Electrode wear rate

It is current practice to impregnate the graphite, traditionally with linseed oil, although synthetic resins are also successful. The concept behind impregnation is to reduce the porosity and hence inhibit subsurface gas evolution or carbon oxidation which would initiate spalling and early anode failure. Electrode processes occur to a depth of 0-5 mm below the surface of the anode and the true current density can be shown to be only I/400th of the value indicated by the superficial geometrical area Acidity has been found to increase the wear rate and so has the presence of sulphate... 

The anode and cathode should be stable in the electrolysis medium, allow the desired oxida-tion/reduction reactions at the highest possible rates with miiumal by-product formation, and be of reasonable cost. In actuality, the electrodes may corrode or undergo physical wear during reactor operation, which may limit their lifetime. Often, if an expensive electrode material is needed for a given reaction, it can be plated or physically coated on a less costly, inert, and electronically conducting substrate. Common anode and cathode materials are listed in Table 26.8. 

Apart from the tunable parameters, such as RF power, gas composition and flow, and substrate temperature, several other factors affect the plasma etch rates, including impurities in or on the material to be etched, film stress, loading, elapsed time from the start of the etch, materials present in the plasma chamber, and wear of the electrode. 

Eor Drilling-EDM different additional electrode materials are used like cemented carbide, tungsten-copper, and silver. The choice depends on the individual process characteristics in terms of low wear, high material removal rate, and good formability. Preferably an... 

With the alternative ECM technique, hard metals can be shaped electrolytically and the rate of machining does not depend on their hardness. Moreover the tool-electrode used in the process does not wear, and therefore soft metals can be used as tools to form shapes on harder workpieces, unlike oonventioned practice. The bases of ECM will first be described in the paper. Then some unsolved research problems will be discussed. Industrial applications, which illustrate how the process is used in practice, will be investigated. 

Electroless nickel coating is used because of its wear and corrosion resistance. Deposition rates (10 pm/h, or 0.4 mil/h) are relatively slow compared to electrode-position methods, but the electroless depositions are more uniform than those of electroplating. Normal thickness is... 

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