Some application specific cart products have a powder coated finish and as with any finish applied to any product, we need to test the applied powder coat to ensure that the finish will last.
Below are descriptions of some of the tests commonly used to verify a powder coating's ability to finish, cure properly and withstand the environmental conditions your cart will be used in.
Adhesion test
Cross hatching. The cross-hatch test is designed to test the adhesion of powder coatings to metal substrates. This is done 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 degrees. The area is then inspected to see if any coating has been peeled from the substrate.
The shaft is bent. This test checks the elasticity and adhesion of powder coatings 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 onto it to create a deep depression. Likewise, powder-coated finishes should not crack or lose adhesion to the substrate in impacted areas.
Durability Test
Salt spray test. This is a corrosion resistance test, performed by scoring or "Xing" the surface of a finished powder-coated panel. The panels are then placed into a chamber where a corrosive fog 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.
Curing and Appearance Test
MEK friction test. This test is used to ensure proper curing of powder coatings on 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 the powder coated part has cured and cooled in the oven, the finished color is compared to the approved color block sample. This visual inspection is a common and quick way to check color. If discrepancies exist, the color can be measured using a Spectrophotometer to provide data that can be compared to known samples and tolerance ranges for a particular color.
Gloss measurement. The glossiness of a powder-coated finished product can be 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 good coating properties, each powder has a certain thickness range and needs to be used within this range. This measurement is made at two different stages in the powder coating process. After the part comes out of the powder room, the powder room technician takes the first measurement using a dry gauge. Technicians can then communicate to the coating engineer whether they are applying the correct amount of powder to the part.
This 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.
