Synthetic Dielectrics:
What Makes Them Different?
flask

      B  y    P e  t  e  r     K  n  o  w  l  e  s      

In order to evaluate today's dielectric fluids it is necessary to compare the evolution of the EDM (electrical discharge machining) machine to that of dielectrics.

In 1943, the Lazarenkos discovered that the erosive effect of capacitor discharges could be used in the processing of metals-hence the discovery of EDM. At first, ordinary air was used as a dielectric and soon after mineral oil derivatives were found to have considerable advantages.

spark_seq_2.gif (42867 bytes)
Chemical satellite electrodes help to evenly distribute the spark		 Kerosene was used in the early years and still is in some third world countries. Since then, improvements in refining processes have made these fluids more acceptable, but their evolution falls short of the technical improvements in EDM machines during the same period.

Consider the early EDMs with tube-type power supplies available in the 1950s. Steady improvements throughout the last 40 years have led to today's state-of-the-art, "transistorized" power supplies. They automatically monitor the cutting conditions and make necessary adjustments to keep the EDM cutting efficiently even in the worst conditions. Servo systems have gone through several stages of hydraulics to today's DC and AC drives that enhance accuracy and cutting capabilities. What about the evolution from manual machines to orbiting, to fullblown CNC controlled systems, automatic toolchangers, robots and Fuzzy Logic?

The fact is, when compared to the evolution of EDM machines, even the most popular, highly-refined, mineral- based dielectrics fall short in overall improvements.
1-2.bmp (172326 bytes) Mineral-Based Fluids
Theoretically, all insulating liquids can be used as dielectrics. However, due to certain criteria demanded by EDM (as explained below) and the direction in which research has taken the technology, only hydrocarbons are used for this purpose today. For most dielectrics available in the United States these hydrocarbons are produced by distilling and highly-refining crude oil (see Figure 1). Many of the most commonly known brands on the market today are produced in this manner. Although "highly-refined" these products still fall short in the evolution of EDM because of two important reasons:

1. It is impossible for the refining process to completely remove all of the unwanted double-bonded and circular molecular chains that form paraffins, naptenics, aromatics, etc. (see Figure 2). Since a mineralbased fluid comes from crude oil, slight traces of harmful components like unwanted molecular chains, as stated above, which make up sulfur are still present.

2. Temperatures in the spark gap (see Figure 3) can reach several thousands of degrees during which these double-bonded chains (see Figure 2) can break and connect with acid radicals, sulfur and other unwanted atoms that can form from the waste product of the workpiece material. This "reverse refining" effect is what causes these dielectrics to develop odors, skin irritants, higher viscosities and generally lose their effectiveness.





Figure 2
burp_seq.gif (34028 bytes)		 Figure 3
Temperatures in the Spark Gap

hero_seq.gif (83699 bytes)

 Synthetics
High-grade, synthetically-produced hydrocarbons are characterized by unparalleled purity and long life expectancies. They are synthetically manufactured by processing gases (see Figure 4) under heat and compression in a synthesizing oven with the help of a catalyst. Only the most desirable chains of hydrocarbon molecules are synthesized to produce a base fluid that is made up of singlebonded, evenly shaped and extremely rigid, durable chains.

 

Figure 4
Production of Hydrocarbons-Synthetics Derived From
Gases

Synthetics Derived from Gases Out of the Synthesizing Oven by Means of a Catalyst, Pressure of Heat

 

 Unsurpassed degree of purity.
Chains of hydrocarbon molecules with the best performance in metal removal and electrode wear can be synthesized.
Absolute freedom from unwanted components such as sulphur and double bonds.


Since synthetics are made from gases, not crude oil, two points should be considered:

1. They are not "refined or chemically altered" therefore they cannot "reverse refine." Since there are no double-bonded or circular chains (see Figure 2), unwanted atoms cannot connect to the synthetic chains to form acids, sulfur, etc. Instead these compounds can easily be filtered away.

2. Some products available today claim to be 100 percent synthetic. Under chemical analysis a pure synthetic (as described previously) will be free of any unwanted hydrocarbons, while an Unpure synthetic may have both the wanted and unwanted hydrocarbons. In this case, it is impossible to determine whether the Unpure product is truly a synthetic at all.

A word of caution, low-grade synthetics like low-grade, mineral-based dielectrics tend to sell for less, but have higher viscosities, offer no real advantages (i.e. long life and no odor) and should be avoided.

next page