Metal Finishing – An Overview
Metal finishing is the process of adding a finish or coating to the surface of the part to make it better looking or more durable. A finish is a surface texture that gives a part particular visual and functional properties. Sometimes a shiny finish is desirable, in which case a part can be polished with a fine abrasive powder until its surface is smooth and reflective. However, a shiny finish is easily scratched, and it makes any imperfections in the surface of the part glaringly obvious. To make a durable finish that hides imperfections, the part can be bead blasted, which is the process of spraying it with tiny glass beads, to evenly roughen its surface.
A coating is a thin layer of some other material on the surface of a part. A familiar finish is paint, which is a cheap way to color and protect a part at the same time. However, paint can peel off, and it sometimes fills in details of the part in unattractive ways. Powder coating is a more durable coating and is created by giving a part an electrical charge and spraying it with a fine plastic powder. The powder sticks to the part because of static electricity, and the part is baked in an oven until the powder melts and flows over the surface of the part. Powder coating can be done in a variety of colors and textures, including ones that look ornamental or antique.
A metal part can also be coated with another metal. Steel can be kept from rusting by galvanizing it, which involves either dipping it in or spraying it with molten zinc. The zinc mixes with the steel at the surface, creating a durable and non-rusting surface. Galvanized zinc is a fairly dull and unattractive coating, however, and for a better looking finish, a part can be coated with a thin layer of another metal in a process called electroplating. In electroplating, the part is suspended in an electrically conductive bath along with a block of the material to be plated onto it. An electrical charge is created between the two pieces of metal, and particles of the plating metal travel through the solution and are deposited on the part in a thin layer. Some metals can be used to coat parts, including zinc, which is shiny and inexpensive, decorative chrome, which is more expensive but has a deep luster, hard chrome, which is very durable, and precious metals like gold and silver. Parts can also be coated without using electricity in a process called electroless coating, which produces a coating of a much evener thickness and uses less energy. Unfortunately, fewer materials can be plated this way, and it is slower than electroplating.
Aluminum can be coated in a process called anodizing, which uses electricity to form a hard oxide skin on the surface of the part. An anodized coating follows the finish of the part almost exactly so it can be made to take on the sheen of satin or high polish. The anodizing process can leave the part looking like aluminum or use dyes to give it a wide range of rich colors. An aluminum part can also be colored to look like gold, brass, and other metals.
Text and graphics can be painted onto a part with a process called silk screening. In the silk screening process, a sheet of silk is stretched on a frame and selectively sealed to create a pattern. The frame is placed on the part and ink is forced through the silk and onto the part surface. The sealant ensures that the ink is only applied in the desired areas, and the part is now imprinted with logos, labels, or other graphics.
Metal Finishing Processes Supported
• Decorative Chrome Plating
• Color Anodizing
• Electro Plating
• Powder Coat
• Dip Galvanizing
• Electroless Plating
• RFI Shielding