The performance level of some commercial coil-coated materials

Abstract

As part of a larger investigation the performance level of a selection of commercially available coil-coated materials had to be established to serve as a basis for comparisons in the rest of the project. It was felt that these results would be very useful for other comparisons also. The performances are presented here for a series of coil-coated materials, established by an independent institute, that will make it possible to ‘place’ similar products in an appropriate context. The paper covers the materials tested, their properties, the performance level of the materials and the performance of the test methods. Thirteen coil-coated systems are examined, together with three referenco systems applied by job coating. The properties tested include colour, specular gloss, metal marking, dirt retention, pencil hardness, coating thickness, coating continuity, adhesion, flexibility, durability by outdoor exposure and artificial tests. Colour and gloss can normally be matched to specified values. Metal marking and dirt retention stayed within acceptable limits. Coating thickness agreed very well with the values specified by the suppliers. The reference systems are much thicker than most of the coil-coated materials, but materials should be judged by their performance and not just their coating thickness. No signs of porosity were found; vacuoles (voids) were found only where expected. The adhesion of all materials is excellent when assessed by means of common coating tests. Flexibility is variable, so materials should be selected with care as far as this property is concerned. Flexibility tends to be high for aluminium substrates and for those galvanized with Plastisol. Substrates with an aluminium-zinc alloy coating are found to be less flexible. Durability is variable. So far about half the coil-coated materials perform in an excellent way for weathering resistance as well as corrosion resistance. Others perform better with respect to just one of these aspects of durability. No materials are classified as ‘poor’ for both aspects of durability. The reference (job-coated) materials are classified as having excellent corrosion resistance, but poor weathering resistance. More information on durability will become available after extended outdoor testing. The artificial weathering and durability tests did not perform well. The ordering of the performance of materials by such tests is unreliable, for it is possible to pass poor materials and reject perfectly satisfactory materials. The relevance of test methods and requirements in existing performance specifications with respect to practical performance should be improved.