Types of Metal Finishing
Metal finishing is used to treat the exterior of a metal product by applying a thin complementary layer to its surface. There are numerous types of metal finishing processes that can be used for a variety of purposes. In this guide, we will review the major finishing methods, as well as applications and considerations for choosing a metal finishing process. Some of the general advantages of applying this finishing treatment to a metal product include:
- Increased durability
- Improved decorative appeal
- Enhanced electrical conductivity
- Higher electrical resistance
- Higher chemical resistance
- Higher tarnish resistance
- Potential for vulcanization
Types of Metal Finishing
- Metal Plating
- Brushed Metal
- Buff Polishing
- Metal Grinding
- Metal Vibratory Finishing
- Sand Blasting
- Powder Coating
- Aluminum Anodizing
- Hot Blackening
- Stainless Steel Polishing
Metal plating machines use a chemical bath to coat or alter the surface of a substrate with a thin layer of metal, such as nickel, Zinc. The electroplating method generates an electric current to coat the substrate, while electroless plating employs an autocatalytic process in which the substrate catalyzes the reaction.
Metal plating provides a number of advantages as a finishing process. It can improve a product’s durability, corrosion resistance, surface friction, and exterior appearance. It is also a useful option for coating other metals. In high-volume production runs, a barrel-finishing machine is a fast and efficient plating solution. However, plating machines are generally not suited for smoothing out surface defects.
Unlike plating, brushed metal finishing is an effective method for removing surface imperfections. These finishing machines create a uniform, parallel grain surface texture to smooth out a product’s exterior. An abrasive belt or wire brush is usually employed to achieve this effect. In addition, the singular direction of the belt or brush can create slightly rounded edges perpendicular to the grain.
If your project requires a smooth, non-textured finish, then a buff polishing machine may be your answer. This machine uses a cloth wheel to buff the product’s surface, resulting in a high, glossy sheen. The process is often used for decorative products that benefit from luster and smoothness.
Buff polishing machines tend to round out a product’s edges, and due to the cloth wheel’s range limits, the process is less effective for applications requiring intricate, fragile, or recessed features.
Grinding machines use friction, attrition, and/or compression to smooth out a metal product’s surface. There are several types of grinding machines designed to deliver different levels of finite smoothness. For example, a ball-grinding mill is an excellent fine grinder for cement products, but may not work for more extensive smoothing projects.
Most metal grinding machines consist of a substrate within a rotating drum. Rod mills are used to make metal rods, while semi-autogenous grinding (SAG) mills and autogenous grinding mills smooth copper, gold, platinum, and silver.
Metal Vibratory Finishing
Vibratory finishing machines are used to deburr products and remove sharp edges. They position material inside a drum filled with abrasive pellets and a substrate, then apply to tumble vibration to create a uniform random texture. The machine’s cycle speed and magnitude of vibration are usually variable, allowing effective treatment for a range of small- to large-sized parts.
Sand-blasting machines are typically employed in projects requiring a uniform matte texture. The process (also known as bead blasting) forces sand, steel shots, metal pellets, or other abrasives into a substrate at high speed. This results in a smooth, clean product texture, particularly in soft metals.
Powder coating applies a decorative finish that is similar to paint but with greater durability. The process involves melting dry plastic powder onto the metal to produce a textured, matte, or glossy coating. A textured powder-coating machine is also highly effective in removing surface defects.
An electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of aluminum parts. There are three types of anodizing (Type I, Type II, and Type III) which use different acids to create the anodize coating.
- Increase wear resistance
- Increase corrosion resistance
- Increase adhesion for paint and primers
- Prevents galling of threaded components
- Increase surface hardness
Hot blackening machines spread a thin layer of black oxide onto a product’s surface to create a matte black finish with high abrasion resistance. It is a high-temperature process in which the product is inserted into a series of tanks containing cleaners, caustics, and coolants. Hot blackening is most commonly used in the production of automotive parts, tools, and firearms.
Choosing a Metal Finishing Process
There are a few considerations that can help you narrow your choices in selecting a metal finishing technique suitable for your project. Some helpful things to keep in mind are:
- Production speed: How quickly does the technique apply finish to the product?
- Cost-effectiveness: Certain finishing machines (such as vibratory tumblers) can be expensive, but may compensate for their price by delivering faster cycle rates
- Metal hardness: harder metals usually require more intense finishing techniques, like grinding, or may need tougher abrasives than those used on softer materials
- Potential for vulcanization