Is static standing in the way of quality and productivity in your shop? This discussion will help you identify sources of static electricity as well as the types of systems available to eliminate it from your production process.
By David Rogers
The fundamental principle for neutralization of static charges is the same, regardless of the technique used. Where a material has a positive surface charge electrons must be delivered to the surface to bring the charge back into balance. Where the surface charge is negative the excess electrons must be removed from the surface to neutralize the charge. The delivery or removal of electrons can be done by one of the these three methods:
• Movement of electrons through the material itself.
• Movement of electrons through another material in contact with the surface.
• Movement of electrons through ioniza tion of the surrounding air.
A fourth method, sparking, occurs when the surface voltage is sufficiently high to cause the air to become conductive. However, the occurrence of sparking is normally due to the lack of application of other methods. More specific approaches to static elimination follow.
Humidity As previously noted, moisture on (or within) a material will tend to leach away static charges down to earth. For example, paper generally has a relatively high moisture content and does not maintain particularly high levels of static. However, if the paper is particularly dry, static can become a severe problem.
Passive ionization The close proximity of a conductor to a charged object will tend to discharge it. For example, a carbon-fiber brush will reduce static charges in materials passed in close proximity to the brush.
Radioactive ionization Radioactive sources cause ionization of the surrounding air, thereby neutralizing surface static charges. A drawback of radioactive eliminators is the radioactive source loses its effectiveness over time and requires replacement on an annual basis.
Active electrical ionization Ionized air can be produced via high-voltage AC or DC, which can then be used to neutralize surface charges. The use of AC or DC systems is application dependent.
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