How to do the aging and corrosion of the screw

Update:21 Sep 2019
Summary:

Screws and zinc coatings during transportation often ap […]

Screws and zinc coatings during transportation often appear white, black, black, etc., mainly due to corrosion caused by galvanized coatings and corrosive media and atmospheric moisture, oxygen, and carbon dioxide exposure.
In order to prevent this phenomenon, the surface state of the good material that can be tried is before the screw processing. Due to the galvanizing process, the surface of the defective screw is easily permeated by corrosive medium such as acid, alkali, salt, etc., and it is difficult to clean and cause corrosion.
Reasonable choice of packaging materials, avoiding the use of plastic products not with zinc, packaging materials, such as galvanized iron sheet metal is the best, in the box can be placed in the humidity of the amount of desiccant to reduce the relative humidity compatible to reduce and prevent harmful gases The erosion of the warehouse. Currently the so-called metal surface treatment of screws and nuts on the market LONGZINC (Nasdaq stock code rust).
In order to prevent the non-standard screw anti-corrosion treatment, it is already degreased, and the Nasdaq rust-proof rust inhibitor tank rust-proof screw nut swims smoothly, or the zinc and chromium compounds are used to form a protective film on the metal surface to form a spray method, and Drying, cooling, and then repeating the process once, the resulting about 5-8 μg, silver grey, based on the thickness of the information provided by the manufacturer of the display, is said to have good rust and corrosion resistance.
Phosphate treatment is a chemical treatment of phosphate containing metal to metal surface to form phosphate protective film phosphating solution, insoluble in water, and has excellent adhesion of phosphate film, as its main purpose bottom layer and coating A metal layer that cold adsorbs the lubricant. Since the phosphate film is composed of a series of different sizes of zinc, manganese, hydrogen phosphate and iron phosphate crystals, the film is porous, has a large specific surface area, and has good absorption, adsorbed coating or a large amount of lubricant. So, often used as a primer, or cold stamping to reduce friction and steel, cold drawn steel wire lubrication layer.
The oxidized steel part will be immersed in an alkali treatment solution containing an oxidizing agent such as potassium hydroxide or sodium hydroxide solution of nitric acid, and maintain its boiling point of about 140 ° C, or nitric acid and sodium hydride nitrate impregnated steel molten salt It is pleasant to remove the surface layer, and the eye of the black iron oxide film in the composition having a mixture of ferrous oxide and iron oxide can be obtained by quenching in water, which is a method for improving corrosion of ferrous metals.