As we in the Northern Hemisphere are getting ever closer to our summer season, our friends in the Southern Hemisphere are gearing up for winter and the effects that it brings for some production environments. Namely, low humidity causing static problems.
One of our good customers in South Africa needed to get up to speed on some issues regarding EXAIR Static Eliminators and static issues in general. Following is a list of questions and the answers I gave to help them gain a better understanding.
- Do the EXAIR Static Eliminators transmit both positive and negative ions?
Answer: Yes, since they are an AC ionizer, the AC wave form changing polarity 50 – 60 times per second (Hz)
causes the ions to be both positive and negative so that either positive or negative charge can be reduced in an application. - What electrostatic field reading (with model 7905 Static Meter) would you classify as being a potentially high static reading?
Answer: A specific static reading would not necessarily be considered high or low for any given application. What I mean is that you want to gauge a static reading as being high or low depending on whether it actually creates a problem in the production environment. The static meter simply puts a number to it so you can at least have a measurable figure to go by when implementing any sort of static elimination solutions. In practice, this means that for one application a 5kV charge might be extremely high and cause many problems. For another application, 5 kV does not cause any problems at all. So, it is somewhat relative. That being said, the full range of the static meter is +/- 20 kV at 1 inch from target. Between 3 and 5 kV is where you will begin to see problems in industrial applications, although they could possibly start at lower voltages. Just to give you an anecdotal frame of reference, if you have ever been shocked by a door knob when walking through your house in your socks, that is about 8 kV of charge that you give to the door knob or other grounded surface when you touch it.
- What polarity static measurement be classed as a static issue? Positive, negative or either?
Answer: Both polarities of charge can cause problems in applications. Thus, the reason for having an AC ionizer, as mentioned above they can work to reduce either polarity charge. - What is the correct procedure for the cleaning of ionizing bars?
Answer: We have a very informative video explaining this process that can be reviewed here. - How do distance and input pressure affect the ability of an air operated ionizer to reduce a static charge?
Answer: The further away an air operated static eliminator is from its target, the longer the time required to reduce the static charge. Also, static will take longer to decay at lower input pressures. Optimum distances for a static eliminator are between 3” and 36” from target. Static reduction will still occur at distances up to about 15 feet away, although at a reduced decay rate. - How does the amount of time in contact between a target material and a static eliminating airflow affect the static charge?
Answer: The time in contact between an ionized airflow and the intended target is one of the most critical factors when considering how one would set up a static eliminator into an application. Since materials are usually moving by a static eliminator at high rates of speed, one way to increase the time in contact is by strategically mounting the static eliminator to blow onto the target at a very low blowing angle. I will usually say, almost parallel to the material if is something like a flat web or similar where that is possible. If you can visualize a static eliminating airflow as a shadow that appears on a side walk. When the sun is high in the sky, the shadow is very short. When it is lower in the sky, the shadow becomes very long. Without making the analogy too complicated, think of the sun as the static eliminator and the shadow as the ionized airflow and the sidewalk as the target. The lower the angle, the longer the contact time. This is optimized mounting strategy to increase time in contact.
Neal Raker, Application Engineer
nealraker@exair.com