Zinc coating methods

Zinc coatings are covered by an ASTM specification (143). Because of the varying purity of 2inc deposits from chloride and 2incate baths, some thickness measuring methods can vary considerably (39). Methods based on physical measurement of magnetic methods (144,145) are used for best accuracy. 

Separate the metal from the environment with a physical barrier. Many corrosion inhibitors make use of this principal to protect metals. Proper use of an appropriate inhibitor may reduce or eliminate pitting. Pits are frequently initiation sites for corrosion-fatigue cracks. The effectiveness of inhibitors depends upon their application to clean metal surfaces. An example of this method is the use of zinc coatings on steel to stifle pit formation. 

Sweep blast or abrading This is a suitable method before application of thick two-pack materials but care is required not to remove too much zinc coating. 

As the protective value of the zinc coating depends largely on the corrosion resistance of zinc, the life of a coating is governed almost entirely by its thickness and by the severity of the corrosive conditions to which it is exposed. Extensive tests and field trials which have been carried out have shown that the life of a zinc coating is roughly proportional to its thickness in any particular environment and is independent of the method of application. 

Although phenylhydroxylamine may be prepared by catalytic reduction,1 by the oxidation of aniline,2 and by electrolytic reduction of nitrobenzene,3 the most feasible method is still based upon the original zinc reduction method of Bamberger 4 and of Wohl.5 Various solvents and catalysts have been used in this reduction, and copper-coated and amalgamated zinc, as well as aluminium amalgam,6 have been substituted for zinc dust. The method herein recommended is essentially one previously described 7 but it has been found 8 that cooling is not an essential, as claimed in the patents. The preparation of the oxalate is also a more recent contribution.9... 

Often the OEM coatings depend on the nature and condition of the substrate to which paint is applied application methods and conditions drying time required and decorative and protective requirements. The substrate most commonly coated with industrial coatings are iron and steel, but also include other metals such as aluminum and its alloys, zinc-coated steel, brass, bronze, copper, and lead. Nonmetalhc substrates include timber and timber products, concrete, cement, glass, ceramics, fabric, paper, leather, and a wide range of different plastic materials. Consequently, industrial coatings are usually formulated for use on either a specific substrate or a group of substrates. 

Discuss methods for determining the thickness of a zinc coating on a iron substrate include discussion on the preparation of standards and on calibration. 

The use of electrocoat or e-coat paints and primers is another technology that found extensive use in the 1980s. Electrocoated paint is applied on the part to be coated in a paint bath, and electrical current is applied. This method enables painting of the most intricate parts. The electrocoated automobiles were more corrosion resistant. The surface rust was approximately three times higher, and the number of perforations were also higher in vehicles that were treated in the standard conventional manner. Some of these differences may be because of zinc coating on the steel and phosphatizing. However, electroplated paint systems had a noticeable effect on corrosion resistance. 

In the selection of a coating method, fliere are usually more real possibilities with zinc than with aluminium. For steel structures, aluminium has mainly been competitive on price only in the form of fliermal spray coatings. 

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