When plastic fasteners rub against each other or the plastic bag they may be stored in, a static charge will develop. This fact probably doesn’t surprise you, as most everyone is familiar with the everyday reality of static electricity.
Most of us will recognize electrostatic discharge (ESD) as a “shock” we get walking across a carpeted floor and touching a metal doorknob. We have all experienced the static cling on a piece of clothing taken from the dryer. The atmospheric discharge of static electricity is the scientific explanation behind lightening.
So why is static electricity so dangerous for plastic parts? When plastic components become charged, pieces of dirt including dust, plastic bits, hair, cutting oils and other debris will be attracted to the charge. Particulate on plastic parts causes problems in situations like medical applications, electronics and semiconductor manufacturing to name a few. Because of the static charge, no amount of ordinary washing, blowing or straining the parts will dislodge the particles. The only way to clean the plastic fasteners is to find a way to release the charge and free the particles. In order to accomplish this task, Electrostatic Discharge (ESD) devices have been developed. To understand how these tools work, we must first examine static electricity in further detail.
Let’s start with the structure of an atom. In the middle of each atom is a nucleus. It is made up of two kinds of particles, protons and neutrons. Orbiting around the nucleus are electrons. While the nucleus is very large compared to the orbiting electrons, most of the atom is empty space.* Protons, neutrons and electrons all have an electrical charge. Protons have a plus (+) charge, electrons have a negative charge (-) and neutrons have no charge, making them neutral. The charge of one proton is equal to the charge of one electron. If an atom contains the same number of protons and electrons, the atom has a neutral electrical charge. The protons and neutrons making up the nucleus are bonded together tightly but the orbiting electrons are not. They are able to move from one atom to another. So if an atom loses electrons it becomes positively charged and if it gains electrons it will have a negative charge.
Some materials like plastic, cloth, and glass do not give up their electrons easily. These are called insulators. Materials such as metals lose their electrons more easily and are called conductors. Since plastics are insulators, they are poor conductors of electricity. Electrical charges tend to build up on the surface of insulators resulting in static electricity. Static electricity is the imbalance of positive and negative ions on the surface of an object. Static electricity is so called because it is at rest, not moving. More accurately, it should be called static charge which means a surplus or a deficiency of electrons that are not moving.
So how does an Electrostatic Discharge (ESD) ionizing device come in? ESD ionizers neutralize a static charge by balancing the ions between the molecules of the gasses in the surrounding air. In order to remove the static charge clinging to the surface of the plastic fasteners, it is necessary to provide more positive and negative ions and to distribute theses ions across the insulating object. The static charge is then neutralized and the plastic parts no longer attract dirt or dust.
The most common industrial ESD devices are corona ionizers which work by applying high voltage to the tip of a sharp point or nozzle. Often these devices have a fan to spread the ionized particles through the air. ESD ionizers are also used in many high tech work environments to control electrostatic discharge. These devises are used to control static on conductors that cannot be grounded or as discussed above on insulators like plastic fasteners.
* While nuclear physicists recognize other subatomic particles we need not consider them in this discussion.
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