Understanding Powder Coating

Wet painting methods consist of solids which are held within a liquid carrier. The liquid must evaporate before a solid coat of paint is produced. Powder coating is a technique used to apply dry paint to the surface being painted. This is a relatively new technique which was first used in Australia around 1967. It is rapidly becoming one of the most popular finishing techniques used today.

Powder coating contains no solvents and is applied directly to the surface. Each powder particle consists of resin, pigment, modifiers, and a curing agent. The powder is applied eletrostatically by either lowering the item into a bed of powder or by spraying the powder directly onto the product with a spray gun. The powder adheres to the surface until it is placed into a curing oven. The oven bonds and melts the powder into a high quality, durable finish.

The surface finisher has two primary types of powder to choose from. Thermoplastic powders will remelt when heated whereas thermosetting powders will not.

The Pros of Powder Coating

The quality of powder coating is superior to most liquid coatings because it provides a finished surface that is chip resistant, corrosion resistant, abrasion resistant, chemical resistant, ultraviolet resistant, and impact resistant. It has a greater tolerance for harsh weather conditions and is more cost effective.

The absence of solvents makes the entire powder coating process environmentally friendly. There are no volatile organic compound emissions and no generation of hazardous waste. With practically no environmental compliance issues the powder coating process is approved by the EPA.

Preparing the Surface

Surface preparation is different depending on the material used. Correct surface preparation is essential to ensure a high quality finished product. To prepare the surface of aluminum you must clean, rinse, etch, and rinse. Grease and oils must be removed with a weak alkali or neutral detergent solution. The surface is etched to remove heavy oxides. Aluminum is dipped into a chromate or phosphate solution which forms a conversion coating on the surface of the aluminum. Once this film is chemically attached to the aluminum it is finally rinsed in demineralized water. Demineralized water reduces the presence of chemical salts which can cause corrosion in humid conditions. This process has two functions. It provides a surface which the powder will adhere to and it reduces the chances of under film corrosion.

Preparing a steel surface may involve cleaning, rinsing, removing rust, rinsing, iron phosphate, rinsing, and acidulated rinse. Exterior application will involve cleaning, rinsing, etching, rinsing, grain refining, zinc phosphating, rinsing, and acidulated rinsing.

After acid cleaning the surface a grain refiner is used before zinc phosphating in order to prevent a coarse sandpaper-like surface with low adhesion. Hot dipped galvanized coatings will require cleaning, rinsing, etching, rinsing, grain refining, rinsing, zinc phosphating, then followed by acidulated rinsing.

Electrostatic Spray

An electrostatic spray gun electrostatically charges the powder causing it to wrap around the back of the part as it moves toward the air offtake system. The powder will cling to the part for as long as the charge remains on the powder. The item is placed in an oven with temperature ranges from 160 to 210 degrees. This creates an abrasion resistant coating which is solid and tough. While undergoing the influence of the heat the thermosetting powder goes through four stages before it comes to a full cure. Those stages are melting, flowing, gel, and cure. Depending on the powder, the finished product will have either a high gloss or matt finish.

Powder Coating Guns

Powder coating guns come in at least three types. The Corona charging gun uses electricity to generate the electrostatic charge. These guns can be either external or internal charging. The Tribo charging guns use friction to create the electrostatic charge. The friction is generated between the powder and gun barrel. The Bell charging gun will force the powder from the perimeter of the bell. Guns are the most commonly used process to apply the powder to the object surface.

Introducing Color

Color is generally added to the powder during the manufacturing process which is done before the powder reaches the coater. The color choices are practically limitless if you can afford to have the powder produced by a manufacturer. The coatings can be applied with several ranges of thickness. Color matching from one batch to the other is usually very consistent.

Installing and Maintaining

During initial installation the powder coating should be protected from abrasive materials. Mortar and brick cleaning chemicals can cause damage to the finished surface. Once properly installed, the surface is easily maintained with periodic washing. At least twice a year the powder coated finish should be washed using soapy water containing a neutral detergent then followed up with a clean water rinse.

With correct installation and regular maintenance the powder coating surface is practically permanent. If bonded correctly it will not crack, chip, or peel.

Powder Coated Products

The building market is now using powder coating on aluminum frames used for windows, doors, and modular furniture. Many light poles, guard rails, signs, and fencing projects are also being powder coated.

The automotive industry uses it on wheels, bumpers, hubcaps, door handles, decorative trim and accent parts. Motor sports hobbyists are now utilizing the powder coating process to finish sports cars, custom choppers, four wheelers, and classic automobiles. Motorcyclists live to polish and ride their shiny vehicles. Powder coating can be used to create a stunning finish which is flawless. A weekly wipe down and an occasional cleaning with a mild detergent will keep the metal shining like new.

Many everyday products also use powder coating. Light fixtures, antennas, and electrical components are a few. Shop owners have display racks, shelving, fixtures, and vending machines. In the office you can find powder coated metal furniture, computer cabinets, pens and pencils, and desk accessories. Parents have powder coated strollers, cribs, toys, and wagons. Farmers own powder coated tractors and equipment while homeowners have lawn mowers, barbeque grills, patio furniture and garden tools. For the fitness oriented they have powder coated golf clubs, bicycles, exercise equipment, and even snowmobiles. Many artists also now utilize powder coating in their sculptures.

Powder coating is rapidly gaining popularity as the best way to obtain a high quality, permanent finish which is easily maintained.