Resources / Solutions / Liquid and Powder Coating of Aluminum Extrusions

There are two principle reasons to coat aluminum extrusions. The first one is to control the appearance for purposes of color coordination, uniformity, or visual appeal. Secondly, to protect the substrate from environmental damage due to acid rain, sulfur pollution, salt corrosion, or excess oxidation. The type of finish selected for aluminum extrusions depends upon the use of the product and the preferences of the market. In some instances no coating is required at all, but when there is a requirement liquid paint or powder coating can be applied.

Powder Coating
Powder coatings are applied electrostatically from an air fluidized hopper. The primary powder ingredients are as follows:

Powder coating is one of the most influential finishing methods introduced in the past several years. This finishing method differs from liquids in several ways, most notably in the application and cure of the film. Electrostatic application enables positively charged powder particles to adhere to a negatively charged (or grounded) aluminum profile. After the proper amount of powder is applied, the profile is baked in an oven where the powder particles are melted to a liquid state, fusing together to form a homogenous film. This fully functional film has final physical properties that meet many stringent performance criteria while also meeting environmental regulations limiting the use of volatile organic compounds (VOCs) inherent in many solvent-based liquid coatings.

Powder coating is one of the lowest cost finishing methods employed today. While material and equipment costs are similar to those incurred for liquid finishing systems, the savings achieved in energy, labor, production, waste disposal, and regulatory compliance make the total cost of powder coating more cost effective than other methods.

Liquid Coating
Liquid coatings are fluid materials that, when applied to a surface, form an adhering film to protect and beautify the substrate. Liquid coatings are composed of three primary ingredients:

Liquid coatings can be classified based on the amount of volume solids they contain. The solid components of liquid coatings are called pigments and binders. The remainder of the composition, the solvents, generally contains volatile organic compounds (VOCs), which are driven off during the curing or baking process. The volume solids form the actual film left on the aluminum extrusion when the VOCs are gone.

Classification of liquid coatings by percent solids is expressed as follows:

Liquid coatings yield a uniform film thickness, resulting in a smooth finish that may be preferred for some applications.

Coating Properties
Although there are significant differences between liquid and powder coatings, both perform two essential functions – cosmetic and protective. It is important, therefore, to look beyond the superficial appearance of the finish and address the physical properties required by the product’s service environment. Consider the following:

• Hardness
• Flexibility
• Mar resistance
• Chemical resistance
• Corrosion resistance
• Chalk resistance
• Color requirements
• Initial gloss and gloss retention
• Protection from color loss due to ultra-violet radiation (e.g., sunlight)
• Other properties unique to the specific service environments

Coating Performance

Ratings: 1=Excellent 2=Good 3=Fair 4=Poor

Cost Drivers
As for all processes and services of manufacturing, there are cost drivers that are included to complete the job. For liquid and powder coating these cost drivers are as follows:

1. Plugging holes
2. Masking
3. Number of paint coatings
4. Filling
5. Packaging
6. Racking
7. Stripping

Whatever your coating needs, Alexandria Extrusion Company has integrated a process that can help you meet or exceed the necessary appearance or protection requirements of your aluminum extruded parts. We have liquid and powder paint capabilities (12’ max), chromate (12’ max), silkscreen, iron phosphate, zinc phosphate, pad printing and non-chrome pretreatments. Along with application capabilities we have resources to test customer specifications using methods such as: cross hatch, over bake, bend testing, impact testing, salt spray, pencil hardness, color, gloss and thickness.

Please contact your sales specialist for additional details on liquid and powder coatings or to talk specifically about other coating options offered by Alexandria Extrusion Company.