Compare different types of polishing finishes

  Traditional finishing of metal surfaces is the process of finishing the surface of a metal part or assembly after machining using a grinding paste, wool beret, and polishing sponge. The purpose of polishing is to remove scratches, nicks, and other surface defects created during processing, while improving the shine and appearance of the surface.

  However, polishing metal parts is not just used for purely aesthetic purposes. Many metal surfaces become discolored over time, often due to exposure to oxygen, heat, and use. Reflective surfaces achieved through metal polishing not only enhance the aesthetic appearance of parts, but also help prevent contamination from corrosion, oxidation, and other forms of quality loss.

  There are three main types of metal polishing used today -- mechanical, chemical, and electrolytic -- and each has advantages and disadvantages that must be considered. If you are unsure of the differences between these three metal finishing techniques, or which one is best for your project, this article will help.

Mechanical polishing

  Mechanical polishing involves the use of physical tools and abrasives to remove abrasive lines, scratches, pits and other imperfections from metal surfaces. Common materials include grinding medium, flat wheel, sandpaper, wool beret, polishing sponge, etc. For ultra-precision polishing, turntables capable of spinning at high speeds and other specialized AIDS may be required. Sometimes manufacturers use mechanical polishing as a preliminary step before electrolytic polishing.

  Although mechanical polishing is accurate and produces a high quality surface finish, it is a specialized process that requires skilled and knowledgeable technicians to get the best results.

Chemical polishing

  In contrast to mechanical polishing, the chemical polishing process achieves a smooth surface finish by immersing the work piece in a chemical solution that dissolves the surface layer of the metal. This process smooths and polishes the microscopic roughness of the workpiece's surface, leaving a specular finish free of burrs, steam stains, and microscopic particles. Chemical polishing results in the formation of passivation layers, which means that the metal is free of debris and convex defects and can be considered frictionless.

Electrolytic polishing

  The electrolytic polishing process is similar to chemical polishing in that the part or assembly is immersed in a chemical solution. The main difference is that electrolytic polishing applies an electric current to the surface of the workpiece, dissolving its metal ions into the electrolytic medium. Increasing the current allows for better control over the amount of surface metal removed, which can be as small as a micron scale material.

  Electrolytic polishing is also well suited for machining fragile parts or those with complex geometric shapes that may be difficult to polish by other means. The process also creates a passivation layer on the metal surface.