Dielectrics IME 63, IME 82, IME 110, IME 126

IME dielectrics are synthetic products manufactured in a catalytic process and posessing greatest disruptive strength. They are clear fluids and are almost odourless. They do not change colour during erosion. They have the same purity as pharmaceutical white oil and contain only a few traces of aromatics. There is no toxic or allergic reaction to contact with human skin or eyes, when IME products are used. The Institute for Research and Material Testing of the State of Baden -Worttemberg has tested this brand of dielectrics i. r. o. operational safety and industrial hygiene. A tolerance limit for workroom air (according to German regulations for the maximum concentration of chemical substances at places of work) is not reached. IME dielectrics have been subjected to extensive tests and have proven themselves in practice for decades. They are explicitly recommended by the leading manufacturers of spark erosion machines.

DIELECTRIC IME 63

Dielectric IME 63 is an extremely thin-bodied dielectric with the least possible surface tension. It is particularly suitable for very fine work, when a very low overcut is required, e.g. the microboring of spinnerets and the manufacture of microelectronic parts.

DIELECTRIC IME 82

Dielectric IME 82 combines high metal removal with low electrode wear, which makes it suitable for general use in manufacturing tools and moulds. Even rough cut operations using an electric current of 600 amps can be carried out with IME 82.

DIELECTRIC IME 110

Dielectric IME 110 is always used when a flash point of over 100° C is required for safety reasons, while much finishing work also has to be done. Dielectric IME 110 lies outside danger class A Ill.

DIELECTRIC IME 126

Dielectric IME 126 is a dielectric for very high metal removal in rough cut operations, such as in the manufacture of forging dies. It can only be used for finishing if the best possible flushing conditions are ensured.

TECHNICAL DATA ON THE DIELECTRICS

TESTING THE VARIOUS IME DIELECTRICS

IME dielectrics have been tested in practice both for metal removal and for electrode wear. The following materials and operational steps were selected for these tests: a) Materials

VW (MM³/min) = metal removal

J % = electrode wear expressed as a ratio (in percent) of the volume of electrode material lost, to metal
removed from the workpiece.

The control settings given represent easy to manage operational steps involving no special difficulties. Metal removal and el ctrode wear were determined by measuring weight differences, which were then converted into units of volume.

Rough cut

When working with copper and steel, metal removal was lowest for IME 63 during rough cut operations, and highest for IME 126. Electrode wear was least for IME 63 and most for IME 126 (see fig . 1). When working with graphite/steel similar results were obtained. Metal removal was highest for IME 126 and least for IME 63. It was astonishing that no measurable electrode wear took place when IME 110 was used.

Finish

When working with copper and steel in the finishing process, IME 126 achieved the highest metal removal. Least electrode wear took place when IME 63 was used (see fig 2).

When working with graphite and steel, IME 126 also achieved highest metal removal. The results of IME 82 were only slightly lower.

All these test results are valid only for the given control settings and materials. They are intended to show the varying influence of the dielectric used on the work process. The excellent results of IME 126 during finishing can undoubtedly not be achieved, unless flushing conditions are optimal.

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Gases produced during spark erosion

The gases produced during erosion consist of dielectric vapours and metallic fumes. The vapours of the dielectrics IME 63, IME 82, IME 110 and IME 126 contain no benzene compounds, such as the polycyclic aromatics of the Benzpyrene type, even after they have been in use for some time. There is no ill effect on health brought about by IME products. However this does not hold true for the metallic fumes that may develop during erosion (e.g. tungsten carbide, titanium carbide, chrome, nickel and molybdenum). It is therefore important for the dielectric level to be as high as possible over the place of erosion, so that most of the metallic fumes can condense in the dielectric. German engineering guidelines (VIDI 3400) prescribe a depth of 40 mm over the place of erosion. However a depth of 80 mm is to be recommended for health reasons. The metallic fumes rising up out of the dielectric cause the same problems as those that develop during the welding of metals. It is therefore advisable to suck off the gases that develop when extensive rough cut work has to be done.

Dielectrics and the human skin

Decades of practical experience with the dielectrics IME 63, IME 82, IME 110 and IME 126, as well as the knowledge of their composition, permit us to state that they have no damaging effect on human skin. Practically only one's hands come into direct contact with the dielectric during work. Remnants that are left sticking to the skin can be removed without the use of cleaning agents that have mechanically or chemically aggressive properties. In this way secondary damage is also avoided. It is difficult to make general predictions on the effect of dielectrics on persons with particularly sensitive skin or with a tendency to allergies, but practical experience has shown that a negative reaction only occurs in very rare cases. (Test reports have been issued by the Institute for Research and Material Testing in Baden -WOrttemberg.) However, metal particles suspended in the impure dielectric do have a negative effect on skin. These particles are microscopically small, hollow, steel globules, open on one side and with very sharp edges. These globules can easily hurt the epidermis and lead to skin damage. Certain medicines, such as Penicillin, can sensitize the epidermis even further. In all these cases it is advisable for a skin protecting cream that is not oil soluble to be rubbed into the hands. Pieces of clothing soaked with dielectric ought to be changed at once.

