Powder coating is a method used to apply a protective and decorative coating to products such as white goods, aluminum extrusions, and automobile and motorcycle parts. Newer technologies have allowed other materials, such as medium-density fiberboard (MDF), to be powder coated using different methods. First used in Australia in 1967, powder coating has become one of the most popular surface finishing techniques in use today.

Powder coating uses a very fine dry powdery-resin that contains a color pigment. The resin is charged by electrostatic methods and then using a spry gun is applied to the metal surface. Because the powder is charged it will adhere itself to the surface of the metal. The metal is then placed inside an industrial oven and baked at approximately 400 degrees or more, which will cause the powder to allow it to flow and form a skin that is more uniform and durable finish, which is resistant to chemicals, wear and tear, and chipping.

Powder coating has a far better impact resistance, flexibility and corrosion resistance than that of liquid paints. Powder coating is a very cost saving and effective alternative to liquid paints. In addition, in compared to liquid paints, powder coatings are environmentally friendly, because they are regulated and free from pollutants.

Powder coatings are most commonly applied by spraying the powder on, using an electrostatic gun, or Corona gun. The gun conveys a negative electric charge onto the powder, which is sprayed on the object that is grounded. Once the object is coated, it is then heated, melting the powder causing it to form a hard coating. Some powder coating company?s use a technique in which they heat the metal prior to spraying the powder so that the powder goes onto a hot surface, however this can lead to problems such as runs caused by excess powder. Another process uses a different type of spray gun called a Tribo gun. The Tribo gun charges the powder by friction, in much the same way you create static electricity by walking across the carpet. The powder becomes positively charge from being rubbing along the sides of a Teflon tube located inside the barrel of the gun. Once charged, the powder particles then adhere to the grounded substrate. However, when using a Tribo gun, it requires a different formulation of powder than that used more commonly in the Corona or electrostatic guns.

The Fluidised Bed method is another method of applying powder coating. With this method, the substrate is heated and then dipped into an aerated, powder-filled bed. The powder adheres and melts to the hot object, and then further heating is required to finish curing the coating. The Fluidised Bed method is most often used when there is a need for the thickness of the coating to exceed 300 micrometers.

Powder coating is expensive, so why should anyone spend that much money. To answer that question, I can only say—You get what you pay for. Yes, powder coating does look just like liquid paint. However, it will protect your motorcycle or other item as if you?ve coated it in armor. Powder coating is an extremely durable, very decorative finish that will out last any liquid paint finish applied to products. It is so popular, that nearly every quality made item is powder coated from appliances, to furniture to the clear powder topcoat on many automobiles. Powder coating is available in virtually any color or finish, including matte or smooth imaginable. It is rust-free, scratch resistant, chip, resistant, resistant to acids and solvents, and it is ecologically friendly.

Products such as outdoor barbeques, swing sets, patio furniture, and garden equipment, appliances, stadium chairs, railings and structural enforcements, tools, engine parts, golf clubs, cart s, ski poles, bindings, computer cases, farm equipment, exercise equipment, store racks, and baby strollers are only a few products that are powder coated. Powder coating makes these and other products chip resistant and fade resistant so that the finish and color will stay looking new for many years instead of a few months.

Originally used only on metal products, today advancements in the technology have developed lower temperature powder coatings that make it possible to coat such materials as ceramics, plastics, and even wood and by adding a clear topcoat, these products look new longer. To put it simply, powder coating protects your investments better, and longer than liquid paints and coatings.

The electrostatic powder coating system is the application of electrically charged powder coating materials to grounded object or parts. The object is then heated causing the powder to flow and cure. However, if the uncured powder coat is damaged or blemished in any way, then the powder can simply be blown off with air or vacuumed and a new powder coat applied.

There are four basic pieces that make up the electrostatic powder spray coating system, which are the powder feeder, power unit, electrostatic spray gun, and powder booth recovery system.

The spray gun is supplied with powder from a feeder unit, which diffuses the powder with compressed air into a fluid-like state. High velocity air flows through a venturi and siphons out the fluidized powder, which is then propelled through the powder feed tubing to the spray gun.

