic film was 16 ounces of force.  In converting media onto rolls, it is very important to control the tension on the web to reduce defects like wrinkles, out-of-round rolls, or stretching.

They explained the setup that they were trying. They had a 4” manifold with two 2” wide “duck-foot” nozzles attached.  They sent a hand drawing to better describe what they were using. (See below).  The issue that they were seeing was too much variation in the blowing force being applied to the film.  To get near the correct blowing force, they had to start at an air pressure of about 18 PSIG.  As they ran the process, the operator would have to adjust the pressure continuously to evenly roll the film onto the core.  The process was out of control, and they wondered if EXAIR had a better way to evenly exert this force.

Dual Flat Nozzle Manifold

Dual Flat Nozzle Manifold

In analyzing the drawing and their setup, I noticed a couple of things that could cause the variations. I modified his drawing to better explain the situation (Reference below).  As compressed air leaves the two flat nozzles, the center section will overlap.  This overlap will cause turbulence in the air flow pattern.  In order to get an even distribution of forces across the width of the product, turbulence cannot exist.  Turbulence is a mixing pattern where the velocity is not linear; thus, causing high and low pressure points on the target.  The other thing that I noticed was the low air pressure that they could not go above.  This limited the precision of the incremental forces.  Because of the fixed openings of the two nozzles, they had to have a ceiling with the air pressure at 18 PSIG for 16 ounces of force.  If they had to “bump” the force level, the change was difficult to hit exactly.  If we divided the 16 ounces of force between 0 – 18 PSIG, we would get roughly 0.9 ounce of force per PSIG.  You lose the accuracy to make fine adjustments.

Overlap of air flow pattern

Overlap of air flow pattern

I recommended our model 110003, 3” Super Air Knife and a model 110303 Shim Set. The Super Air Knife blows compressed air across the entire length.  Without any overlap, the flow is laminar, and the velocity profile is moving in the same direction.  Thus, an even force across the entire 3 inches.  The Shim Set comes with additional shim thicknesses of 0.001”, 0.003”, and 0.004” thick (the standard thickness of 0.002” is installed in the Super Air Knife). In working with such a precise force requirement, they needed additional options for more control.  They could change the shims as a coarse adjustment and adjust their pressure regulator as a fine adjustment.  This combination gave them the best results to accurately dial in the correct force and not damage the material.  With the maximum requirement of 16 ounces across 3 inches of film, they were able to change the shim to the 0.004” thickness.  For the model 110003 Super Air Knife, it put them at a maximum pressure of 86 PSIG, not 18 PSIG.  Thus the increment was now 0 – 86 PSIG for 16 ounces of force, or 0.19 ounces per PSIG.  There was much more resolution to make smaller changes to the force levels thus optimizing their adjustment range.

Super Air Knife with Shim Set

Super Air Knife with Shim Set

In replacing the competitor’s product with a Super Air Knife, our customer had all the necessary control to wrap rolls of film without issue. The setup with the nozzles on a manifold design resulted in turbulence, which was noisy and produced inconsistent results.  It also restricted their adjustment resolution in changing forces, as they do not use shims.  If you would like to exert a greater degree of precision blowing with products like the Super Air Knife, please contact us. We would be happy to discuss your application and help you meet such goals.

John Ball
Application Engineer
Email: johnball@exair.com
Twitter: @EXAIR_jb

Static Electricity – What is it?

Now that the air is cooling and the humidity is dropping, you may often experience the phenomena of static electricity, and the resultant shock when touching something metal. As a child, you may have learned about static electricity by rubbing a balloon on your head and then seeing it stick to the wall. What is the science behind static electricity?

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All materials are made up of atoms, which have a positively charged core called the nucleus surrounded by a cloud of negatively charged electrons.  Each material is different, and in some types of materials the positive nucleus has a very strong pull on the electrons while in other materials the pull is very weak.  If we were to put a strong  pull material in contact with a weaker pull material, atoms from the weak pull material will migrate, and when the materials are separated, additional electrons will remain with the strong pull material.  Due to the overall increase in electron quantity, the material becomes negatively charged and the other material becomes positively charged. If the materials are rubbed together, the opportunities for the electron migration increases, and thus more electrons are exchanged.

Electrons build up more easily in dry conditions. When the air has humidity, static build up is less common because a very thin layer of water molecules coat most surfaces, which allows the electrons to move more freely and make most materials conductive and static free.

In some cases, static electricity can be a good thing – laser printers and photocopiers use static electricity to transfer ink from the drum to the paper.  Also, some power plants and chemical factories use static electricity  to remove pollutants in a process that takes place within the smokestack.

But generally when EXAIR gets involved, it is because the static electricity is causing an unwanted build up of static charge that affects a manufacturing process. The results of a static charge imbalance can result in a shock to an operator, materials sticking together, poor print quality, sensor or counter malfunctions, bad surface finish, or any number of other problems.

EXAIR offers systems for total static control, such as the Super Ion Air Knife and Ionizing Bars for wide applications such as paper, film and plastic webs, the Super Ion Air Wipe for narrow, continuously moving materials such as wire, tube, or extrusions.  Also offered are the handheld Ion Air Gun for use on three dimensional parts prior to assembly, packaging painting or finishing. Other options include the Ion Air Cannon for limited space or remote mounting applications, Ion Air Jet for tight spaces and concentrated airflow, and the Ionizing Point to provide close distance and accurate static removal.

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Super Ion Air Wipe

To discuss your static elimination concerns , feel free to contact EXAIR and one our  Application Engineers can help you determine the best solution.

Brian Bergmann
Application Engineer

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Twitter: @EXAIR_BB

Spark Photo Credit – Eric Skiff – via Creative Commons License

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