"7 Golden Rules" for working with the IME Dielectrics

• Correct handling of dielectrics begins with the proper storage of packing drums:
  
• It the drums are stored out of doors, they should always lie down and never stand upright, so that no rain water can seep in.
  
• When the dielectric is filled into the machine, suitable, clean pumps or containers must be used. Pumps that have been used for acid or caustic solutions destroy the best dielectric at once. PVC tubes are not oil resistant and will become rigid after they have been used for some time.
  
• Anticorrosive agents, used to protect the machine during transport, must be removed before the dielectric is filled in.
  
• Chlorinated hydrocarbons (e.g. trichloride, tetrachloroethylene, trichloroethane or Freon 12) are deadly for the dielectric. The electrical spark causes the hydrocarbons of the dielectric to combine with the chlorine atoms to form hydrochloric acid. A spark erosion machine must therefore never be cleaned with trichloride or a similar substance. It is better to use a few liters of dielectric for this purpose. Moulds that have been cleaned in trichloride must be absolutely dry before being mounted in the machine.
  
• Acids, used to pickle the electrode, must not be allowed to get into the dielectric.
  
• The hydraulic system of a spark erosion machine should be absolutely leakproof. Not more than 1-2 % additions of hydraulic fluid should ever get into the dielectric, as the large amounts of additives in these oils will otherwise lead to malfunctioning. Machines with electric servo motors do not have this problem.
  
• Again and again, leaks in the water cooling systems of dielectric units lead to a "miraculous" increase of the dielectric and to rusty tables. IME dielectrics separate quickly and completely from water, and so the water can be drawn off from the bottom of the tank, or the dielectric can be ladled out after about one day. The dielectric can then be used again.
  
• If you adhere to these rules when working with dielectrics, they will last for about one or two years in paper filter units and for about 10-20 years in units with precoated filters.

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A new way to better dielectrics

Every experienced operator of spark erosion machines is acquainted with the phenomen that better results are obtained with a used dielectric than when it has just been renewed. The reason for this is that finely dispersed waste particles make it possible for ionisation channels to build up more rapidly. In tests a fresh dielectric is always put to use for at least half an hour before the actual test phase is begun. Many years ago our firm also conducted experiments using dielectrics to which metal pigments or organometals had been added. It was intended to induce a "controlled" effect of increased metal removal. Unfortunately most of these additives settled on the bottom of the work tanks even when their specific gravitiy was very low (e. g. with powdered aluminium) - or were taken up the filters. Only after these microparticles had been reduced in size even further, was there a real improvement in metal removal.

The starting point for the development of dielectric IONOPLUS IME-MH was the idea of formulating a dielectric that could be used for rough cut as well as finishing and polishing processes. In addition it was intended that it should increase metal removal and decrease electrode wear. From a physiological point of view the new dielectric was to be absolutely unharmful, so that it would no longer fall under danger class A III for inflammable liquids. Of course it also had to be devised for use with all conventional filter systems and had to be simple to dispose of.

This goal has been reached by using substances floating in the dielectric in finest distribution, substances that turn into stronger dipoles than the surrounding hydrocarbons when they come under the influence of an electrical field. On application of an electrical current, these chemical satellite electrodes align themselves along the lines of electric flux in the electrical field, an channels of increased electrical conducting capacity develop in the dielectric liquid. In this way the discharge channels required for spark disruption can build up more rapidly than usual. This in turn leads to a steeper increase in ignition voltage and in this way to faster spark disruption. Thus the amount of metal removal per unit of time is significantly increased.

In contrast to conventionai dielectric liquids the dielectric IONOPLUS IME-MH does not induce a direct flow of electrons from cathode to anode. On their way most of the electrons are attracted by the finely distributed satellite electrodes and conducted along a widely ramified network of channels. Since they lose part of their kinetic energy in the process, they hit the anode with relatively litte energy. A decrease of ignition time delay is achieved at the same time, because of the steep increase in ignition voltage. Both of these effects lead to a decrease in anode wear. In comparison to conventional dielectric liquids electrode wear is therefore reduced by up to 30%.

In spark erosion for finishing purposes (with reversed polarity) the work piece serves as anode. Again the satellite electrodes dampen the impact of the electrons, that now hit the work piece with less kinetic energy and more widely distributed than when a conventional dielectric has been used. The satellite electrodes lead to a faster build-up of the ionisation channel and thus make it possible for less average space current to be applied in pocessing the work piece.

By means of this new technique very well polished workpiece surfaces with a surface roughness of less than 0.1 pm can be produced. This polishing performance L r. o. surface quality and speed cannot be achieved with conventional dielectric fluids.

The use of highly polarized substances in the dielectric IONOPLUS IME-MH also has a very positive effect on its dispersing qualities. The waste particles produced by the spark erosion process are hurled explosively out of the work. area in the finest distribution. This reduces the tendency for short circuiting and leads to an undisturbed process in spark erosion. The reason for these good dispersing qualities are the electrical dipoles aligned in the satellite electrodes, leading to a quicker distribution of the waste particles due to their electrical repulsion forces.