Surface finishing is a broad range of industrial processes that alter the surface of a manufactured item to achieve a certain property. Finishing processes may be employed to: improve appearance, adhesion or wettability, corrosion resistance, tarnish resistance, chemical resistance, wear resistance, hardness, modify electrical conductivity, remove burrs and other surface flaws, and control the surface friction. An unfinished surface is often called mill finish.
Polishing Surfaces
One process used to finish many product surfaces is polishing. Polishing is the process of creating a smooth and shiny surface by using a chemical action, leaving a surface with a significant specular reflection. In some materials (such as metals, glasses, black or transparent stones) polishing is also able to reduce diffuse reflection to minimal values. Two common methods for plastic polishing include vapor polishing and flame polishing.
Vapor Polishing Method
Vapor polishing is a method of polishing plastic products to reduce the surface roughness or improve clarity. Typically, a component is exposed to a chemical vapor causing the surface to flow thereby improving the surface finish. This method of polishing is frequently used to return clear materials to an optical quality finish after machining. Vapor polishing works well in the internal features of components.
Surfaces for Vapor Polishing
Feature size changes of the plastic component generally do not occur. Post stress relieving is usually required. Plastics that respond well to vapor polishing are polycarbonate and acrylic. The technique is also being used to improve the surface of objects created with 3d printing techniques. As the printer deposits layer upon layer of material to build the object, the surface is often not entirely smooth. The smoothness of the surface can be greatly increased by vapor polishing.
Flame Polishing Method
Flame polishing is a method of polishing a material, usually thermoplastics or glass, by exposing it to a flame or heat. By melting the surface of the material, surface tension smooths the surface out. Operator skill is critical with this method.
Surfaces for Flame Polishing
When done properly, flame plastic polishing produces the clearest finish, especially when polishing acrylic. This method is most applicable to flat external surfaces. Flame polishing is frequently used in acrylic plastic fabrication because of its high speed when compared to abrasive methods. In this application, a torch burning hydrogen and oxygen is typically used, one reason being that the flame chemistry is unlikely to contaminate the plastic.
