Aug 23, 2022 11:00:00 AM | 7 Min Read

The Difference Between Anodizing & Coating for Aluminum Window Frames

Posted By Reynaers Aluminium
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The Difference Between Anodizing & Coating for Aluminum Window Frames

Should you use anodizing or powder coating for your aluminum frames? The choice can be difficult because both finishing procedures help protect the aluminum against corrosion, which can weaken the metal over time. Here at Reynaers Aluminium, we offer both types of corrosion-resistant finishes for our aluminum windows, doors, and curtain walls, but let’s take an in-depth look at both processes so that you can make an informed decision.

Aluminum Anodizing

The process of anodizing metals has been around for more than a century. It uses an electromechanical process that oxidizes the aluminum. The process starts by dipping the aluminum in a solution to remove surface debris, like dirt and grease, and etching the surface of the metal to make the anodization process more effective. Lastly, an electrical charge is run through the metal in the bath. Once the charge is activated, the oxygen in the electrolyte solution starts to deposit on the aluminum, where it reacts with the metal to create an oxide coating.

The expected useful life of the oxide coating depends on its thickness. Once the coating has formed, it can be dyed in various colors or left in its natural state, depending on your needs.

Is Anodizing Environmentally Friendly?

Anodizing is considered environmentally friendly for aluminum finishing and can help improve the sustainability of your building. The process does not create any VOCs or heavy metals; most of the waste created by the anodizing process can be used in other industries. For example, the aluminum sulfate produced by the anodizing process can be used by wastewater treatment plants, and aluminum trihydrate is often used as a fire retardant.

Pros of Aluminum Anodizing

  • Aluminum anodizing typically lasts 20 years.
  • The oxide layer is part of the metal.
  • The coating is resistant to peeling.
  • Anodizing offers a better metallic finish because the oxide layer is see-through if it’s not dyed.
  • Anodized metal does not change color due to exposure to sunlight.
  • With thick coatings, the aluminum surface can be renewed by removing a little of the coating, which can increase the lifespan of the finish by as long as twenty years.

Cons of Aluminum Anodizing

  • Thin anodized coatings are not recommended for window frames or curtain walls.
  • The coating may need additional chemical coatings to protect it from acid rain.
  • It can develop the appearance of dirt and stains after several years, but detergent can generally remove it.
  • Once the oxide layer has completely worn down, the metal must be painted or replaced.
  • One of the significant issues is that in case of scratches, it can’t be touched up with our touch-up pencils.
  • For colored anodization, it is also important to note that due to the anodization process, there is always a minimum and a maximum control sample, and the final finish will vary between those two control samples. Appearance from one profile to another might look different even though they will be assembled in the same position. 

Aluminum Powder Coating

Powder coating is a surface finish similar to wet painting. It is considered an organic coating, whereas anodizing is not considered an organic coating. The powder coating process involves using a spray gun to apply the powder electrostatically to the surface of the metal. The durability and longevity of a powder coating depend on how the metal was pretreated and the type of resin and pigmentation used. It is recommended that powder coatings be factory applied for best results.

Types of Resins Used in Powder Coating

It’s essential to use the right resin to achieve the desired results. For most outdoor applications, that resin should be polyester , while powder coatings on metal for indoor applications can use epoxy resin. Other resins used with powder coatings include acrylics, urethanes, polyurethanes, FEVE , and TGICs. When considering which type of resin to use, it’s best to consult the AAMA Specifications for Painting Architectural Aluminum.

Is Powder Coating Environmentally Friendly?

Powder coating is also considered environmentally friendly, especially when compared to liquid paints. It does not emit harmful fumes, and it doesn’t contain any VOCs or HAPs. If any powder coating falls to the floor as overspray, it is collected and reused rather than dumped into landfills. This means that when you use a powder coating on your window frames, you are building a greener building.

Pros of Aluminum Powder Coating

  • It is considered an affordable option.
  • It improves the corrosion resistance of aluminum.
  • There are several color options available.
  • It can hide the marks created by casting and mill finishing the aluminum.
  • It helps increase the hardness of the metal.
  • It creates a smooth surface with color uniformity.
  • It is low maintenance.
  • It can easily be touched up with our touch-up pencils.
  • Custom colors can be created upon request.
  • Cradle to Cradle [C2C] and LEED credits available

Cons of Aluminum Powder Coating

  • It can chip off over time, if not properly applied.
  • Colors are susceptible to fading from sunlight exposure.
  • Powder coating is not recommended for extremely thin coatings.
    • Note that Reynaers use a min of 60µ [2.4mils] thickness

Aluminum Windows With Reynaers Aluminium

Reynaers Aluminium offers powder coated and anodized window frames and doors that meet AAMA standards. We offer AAMA 611 for anodization and AAMA 2604 for powder coating. With AAMA 2604, we focus on getting our clients the best warranty for their coating. To ensure you get the right look for your windows, we offer color swatches, and we can answer all your questions regarding durability and protection levels for each of our coating options.

Pre-Anodization Before Powder Coating

Pre-anodization is an additional step in the pre-treatment process for powder coating. This process creates a thin layer of aluminum oxide on the aluminum surface and aids in corrosion resistance and adhesion of the powder coating.

Pre-anodization is the last step before applying the powder coating, and, similar to traditional anodization, the aluminum is dipped into a sulfuric acid solution, and an electrical charge is put through the solution. This converts the aluminum surface into aluminum oxide. In a traditional anodization process, the oxide layer would be sealed; however, in pre-anodization, it is not, and the piece moves on to powder coating.

This additional aluminum oxide layer protects the metal from corrosion for up to ten years and helps prevent chipping of the powder coat. Pre-anodization before powder coating adds the anti-corrosion properties of anodization to a powder coat finish while eliminating the potential variance of shades across pieces that are only anodized. Pre-anodization offers the best of both worlds, but this process isn’t available everywhere. Only a handful of companies worldwide can provide this additional step, including Reynaers.

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Topics: Windows, Doors

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