How Does Powder Differ from Paint?
Paint in general is a solid pigment in a solvent solution. It is applied wet and either air-dries or is baked dry in an oven. As the paint dries, the solvents evaporate, releasing any VOC (volatile organic compounds) contained in the solvent, leaving a thin (less than 1mil) dry film of colored pigment and resin.
Powder coatings, in general, are finely ground plastic particles. The powder is fluidized using clean compressed air, and either pumped through a gun, electrically charged, and sprayed onto a cold, grounded part, or a hot part is dipped into the fluidized powder. In either case, after cooling the part is then placed into an oven where each particle of powder melts into the particles near it and together, they flow into a uniform film, ranging from 2 to 20 mils thick.
How Long does Powder Coating Last?
The life of the coating depends on the application. For corrosion and abrasion coatings, two months may suffice, however 2-3 years is not atypical. For outdoor applications, five to seven years with minimal color and gloss reduction is usual, however for patio furniture, rust may occur at welds within 1-2 years. High-end architectural applications meeting AAMA 2605 specifications can be warranted for 10 to 20 years. For electrical applications such as bus bars, coatings may last as long as 10-15 years. In general, the life expectancy of powder coating is longer than paint, making it a more reliable finish.
How Thick is Powder Coating?
Average cold application to a flat plate would be 1-3mils or .001″ to .003″. Application to a warm part can result in 3-5 mils. Spray or fluid bed dip on a hot part can achieve 8-12 mils, and multiple coats, depending on the powder resin, can yield a thickness in excess of 125 mils or 1/8 inch.
How is Powder Coating Applied?
All powder-coating applications begin by either fluidization of the powder with compressed air or through vibration of the powder. Finely ground plastic powder is placed in a reservoir that is attached to an air plenum. The plenum and reservoir are separated by a porous membrane, which allows only air to pass through it. When clean, compressed air enters the plenum, it moves through the membrane and aerates the powder, giving it a fluidized quality. In this fluidized state, the powder may be pumped like a liquid to a spray gun. There are two primary methods of powder coating: Electrostatic Spray and Dipping.
Electrostatic Spray: The most common method of powder application is electrostatic spray. The powder is pumped, using compressed air, from a fluidized reservoir through a spray gun. At the tip of the gun is a wire from an electrical power source, usually high voltage with micro amperage. The electricity from the wire creates a “corona” field area around the tip of the gun. When the powder passes through the corona field, the powder particles pick up an electrical charge. When these particles come in contact with a grounded metal part, they are electrostatically attracted to that part. The powder sticks to the part until the part can be placed in an oven where the powder melts and cures to the part.
Watch our video on electro-static powder coating.
Fluid Bed Dipping: Another method of application is called “fluid bed dipping”. The part is heated to a temperature above the melting point of the plastic. The part is then dipped into the fluidized reservoir and the powder in contact with the part melts onto it. When the proper amount of powder has melted on to the part, the part is removed, any excess powder is blown off, and the part is placed in the oven for final curing. Our largest Fluid Bed Dipping is 8’ long X 3’ wide X 4’ Deep.
Watch our video on Fluid Bed Dipping application of powder-coat.
What Colors are Available?
As with paint, there are an infinite number of colors and textures available, many of which are stock. Two common color standards that many suppliers use for color specification are RAL colors and Federal Standard colors. Unlike paint, powder cannot be made a pound at a time, so color matching is often more costly. Fortunately, there are many different powder suppliers, and they each have their own array of colors and textures. The RAL Color Chart is available below for your convenience.
How do the Powders Differ?
There are two main types of powder coatings: Thermoplastic and thermoset. Thermoplastic powders flow when they are heated, but do not fully cure, or crosslink. After they cool, if they are re-heated, they will re-soften. They never completely set up. Thermoset powders cure when they are heated, and their resins crosslink, finishing a chemical process that cannot be reversed.
The basic powders are epoxy, urethane, nylon, vinyl, and floropolymers. Each of these resins has its inherent strengths and weaknesses, depending on the application.
What if I Just Wanted Something Coated Black?
Henry Ford would have had a hard time as a powder coater. There are probably over 50 different ways to make something black. There are at least 20 different shades of black, and each powder supplier has several. There is flat black, low gloss black, varying percentages of gloss black, full gloss black, black texture, black wrinkle, black hammertone, etc. There is also black epoxy, black polyester, black nylon, black hybrid, etc. So, if you just want it black, you may still have to answer a few questions.
Can You Match a Color?
Yes. If a customer has a paint chip, a powder supplier can match it, both color and gloss. It may not be an exact match, but it will be very close. Also, colors approaching red, orange, and yellow are more expensive, and you may have to fulfill a minimum order quantity. So, if you want to coat a doorknob to match the electric yellow paint on your house, you may end up buying enough powder to coat the entire floor of the house, for the cost of a used sedan.
What is Your Turnaround Time for Parts?
Our normal turnaround is 4 to 8 working days. That means if we receive your part on Monday the 1st, we will usually ship it no later than Thursday the 11th. Most parts ship within one week, and repetitive jobs have scheduled production days.
What is Your Part Size Capacity?
Currently, our batch capacity is from 8ft high to 2ft wide and 5ft tall. Our line capacity is 25ft long, 3ft wide, and 8ft high.
How Do You Package Finished Product?
For smaller jobs, we use cardboard, foam, and shrink-wrap for packaging. For repeat jobs, we recommend reusable containers. Jobs are usually quoted with the customer responsible for all packaging supplies other than cardboard, foam, shrink-wrap, and banding.
What Quality Checks are Done?
Incoming parts are briefly inspected for damage. In process, parts are checked for cleanliness, proper masking, thickness, cure, and adhesion. Records are kept for wash line titration levels, thickness, cure, and adhesion tests. When required, holiday spark testing can be done to 20,000 volts, cure temperature recordings can be made, and process and material certifications can be sent with finished products.
What Environmental Issues Do You Face?
As with all manufacturers, environmental concerns are paramount. One of the reasons that the powder coating industry is growing is the fact that most powders contain no VOCs. They are non-flammable, non-toxic, non-hazardous inert plastic powders. There are no regulatory constraints involved with the powders directly. As far as wastewater is concerned, our batch cleaning uses iron phosphate which requires disposal through a licensed industrial waste management company. All other processes are in full compliance with environmental regulations. We utilize Henkel Bonderite NT pre-treatment systems which is sustainable, non-polluting, and accepted by municipal wastewater treatment. All non-process and off-line wastewater is sent directly to municipal sewer plants for treatment.
Is Powder Cost Competitive with Paint?
Even though the material and process cost of powder coating are higher than they are for paint, powder remains competitive. Government and environmental regulations have greatly affected the handling and disposal of paint and paint biproducts.