In Aluminum powder coating, First, clean the aluminum. Then, spray dry powder onto it. Next, bake it in an oven to melt the powder. Finally, let it cool. This makes a strong, protective finish. Different colors of powder can be used. The coating is tough and lasts a long time.

This article will help you discover suitable aluminum powder coating techniques. Learn its various benefits and versatility across applications.

What is Powder Coating?

Generally, powder coating techniques are associated with dry finishing. That kind of special powder is usually made from resins, pigments, and additives.

Resin in this case makes up about 50-60 % of the powder. Meanwhile, pigments contribute to producing color and take 20-30%.

Additives purposely improve consistency, like what flow agents do. It takes 5-10 %. The electrostatic charge helps in evenly covering surfaces with good powder adherence. For this, there is a spray gun. This serves the purpose of charging the powder particles negatively at a high voltage of 30-100 kV.

The process moves ahead by grounding the workpiece. That is what makes objects attract charged particles. So the powder sticks evenly.

Types of Powder Coating

• Thermoset powder
• Thermoplastic powder

Thermoset powders

The thermoset powder formation includes epoxy, polyester, acrylic, and polyurethane.

• Chemical and temperature resistance (up to 250°F) are the qualities of epoxy, making it suitable for appliances.
• Polyester effectively stops the impact of UV radiation and is best suited for outdoor objects. This coating lasts 10-15 years outdoors.
• Acrylic, with its glossy finish, is an excellent match for automotive parts.
• Polyurethane usually involves tough handling and that is why it is ideal for industrial equipment.

Thermoplastic powders

The nylon and polyethylene form thermoplastic powders.

Nylon can prevent the wearing of equipment like gear. This is because it contains a good tensile strength of 8,000-12,000 psi.

Polyethylene avoids moisture impact and is commonly used for pipes.

Benefits of Aluminum Powder Coating

1.   Corrosion Resistance

The reason coated aluminum parts do not corrode is that powder coating works in two ways. One of them is barrier protection and the other one is electrochemical protection.

• Barrier protection does not let moisture, water, or chemicals reach inside the substances.
• Electrochemical protection works to stop part rusting. For this, it blocks electrical currents.

Several types of coatings offer different protection levels. For instance, when undergoing salt spray tests, epoxy coatings last around 1,000-1,500 hours.

Meanwhile, polyester coatings remain unaffected for around 500-1,000 hours.

The purpose of the salt spray testing is to determine the genuine ability of coatings to stop rusting.

2.   Durability and Longevity

Powder coating on aluminum is 100% effective in giving them protection against abrasion, scratches, and impacts. This is why the object becomes durable.

Abrasion resistance

The coated part checks to measure its abrasion resistance. For the moment, a taber abrasion test occurs.

Scratch resistance

Scratch resistance can be checked via a pencil hardness test.

Impact resistance

Impact resistance with falling weight test. In this test, it is analyzed that the coating can handle 160 in-lbs of impact.

Curing schedules

Besides these properties, the curing schedule is also considerable in case of durability and longevity.

For example, when the curing temperature completes its 1 cycle, it shows the hardness improvement of 2024-T3 aluminum.

Meanwhile, the cycle 5 position shows how it stabilizes the mechanical traits, giving long-lasting performance ability.

UV-resistant

Powder coating protects objects from UV impacts along with weather. There are QUV tests available to check polyester coatings’ lastability. That can withstand for years without causing fade.

3.   Aesthetics

There are a lot of things that coating can produce on surfaces, ultimately increasing their aesthetics. For example, colors, textures, and gloss levels.

The metallic finish and pearlescent pigments create an impressive look. Meanwhile, glossy impact ranges from matte 10% to high glossy up to 90%.

4.   Environmental Benefits

The additional benefit of coating could be one of its eco-friendliness. There are almost fewer chances of volatile organic compounds (VOCs).

Liquid coatings, however, expose 3.5-4.5 pounds of VOCs per gallon.

Additionally, the unused powder can be brought back into the process or recycled. Personnel can reuse around 95% of overspray.

5.   Cost-Effectiveness

Working with powder coating is easier than those liquid options. The process is faster, uses less material, and needs fewer workers. All these factors make it much cheaper, around 20-30%  than liquid coating.

Preparation of Aluminum for Powder Coating

Cleaning and Degreasing:

You must make sure the aluminum surfaces do not contain any dirt, debris, or other unwanted elements.

In this case, various cleaners serve the purpose of cleaning the objects. For example, oil and dirt can be cleaned through alkaline cleaners. They occur at a pH of 10-12.

Acidic cleaners remove rusting portions of the object and their scale. They perform at a pH of 1-3.

Solvent-based cleaners clean off heavy oil and grease areas well. They evaporate, taking approx. 5-10 minutes.

Sanding and Blasting:

Once cleaning is done, the things you can use to roughen surfaces are sanding or blasting. In addition to this, choose the grit size associated with blasting between 60 and 120.

To remove heavy rust, use coarser grit with 60-80. Similarly, to make surfaces more smooth use finer grits (100-120).

