Refer this link:https://books.google.co.in/books?id=OrlG98AHdoAC&pg=PA118&lpg=PA118&dq=method+for+removal+of+carbon+layered+deposition&source=bl&ots=huPFUGz8zp&sig=xjUZE-Aa1Rta2LTs_18HyTo9zGU&hl=en&sa=X&ved=0CCwQ6AEwAmoVChMIqZzzrPf6xwIVw7qOCh3fsASc#v=onepage&q=method%20for%20removal%20of%20carbon%20layered%20deposition&f=false

Good question, actually a question I had. Some machinists use thin sandpaper to remove carbon which is not a good practice as it can alter the dimensions of the tool.

Sometimes the carbon layer act as a protective layer preventing anode erosion.

Let me quote something I found from an article. 

Quoting; "...........When the dielectric fluid used is hydrocarbon oil, it decomposes into

carbon particles and other by-products because of the high heat inside the gap. The carbon particles will deposit themselves on the anode surface to form a carbon layer. The deposed carbon layer can protect the anode from erosion, and this is the main

reason why a tool with positive polarity is preferred in EDM with kerosene .............." .

Quoted from  "Electrical discharge machining of Ti6Al4V with a bundled electrode by Lin Gua, b, , , Lei Lia, Wansheng Zhaoa, K.P. Rajurkarb"

doi:10.1016/j.ijmachtools.2011.10.002 

I suggest using an ultrasonic cleaning equipment to clean those electrodes used in EDM. The method may be reliable and performing for that task and works by using a chemical bath and then applying a ultrasonic beam. A possible equipment supplier is CMFS/Miraclean.

for carbon removal from electrode. You can fix the elect rode in the chuck of lathe machine and with the help of emery paper you can remove it uniformly while the elect rode is rotating...

Thank You all for answering.

I have a question to Mr. Silvio Luis, which type of chemical/ cleaning media is preferable for cleaning of copper in ultrasonic cleaner.

The chemical bath varies from manufacturer to manufacturer but as usual there are some common baths used for this purpose:

1) 5% citric acid + 0,1% sodium chloride

2) 4% acetic acid

3) coarse zinc powder + 10% caustic soda

Anyway the efficiency of the cleaning heavily relies also on the ultrasonic cleaner project characteristics so each manufacturer has its own bath solution.

I am of the opinion that they should check their sparking conditions again. Basically black layers or carbon deposits occur only if the arc erosion is primary. In special cases they can be eliminated by an improved flushing the still. It is even better, however, to verify the process parameters.

You can assume that they reach 95% of the discharge machining, which runs in the optimum parameter range, no deposits of this type. Do you want to check but also "unacceptable" parameter ranges, then you need to take advantage of the already made proposals to remove the black layer.

Best regards

Hans-Peter Schulze

There might be a possibility of arcing in my perspective. The optimal selection of flushing as well as distance between tool and electrode may helpful to reduce the carbon deposition. 

Please read my manuscript through the link given below, if it is possible. It may help you.

http://www.tandfonline.com/doi/abs/10.1080/10426914.2013.811749

Going on from Vineet's  response of

"fix the electrode in the chuck of lathe machine and with the help of emery paper you can remove it uniformly while the elect rode is rotating..."

In the UK the Health and Safety Executive  (www.hse.gov.uk) have now banned the practice of using emery paper on a item that is rotating in a chuck.

Regards

Neil

Is there any side effect or properties changes of electrode after ultrasonic cleaning?

I'm using distilled water as media in ultrasonic cleaning.

I have tried ultrasonic cleaning.. It isn't much useful.. I suppose a portion of carbon layer is deposited as carbide layer and hence you might not be able to remove it without loosing some of the copper atoms..

Plasma cleaning would be a method for you to explore. It burns off the carbon layer without reacting with the copper layer beneath. If you have a plasma cleaner you could give it a go. I would suggest you start with short plasma cleaning time initially. Extended plasma exposure may cause sputtering and remove copper.