In Electro Discharge Machining (EDM) process, graphite is a material which is commonly used as a tool electrode material. However, since the process is carried out in a hydrocarbon based dielectric medium (mostly), the material being porous, tends to absorb the oil.
Since tool wear is an important aspect of study in EDM process and the assessment of the same is usually done based on weight difference of the electrode before and after machining, the oil content in the electrode will give erratic results and it is necessary to remove the same before weighing.
What are the possibilities that can be used for removing the oil absorbed by the graphite material in this manner?
You can soak the graphite block in a volatile organic solvent, like pentane, in which the oil fully dissolves, and then afterwards evaporeate off the pentane. Better do a solubility test with the oil and the pentane before.
Instead of pentane you can use also washbenzine (sometimes also called petroleum ether, but chemically speaking it is not an either, but rather a hydrocarbon mix with short chain length, e.g. C5 ... C6). The advantage of using pentane or washbenzine is that they are practically not toxic, but they are flammable and can also produce explosive atmospheres together with air, so you have to do this ideally in a fume hood or another well-vented environment with no ignition sources around.
You can also use toluene as solvent, but that is carcinogenic, so here you really need to use a fume hood, and proper personal protective equipment like nitrile gloves and safety glasses etc.
The suggested solutions are good and fast, which would disturb me while eroding the additional solvent. Perhaps pentane still at least critical.
Slightly higher time we have operated. One possibility is to store the tool permanently in the dielectric, so that the pores are constantly filled with oil. The weighing is then steadily with the oil in the pores, but the eroded volume would also be a mix of workpiece material and dielectric.
A second solution is to bring out the dielectric by slight heating after each edit.
Thank you Dr. Steffen Berg and Dr. Schulze for your responses.
Will heating of the graphite block in the oven will have any effect of the external appearance of the same? Is there any chances of specimens catching fire as the same is soaked in hydrocarbon oil and this may distort the surfaces of the tool electrode?
I have in two papers in which they have mentioned the same procedure. They heated the specimen to 300oC for 4 hrs before machining, took the initial weight, used it for machining, again kept it at 300oC for 4 hrs and took the the final weight.
Can this be considered as the right procedure?
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