When the average person talks about custom metal fabrication, they typically focus on engineering and design, material selection, or the types of welding processes that are used. The types of metal fabrication finishes, however, can have a major impact on a finished product’s durability, functionality, and appearance.
Unlike anodization or metal plating finishes which can actually alter a material’s surface, metal fabrication painting and powder coating are applied onto a surface. The techniques provide a much wider selection in regards to a product’s appearance and come in varying degrees of durability.
What is the difference between painting and powder coating and which is best for an application?
Painting and powder coating may sometimes have a similar appearance. Painting, however, is a wet application — typically an epoxy or enamel — that is applied to a surface and allowed to dry. Powder coating uses epoxies and polyester powders that are applied and melted to a surface. Not all objects should be subjected to the high temperatures required to cure powder coating, however, so take that into consideration when choosing a finish.
Both of these metal finishing types have their place and either may be used in some applications. Understanding the following benefits and drawbacks of each can help determine which is best for a metal fabrication project.
The up-front investment in powder coating equipment is typically higher than painting equipment, but requires less technical knowledge for the operator. Powder coating equipment uses a 3–7 step conveyor system, and the overall cost to the customer can vary. For small batch jobs, painting is typically less expensive. For components produced in mass, however, powder coating will likely cost less per part.
Challenges. Issues that can drive up costs for either are the quantity of items being finished. There are often minimum set-up charges, so those costs are amortized across the total number being finished, whether two components or 20. Each product will have a technical data sheet outlining how it should be applied (number of mils, air pressure, viscosity, etc.). If a customer instructs that an application should exceed the supplier’s specifications, it will add costs.
Both a painted surface and powder coat finish can be ultra thin (between 15-25 microns, or .5 to 1 mils), which is important in extremely high tolerance projects. Generally, paint can be layered to be much thicker if the need arises. Powder coating is usually a single layer and can be applied in varying thicknesses.
Challenges. The thicker the finish, the more opportunity there is for imperfections, especially with paint which would require multiple coats. A good quality control process can minimize this issue. For both painting and powder coating, a thicker surface means longer drying or curing times which adds costs.
Painting has a nearly endless selection of colors and finish options, from matte to the type of high gloss finish found on luxury vehicles. If you’re looking for a textured finish, powder coating offers more options. When properly applied both finishes will be even without drips or uneven sections.
Challenges. Powder coating can present challenges on larger components that have varying material thicknesses. When going through the heat treatment, it has a tendency to cure faster or slower depending on the varying metal thickness and can actually burn in some spots. It can create a checkerboard appearance or uneven shading due to inconsistent cure times.
Some paints present challenges, too. Enamel paints don’t dry quickly and require more handling. Epoxy paints, like MIL-DTL-24441 and MIL-DTL-22750 commonly used on defense industry electrical enclosures, are more user friendly. Specifying which finish to use on an assembly is a common oversight on RFQs, so be sure to include the information to ensure an accurate quote.
While appearance is important, a major function of the finishing process is to provide protection from rust, corrosion, and external wear and tear. Powder coating results in a durable finish, slightly more durable than painting. Both are relied upon by various industries to deliver both form and function.
Challenges. In the event a chip or scratch occurs, touch-up on a painted surface is easier than powder coating and will have a better appearance. On a Naval vessel, for example, crews would likely only be able to use a wet touch up process. While you can touch up a powder coated surface with wet paint, the color and finish wouldn’t match well and its appearance would appear marred. When done correctly, a paint touch up would likely be imperceptible.
Proper masking can be as important as the finish being applied. Both powder coating and painting require masking to prevent areas of a surface from being coated. An example might include avoiding the perimeter of a hole where a gasket or bolt needs to be fastened.
Challenges. Critical components might require extremely high masking tolerances within .001 inch. If something is painted or powder coated outside that threshold and it goes to assembly, issues can arise. Take, for example, the hole with a bolt. If the finish unintentionally comes into contact with the bolt when torque is applied, the paint or powder coat will mushroom or crack. The issues are exacerbated on thicker finishes, making the potential for problems more prevalent on powder coating.
Most surfaces that receive a painted or powder coated finish require some form of precoat treatment, whether sandblasting to remove any imperfections or possibly a chemical conversion or iron phosphate spray to improve adhesion.
Challenges. If a customer wants a highly polished finish, more prep is required to eliminate welding heat marks and other surface imperfections. Most metal fabrication companies do not have in-house finishing facilities and need to send out their components for both the pretreatment and painting or powder coating. If a steel item needs to be sandblasted, it needs to be finished (masked, caulked, and painted) within 24 hours before the potential of flash rusting occurs. When a metal fabricator relies on outside parties to do both the blasting and coating, it’s difficult to coordinate transit and schedule times.
Having in-house painting capabilities helps to alleviate many of the challenges noted above. It also improves quality control and scheduling, and helps drive down costs. Fox Valley Metal-Tech has in-house painting facilities for both commercial and defense industry painting processes that have been audited and approved by multiple defense customers.
Explore how Fox Valley Metal-Tech can serve as a one-stop facility for your next metal fabrication project, from start to finish. Contact one of our experts today, and remember to download our helpful RFQ checklist below.