Process Conditions For Chemical Polishing

The basic principle

Chemical polishing is to produce polishing effect without power supply, its polishing principle and the use of current effect of electrolytic polishing in the essence of not much difference. The effect of chemical polishing is generally worse than that of electrolytic polishing. In chemical polishing, due to the uneven quality of the material, local potential differences are caused, resulting in a local cathodic-anodic zone, forming a local short-circuit microcell, which causes local dissolution of the anode. And in electrolytic polishing due to the role of the applied potential can completely eliminate this local cathodic area, a comprehensive electrolysis, so the effect is better.

Control of process conditions

①Temperature. When chemical polishing, the dissolution rate increases significantly with the increase in temperature of the polishing solution. In addition, strong oxidizing acid (such as concentrated nitric acid, concentrated sulfuric acid, etc.) at high temperature oxidation will also be significantly increased. In chemical polishing, as the dissolution and oxidation of these acids occur simultaneously, the polishing solution is in most cases heated to a higher temperature before chemical polishing is carried out. Need to raise the temperature and then chemical polishing of metals such as steel, nickel, lead, if the temperature is below a certain value, there will be no light corrosion surface, so there is a critical temperature for the formation of a glossy surface, in the critical temperature above a certain temperature range, the best polishing effect. And this temperature range varies depending on the composition of the solution. If higher than this temperature range, will form pitting, local stains or spots, so that the entire polishing effect is reduced. In addition the higher the temperature, the greater the dissolution loss of the metal surface.

② Polishing time. To get a good polishing effect, you need to spend a certain amount of time. If the polishing time is too short, can only get no lustrous pear skin-like surface. If the time is too long, not only the dissolution loss increases, but also the processing surface will appear stains or spots. Therefore there is an appropriate time range, which is affected by the material, the composition of the polishing solution and polishing temperature and other factors, usually difficult to predict, except with experimental determination, there is no other method. Hydrogen is often generated in chemical polishing, which is a problem that must be borne in mind when polishing materials with hydrogen embrittlement sensitivity. In addition, annealing effects can occur at polishing solution temperatures of up to 100-200°C. In order to minimise the effects of hydrogen embrittlement and annealing, it is necessary to choose the shortest possible polishing time in the most suitable temperature range.