A Guide to Powder Coating - What You Need to Know

Powder coating is an advanced method of applying paint to metal components, providing a durable layer of protection and superior resistance to corrosion. The powder is applied electrostatically and is then cured with heat in order to create a high-quality finish that adheres well to the substrate. Powder coating is typically used in the automotive, aerospace, lawn & garden, and industrial industries.

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This type of coating system feeds chips or powder particles electrostatically to a spray gun, which heats and sprays the powder onto the substrate. This process ensures an even coating of the components and creates a finish that is resistant to scratches, abrasion, and corrosion.

Powder coating also offers an array of color choices, with custom tint options available as well. The finished product is easy to clean and maintain due to its smooth surface and long-term pressure resistance.

The durability and strength of the coating are superior to older painting techniques, such as liquid painting. The powder is sprayed onto the substrate and then accelerated in an oven to fuse into an anti-corrosive layer, preventing harsh weather conditions from deteriorating it.

This process also creates a seductive finish on items, enhancing their aesthetics as well as their useful life. It can be applied to many metals like iron, aluminum, galvanized steel, stainless steel, brass and copper for stronger results than other conventional coatings.

Process of Powder Coating

The actual process of powder coating is quite simple. The item to be coated is cleaned and pre-treated with chemicals to prepare it for the finishing step. Then, a powdered coating material is electrostatically applied with special equipment. The coated parts are then baked in an oven in order to fully cure and harden the finish, creating a strong bond between the part and the product.

The end result is a durable, attractive finish that can last a long time if properly cared for. Additionally, powder coating comes in numerous colors and textures so you can always find something that’s aesthetically pleasing.

This process adds a layer of protection from wear, tear, rusting, corrosion, abrasion, and fading. It also helps seal out moisture and chemicals that can otherwise cause damage.

Powder coating is also an eco-friendly finishing method as it doesn’t produce any VOCs (Volatile Organic Compounds) in the air or ground. In today’s world where environmental awareness is increasing rapidly, this makes powder coating an attractive option for industrial applications.

Powder Coating Advantage

Powder coating offers the advantage of being a more ecological choice compared to paint or other finishes. Unlike traditional wet painting, powder coating does not require an external solvents and emits few VOCs.

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This means it is safer for both the environment and workers alike as it produces less hazardous waste and has fewer emissions than other typical finishes. Additionally, powder coatings are also resistant to corrosion and resistant to most chemicals and abrasive materials, making them perfect for items that need constant exposure outdoors.

You have questions, we have answers. In each issue of PCT, our extensive network of powder coating experts provides information to help you with your powder coating challenges. Let us know what’s keeping you up at night and we’ll do our best to help you get a good night’s sleep!

In a Jam
Q: I have a powder coating line and am experiencing problems with the grounding of my parts. Specifically, the problem is with the load bars on my conveyors. Is there a particular hook material or finish that is required for a good ground? We are currently considering removing our load bars to have them sand blasted. Is this a good solution? Looking for advice to get us out of our jam.

A:First, you are addressing one of the most important components for achieving a quality finish on your products in checking your ground. For both meeting the safety standards and obtaining the best transfer efficiency, all parts should be grounded and verified with a Megohmmeter. You should have less than 1 meg-ohm of resistance. It is best to start at the lowest part on your hanger and check each part, moving up the rack or hooks. You might be good near the top, but all it takes is one hanger or part to be covered with cured powder to prevent a proper ground. Normally, standard mild steel without any coating on it is used for load bars to provide the best electroconductivity for your ground. In your case, it appears that you have identified the issue as being with your load bars. To achieve a better ground, you are on the right track having the load bars blasted or chemically stripped. However, you should consider further investigation into “why” this is happening. It might be that your parts being coated are too close to the load bar and causing the load bars to be coated during the powder coating process. If this is the case, look into using longer hangers to get them further away from the powder cloud. You might also double check the air flow in your booth including cross draft and through the roof slot. The booth might be out of balance or need more air flow (typically 100 to 120 fpm) through your openings.