Blasting media

Blasting media uses sand (for heavy rust), steel grit (for tough surfaces), and aluminum oxide (for fragile objects).

The purpose behind blasting media is to prepare the surface to adhere well to coatings. However, too much blasting makes aluminum thin or over-rough.

Chemical Pre-Treatment

Chromatin:

The chromating process works using chromium oxide. It ends up giving fine and thin layers of up to 0.1-0.5. The shades it creates could be yellow, green, or clear.  This process does not cost much but is somehow less durable.

Anodizing:

Anodizing uses an electric current. That makes a thick oxide layer of 5-25 micrometers. It is worth making parts durable but costs are higher.

Importance of Proper Surface Preparation

Inadequate cleaning processes cause coating defects. In that case, peeling, bubbling or uneven coverage occurs, and porosity, even if the applied coatings are of high quality. Then it would be harder to maintain durability and performance. For this reason, proper preparation is very important.

Powder Coating Process for Aluminum

The five main steps of aluminum powder coating here are:

• Pre-treatment
• Application
• Curing
• Cooling
• Quality Control

1.   Pre-treatment:

The contaminants (dust, oil, and rust) that a manufactured part contains actually do cause trouble during coating. Therefore, make sure the surfaces are clean.

Among several options, alkaline solutions remove oil and dirt easily. Acid etching aids in getting rid of rust.

But in the case of creating better stickiness, chemical reactions like phosphating are good ones. They can create thick layers around 1-3 micrometers.

Blasting media, like sand or steel grit, allows you to scrub the surface, causing roughness to a profile of 1.5-4 mils (38-102 mm). Roughened surfaces hold coating well.

2.   Application:

Electrostatic spray guns like Corona and Tribo are two different ways that can be used to apply powder.

Corona guns work using voltage and tribo use friction to charge particles.

Both processes spread powder coating evenly and achieve a 2-4 mil (50-100 micrometers) thick layer.

However, hold control of air pressure and powder flow rate to maintain uniformity.

Advantages:

The reason complex-shaped parts get even coverage is because coatings work well.

Disadvantages:

There is a need for proper attention to handle voltage and distance.

3.   Curing:

The baking step will occur after applying powder. During this, personnel heat the object in an oven or use infrared (IR) heaters.

If the powder is thermoset, then it would cure at 300-400°F, taking 10-20 minutes in an oven. The crosslinking causes because of the coating to get harder and more durable.

Conversely, this kind of thermoplastic powder usually melts at 350-450°F. They fuse into a smooth coat.

Using the IR method, rays quickly heat the part, taking as little as 2-5 minutes.

Basically, curing schedules are the parameters that affect hardness levels. They usually range from 2H to 9H on the pencil hardness scale.

Temperature Control and Humidity

The improper temperature and humidity are all major issues to begin with. That eventually burns the coating when overheated or causes incomplete curing when too little heat.

Additionally, humidity must be controlled under 50% to prevent defects.

4.   Cooling and Handling:

In order to get accurate results, cured parts must undergo a cooling process.

Cooling methods

Cooling stages commonly include two methods. That is air cooling and water quenching.

Air cooling works for 10-15 minutes. Meanwhile, water quenching is the fastest way but somehow can cause thermal shock.

Handling:

Handle coated aluminum parts with care. In addition to this, you can wear gloves and use padded racks. These handling techniques avoid scratches or dents as a result.

5.   Quality Control Measures:

Quality control tests ensure the coated parts meet their stated standards. They include:

• Film thickness: The thickness gauge helps measure the film of the coating. The ideal range falls under 2-4 miles.
• Adhesion: You check how well the coating sticks to surfaces using a cross-cut test. It must not peel off to pass this test.
• Impact resistance: The falling weight test measures how much a coated part reacts upon impact.
• Salt spray tests: It checks the corrosion resistance limits of aluminum.

Common Applications of Aluminum Powder Coating

Architectural Components:

The UV rays and weather resistance are the attributes that make powder coating ideal for curtains, walls, and handrails.

It does not fade out and lasts longer. Also, their color options and finishes aid in getting a beautiful appearance.

Automotive Parts

There’s the advantage of coatings’ toughness and scratch-resistance finish for car wheels and trim. Additionally, its impact and chemical resistance (road salt) do not lose their visual quality.

Aerospace Components

In an aluminum powder coating,

there are the best properties of lightweight and high-temperature resistance. That is why they are suitable for brackets and panels. This is because aircraft parts encounter intense conditions.

Marine Hardware

In case of stopping saltwater corrosion impact, marine uses coating for boat rails and fittings. As such, the coating passes the salt spray test; it can handle harsh marine environments.

Furniture and Appliances

The cleaning process of coating is very easy so it can be used for outdoor furniture and appliances.

Its other features, like scratches, UV, and impact resistance, are beneficial for these parts, making them more durable.

Conclusion

In addition to durability, beautiful looks, and environmental benefits, aluminum powder coating adheres to the stated qualities. Various industries, therefore, including automotive, aerospace, marine, and furniture, are benefiting from it. Before applying it, weigh all the parameters. That’s regarding its techniques and processes, which result in better and long-lasting finishes.