STATIC ELECTRICITY: Denoting or pertaining to electricity at rest. How
simple and inadequate this definition is of a phenomenon that creates
problems which cost industry billions of dollars per year. A clearer
understanding can be gained by explaining lightning. Static electricity
in the atmosphere remains at rest until the potential gradient, between
clouds, reaches a level that causes the insulator between clouds, in
this case air, to break down or fail, and lightning is created to equalize
the potential gradient. For the brief instant the lightning flashes,
the static electricity is no longer at rest.
What do we know about this phenomenon called "static electricity"?
What is it and how do we get rid of it or at least control it? Well,
let's examine it.
Static electricity is generated by an unbalance of the molecular construction
of relatively non-conductive insulators such as plastics and paper.
All matter is composed of atoms. A balanced atom contains positive
charges that are present in the nucleus of the atom. An equal amount
of negative charges orbits this nucleus in the form of electrons.
Both charges are equal and, therefore, the overall charge of a balanced
atom is zero. However, should this configuration be disturbed and
several electrons removed from this atom, we end up with a greater
positive charge in the nucleus and a deficiency of electrons, which
gives you an overall charge in the positive direction. Conversely,
should we add a few extra electrons, we have an overall charge of
negative, due to the fact that we now have an excess of electrons
and the net charge is now in the negative direction. See figure
Some materials such as glass, hair, and Nylon tend
to give up electrons and become positively charged. Other materials
such as Polypropylene, Vinyl (PVC), Silicon, Teflon, Silicone tend
to collect electrons and become negatively charged. The Triboelectric
series is a listing of various materials and there tendency to charge
positive or negative.
The ability of material to surrender its electrons or
absorb excess electrons is purely a function of the conductivity of
the material with which you are working. For example, a pure conductor,
such as copper, has a rigid molecular construction that will not permit
its electrons to be moved about freely. However, as you approach the
semi-conductor range, such as some bond papers, the ability of this
material to surrender its electrons is relatively easy and can be accomplished
by friction, heat or pressure. As you approach the purely non-conductive
materials, such as plastics, it is extremely easy to disrupt the molecular
construction and cause the material to charge with the slightest friction,
heat or pressure. If the conductivity of your processed material can
be controlled, then, preventing static electricity becomes relatively
For example, adding surface conductivity to plastics will move
them up into the higher conductivity range and prevent the build up
of static electricity that is caused by friction. This is normally
accomplished by use of additives such as moisture and anti-static sprays.
The average anti-static spray is made up from a soap based material
that's been diluted in a solvent, such as mild alcohol. A fire retardant
is added to combat flammability of the solvent. A short time after
contact with your material, the fire retardant and solvents evaporate
leaving you with a conductive coating on the surface of the material.
The plastic has now become conductive and as long as this coating is
not disturbed, it will be difficult to generate static electricity
in this material.
Solutions to Reduce or
Eliminate Static Electricity
By following the above steps, you can reduce
the hazards of building up high charges of static electricity to a point.
However the above steps are passive and of limited effectiveness.
An active method static control is by ionization. It is important
to understand that static electricity cannot be entirely eliminated.
In fact, the terminology, "static eliminators," is definitely
Static eliminators are really ionizing units that produce
both positive and negative ions to be attracted by the unbalanced
material so that neutralization does occur. For example, a
charged piece of material can be neutralized by utilizing a
static neutralizer. However, it does not eliminate the static
electricity because, if the material is again frictioned after
being neutralized, static electricity will be generated.
In order to gain the most benefit from your static neutralizing
equipment, it is important that you understand how they operate
and how they provide the means of neutralization. Most electronic
static neutralizers are constructed by placing a high voltage
on a sharp point in close proximity to a grounded shield or
casing. There are two basic types static control ionizers-
AC & DC.
With Alternating Current ionizers the high voltage alternates
current pulses through the 60 cycle operation, the air between
the sharp points and the grounded casing is actually broken
down by ionization and therefore both positive and negative
ions are being generated. Half of the cycle is utilized to
generate negative ions and the other half is utilized to generate
positive ions. On 50 or 60 cycles per second power grid polarity
is changing ionization every 1/100 or 1/120 of a second.
DC ionizers also put a high voltage on a sharp point but need
to produce the opposite polarity by a second power supply or
some kind of circuitry to switch polarity.
Both AC and DC Systems have advantages. The application, cost,
performance, space are all factored into deciding the proper
type of ionizer to use.
