Dielectric Fluid

Our Products

The Importance of Dielectric Fluid

Being a disposable commodity, dielectric fluid is easily overlooked, its importance to EDM underestimated and cheap
alternatives for it sought. This belies, however, the central role that dielectric fluid plays in the EDM process.
Dielectric fluid is a liquid insulator, resisting electrical discharge. A liquid dielectric becomes conductive for a
short period when the applied voltage exceeds a certain threshold, rendering inherently unpredictable forces
predictable. Consequently, a fluid without these dielectric properties is inherently dangerous, and does not provide
the controlled discharges that make EDM characteristically accurate.

Definitions

Aromatic Content

Though the definition of aromatics has been expanded to any molecule with a particular flat and circular structure,
aromatic content refers to the presence of hydrocarbons such as benzene. Aromatics can cause skin irritation in
operators, and can affect the longevity of rubber EDM machine components. Since aromatics are commonly found in
petroleum and its distillates, synthetic dielectric fluid has lower aromatic content than comparable petroleum-based
fluids.

Color

Color normally does not imply anything about performance, as sometimes manufacturers add dyes to their dielectric
fluid. The exception is yellow fluid, which is a sign of oxidation. Oxidation changes the chemical properties of
dielectric fluid and negatively affect performance.

Dielectric Strength

Sparks are responsible for the erosive effects of EDM, and a spark is the temporary creation of a conductive channel
in an otherwise insulating medium. This depends on the strength of an electric field. Electric field strength is
proportional to the inverse square of distance—known as the spark gap in EDM—and this gap needs to be very small in
order to ensure consistent sparking. The most effective way to reduce spark gap size is to drill in a medium with a
high dielectric strength, which is the measurement of a material’s ability to curb an electric field.

All dielectric fluids have a high dielectric strength by definition. Dielectric strength can be too high, however. A
spark gap that is too small can increase electrode wear and slow down machining.

Flash and Fire Points

Flash and fire points are related, but there are subtle differences. The flash point is the temperature at which
dielectric fluid will ignite in the presence of a spark or flame. At the flash point, there will not be continuous
flame.

The fire point is the temperature at which a fire will be sustained. Ignition will still not be spontaneous, and
needs an ignition source.

Fluids with higher flash points are safer. Fluids with high flash points also have greater viscosity. Because of the
role that dielectric fluid plays in flushing, a high viscosity can be a problem, particularly when the spark gap is
small. Applications requiring a small spark gap and lower viscosity fluid also demand less current, which
contributes greatly to heat.

Odor

High quality dielectric fluids are generally odorless. The presence of odor may be a sign of aromatics or other
undesirable impurities.

Oxidation

This is the chemical reaction between dielectric fluid and oxygen. Heating and contamination exacerbate oxidation,
though high quality dielectric fluid resists it.

Pour and Cloud Points

The pour point is the lowest temperature at which a dielectric fluid will pour. The cloud point is the temperature
at which certain compound in the dielectric fluid precipitate out, lending a cloudy appearance. Neither of these
points change dielectric fluid characteristics at normal operating temperatures.

Sulfur Content

Products refined from petroleum will have some amount of sulfur. Dielectric fluid with too much sulfur are more
hazardous when burned than highly refined dielectric fluids. Sulfur content should be lower than 5 p.p.m.

Synthetic Fluid

Synthetic dielectric fluid is generally more viscous than petroleum-based fluid, with a high flash point and better
resistance to oxidation.

Viscosity

Viscosity is a liquid’s resistance to flow. Due to the importance of flushing in EDM, low viscosity is generally
preferred over high. High viscosity may have to be accepted in some circumstances since dielectric fluid with a high
flash point also has a high viscosity.

Tips

Choosing the Appropriate Fluid

Mineral oil should never be used as an alternative to dielectric fluid. Dielectric fluids not expressly designed for
EDM can be hazardous, and wear down machine components.

For rough work using large currents, dielectric fluid should be used with a high flash point. Large currents make
for a larger spark gap, which is easily flushed, so viscosity is a non-issue.

For finishing work with small currents, dielectric fluid with a low viscosity should be used, to assist in flushing.
The low flash point of a low viscosity fluid is not an issue at lower amperages.

Petroleum-based Versus Synthetic

Synthetic fluid is generally superior to petroleum-based fluid. It is better for operators and machines, has a
longer life, and better performance. Synthetic fluid is more expensive, however.

Besides being more economical, petroleum-based fluid is generally less viscous than synthetic fluid, and is slightly
better-suited to finishing applications. Due to its other advantages, synthetic fluid may still be preferable in
these circumstances.

Filtering

Quality filtration is a simple way to improve the performance of your dielectric fluid. Due to the role of
contaminants in oxidation, dirty dielectric fluid becomes unusable more quickly. Make sure that filters are high
quality to extend the life of your dielectric fluid.

Combining Fluids

Combining fluids is generally not advisable, as the characteristics of different dielectric fluids do not combine in
a straightforward way. Mixtures of dielectric fluids can exhibit unpredictable characteristics, and generally
perform poorly compared to their pure constituents.

Replacing Fluid

Prior to replacing dielectric fluid, care should be taken to clean all parts of the EDM machine, including hoses,
pumps, and reservoirs. Filters should be replaced. As little of the old oil should be left as possible. This is
especially important when replacing one type of oil with another.

Avoid Contamination

Common sources of contamination are water and hydraulic fluid. Water can reduce a dielectric fluid’s dielectric
strength, and can seep into drums. To prevent this, drums of dielectric fluid stored outside should be placed on
their sides.

Dielectric fluid contaminated with hydraulic fluid should be replace immediately. Besides compromising dielectric
fluid performance, hydraulic fluid can damage filters and other EDM machine components.

Health and Safety

Though dielectric fluid is generally safe, as with any industrial chemical, certain precautions should be taken when
handling it. Direct skin exposure to dielectric fluid should be strictly limited. Gloves should be worn if possible,
and work areas should be adequately ventilated.