The Effect of Edge Preparation on Coating Life Phase. Phase 2

Prepared in cooperation with Franklin Research Center, Philadelphia, PA.

The test This report deals with the results. of Phase Two of a project entitled Effect of Edge Preparation on Coating Life . Phase Two consisted of a program developed on the basis of the results obtained during Phase One of the overall program. The variables tested in Phase Two included 1. 2. 3. 4. Flame Edge radius Coating system Application method Test method cut edges were used as control samples. Three different edge radii were selected and compared with the coating performance on flame cut or sharp edges. Originally there were four coating systems considered for this test program: two inorganic zinc systems (water-based and solvent-based), coal tar epoxy and polyamide epoxy. The water-based inorganic zinc was eliminated . because of its unsatisfactory adhesion to the steel substrate. The two coating application methods comprised hand brushing the edges followed by airless spraying the entire sample surface, and airless spraying only. Immersion pressure and salt spray testing constituted the two corrosion test methods. In all cases the test samples were sandblasted to SP-10 finish prior to the application of the paint systems. Chipping, blistering and rusting were the primary indications of coating failure. The best overall coating performance was obtained with samples having 1/8 inch (3.2 mm) edge radius coated with polyamide epoxy applied by airless spraying only. The edge performance of the coating systems decreased with an increase in edge sharpness. Flame cut edges are not recommended for applications which require equal coating performance with flat surfaces.