If the material being neutralized is charged positive,
it will immediately absorb negative ions from the static neutralizer
and repel the positive ions. When the material becomes neutralized,
there is no longer electrostatic attraction and the material
will cease to absorb ions. Conversely, if the material being
neutralized is charged negative, it will absorb the positive
ions being generated by the neutralizer and repel the negative
ions. Again, once neutralization is accomplished, the material
will no longer attract ions. See figure below.
Nuclear-powered equipment may also be used to generate ionized
air for static neutralization. These devices, powered by Polonium
210 isotopes which have a half-life of only 138 days, are continually
losing their strength and must be replaced annually. They are
more expensive and less effective than electrically powered
devices. These nuclear devices cannot be purchased and are
leased by users. One year lease costs are usually more than
the purchase price of comparable electrically powered devices.
this article for addition information on the unique issues
related to high speed applications.
Learn more about
static control for Electronics and Electrostatic Discharge
(ESD ) issues.
In order to solve problems related to static electricity, certain basic
steps must be taken. The logical approach should be:
the problem using a static meter.
B. Define the problem and goals needs to be reached to consider the
C. Determine the solution
options with the help of experienced engineers
D. Select the proper
equipment to solve the problem.
Trouble shooting a static electricity problem, some sort of measuring
equipment is helpful. For example, an ElectroStatics, Incorporated Model
9000 electrostatic meter will measure the amount
of static electricity that is present and identify the polarity
as either positive or negative. Measuring and locating static
electricity will remove the mystery often associated with this
Once the problem is identified and goals defined, the
solution options should be considered next with the help from the experienced engineers at Electrostatics, Inc.
Before any problem can be solved it must be identified. Is your problem
related to static electricity? An in-depth analysis should be made
with the necessary
equipment and experience to
identify and solve the problem.
Removing or neutralizing static electricity by induction is the simplest
and oldest method. Tinsel or special wire are the most common tools for this application.
However, tinsel is oftentimes misused, get dirt and damaged and, therefore, oftentimes
not successful. The first thing that must be recognized is the fact
that any induction device, such as tinsel, will never reduce or neutralize
static electricity to the zero potential level. This is due to the
fact that a threshold or beginning voltage is required to "start" the
process and that voltage is high.
First, the correct induction equipment must be utilized. The
induction bar must be well grounded electrically. The induction bar
must be stretched tight and placed 1/4 of an inch from the material
to be neutralized. There must be "free air space" under the material
to be neutralized directly under or over the spot where you place the
tinsel. In this fashion the induction will reduce static electricity
on both sides of the static laden material.
Actually, if the above steps are utilized, the sharp ends or
points of the grounded induction device will ionize the air over the
surface being neutralized, because the grounded sharp ends are placed
within the electrostatic field that is present due to static electricity.
If the static charge is negative in polarity, the electrostatic field
is negative and positive ions are generated via the grounded sharp
ends of the induction device and the positive ions are attracted back
to the static laden surface. Conversely, if the static charge is positive
in polarity, negative ions will be generated by the grounding induction
device and attracted back to the charged area.
Induction does work but is limited to reducing the level of static
to a threshold level which usually still very high and usually higher than what is needed to reduce or eliminate problems related to static electricity. Ionization
or active static control is the best way to reduce static charge
on non conductive surfaces to very low levels.
It is also possible to disturb the molecular construction of your operator.
As ridiculous as this sounds, if an operator is isolated by standing
on a wooden floor or wearing crepe rubber soles, he will soon pick up
a voltage gradient. For example, it is possible for an operator to charge
to several hundred volts each time he handles a piece of charged plastic.
As he handles many different pieces, he will become charged to a higher
voltage gradient until a flash-over will occur and the operator receives
a shock, and or damages a static sensitive device. This can be prevented
by having your operator stand on a grounded conductive mat, by the use
of personnel grounding equipment that is commercially available and by
ionization. Read more
about ESD static control,
Personnel grounding equipment becomes important if your
operators are sitting while working. This is the best means
of isolating operators and, therefore, they become extremely
vulnerable to static discharge due to charging. This phenomenon
can be related to an individual dragging his feet on the living
room rug and then discharging himself by touching a well grounded
In addition, grounding of all your plant machinery and
related equipment is most important. It never ceases to amaze
us that so many plants are operating machinery that is not
grounded electrically. Besides the safety factor, a grounded
machine will help drain off extremely high charges of static
electricity from partial conductors. Remember, grounding is
only an aid to reducing your problems with static electricity.
It is not a solution.
For example, grounding your operators will not drain
off static electricity from their clothing. Also, it will not
drain off static electricity from a plastic container one maybe
holding. The conductivity of some clothing and most plastics
is so low that electricity cannot flow to a ground; hence, "static
electricity." To solve this problem, ionization or active static
control must be utilized.