Лако-красочные материалы — производство

At present, when manufacturing metallic aircraft the most widely used surface preparation method is a combination of cleaning, pickling and anodizing (as described above). Usually, the raw aluminum parts are precleaned with organic solvents, followed by alkali degreasing, pickling in diluted hydrofluoric acid in order to remove accumulations of copper on the surfaces and staining caused by the alkali pickling process, then pickling in chromosulfuric acid for 30 min, and finally anodizing in phosphoric acid or chromic acid. Unfortunately, this method is very labor-intensive, involving intermediate back-washings, and is highly problematic and expensive from both toxicological and ecological viewpoints. As the components to be bonded must undergo an overall treatment, the finally anodized surfaces must also be coated in the nonbonded areas, because the anodized surfaces have visually unap­pealing properties. Consequently, the surfaces are primed first and then painted in the nonbonded areas. This surface preparation method requires a very intensive control of the pickling and anodizing baths, with regards to their chemical composi­tion and temperature and finally, during anodization, the current that is applied. This is the most important starting point for future optimization, since the chromic pretreatment methods will clearly need to be substituted by other methods on the next occasion. In general, however, aircraft manufacturers at present have special authorizations to continue using a pickling process followed by chromic acid anodizing, mainly because the modification of a permitted manufacturing program requires costly certification. Nonetheless, alternative methods of anodization have been intensely investigated. For example, in the United States a phosphoric acid anodizing process has been widely used in aircraft manufacture which is less critical with regards to environmental technology and toxicology, but which still requires an initial pickling in chromosulfuric acid. Other new anodizing methods currently under development in the United States include a boric-sulfuric acid anodizing process.

As mentioned above, the surface preparation of fiber-reinforced plastics is essen­tially mechanical in nature, and is therefore less critical with regards to ecological viewpoints. When the ‘peel-ply’ method is used — that is, when peeling off a fabric inlay — it is important to consider that the type of fabric used will influence the adhesive properties of the surface thereby created. In order to avoid such an uncontrolled influence the surfaces may also be ground, if necessary, using a mild process such as Scotch-Brite®.