The paint coating on vehicles offers much more than mere aesthetics. It provides protection to the vehicle’s bodywork. To ensure this protection, a battery of tests is conducted to evaluate the resistance of the paint film components.
Most tests are regulated by the American Society for Testing and Materials (ASTM), which provides very precise instructions on how these tests must be performed. Here’s a brief description of some tests.
Adhesion (ASTM D3359)
Poor paint film adhesion could lead to delamination, flaking, and ultimately corrosion. Adhesion is verified using a cross-hatch test. A series of cross-hatched cuts are made on the finish using a special multi-blade cutter. Adhesive tape is then applied and pulled off. If the paint stays in place, the finish has passed the test.
Scratch Resistance (ASTM D3363)
Scratch resistance is measured with a pencil hardness test. A series of lead pencils is drawn across the surface at a 45-degree angle. The pencil that doesn’t mark the surface determines its hardness level.
Chemical Resistance (ASTM D1308)
Automotive finishes are exposed to various chemical substances. Whether it’s gasoline or bird droppings, these elements can degrade the paint film. The finish is exposed to solvents, acidic or alkaline substances at different concentrations over specified periods, and their performance is evaluated.
UV Resistance (ASTM D5894-21)
Finishes are exposed to UV radiation for specified periods. Colour retention, gloss loss, and physical degradation of the finish are measured. Good performance ensures long-term durability of the finish. The paint on a vehicle exposed to UV rays in Florida, for example, is likely to degrade faster than a vehicle in Quebec.
Corrosion Resistance (ASTM B117)
Rust is a vehicle body’s worst enemy. Moisture and road salt are the main culprits of corrosion. Manufacturers expose finishes to salt spray and evaluate the finish’s performance. The longer the resistance, the better it is for the vehicle.
Impact Resistance (ASTM D2794)
Whether from stones, hail, or minor collisions, an automobile’s finish risks being slightly dented and chipped. Impact resistance is tested using steel balls of different weights that are dropped onto the finish. The damage is then evaluated to see if the finish meets requirements.
Environmental Testing
Environmental testing for automotive finishes consists of a combination of outdoor exposure tests and accelerated laboratory testing. Auto manufacturers can’t wait years to know if a finish is durable long-term. Therefore, they simulate the stresses that the finish will undergo over several years.