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Static Electricity Static Control explanation and techniques to control the phenomenon of static electricity and how to control it
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Static Electricity & Static
Control
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.
CAUSE
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 below.
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.
CONDUCTIVITY
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 easy.
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.
Passive Solutions
INDUCTION
Removing or neutralizing static electricity by induction is the simplest
and oldest method. Tinsel is the most common tool for this application.
However, tinsel is oftentimes misused 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.
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. Ionization
or active static control is the best way to reduce static charge on non conductive
surfaces to very low levels.
GROUNDING
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 lamp.
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.
Active Solutions
IONIZATION
By following the above steps, you can reduce the hazards of
building up high charges of static electricity. 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 misleading.
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.
Please review 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.
SOLUTION
In order to solve problems related to static electricity, certain basic
steps must be taken. The logical approach should be:
A. Identify the problem using a static meter.
B. Define the problem and goals needs to be reached to consider the
problem solved.
C.
Determine
the solution options with the help of experienced engineers
D. Select the proper equipment to solve
the problem.
To identify the problem, some sort of measuring equipment  must
be used. For example, an ElectroStatics, Incorporated Model
9000 electrostatic locator 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 phenomenon.
Once the problem is identified and goals defined, the solution
options should be considered
next with the help of experienced engineers.
Can the static electricity be controlled by grounding, induction,
ionization or a combination thereof?
In making this decision, keep in mind the facts mentioned, relative
to conductivity. With pure conductors or partial conductors (such as
the human body), grounding should be considered. However,
if you are working with insulators, such as plastics, ionization must
be added.
PROBLEM IDENTIFICATION
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.
Model 9000
static meter
Industrial ionization blowers
Broad area static control
Ionization Nozzles
Part blow off and pin point static control.
Static Control
Blow off Gun
ESD protection, Part blow off, pin point static control
Static Bars
Static control for webs and sheets of plastic, paper glass or other
non conductive material
Overhead ionizer
ESD protection and light duty static control
Table Top Ionizer
ESD protection and light duty static control
Web Cleaners
Remove static and actively clean a surface
ElectroStatics, Inc.
352 D Godshall Drive, Harleysville, PA 19438-2017
Tel: (215) 513-0850 FAX: (215) 513-0855
Websites: www.electrostatics.com
& www.webcleaning.com
©1996-2008 Electrostatics Incorporated
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