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Ionizers and Static Eliminators Selection Guide

Ionizers Selection GuideStatic Eliminators Selection Guide

Image Credit: NRD, LLC | Panasonic Electric Works

 

Static eliminators or static ionizers eliminate static and dust and can neutralize and clean surfaces at remote distances. Static neutralization is a practical method of static reduction; however complete static elimination is not readily attainable. In its simplest form, a static eliminator or static ionizer is a static reduction device that produces positive and negative ions which are attracted to an unbalanced surface or material. As long as friction is not reintroduced, static electricity remains at minimum levels. Since static eliminators vary in terms of capabilities, a careful consideration of performance specifications is an important part of product selection.

 

 

Static Electricity

Static electricity is a stationary electric charge imposed on a solid surface. The solid surface either gains or loses electrons by interacting with other materials or surfaces, most commonly after any amount of friction has been applied. The resulting surface will have an excess of either positive (+) or negative (-) charges that attract opposing charges and repel like charges. The study of stationary or slow moving electric charges is known as electrostatics.

 

Static Eliminators Selection Guide

Image Credit: Physics Workbook

 

The electrostatic forces causing attraction and repulsion can be explained by Coulomb's Law. Coulomb's law states: "The force of attraction or repulsion between two point charges is directly proportional to the product of magnitude of each charge and inversely proportional to the square of distance between them."

 

Coulomb's Law

Where:

Fe = Electrostatic Force

k = Coulomb's Constant

q1 = Charge of Point 1

q2 =Charge of Pont 2

r = Distance Between Charges

 

The electrostatic forces described by Coulomb's Law interfere with industrial processes. Unfinished surfaces may attract dirt, repel paints or coatings, cling to other objects, generate sparks, or otherwise cause irregularities in the finished product. Ionizers and static eliminators are designed to dissipate static electricity, ensuring a clean environment and preventing production defects from occurring.

 

Operation

Ionizers and static eliminators  use one of several operating principles in order to neutralize an unbalanced surface. 

 

Corona Discharge

Corona discharge static eliminators produce positive and/or negative ions by placing a high voltage on a sharp-pointed electrode in close proximity to a grounded shield or casing. With the voltage applied the air between the electrode and the grounded casing is broken down by a static ionizer, generating ions. Various types of corona discharge methods are based on the number of electrodes and voltage source used. AC systems generate positive ions during the first half-cycle of the waveform and negative ions during the second half-cycle of the waveform. DC systems only produce a single polarity from a single electrode. DC systems that use both positive and negative electrodes may suffer from poor ion balance at longer distances. Pulsed voltage systems produce higher ion densities due to the stepped waveform.

 

Static Eliminators Selection Guide

Image Credit: Shimadzu Scientific Instruments, Inc. 

 

Research suggests that a 5 mm pitch is ideal for most static reduction devices.

 

A tighter pitch does not necessarily increase the effectiveness of static elimination devices such as static neutralizers and static cleaners. Static eliminators are often made of stainless steel fiber and conductive acrylics; however, the use of fibrous static reduction materials is not recommended if fiber shedding could cause electrical problems inside machinery. In such cases, liquid static cleaners are suitable choices.

 

Photoionizer

Photoionizers use the photoelectric effect to neutralize static electricity. Soft X-rays ranging from 3keV to 9.5keV are emitted by the ionizer. Stable atoms and molecules near the work surface become excited and share valence electrons, producing ions that interact with and neutralize charged objects and surfaces. Photoionozers have no electrodes to maintain, do not require pressurized air, and neutralize fast moving objects.  

 

Ionizers Selection Guide

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Shielding is required to isolate soft X-ray radiation.

 

Device Types

Static elimination devices are used to reduce static electricity generated by production processes that involve plastics, paper, textiles, and other non-conducting materials. The following device types cover common types of static elimination devices while several specialty, proprietary, or application specific devices are also available.

 

 

Benchtop devices are used to neutralize a localized work space and are not designed for in-line processes or to eliminate static charges over larger areas.

 

Ionizer Selection Guide

Image Credit: Digi-Key Corporation

 

Blow off guns are handheld static eliminators that use compressed air to control the flow of ions toward the work area to be neutralized.

 

Static Eliminators Selection Guide

Image Credit: All-Spec Industries

 

Ceiling emitters are designed for use in large areas, like cleanrooms. The ceiling mount along with an air supply, blower, or other ventilation device allows static removal over larger distances.

 

Static Eliminator Selection Guide

Image Credit: TAKK Industries, Inc.

 

Ionizer bars may or may not require an air source. Devices without an air supply suffer from a limited range while devices that use compressed air can displace or disturb sensitive and lightweight products and materials. They are mounted at a calibrated distance as to produce ions at a targeted area without overshooting or suffering from poor ion balance.

 

Ionizer Selection Guide

Image Credit: Terra Universal, Inc.

 

 


NFPA Standard

The National Fire Protection Association (NFPA) recommends the installation of a static eliminator or static cleaner for coating and printing applications. The breakdown of stationary charges can generate a spark and pose a fire hazard. The specific standard, NFPA 77, outlines accepted practices that apply to the identification, assessment, and control of static electricity for purposes of preventing fires and explosions.

 

 

Static Eliminators Selection Guide

Image Credit: NFPA

 

 

 

References:

 

Coulomb's Law

 

Static Eliminators

 

Types of Corona Discharge Static Removal Devices