Chip Resistance ASTM D3170
Chip Resistance of Coatings (Gravelometer) ASTM D3170, SAE J400
The Gravelometer is an essential tool for evaluating the durability of surface coatings, such as paint, clear coats, and metallic plating, to chipping caused by flying objects like gravel. This test is commonly used to simulate the effects of gravel or other debris on automotive parts.
Test Procedure
The test procedure involves mounting the sample at the back of the Gravelometer, which then projects approximately 300 pieces of gravel using air pressure. After the impact, the test sample is gently wiped off with a clean cloth, and tape is applied to the entire surface. Upon removing the tape, any loose fragments of the coating are pulled off, and the appearance of the tested sample is compared to standard transparencies supplied by SAE. The test results are then used to determine chipping ratings, and a visual examination can be used to describe where in the coating/substrate system the failure has been induced.
Specimen size
The Gravelometer requires a coated panel with a size of 4 inches by 12 inches.
Data
Chipping ratings are determined based on letter-number combinations, where the letter designates the size of chips being counted, and the number represents the number of chips of that size. For instance, B6 indicates 10-24 chips that are 1 to 3 mm in size. Point of Failure refers to the coating layer where the primary failures occur. For example, P/T indicates that the point of failure is between the primer and the top coat.
Conclusion
The Gravelometer is a crucial tool for evaluating the resistance of surface coatings to chipping caused by flying objects. This test provides important data that can help in product development and end-use performance testing, particularly in the automotive industry.
Test method (overview)
The ASTM D3170 standard, titled "Standard Test Method for Chipping Resistance of Coatings," provides a comprehensive methodology for evaluating the durability of coatings against chipping caused by stones or other flying objects. Here's a detailed breakdown of this test method:
1. Scope
1.1 Objective: Determine the resistance of coatings to chipping.
1.2 Units: Primarily metric units.
1.3 Safety Considerations: Users must establish appropriate safety and health practices.
2. Referenced Documents
Lists ASTM Standards (D 609, D 823, D 1005, etc.) for preparation and measurement techniques relevant to the test.
3. Summary of Test Method
3.1 Process: Standardized gravel is blasted at coated specimens under controlled temperatures. Chipping is assessed post-impact.
4. Significance and Use
4.1 Application: Vital for industries (e.g., automotive) where chipping resistance is crucial. Performance at low temperatures is a key consideration.
5. Apparatus
5.1 Gravelometer: Two types specified with design requirements.
5.2 Gravel: Defined size and type.
5.3 Tape: Specifications for the tape used in the test.
5.4 Temperature Equipment: Options for temperature control.
5.5 Transparent Grid: For chip counting.
5.6 Chipping Rating Standards: Photographic standards for assessment.
6. Test Specimens
6.1 Specifications: Details on specimen composition, preparation, and size.
6.2 Coating Details: Information on coatings used on the specimens.
7. Procedure
Steps to condition specimens, set up the gravelometer, perform the test, and post-test procedures including tape application for chipping assessment.
8. Chip Rating Systems
8.1 Methods: Two methods for chipping evaluation - physical count and visual comparison.
8.2 Evaluation Area: Specifies the area on the specimen to be evaluated.
8.3 Rating System: Explanation of the number-letter combination used for rating.
9. Physical Count Procedure
Detailed steps on how to count and record chip sizes and numbers using the transparent grid.