The powder feeder also allows for a controlled flow of powder to the guns. The system has independent controls for powder and air volume, which allows for adjustable dilution ratios so that the desired thickness coverage can be attained for each object. The powder feeder has the capability of providing ample discharge pressure and velocity to feed an electrostatic gun to approximately 25 feet away.

When the powder leaves the spray gun, it does so in the form of a diffused cloud, which is propelled toward the workpiece. A charging electrode at the front of the spray gun is powered by a high voltage, low amperage power unit, which emits a field charge that imparts a negative charge onto the particles of powder. This negative charge causes the powder to seek out and attach to the grounded work piece.

In closing the functions of the electrostatic powder spray gun are to shape and direct the flow of powder, control the size, shape, and density of the powder pattern, impart an electrostatic charge to the powder being sprayed and control the accumulation of powder onto the objects that are being coated.

The most popular powder coating systems are the turbo electric or corona/electrostatic charging spray guns. These systems have been used for several years and have both seen significant improvements over these years. When deciding to purchase a spray gun, possible the most important question to answer is, which one would be right for you and your business? To answer this question, first it's important to understand the basic principles behind of each type of spray gun and the type of results each delivers.

Corona/ Electrostatic: The corona spray gun has an electrode located near the tip of the gun. This electrode is charged with a high voltage, low amperage power unit, which emits a field charge that imparts a negative charge onto the particles of powder that results in the powder being attracted to the grounded work piece. Positive polarity generators are used primarily for charging nylon powders.

The corona spray gun works by producing a corona discharge which is an electrical discharge brought on by the ionization of the powder surrounding the electrode, which occurs when the potential gradient exceeds approximately 30 kV per centimeter, however these conditions are insufficient to cause complete electrical breakdown or arcing.

Powder particles exiting the gun travel near the electrode where they accumulate a negative charge. However, not all of the powder particles accumulate a charge as some are shielded from other particles in the charging zone. These particles may be carried and deposited onto the object through the flow created by the charged particles, similar to a tree branch being carried in a river current. Tribo: Tribo-charging guns create a charge on the powder particles via intimate contact with polytetrafluoroethylene from the gun walls. This occurs when the two differently charged materials are brought into contact, and a transfer of electrical charge occurs eliminating the imbalance between the two objects. The degree and direction of the charge transfer depends greatly on many factors, such as the chemical and electronic structure of both materials.

Polytetrafluoroethylene or PTFE, which is commercially known as Teflon is typically used as the powder contact walls in a Tribo gun. The powder particles are a composition of resin, pigment, fillers, and depending on the type of effect could include other additives such as metallic flecks. Most finishing powders become positively charged when they come in contact with the Teflon walls.

Tribo guns charge the powder particles when the powder particles contact the Teflon walls. The more contact the powder particle makes with the walls the greater the charge on the particles. As long as there's Teflon in the gun for the powder to make contact with, the powder will become charged. For this reason, the airflow from the gun plays a very important with a Tribo gun transporting the powder particles onto the object being coated.

Powder containment is the first requirement of any powder coating system, as breathing in powder spray dust is hazardous to one's health. In addition, ADI, which is the mixture of Air, Dust, and an ignition spark, can cause the dust to catch fire or even explode. To properly contain oversprayed powder, the booth must be designed to provide an average face velocity between 80 fpm and 100 fpm airflow over all openings with the exceptions of: parts taller than 6?0?, parts that are heated above 120oF, short hook up to but not exceeding 18?, and cross drafts of excess of 60FPM in the booth area.

If there is too much airflow, the powder will be drawn away from the parts being coated. Many shops that have an in creased airflow tend to overcompensate with a higher powder-flow rate and decrease first-pass transfer efficiency. This can and has lead to poor application finishes.

Another important factor to consider in the powder booth design is the canopy or enclosure, which contains the over-sprayed powder. The booth canopy resembles a small room with four walls, a floor, and a ceiling. The ceiling has a slot, which runs lengthwise that hangers from a conveyor protrude from to support the parts, or objects that are being coated. The main goal is for the parts or object being coated to receive high first-pass transfer efficiency therefore the powder must be attracted to the part or object and not the walls, floor and ceiling of the booth. To accomplish this, the area around the spray guns must be constructed out of low, non-conductive material, allowing the electrostatic field emitted by the powder guns to attract the powder the part and not the walls, floor or ceiling of the booth.

