What Causes Static Electricity?

We’ve all been shocked before. And no, I’m not talking about the feeling we all here in Cincinnati felt when the Cincinnati Bengals finally fired Marvin Lewis… I’m referring to the discharge you’ve likely felt on a cold winter day after walking across a carpeted surface and touching a door knob. This electrostatic discharge is a result of static electricity. To understand how this static electricity is generated, let’s first go back to basic chemistry class and talk about the atomic structure of an atom.

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An atom consists of three basic particles: protons, neutrons, and electrons. The protons (positively charged) and neutrons (neutral charge) form the nucleus. Outside of the nucleus, electrons (negatively charged) are quickly zipping around in orbits at specific distances from the nucleus. These electrons are bound to the nucleus due to electromagnetic force. Opposite charges attract, since the protons in the nucleus carry a positive charge this acts on the negative charge of the electrons and keeps them in orbit. The closer the electron to the nucleus, the stronger the bond and the more energy required to break that electron from its original orbit.

When an atom gains or loses an electron, it affects the balance that occurs within an atom. If an atom gains an electron, it now has more electrons than protons. This results in a negatively charged atom. The opposite can be said if an atom loses an electron, it now carries a positive charge. This charge imbalance is where static electricity comes from. Both positive and negative charges will remain static until contacted by or in close proximity to a conductive or grounded surface.

The strength of this charge will depend on a few different factors: the types of materials, surface area, environmental conditions, etc. will all play a role in the generation of a static charge. The triboelectric series is a scale, listing various different materials and their tendency to become positive or negative. Those at the far end of the spectrum have an increased propensity to gain or lose an electron, while those in the center are more likely to remain balanced. When two materials on opposite ends of the spectrum come into contact with one another, it poses the greatest risk of generating high levels of static electricity. The chart below shows some common materials and where they fall on the tribolectric series.

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When materials carry a static charge, a variety of problems can ensue during manufacturing. These can manifest in the form of painful shocks to operators, materials jamming or tearing, sheet feeding problems, discharges causing imperfections in the material appearance, etc. To remove the charge, we need to introduce static eliminating ions to balance it out. EXAIR’s full line of Static Eliminators create an equal number of both positive and negative ions to saturate the surface of the material and neutralize any charge present.

With a wide range of different solutions all available from stock, EXAIR has the solution to your static problems this winter. Give us a call and we’ll be happy to discuss the application and help to identify the best method to mitigating any static issues in your processes. Take advantage of EXAIR’s current promotion (now through the end of March) and receive a free AC Sensor with your Static Eliminator purchase!

Tyler Daniel
Application Engineer
E-mail: TylerDaniel@exair.com
Twitter: @EXAIR_TD

 

Atom photo courtesy of janjf93 via Pixabay Creative Commons License

How It’s Made: Static Charge

For me, one of the first signs that winter is here takes place at the grocery store. I’ll stop on the way home to pick up a thing or two, and proceed to the automated self-scan…not because I don’t like people, but because they’re the closest to the exit and, while I DO actually like a LOT of people, I REALLY like dinner. Anyway, the drop in humidity that comes with colder temperatures outside leads to what the buried-wire pet containment folks call a “mild correction” when I touch the self-scan terminal.

I won’t rehash my disdain of cold weather (like I did here, herehere, or here) and while those nuisance static shocks aren’t at the top of the list of reasons why, they actually can be quite severe in other cases.  For example, the minor jolt you get from touching a grounded terminal after pushing a rubber-wheeled shopping cart over the vinyl-tiled floor of the produce aisle isn’t near as bad as the shock that a plastic extrusion machine operator gets when he touches a conveyor duct carrying hundreds of pounds of plastic pellets per hour.

Why one is so much worse than the other?  To fully understand the answer to that question, we’ll need to better understand how static charge is generated.  Scientists have been studying the phenomenon since at least the 17th Century, and studies continue to this day of its creation (mainly at universities) and control (right here at EXAIR Corporation.)  Simply put, when two solid surfaces touch each other, the contact can result in electrons in the outer valences of atoms on one surface to “jump ship” and end up in the outer valences of atoms on the other surface.

It’s called the triboelectric effect.  The prefix “tribo” comes from the Greek word “to rub,” and while many common demonstrations of static charge involve rubbing…for example, rubbing a balloon on a wool sweater sleeve and ‘sticking’ it to the wall…mere contact is all it takes – and that’s where we’ll start:

Static charge from simple contact between this injection molded plastic part & the mold caused defects in a subsequent metallic coating process (left,) which were eliminated after an EXAIR Super Ion Air Knife was installed (right.)

Separation of material – lifting the top sheet from a stack, peeling off a protective layer,  or unrolling plastic film, for example – can also cause those weaker-held electrons to leave one surface for another.

Separation of contacting surfaces can generate a considerable static charge. The 16.9kV charge on this roll of film (left) shortened the life of print heads in a downstream process until EXAIR Ionizing Bars (center) dissipated the charge to an inconsequential 0.4kV (right.)

Some processes involve surface contact, and separation.  And more contact, and separation.  And oftentimes, one surface is in relative motion with the other…and that’s what REALLY puts the “tribo” (“to rub,” remember?) in “triboelectric effect.

The constant motion of these plastic jugs on the conveyor (left,) generated (and multiplied) a static charge so great, it resulted in adhesive labels folding or wrinkling while being applied. A pair of EXAIR Super Ion Air Knives (right) solved the problem.

These are just a few examples of the mechanisms behind, and the solutions for, static charge.  For more details, I encourage you to read EXAIR’s Basics Of Static whitepaper (registration required) or watch our recorded Webinar: Understanding Static Electricity.  If you have a static problem you’d like help with, give me a call.

Russ Bowman
Application Engineer
EXAIR Corporation
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