If you must use ASTM D2794 (e.g., customer insists):
A hemispherical punch that transfers the force from the falling weight to the test panel. impact test astm d2794
The indenter strikes the (metal back), causing the coating on the opposite side to be rapidly stretched outward (tensile stress). This is more severe for coatings and simulates impact from behind (e.g., dent from inside a panel). If you must use ASTM D2794 (e
| Component | Specification (ASTM D2794) | |-----------|----------------------------| | | Hemispherical steel tip, diameter 0.625 ± 0.002 in (15.9 mm) | | Die (support) | Flat steel plate with circular opening 0.64 ± 0.02 in (16.3 mm) diameter, beveled edge (0.06 in radius) | | Guide tube | Vertical, internal diameter 1.5 in (38 mm), minimum length 24 in (610 mm) | | Weight | 2 lb (0.9 kg) or 4 lb (1.8 kg), with adjustable drop height | | Base | Heavy steel base to prevent rebound energy loss | | Depth control | Mechanism to prevent reverse-side impact from exceeding specified depth (not always present in older units) | internal diameter 1.5 in (38 mm)
| Coating type | Typical reverse impact (in·lb) | Notes | |--------------|-------------------------------|-------| | General industrial enamel | 20–40 | Often fails at lower end | | Automotive clearcoat | 40–80 | Requires very flexible chemistry | | Polyester coil coating | 80–160 | High flexibility for post-forming | | Epoxy powder coating | 80–120 | Thicker films (2–4 mils) | | High-build polyurethane | 100–160 | Impact modifiers added | | PVDF (Kynar) | 120–180 | Extremely flexible |
ASTM Committee D01 (Paint and Related Coatings, Materials, and Applications) withdrew D2794 due to:
The Impact Test ASTM D2794 considers several key parameters: