By definition, metal is a material that can be opaque, ductile, malleable, and lustrous (especially when newly prepared or polished) that are a good conductor of electricity and heat. The five most popular types of metal are steel, iron, aluminum, zinc, and bronze.
Metals are utilized in various industries. Some of which are construction, electronics, medicine, machinery, automobiles, and aesthetics (decorative). Because most metals are prone to wear and corrosion, there are several methods to protect and maintain this versatile material. Popular methods are painting, greasing, galvanizing, coating, and finishing.
What is metal finishing?
Metal finishing is the final step in the manufacturing processes involving metals. It treats the exterior of a metal product or component with a thin layer of augmenting material for added protection. This critical step is done to deliver aesthetics and ensure environmental protection for the material. Sometimes, it is also undertaken to reduce surface roughness depending on how the part will be utilized. The term metal finish also includes procedures of metal cleaning, descaling, deburring, de-rusting, etc.
What are the advantages of undergoing the metal finishing process?
Besides completing how a piece of metal will look, a metal finish also provides numerous benefits and features to the already strong and customized steel. When choosing which metal finish to apply, keep the specific intention in mind. Considering these details, the following advantages would undoubtedly be secured:
- Increased durability
- Higher electrical resistance
- Improved decorative appeal
- Higher chemical resistance
- Enhanced electrical conductivity
- Higher tarnish and corrosion resistance
- Reduced friction
- Higher abrasion resistance
What are the different types of metal finishes?
Those who work with metals carefully weigh their options when choosing the type of metal finish to use for a particular project. Take a look at the different types of metal finishes and decide which is suitable for your current project:
Wet paint is the traditional metal finishing process. It involves the application of liquid paint to a metal surface via a spray, a pump, or a pressurized vessel. The process begins by thoroughly cleaning a part of the product. Then, it is followed by spraying 15 to 20 micrometers of liquid paint onto the surface. The process is repeated and continued until the part is evenly coated to the required paint thickness.
To change up the surface of the metal, this process starts with a chemical bath. Most metals used are cadmium, chromium, nickel, and zinc. Metal plating is frequently done to make additional features to the metal. The added layer of metals furthers the product’s overall resistance. It also increases its durability by covering the base metal and protecting it from corrosion, chemical damage, and wear and tear.
Metal plating also includes another process called electroplating. Here it generates an electric current to coat the base metal. Then, electroless plating is done to stabilize the reaction. Machine tools and drills are the products that usually use these finishing processes.
Electrocoating or e-coating is almost the same as electroplating. Similarly, an electric current and chemical solution work together to layer a coat on the component’s base. However, instead of using other metals, the solution contains electrically charged paint particulars such as acrylics or epoxies, serving as primers over the substrate. The primer then improves the adhesion of the next layer of protection or paint.
E-coating is famous for being an affordable option for metal finish. It has a low-cost-per-square-foot rate because of its ability to accommodate part complexity and volume. Since it is also applicable to almost any type of metal, it is a popular choice.
The first type of blasting method for metal finishes is sand-blasting. This method utilizes abrasives such as sand and metal pellets forced onto a base layer at high speeds. Commonly applied to soft metals, it results in a clean and smooth texture. Sand-blasting is excellent for projects requiring a uniform matte surface.
The second type of blasting method is shot peening. Shot Peening uses compression in applying stress to the base layer of the metal. This step improves the product’s fatigue resistance, stress corrosion, and cracking resistance. Done by a cold working process, it counteracts tensile stress, which naturally occurs in manufacturing. This way, compressive stress is applied to all surfaces.
This method consists of simple water and oil-based paints. These are used to put on a light, temporary, and inexpensive protection to the product. Doing this can protect against corrosion. However, a layer of paint is considered inadequate even if the metal itself is strong enough.
Powder coating involves heat curing of dry thermoplastic polymer powder onto the metal. This process is similar to basic coating, but it provides more outstanding durability. It produces either textured, matte, or glossy coating effects. The use of powder coating hides the defects in the base material. Affixing the powder coat proves to be solid and accurate enough to overlay on any of the rough spots in the substrate.
Four methods use abrasives: polishing, buffing, honing, and lapping. Mainly, these are used to diminish surface roughness in metals, especially after the machining process. These methods are exact. The roughness is measured in micro-inches, and the abrasion is used to smoothen the rough surfaces of mating parts by rubbing them against each other. It is noteworthy that these methods are primarily used to improve the aesthetics of the material.
If your material is aluminum, anodization is the method of choice. It involves an electrolytic passivation process. An electric current is passed through the anode (aluminum parts) and a cathode (usually flat aluminum bars). Thus the method is called anodization. By increasing the thickness of the natural oxide layer of the product, the process reduces the possibility of corrosion and wear. In addition, it also improves adhesion for paint and primer.
Chemical Film Coating, also known as Chromate Conversion, Alodine, or Iridite, is a chemical conversion coating used to passivate aluminum. Like anodizing, it aims to be a corrosion inhibitor and improve the adhesion of paint finishes and other coatings. However, the latter is the better choice to achieve the said goals. Nonetheless, it still creates a base for organic layers while leaving unaffected product dimensions.
As the name implies, case hardening is forming a hardened layer around a metal component that serves as a protective barrier. This method is an excellent option for metal parts subject to abrasive and high-pressure environments but is safe from corrosive environments. Remember that case-hardened materials can never be welded. Types of case hardening options are carburizing (adding carbon), nitriding (exposing to nitrogen), cyaniding (incorporating carbon, nitrogen, and a carburizing bath containing cyanide), and flame hardening (uses oxyacetylene and water). In all options, heating up to 9000 °C is involved.
How do you choose the metal finish for your project?
To narrow down your choices, here are helpful things to consider:
- Speed: How quickly does the method apply finish to the product? This will be a critical factor if you need the metal part soon.
- Budget: Some equipment used in finishing can be expensive. However, the efficiency of these machines may compensate for their price by delivering faster and earlier. Processes involved may also prove more beneficial if they add features to your product.
- Durability: Harder metals typically require advanced and more intense finishing methods.
SEI Castings offer custom castings, enclosure, and waveguide components. We also provide various options for your project’s required finishing. For more information about our products and how we can customize your project, call us at (408) 374-1031.