Chipping Resistance Testing
University of Dayton Research Institute (UDRI) employs their CLG-LP-044 laboratory procedure for performing foreign object debris (FOD) testing on 4×6 inch coated panels according to ASTM D 3170 Standard Test Method for Chipping Resistance of Coatings. Cured, coated panels are tested in triplicate by mounting in the target chamber of the Gravelometer and firing one pint of 3/8 – 5/8-inch water eroded alluvial stones at the test panel with an air gun operating at 70 psi. Loose gravel is removed from the panel with an 898 filament tape, and the panel is rated by a visual comparison to transparent standard chips.
UDRI performed chipping resistance testing on Gentoo treated and untreated LHE Zn-Ni 4130 steel panels, as well as on Gentoo treated and control MIL-PRF-23377 epoxy primer with MIL-PRF-85285D grey urethane topcoat painted LHE Zn-Ni 4130 steel panels. No reportable differences were observed in coating chip protection between the Gentoo treated and untreated bare steel panels.
After chipping resistance testing, the damaged panels were placed into an ASTM B117 salt fog chamber. After 2136 hours of exposure, the Gentoo treated steel and Gentoo treated primed/topcoated, steel panels demonstrate significant corrosion improvement over the bare steel and painted steel control panels. This Gentoo treatment is providing added exposure protection as a function of impact over the control panels.
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Figure 10: 2136 hours of B117 Salt Fog Exposure of FOD Tested Bare and MIL-PRF-23377 primer with MIL-PRF-85285D topcoat painted LHE Zn-Ni plated HSS panels with and without Gentoo
Chipping resistance testing was repeated with LHE ZnNi plated 4130 HSS panels with a MIL-PRF-23377J Type I Class N chrome-free epoxy primer and topcoated with CA8201/F17925 MIL-PRF-85285 Type I Class H white glossy urethane paint with and without Gentoo. Bare LHE ZnNi 4130 with and Gentoo surface treatment was also included.
No significant differences resulted in the chip protection ratings between the surface treated and untreated panels. Panels were placed into ASTM B117 salt fog for 2000 h of exposure. Red rust spots are visible on the painted control panel, while the Gentoo panels remain unchanged (Figure 11).
Figure 11: ASTM B117 Exposed, Chipping Resistance Tested LHE ZnNi plated 4130 HSS bare and painted panels with and without Gentoo