Electrolyte optimisation for effective plasma electrolytic polishing of brass

Polishing of musical brass instruments is a very labour, material and time intensive process, with the main goal being to produce an instrument having very glossy surface. Here, plasma electrolytic polishing (PEP) could be applied, potentially increasing the efficiency of the manufacturing step. However, PEP of brass alloys is known to be challenging, since the use of unadapted electrolytes leads to the increase in surface roughness and/or reduced gloss of a part with increasing the PEP time. In this study, three different electrolytes developed for polishing brass CuZn28, were investigated at varying operational conditions. Namely, process time and applied voltage. The obtained experimental results demonstrate, that by selecting a suitable electrolyte, brass samples, can be successfully polished using the PEP technology with resulting surface smoothening from maximum value of Sq = 0.28 mu m to minimum value of Sq = 0.16 mu m for the same sample and more than 21 time increased gloss at measurement angle of theta = 20 degrees. It is also observed that the change in applied voltage has lower impact on the final sample gloss as it does on the final surface roughness. Finally, sample gloss does not change significantly by increasing the treatment time. However, depending on the electrolyte suitability, increase in PEP time might result in the increase or decrease of the final surface roughness.