The Effect Of Edge Preparation On Coating Life

Presently, there is not a standardized method in the U.S. Shipbuilding Industry of preventing premature coating failures along sharp edges and at surface discontinuities in flats. Such coating failures can lead to product contamination and high repair costs. A lack of standardization and definition of what requires special preparation and/or repair have of course created a considerable amount of misunderstanding among the parties involved. Faced with similar dilemmas, several shipbuilding nations have very recently issued standards or guideline documents for sharp edges and/or defective flat surfaces. The countries are Japan, Sweden, France, Italy and West Germany. Copies of such documents obtained during Phase 1 of this project can be found in the Annex to this report.

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.

Hard machining is a relatively recent technology that can be defined as a machining operation, using tools with geometrically defined cutting edges, of a work piece that has hardness values typically in the 45-70HRc range. This operation always presents the challenge of selecting a cutting tool insert that facilitates high-precision machining of the component, but it presents several advantages when compared with the traditional methodology based in finish grinding operations after heat treatment of work pieces. Machining of Hard Materials aims to provide the reader with the fundamentals and recent advances in the field of hard machining of materials. All the chapters are written by international experts in this important field of research. They cover topics such as: • advanced cutting tools for the machining of hard materials; • the mechanics of cutting and chip formation; • surface integrity; • modelling and simulation; and • computational methods and optimization. Machining of Hard Materials can serve as a useful reference for academics, manufacturing and materials researchers, manufacturing and mechanical engineers, and professionals in machining and related industries. It can also be used as a text for advanced undergraduate or postgraduate students studying mechanical engineering, manufacturing, or materials.