Industrial Static Control

What is Static Electricity?

Electric charge at rest, generally produced by friction or electrostatic induction. Triboelectrification the process whereby charge transfer between dissimilar materials, at least one of which must have a high electrical resistivity, occurs due to rubbing or mere contact.

Introduction to Electrostatics

The class of phenomena recognized by the presence of electrical charges, either stationary or moving, and the interaction of these charges, this interaction being solely by reason of the charges and their positions and not by reason of their motion.

At least 90% of the topics that are normally classified as electrostatics are concerned with the manipulation of charged particles by electric fields. When a particle becomes charged by rubbing or by other means, it has either a surplus or a deficit of electrons. A body with a surplus of electrons is said to be negatively charged; a body with a deficiency, positively charged. The amount or quantity of charge on a body is expressed in coulombs (positive or negative). A coulomb is an enormous amount of charge, and in most electrostatic situations charge levels of a small fraction of a coulomb give rise to significant effects. Electrostatic forces exist between charged bodies. Bodies with like charge repulsive forces, while oppositely-charged bodies experience attraction.

Principles

If two bodies are charged to Q₁ and Q₂ coulombs separated in vacuum by a distance of r meters, the force F in Newtons between them is given by Coulomb's law:

F = (Q₁Q₂)/(4πε₀r²)

In electrical science, ε₀ is an important constant known as permittivity or dielectric constant of free space, and is also sometimes called the primary electric constant. It has the value

ε₀ = 8.85416 x 10^-12 farad per meter.

Coulomb's law shows that a body charged to Q₁ experiences a force due to the presence of another body charged to Q₂. Q₂ may be considered to influence the whole of space surrounding it because if Q₁ were to be positioned anywhere it would experience a force due to the presence of Q₂. The property of a charge to influence the whole of space can be modeled by a three-dimensional force field permeating the whole of the space surrounding the charge Q₂. This field is called the electric field.

When there are many charged bodies present in an environment, the force that would be exerted on a charged particle at any location can be found by calculating the field at the location due to the presence of each charged body separately, and the net field is obtained by adding up the individual components.

A system of charged particles or bodies is unstable unless the particles are prevented from moving, since the like-charged particles will repel each other until they are infinitely far apart, and oppositely charged bodies will attract one another and come together. The system has potential energy. The potential energy of two charged particles separated by a distance r can be shown to be given by this equation:

Potential energy = (Q₁Q₂)/(4πε₀r) joules

Charging methods

The three principal methods of applying electric charge to objects are corona charging, induction charging, and tribocharging.

The corona-charging method relies upon the impact of charged atoms or molecules (ions) on charged bodies. Copious quantities of ions may be generated by a corona discharge, which is a region in which an intense electric field acts upon air molecules and ionizes them so that free ions are produced. A sharply pointed electrode maintained at a high positive or negative potential induces a stream of positive or negative ions which may be used for charging surfaces. The stream of ions from a corona point is usually so intense that neutral air molecules become entrained in the flow to produce a corona wind which can deflect a candle flame. Ions from a corona discharge may be used to charge isolated bodies, insulating surfaces or particles by simply directing a corona wind onto the surface to be charged. In the case of particles, it is normally sufficient for them to pass through a corona discharge region to receive a significant charge from ion-particle collisions.

Surfaces may be charged by exposure to an electrostatic field. If the surface is a liquid and it is disrupted into droplets, they will be electrically charged. Induction charging of equipment and personnel may occur when they are exposed to an electric field. Personnel charged in this way may generate electrostatic discharges when approaching grounded surfaces. Sensitive microelectronic devices can be damaged and computer data can be corrupted by such discharges.

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