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
Pulsed DC eliminators Pulsed DC eliminators, like their AC counterparts, produce ionized air by using high voltage. Whereas the AC units operate at supply frequency the pulsed DC units operate at lower frequencies, often between 0.5-20 Hz. The low frequency of operation lends pulsed DC equipment to long-range neutralization. The ionizing bar consists of a series of emitters connected alternately to the negative and positive outputs (Figure 4). The casing of the bar is made of plastic, so there is no proximity earth.
The output from the power supply is effectively a square wave switching from negative to positive at the chosen frequency. Looking at the positive half of the wave form, the controller switches on the high output voltage connected to the positive emitters. This then sets up an electric field between the emitter and the surrounding earthed objects. At the sharp point of the emitter this field is extreme-ly strong, and in similar fashion to the AC eliminators, positive ions are produced. The similar charge of the ion and the emitter drives the ions away from the bar. Long-range pulsed DC bars can be very effective in screen-printing production by eliminating electrostatic charges from screens without causing drying.
Understanding the magnitude—and, in some cases, the polarity—of the charge to be neutralized is a critical part of selecting the proper system for static elimination. In cases where AC eliminators are appropriate, you need to know the magnitude of the static charge so that you can select the correct eliminator bar. In cases where pulsed DC equipment is appropriate, it’s important that you determine the magnitude and the polarity of the static charge in order to correctly set the output’s power and bias.
Measuring the actual amount of surface charge is quite difficult, but you can use a device dedicated to this application to measure the electric field generated by a statically charged object, the unit of which is volts per meter. Measuring the field at a known distance enables you to deduce the surface voltage.
How much do you charge?
Evaluating the causes of static electricity in your shop is the first step to gaining control over the situation. Take a look at the ways in which your equipment runs and how your staff handles substrates. Monitor the environmental conditions in the workspace, keeping a close eye on temperature and humidity. From there, you can determine how much of a charge you generate. Finally, working with a specialist who can use the data you’ve collected and assist you in your efforts will ensure that you implement dynamic solutions to your static problems. n
Glossary of Electrostatics Terminology
Capacitance: A measure of the ability of a substance to hold charge.
Coulomb: The unit of measure of electrical charge.
Conductance: The higher the conductance of a material the easier charge will flow through it. Metals are very conductive.
Electron: A small atomic particle with a negative charge (1.6 x 1019 coulombs).
Ion: A molecule or atom with an electrical imbalance (a negative ion has an excess of electrons, a positive ion has a deficit of electrons).
Resistance: The higher the resistance of a material the harder it is for charge to flow through it. Insulators such as plastics are very resistive.
David Rogers is international product manager for Meech Static Eliminators. He’s been with the company for the past 13 years and was appointed to his current position this year. Rogers previously worked for Meech in technical sales support, and he continues to use his applications expertise and product knowledge to increase productivity and profitability in industries such as printing, plastics, converting, and packaging.
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