![]() The result is that ordinary steel is unsuitable for many coatings tests. Steel stored for a long time with rust inhibiting oil will react to form an incomplete oxide known as oil stain.Rust varies with the care taken in handling (a) at the steel mill, (b) during transport and storage, and (c) during fabrication.This carbon smut is impossible to remove except by mechanical abrasion. All too often, carbon smut is actually baked onto the steel during the high temperature annealing process which follows rolling. Surface cleanliness varies with the mill’s cleaning procedure, especially the procedures used to control carbon smut.Surface texture varies with the condition of the rollers used by the steel mill to cold roll the steel to its final thickness.Surface problems can come from a number of sources: Unfortunately, ordinary commercial sheet steel displays wide variations in the surface properties which affect the bonding of coatings. If coatings tests are to be reliable and reproducible, they must be performed on a substrate which is reasonably consistent from test to test.
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