How To Polish Metal Surfaces To a Mirror Finish

Mirror polishing is a polishing process that gives a mirror effect to the surface of a product. The process is commonly used for lift cabins, aerospace equipment parts, moulds, automotive parts, medical machinery, decorative items, etc. Such products require a glossy appearance. The surface after polishing treatment is scarless, bright, smooth, no relief, no metal disturbance layer, no crater like mirror surface state, is the ideal mirror polishing effect. 

Here we will learn about the process and methods of mirror polishing.

Mirror polishing requires several grinding and polishing sessions and the surface roughness of the product workpiece should be at least 12 grades. The mirror polishing process is a step-by-step polishing process using different roughness of polishing sandpaper, using flexible polishing tools and abrasive grains or other polishing media to finish the surface of the workpiece. Mirror polishing should pay attention to the order can not be chaotic, at first can not use fine sandpaper polishing, fine sandpaper is not to wear off the coarse knife marks, with fine sandpaper polishing the surface of the workpiece looks very bright, but a closer look actually see a lot of rough texture is still on the surface. The correct sequence should be to first grind off the rough texture with an oil stone, then sand with fine sandpaper, and finally polish with polishing paste or abrasive paste to achieve a mirror finish.

In order to obtain a bright electropolished surface, the microscopic roughness of the surface must be reduced to a level below the wavelength of light. In order to achieve this, it is usually considered that the compacted layer, which is thicker, denser and easier to passivate than the intermediate mucilage layer, can be a highly viscous mucilage layer or solid layer that is close to saturation. In this way, the dissolution of the metal occurs in the dense film and the rate of formation of the dense film should exceed the rate of dissolution of the film, which is a prerequisite for the existence of the dense film. Under the special conditions of almost no convection, it becomes so thick and more dense that it can even appear as an interference colour of light. In such a thick mucus or solid film, the anodic current density becomes so small that the micro-convex part can be dissolved and the micro-concave part no longer dissolved for the purpose of micro-flattening.

All parts of the surface are micro levelled as a similar state exists in many parts of the metal surface. The end result of this disordered micro-flattening of the surface results in a shiny metal surface. Thus, electrolytic polishing is in fact the result of macro levelling (primary current distribution) and micro levelling (secondary current distribution) of the anode surface. With only macro-leveling, the anode surface can only become smooth, not shiny.

Some electrolytes can have both macro levelling and micro levelling. In the first stage of polishing with a polishing machine, the viscosity of the slime film formed is not high enough, so it only acts as a macro leveller. When macro levelling is carried out to a certain extent, the mucus film formed is more viscous and closer to the metal surface, so it can also play the role of micro levelling, thus achieving the effect of real polishing.

To obtain a good mirror effect, you must carefully choose good quality polishing tools, such as oil stones and sandpaper, so that the mirror effect can be greatly improved. The polishing master must be experienced so as to ensure that no major problems occur when polishing the workpiece, and if you are a novice, you will need to undergo several training sessions before taking up the job. Therefore, it is very important to choose an experienced and reputable OEM polishing factory.