Distance:

Gun to booth wall distance and gun to part distance are booth very critical issues in receiving high first-pass transfer efficiency. Therefore, the tip of the powder gun must be a minimal of 12? inside the boot to ensure that the electrostatic field is attracted to the object being coated and not the booth canopy. If the powder booth is not wide enough to place the gun inside the booth, then booth wall extender can be added at the gun opening to allow for added space between the tip of the gun and the booth wall. This will also shorten the time needed for booth cleaning during color changes as well as result in more powder being attracted to the part.

There are many variables in the placement of the gun, which depend on the line speed as well as the part specification. However, the place of the gun is usually 8 to 12 inches from the part being coated.

Another vital factor with the powder booth is the issue of humidity and temperature as both can greatly affect the performance of the powder coating system. The powder coating system should always be installed in an environmentally controlled room where the temperature remains between 70 to 80 degrees Fahrenheit and the humidity does not go below 47% nor exceed 55%. Any change in either the temperature or the humidity will affect fluidization, filter efficiency, filter life, as well as have an effect on the powder.

When purchasing the equipment you will need for powder coating, the most expensive investment will be the oven. Once the part or object has been powder coated it is then placed in the oven, where it is baked at 400 degrees Fahrenheit for 10 minutes. If you do not have an oven that will allow you to bake items at 400oF for 10 minutes, you cannot powder coat.

As the part bakes in the oven, the powder paint melts, flowing into a beautiful and very durable finish that doesn?t contain any unsightly runs or drips, which are often seen when wet paint is used. If mistakes are made prior to baking, the powder coating can easily be blown with a low-pressure air nozzle and the part recoated. However, once the item has been cured in the oven, mistakes can only be corrected by removing the finish with sand blasting or burning it off. There are cold liquid strippers available, however they are extremely slow, and hazardous and have been known to damage the metal.

The size of oven that you will require will depend on the size of the items you plan to powder coat and how many items you will be powder coating at one time. The larger the oven, the more products you will be able to powder coat at one time, however, the as the oven size increases so does its cost. Small 6′ x 8′ x 10′ walk-in gas ovens average in priced of approximately $30,000, while larger 100′ ovens with pass-through conveyers can cost in excess of $100,000.

When choosing between gas and electric ovens, they both work equally well. If properly designed, infrared ovens work well also. Electric ovens do have one drawback in that they take longer to reach the proper baking temperature. Therefore, if this will be a problem for you, then gas should be your best choice.

When powder coating, the finish is very durable. However, chipping can be a problem with powder coating if the part was not baked long enough and/or kept at the proper cure temperature.

Nearly any metal part or object can be powder coated. However, in order for parts to be powder coated, they must be able to withstand the curing temperatures of approximately 350-450F for 15-30 minutes. Because of this, parts such as cylinder heads, that are made out of plastic substrates or other materials that might warp cannot be powder coated unless low cure powders are used. Unfortunately, many paint shops are not skilled in this application.

In addition, the parts must be able to also endure the powder coating's additional thickness, as they are thicker and heavier than liquid paint. Parts such as cylinders and cylinder heads should not be powder coated. These parts are designed to dissipate heat by powder coating these parts it can inhibit their performance.

Other items such as aluminum wheel spindles, wheel billets, scuba tanks, etc. should not be powder coated either unless they are powder coated using cooler curing powders. The reason is that the higher temperatures required to cure standard powder coatings can causes the ductile aluminum to become brittle.

The powder pump supplies powder to the gun in a uniform and steady rate. Powder pumps usually use a venturi to deliver the powder from the supply hopper to the powder spray gun. For first-pass transfer efficiency, the operator wants to use the lowest flow rate as possible while still maintaining coverage through each spray gun being used. The reason for this is that the more powder that passes over the gun electrode creates a shielding so that each particle picks up less of a charge. Therefore, less powder is more effective when dealing with transfer efficiency. To achieve first-pass transfer it is better for companies to add additional powder guns and maintain outputs low than to increase the output of the existing guns. The majority of powder pumps are made with engineered plastic to provide the maximum resistances against wear. In addition, many are available in configurations for either corona-charging or Tribo-charging spray gun systems

In the past, powder coating was used only for metal. This was mostly due to the facts that wood had moisture related to their sap content, have low conductivity, and exposure to high temperatures caused the gain or fibers to rise and the wood to be distorted or charred. However, because of the development of UV-powder coating and thermosets, materials such as wood, plastic, and preassembled parts can now also be powder coating.

