What Is Powder Coating?
Powder coating is a multi-step finishing process. In the first step, a product (usually a metal part) is cleaned and prepared for coating. Next, it is coated with a fine powder. In the final step, the part is moved into a curing oven, the product is then heated in the oven, allowing the powder to melt and flow into a uniform coating that adheres to the part surface. This creates a durable and attractive coating around the product once the melted powder cools and hardens.
Our Powder Coating Process
Pre-Treatment/Surface Cleaning
To achieve the best results with our powder coating process, we clean the surface of all products by pretreating them, so they are free of dust, debris, oil, rust, old paint or finish material. Anything left on products prior to coating will affect the powder’s adhesion and durability.
- Depending on the product and customer requirement we pretreat the product:
- If oils, solvents, or chemical residue covers any part of the product surface, we will immerse the parts in a detergent and/or chemical pre-treatment agent, such as iron phosphate. We then use hot water or steam to clean and then chemically prep the parts.
- In some operations, we may use a heat dry where just-washed parts are heated to evaporate any water or chemistry still on them. This step can also help parts reach an optimum temperature for powder application. This can be done by placing the parts in an oven or on a hot plate.
- Based on customer request and mostly for overseas cold weather customers the biggest threat to the parts is rust and its corrosive effects. We either Hot Dip Galvanize or Zinc Electroplate the parts before powder coating them.
Powder Coating
Our expert Powder coaters apply with a special Powder Spray Gun, best quality electrostatically charged powder giving an even effective coat to all products. The spray is conducted in a clean spray booth ensuring efficiency.
Powder Curing Oven
After product are powder coated, the final step is to place them inside a specially designed Powder Curing Oven at a set temperature. Once the oven is up to the set temperature, the temperature stabilizes. The coated products are exposed to precisely heated air for a set period. Once the curing process is complete, the parts are removed and allowed to cool before being handled.
Inspection
Coating Film Thickness Test
A film thickness test determines the thickness of the powder on the part once it’s been cured which we determine with the help of a Dry Film Thickness gauge. A common range to look for is 2-3 dry mils (thousandths of an inch). A coating of 2-3 mils usually provides complete coverage of the powder over the metal.
Uniformity/Cure Test
Cure test ensures that there aren’t any areas of over bake (where the powder has cured in a dry and brittle fashion) or under bake (where the powder has not completely cured). A cure test is conducted by rubbing 20 double rubs (back and forth over the same spot) of methyl ethyl ketone-soaked cotton swab lightly over a cured panel or part (an inconspicuous area of the part is to be used if acceptable). Usually,we can see failure after about only three or four passes. If the finish deteriorates to the point that we can see exposed bare metal, either cure is lacking,or the powder is defective. If the coating softens but then recovers, then it is fine.
Adhesion Test - Tape
Before this test we make sure the part or test panel is clean and dry. Using the utility knife, we scribe (cut through the coating to the metal)a section of the product five times one way and then again 5 times perpendicular to the first scratches. This gives part’s coating a grid-like appearance. After making the cuts, we put a piece of tape over the grid and smooth out any air bubbles. The tape completely covers the grid. We pull the tape off aggressively and look at the tape and the part. An acceptable result shows only a little of the powder coming off from the grid cuts. If a square or two of coating is removed, adhesion can be suspect. If coating comes off in a sheet, then we have an adhesion failure.
Visual Inspection
All products are visually inspected at the packing time to make sure that there aren’t gaps in coverage, bubbles, warping or poor coating application.
Corrective Action
Rejected items are separated and QA team inspects each rejected item and decides action items which could be repair for minor defect by touching or re-coating for defects of considerable size.