A: Yes, although this can be a touchy situation if the specifications are not clear for everyone in the supply chain. Powder coating characteristics generally fall into three categories: • Surface appearance such as color & gloss. • Physical properties such as texture or smoothness. • Environmental durability such as outdoor UV requirements or salt spray corrosion resistance requirements. These characteristics should be defined by you to meet the desired requirements. These can be given to the custom coater and their suppliers. With a clear definition, it should stop any finger pointing as all would understand what specification/ characteristic is required. The following are some tests that can be used to set the characteristics:
• Gloss: using a Glossmeter as in ASTM D523.
• Color: using a Colorimeter as in ASTM D.
• Smoothness: PCI Smoothness Standards as defined in PCI Technical Brief #20.
• Distinctness of Image: either visual observation or meter as in ASTM D.
• Contrast Ratio: for special substrates or reflectance instruments as in ASTM D or PCI Technical Brief #3.

Other physical characteristics that may be considered are film thickness, impact resistance, flexibility, adhesion, hardness, abrasion resistance, edge coverage, chip resistance, and post machining (drilling and tapping). Some environmental characteristics to consider are solvent resistance, stain and chemical resistance, humidity resistance, salt spray resistance as per ASTM B523, weathering UV resistance as per ASTM D822, and temperature resistance. One method would be to take a sample product that meets your requirements and send it to a lab to have the characteristics measured and documented which can then be used to set your standards. Another way would be to work with a powder producer to discuss and set these standards. One thing to remember, the tighter the standard and more characteristics that are required can increase the cost of the material and manufacturing of the product. You should keep the specification to what is needed for your product.

The Flame
Q: I am new to powder coating and serve as our company’s health and safety manager. I was trying to find information on the flammability and combustibility of powder coating in addition to what is on the material safety data sheets (MSDS). Would you be able to point me to where I can find such information?

A: As each powder coating is a unique formulation and has its individual characteristics, the MSDS would be the best place to find this information for any particular powder. However, if you are looking for some general information on powder coating flammability and combustibility you can refer to the National Fire Protection Association’s NFPA® 33 Standard for Spray Application Using Flammable or Combustible Materials. Specifically, the following chapters:
• Chapter 15—Powder Coating.
• Annex A—Explanatory Material.
• Annex C—Determining Ventilation Airflow for Powder Application Systems.
• Annex D—Fire Record. Your best bet would be to start in the Annex C section which covers determining ventilation airflow for powder application systems. It has great explanations as well as calculations and representative test data for various types of powder.

Real World Results
Q: We have been manufacturing our product for many years and I am looking to improve our coating performance. Our product is used outdoors, and our mission is to provide top quality performance for our customers. We need to know if there are any guidelines to correlate impact test results with real world performance. For example: XX foot-pounds would equate to a ¼ inch hail or YY foot-pounds is considered “tough,” etc.? Can you help me understand the correlation or point me to some testing that has been completed?

A: There is not a true correlation between impact testing and hail. However, standard durable polyesters can easily achieve 160/160 inch-pounds (direct/indirect on a Gardner impact tester) of impact performance but have limited weathering performance. Superdurable polyesters can achieve 120/120 inch-pounds of impact performance and have significantly improved weathering performance. Not all superdurables will have this; most superdurable polyesters have significantly reduced impact performance. You need to check the technical data sheet (TDS) to determine if a particular superdurable has what you are looking for or contact a powder coating manufacturer for advice.

Clean Enough
Q: We manufacture parts that are primarily cast iron and machined for use in the automotive, agricultural, and construction equipment (ACE) industries. We are not sure if we are cleaning our parts properly prior to powder coating them. What steps should we take to ensure that we are getting a quality finish that will meet the performance expectations?

A: As always, it is suggested that you start with the end performance expectations. Since your parts are used in the automotive and ACE industries, performance requirements will most likely include high corrosion resistance. To achieve this, the cleaning and pretreatment process plays a crucial role. First, you must review the types of machining lubrication used during the fabrication process and determine its ingredients. For example, is the lubrication an oil-based product or does it include other items such as surfactants, waxes, or other ingredients? Give this information to your pretreatment chemical supplier so they can determine the best chemistry for your cleaning stage(s). Also, depending on a few variables, they can determine whether the parts should be processed in a spray application or an immersion tank. Remember, if you do not remove the oils and other contaminants, they will be captured below the conversion coating and powder layers, leading to a premature failure. The next step will be to determine which type of conversion coating will meet the corrosion resistance requirements. Again, your chemical supplier can explore whether an iron phosphate, advanced pretreatment chemistry such as zirconium, or a zinc phosphate chemistry would be best suited for your product. To determine which scenario would work for either the cleaning or conversion coating, send some test parts to the chemical supplier’s lab so they can run trials. By changing the variables, you will be able to see which method and chemistries best meet your performance requirements.

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