FREQUENTLY ASKED QUESTIONS

What is powder coating?

Powder coating application is defined as the process of painting a surface with paint in powder form using application equipment (powder coating guns) that transmits an electrical charge to the paint so that it can adhere to the parts. Once the part is covered with paint, there is a curing process where the paint is taken to its melting point. The liquefied paint flows over the surface forming a uniform layer on the part that solidifies into a strong and durable finish, resistant to scratches, cracking, blistering, UV radiation, and oxidation.
What advantages do powder coatings have?

QUALITY: The characteristics of powder coatings enable having consistency and uniform finish that are superior to other paints, avoiding problems such as lack of paint, drop marks, paint spills and bubbles. They provide extremely resistant finishing that gives an added value to the products. In general, the performance of powder coatings in properties such as impact resistance, flexibility, and corrosion resistance are superior to those in liquid paint. Powder coatings enable resistance to cracking and flaking during the product’s lifetime, making this a property that is used in marketing when offering a product with a “powder coating” since it creates an image of strength.
 
ECONOMIC: The application of powder coatings usually offers savings in energy costs, labor costs, re-work costs, use of raw materials, containment and production line efficiency when compared to the application of liquid paint. The advantage, both for the manufacturer and the final consumer of a product with a powder coating, is that they will obtain a product with a superior finishing at a reasonable cost.
 
ENVIRONMENTAL: Nowadays, environmental issues are of great interest and importance to the government and general public. Unlike many liquid paints, powder coatings comply with environmental regulations. Liquid paints usually contain solvents that contribute to air pollution and, in some cases, affect the ozone layer. Powder coatings are free of these pollutants. Liquid paint processes can generate sludges that will have to be confined for disposal. Correctly formulated powder coatings do not generate this type of waste.
What causes non-adherence of paint?

Lack of adherence of the paint can generally occur due to two reasons: poor pretreatment and lack of curing. To avoid a poor pretreatment, ensure regular titration of the tanks and assure that the oil to be removed from the parts is water soluble and silicone free. To detect a lack of curing, it is advisable to use a data pack test to ensure that the parts reach the necessary temperature for the recommended time as indicated by the paint’s technical data sheet.
How can I keep the threads or certain parts from getting paint on them?

There are different types of caps and plugs, as well as tape which resists the curing oven’s temperature, that are used to keep the paint from adhering to critical parts and are removed at the end of the painting process. Most caps and plugs are reusable.
How does the powder coating paint gun work?

The powder coating spray guns use a container called a “Hopper” where the paint is deposited, and air is introduced through a membrane in the bottom to keep the paint in fluidization. The fluidized paint is taken up with a pump using compressed air and is transferred to the tip of the gun. The gun is designed to convey an electrical charge to the paint, which will adhere to the part that is grounded with the conveyor. The electrostatic charge can be discharged through voltage, which is called a “Crown” system, or through dust friction along the barrel of the gun, called a “Tribo” system.
What are the typical quality tests used to evaluate powder coatings?

Salt spray test (ASTM B117)
A 5% saline solution at a temperature of 33 – 36 °C is used in a sealed chamber. An “X” shaped scratch is made reaching the metal substrate on the panel or part to be evaluated. It is introduced into the saline chamber and inspected every 24 hours. For iron phosphate pretreatment, the common requirement is 500 salt spray hours. After the time requested by the customer has passed, the part must be removed from the chamber and evaluated for peeling greater than ¼” in any direction from the “X” shaped line.
 
Impact Test (ASTM D2794)
A phosphatized and painted 0.036” gauge panel is tested. The paint must resist an impact with a ½” Gardner brand bullet at a height of 26”. The direct and reverse impact must be evaluated. There should be no cracking or loss of adherence in the impact zone. It is recommended using 3M 250 or Permacel #99 adhesive tape applied on the impact zone. There should be no paint peeling upon removal of the tape.
 
Chemical Resistance (ASTM D1308)
About 10 drops of test solvent, consisting of toluene 95% weight and methyl ethyl ketone 5% weight, are placed on the painted surface. Let stand for 30 seconds. Clean with a soft, dry cloth. The coating should not show more than a slight circular mark.
 
Paint Adherence (ASTM D3359)
Parallel lines are scratched on the painted substrate ensuring they reach the metal. For thicknesses between 2 – 5 mil. it is advisable to make 6 lines 2mm apart and 20mm long. Afterwards, another 6 lines are to be made, perpendicular to those previously created. It is recommended using 3M 250 or Permacel #99 adhesive tape applied over the scratches. Upon removal of the tape, no paint should flake off within the grid and the tape may only contain small traces of paint along the lines marked.
 
Hardness Test (ASTM D3363)
“Faber-Castell” brand pencils are used to measure the hardness of the paint. Usually, the customers’ specifications request that the paint shall not show markings made with a 2H pencil.
 
Flexibility Test (ASTM D522)
The test is carried out on phosphatized and painted 0.036” gauge panels. The paint must resist bending to 180° over a tapered mandrel ¼” in diameter. There should be no cracking or flaking of the paint. It is advisable to apply 3M 250 or Permacel #99 adhesive tape. There should be no flaking upon removal of the tape.
 
Gloss Test (ASTM D523)
A painted plate or a flat plate is tested with a Gardner gloss meter at 60°. The paint’s gloss should not vary more than +/- 5% from the specs on the paint technical data sheet.
Which types of resins can be applied with powder coating?
Which types of resins can be applied with powder coating?
What is the Faraday´s Cage Effect?

Faraday´s cage occurs in corners where there are walls at 90° angles. These corners create an electromagnetic field that keeps paint from being deposited normally. To avoid Faraday´s  cage and cover the part evenly with paint, the painting equipment’s voltage parameters must be adjusted and have these areas retouched manually.
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