Chip Resistance Test of Coatings is done by using Gravelometer following ASTM D3170 test method. This test determines the chipping resistance of coated surfaces while simulating the effects of gravel or other small items on automotive parts.
Chip Resistance ASTM D3170 determines the chipping resistance of coated surfaces. Coatings such as paints, clear coats, and metallic plating are prone to chipping damage caused by the impact of small pebbles, gravels, or some other flying objects. This test is designed to produce a controlled amount of impact by the gravels on the coated panel and simulating the effects of gravel or other small items on automotive parts.
This test is done using agravelometer. The test plate with a coated surface is mounted inside the gravelometer. Standard size road gravels, approximately 300 pieces, are projected through a controlled air blast at the coated specimens. The process is conducted under controlled temperature conditions, generally ambient temperature. Next, the test sample is taken out of the Gravelometer and softly wiped off using a clean cloth. After this, a tape is applied to the whole of the impact surface and then removed to pull off any loose debris of the coating material. To determine the extent of chipping, the test specimen is compared to standard transparencies given by SAE. The effect of gravel impact on the coated surface can also be evaluated by visual examination.
A coated metallic panel of dimensions 4 inches by 12 inches is used for the test.
Results are provided in the form of Chipping Ratings, which are letter-number combinations that communicate different chip sizes and the number of chips for each size. The chip sizes are designated by letters and the numbers are given to designate the number of chips of that size. For example, the combination B6 indicates 10-24 chips of 1 to 3 mm in size. Another criterion is the Point of Failure, which describes the coating layers where the primary failures occur. For example, P/T indicates that primer and the topcoat is the point where failure has occurred.