The process for coating wood using the new UV or thermoset powders is similar to those using conventional powder coatings for metal. When thermosets are used, they are heated to the powder's melting point until the coating particles fuse into a continuous coat. With UV-powder coating, the powder is heated in a melt flow oven, and then cured for a few seconds under UV lamps. When powder coating wood, the application steps are as follows:

1.Preconditioning is required, which involves the wood product being heated in an infrared or convection oven in order for the wood to reach the required conductivity, and release gasses. The surface temperature is equalized between 200 and 220oF before it enters the spray booth. The moisture in wood must remain equalized over the entire surface at approximately 4 to 6% or greater in order to maintain conductivity for the powder to adhere to the surface. Because heat causes evaporation of moisture, carefully controlled preheating is mandatory.

2.The application of the powder coating is the same as with conventional powders with the use of either a Corona or Tribo spray system.

3.The curing process depends on if UV powders or thermosets were used. UV powders are initially melt flowed in infrared ovens or in convention ovens, then cured under UV light for a few seconds, whereas thermosets are cured by infrared or convention ovens. Curing times, temperatures, settings, and wavelengths will vary with film and substrate thickness, powder, and substrate size and shape.

4.The cooling process can occur in the open air, or thermosets may be placed in a forced air tunnel.

Once the wood product has been coated, recovery systems that use cyclones or filtration to recover overspray can successfully recover approximately 99.9% of the oversprayed powder. The reclaimed powder can be reused as is, thus adding to the economical benefits of UV-powder coating.

Powder coating has a far better impact resistance, flexibility and corrosion resistance than that of liquid paints. In addition, powder coating is a very cost efficient and effective alternative to liquid paints, plus it is environmentally friendly, because it is regulated and free from pollutants. Because of these and many more benefits, powder coating is used on literary thousands of products today.

Appliances: The appliance industry uses powder coating on the front and side panels of ranges and refrigerators, washer tops and lids, dryer drums, air-conditioner cabinets, water heaters, dishwasher racks, and cavities of microwave ovens. In addition, powder coating has replaced porcelain enamel on several washer and dryer parts.

Automotive: The automotive industry uses powder coating on wheels, bumpers, hubcaps, door handles, decorative trim and accent parts, truck beds, radiators, filters, and numerous engine parts. BMW and Volvo were the first to use a clear powder topcoat, which provides excellent protection to the automobiles color coat, ensuring that the car will maintain its showroom shin longer.

Architecture/Building: The architecture and building industry has benefited as much from powder coating than any other industry. Powder coating has been used on rebar, tools, as well thousands of commercial, industrial, government, residential, historic and institutional buildings world wide.

Everyday Products: There is an immeasurable amount of everyday products that are powder-coated including lighting fixtures, antennas, and electrical components, tractors, farm equipment, golf clubs, golf carts, ski poles and bindings, snowmobiles, bicycles, and exercise equipment, display racks, shelves, store fixtures, and vending machines, office equipment, metal furniture, computer cabinets, mechanical pencils and pens, thumbtacks, and other desk accessories. Other items include baby strollers, cribs, metal toys, wagons, tricycles, hobbyhorses, etc. Around the home the following you?ll find that the following items are also powder coated: lawn mowers, snow blowers, barbecue grills, patio furniture, garden tools, electronic components, bathroom scales, toolboxes, and fire extinguishers. Nearly every product that we use today is powder coated, which ensures that we will be able to use that item longer.

Non-Metal Products: If you thought that powder coating could only be used on metal, guess again. Because of recent technology developments of powder that can be cured at lower temperatures, powder coating can now be used on ceramics and some wood and plastic applications. Powder coating on wood has grown to include such items as home-office furniture, kitchen cabinets, children's furniture, and outdoor grill tables. Powder coating ensures that these products retain their new look much longer.