The Process For Powder Coating Stainless Steel
Because of its strength and durability, steel is commonly used in numerous commercial and residential applications. However, not all steel is the same. Mild steel, while great for both commercial and residential applications, is susceptible to corrosion, so applying a protective coat of paint is often reasonable.
However, why would anyone consider protecting corrosion-resistant metals, such as stainless steel alloys, from corrosion? Well, as it turns out, stainless steel can corrode in certain circumstances, and a powder coating is among the best ways to apply a protective coating to your stainless steel applications.
In this article, we'll discuss the process for powder coating stainless steel, whether it can and should be done, and why anyone would go through the trouble of additionally protecting an already corrosion-resistant material.
Why Powder Coat Stainless Steel?
Stainless steel is a strong, corrosion-resistant, and rather versatile alloy, but it's not entirely corrosion-proof. In fact, if you're living anywhere near a seashore, a chemical plant, or an otherwise moist and stormy environment, stainless steel will eventually begin to corrode.
Other causes for stainless steel corrosion might include superficial damage to the stainless steel surface, which naturally has a passive protective layer of chromium oxide. Admittedly, the protective layer is self-healing, but if your application demands additional protection, powder coating is the way to go.
It can, in fact, extend the longevity of your outdoor stainless steel fixtures and structures by forming a completely sealed protective layer around the steel. The main advantage of powder coating over typical liquid paint is that it's much more durable and doesn't crack unless severely damaged by significant impacts of cuts.
In fact, it's an excellent long-lasting topcoat solution if you're placing a stainless steel alloy in a non-hygienic, highly corrosive environment. But that's not all; besides its significant durability, powder coating also allows for customization — it offers vast color and surface finish choices.
How Does Powder Coating work?
Powder coating is a dry finishing process that involves polymer resins combined with pigments, adhesion agents, leveling and flow modifiers, and various other additives. These ingredients are processed into a uniform powder which is then applied to metal surfaces through a process called electrostatic spray deposition.
Despite the fancy terms, it's a pretty simple concept. The powder is electrostatically charged, so it sticks when sprayed over the grounded metal surface. After application, the powder-coated steel undergoes a curing process, during which the coating powder chemically reacts and produces a long molecular chain.
The curing process depends on the type of powder coating formulation:
- Thermoset — this formulation cures by subjecting the powder-coated steel to heat. However, chemical fusion is irreversible, meaning that it can't be melted again once it sets. Thermoset powders are great for applications involving impacts, wear, and corrosion.
- Thermoplastic — this formulation is also cured by applying heat, but its chemical composition doesn't change with heat, so it can be softened or melted after curing.
- UV-curable — this formulation reacts under UV light. The benefits of powder coating using UV-curable powders lies in faster curing cycles and lower temperature requirements. This allows for powder coating of otherwise temperature-sensitive substrates, such as wood or plastics.
How to Powder Coat Stainless Steel?
Powder coating is used to coat metal surfaces with a thin, protective layer of synthetic resin, and when applied correctly, the resulting product has the strength and flexibility of steel, as well as the ideal color, texture, and corrosion resistance.
The process details may vary slightly, depending on the stainless steel alloy used in the process. Here are the general steps followed during the stainless steel powder coating process:
Surface Cleaning
Oil and grime must be removed for powder coating to work properly. The surface of the metal is thoroughly cleaned using non-corrosive solvents since surface impurities could disrupt the binding between the metal and the polymer.
Passivating
Passivating, also called pickling, is the process of carefully treating metals with slightly corrosive chemicals to remove a thin coating on the surface of stainless steel. The harsh chemicals employed in this preparation process could lead to corrosion if the pretreatment isn't carried out very carefully.
Here, it's important to remove any spots where the distribution of alloying compounds has been disturbed, like areas close to welds, welds themselves, chipping, and any dents or scratches made to the metal surface.
Sandblasting
Any lingering contaminants that the first two stages missed are removed by sandblasting. After the part has been blasted, it is once more carefully and completely cleaned to remove any sandblasting residue.
Powder Coat and Primer
An electrostatic charge is used to apply primer and powder coating layers. Despite being relatively thin, these layers are very robust. They are applied without the use of paint, ensuring that the final surface is free of pinholes.
Curing
To guarantee that the resin bonds and hardens to the proper level after application, the powder coating is cured depending on the formulation — most often, it's oven-cured. The completed product can survive corrosion and abrasion if the curing process is done properly.
What's the Difference Between Powder-coated Steel and Stainless Steel?
Well, that depends on whether we compare powdered-coated carbon or stainless steel to untreated stainless steel. In most cases, besides the obvious differences between steel and stainless steel, the main factors usually include the application and price.
Stainless steels designed for hygienic applications, such as biomedical applications, don't usually feature powder-coat finishes. However, non-hygienic applications, such as industrial hardware, fixtures, construction elements, and some tools made of steel, can use a powder coating.
In most cases, things like hand wheels, various types of knobs, and machine crank handles can be made of carbon steel and treated with powder coating. Unless specifically required, making these out of stainless steel and subsequently applying powder coating would severely increase the production price of said elements.
So, powder-coating carbon steel is a more viable option for certain applications. However, if your project requires the use of stainless steel for technical reasons — due to the material's properties — powder coating is a viable way of protecting stainless steel and prolonging its lifespan.
Summary
Powder-coating stainless steel is a viable option if you're looking to protect the material from the harmful effects of harsh environments, chemical solutions, and typical wear and tear. If you want to learn more about Steel and its types, please visit Reid Supply, and refer to their Engineer Resource Guides or some of their guides on various types of steel, including stainless and surgical steel.