Adhesion test
The purpose of the cross -hatch test is to check the adhesion of the powder coating to the metal substrate. It is performed by cutting a cross-hatched grid pattern all the way into the coating and onto the substrate. Special pressure sensitive tape is then applied to the cross-hatched area and quickly peeled off at an angle close to 180°. The area is then inspected to see if any coating has been peeled from the substrate.
Mandrel Bend – This test checks the elasticity and adhesion of the powder coating to the substrate. The cured sample plate is placed into a small device that bends the plate onto itself. Coating should not crack or lose adhesion in flexed areas.
Impact Test – Similar to the mandrel bend test, the impact test deforms a sample panel to test powder coating adhesion. A sample plate is placed in the testing machine and a ball is dropped on it to create a deep depression. Likewise, powder-coated coatings should not crack or lose adhesion to the substrate in the impact area.
Durability Test
Salt Spray Test – This is a corrosion resistance test performed by drawing a line or "X" on the surface of a finished powder coated panel. The panels are then placed in the chamber, to which a corrosive mist is applied. The panel is removed from the chamber at set intervals and the distance the coating "creeps" from the scribe is measured and recorded. If the amount of creep does not exceed the allowable distance within a predetermined time interval, the panel passes the test.
Cure and finish testing
MEK Rub Test – This test is used to ensure that powder coatings are properly cured to the substrate. Apply methyl ethyl ketone (MEK) to the surface of the part or panel and wipe with a cotton swab. Degradation or loss of paint adhesion to the substrate was observed in this area.
Color Matching – Once our powder coated parts have been placed in the oven to cure and cool, the finished color is compared to an approved color powder sample. This visual inspection is a common and quicker way to check color. If discrepancies exist, the color can be measured with a spectrometer to provide data that can be compared to known samples and tolerance ranges for a particular color.
Gloss Measurement – The gloss of a powder coated finish is verified by measuring the specular reflection of its surface. The test is performed using a gloss meter, which shines light onto the part's surface at a fixed angle and then measures the amount of light reflected from the part. If the measurement is out of tolerance, it may indicate that the powder coating is not curing properly.
Coating Thickness Test
In order to obtain better coating performance, each powder has a certain thickness range and needs to be used within this range. HUI makes this measurement at two different stages in the powder coating process. Once the part comes out of the powder room, our powder room technicians take the first measurement using a dry gauge. Then, if the technician applies the correct amount of powder to the part, it can be passed on to the painter. Immediate feedback is beneficial because it catches possible lightly or heavily coated parts before the powder cures and it is too late to fix the problem. After the part has cured, check the mil thickness again to ensure that the coating thickness is within tolerance for the specified powder.
