The Boundary Layer and Static Elimination

Boundary layer

I recently spoke with one of my colleagues at our Finland distribution partner, Projecta Oy. He had an application for static elimination on a large paper producing machine. He has applied our Ion Bar to paper machines in the past to eliminate static. In this case though, the line speed was more than double that of his previous application at about 1450 meters per minute. He was not sure if he could apply EXAIR Static Eliminator to the affected machine or not, simply due to the line speed.

Actually, use of a Super Ion Air Knife, or rather a few of them (due to machine width) is right in line with what is recommended. When the application involves a high-speed, moving web there is the issue of a boundary layer of air that moves along adjacent to the web which can affect the static elimination result if not approached properly. The boundary layer can prevent static eliminating ions from reaching the surface of the statically charged web and must be overcome to be effective.

Super Ion Air Knife, with it’s powerful laminar air flow, is the right choice on a web-based application like this one. Setting the unit up so that it blows parallel to the web but in the direction opposite the web travel creates a counter airflow which disrupts the boundary layer and allows the static eliminating ions to come into contact with the moving web to neutralize the charges present.

There is also a secondary benefit in that the Super Ion Air Knife, by being mounted in such a way, enables a much longer time in contact between the ions and the charged surface. This has the net effect of being able to reduce the static charge down to a much lower level before the web passes this area. Since slowing the web speed down is not an option in these cases, the only way you can effectively create dwell time within the ionized airflow is to extend the distance over which the web is treated and using the Super Ion Air Knives in this way allows the user to do that.

Neal Raker, Application Engineer

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