Solo Systems, Inc.
4001 Industrial Street * Rowlett, TX 75088
800.259.5570 * 972.475.5569

The function of the electrode is to deliver the generator power to the web.  It does this by
presenting the high voltage to the air gap between the electrode and the insulated treater roll
which carries the web.  The power stresses the air to the point at which it ionizes causing
corona to form and the web is treated.

The degree of treat is a function of the intensity and duration of the corona discharge per
unit area.  A shoe-shaped electrode which is concentric with the surface of the treater roll
exposes the film to corona longer than a bar or knife edge electrode, so treat levels increase.  
Because the corona spreads more evenly, hot spots are reduced and damage to the web and
roll insulation is avoided.

The graph below shows the most effective shoe size for different line conditions.  To read
this graph, find the intersection of your treat width with your generator power rating.  The
shoe width (in inches) is shown directly below this intersection at the bottom of the chart.  

Please note the graph assumes a generator frequency of 9.6 kHz and .125" thick Solo
Systems E-3 Epoxy treater roll coating.

Generator Frequency
Shoe area per kW
3 kHz solid state
70-100 inches squared
9.6 kHz solid state
30-47 inches squared
17 - 18 kHz
20-24 inches squared
25 kHz  
12-18 inches squared

The bare roll system is presently the most common option for treating conductive materials
like foil.  The electrode in a bare roll treating system does double duty.  It not only delivers
power to the web, it carries the nonconductive surface necessary for corona to form.  
Therefore, the key to successful bare roll treating is in the electrode design and construction.

In any system, the electrode carries off approximately one half the heat produced by the
corona.  Insulated electrodes run hotter than conventional electrodes.  The insulating
material must be exceptionally heat resistant, and the system adequately cooled during
operation for acceptable service life of the insulation.

Several manufacturers supply insulated electrodes made of glass, ceramic or composite
materials.  The more heat resistant materials, such as glass or ceramic, are brittle and easily
damaged by impact, such as  a splice in the web.  The composite materials are tougher;
however, they must be void-free to prevent corona developing in air pockets inside the
insulation and shortcircuiting the system.

Adequate bare roll treating systems are available.  They are typically more expensive and
less durable for conventional applications.  However, it is possible to develop a successful,
bare roll treating system for conductive web materials.

The gap between the roll and the electrode provides a controlled volume of air in which
corona can be formed.  This happens because the air gap between the electrode and the roll
coating has the least dielectric strength of the electrical components.  By applying the right
output voltage to the electrode, the air can be maintained in the ionized state commonly
called corona discharge.

The power delivered to the air gap is a function of the gap spacing, the applied electrode
voltage, the dielectric constant and thickness of the coating, and the output frequency of the
power supply.  If the web is thicker than 4 or 5 mils, its capacitance should be included in
the electrical equation.

It is important to maintain an accurate and correctly proportioned air gap in order to
deliver full-rated generator power to the web.  If the air gap is too wide the excess voltage
required to start corona can damage the web or the roll coating.  Corona discharge becomes
harder to start as the gap becomes wider.  If the air gap is too narrow, maintaining the gap
evenly across the width of the web becomes too critical for production efficiency.

An uneven air gap across the width of the web will produce uneven treat levels across the
web.  A constant gap will produce consistent treat measurements.
Adjustable 1" segments shown in retracted
position.  The blue rolls are coated in Solo
E-3 Epoxy.
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Solo Systems, Inc.
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