Screw the screw galvanized anti-corrosion treatment

Screw the screw galvanized anti-corrosion treatment

Screw the screw galvanized anti-corrosion treatment


For zinc and other metal plating compared to the most inexpensive price, and the corrosion resistance of zinc in most cases far superior to steel, zinc coating to protect the discrete part, hole, rupture and expose the steel trimming Department . So screw or vulnerable to the general atmospheric corrosion of galvanized screw Most, but not screw plate or rod shape, as no change or a smooth surface, so the thickness of zinc coating uniformity in all parts of a rare, often head into the thickest, Thread mountain front Secondly, the thinnest thread valley. To cope with the mass production of screws, reduce costs and increase production, usually into the barrel zinc plating method approach, this method is a frame from the barrel into the barrel electrode to make electrical distribution conductors, the conductive wire contact with the screw, while barrel rotation and mixing screw, the screw even with the electrode contacts. However, current off at this time, it is difficult to form a uniform current density, it is easy to different zinc thickness.

Plating zinc plating can be used acidic and alkaline plating bath solution of two acidic zinc sulfate electroplating solution as the main ingredient, inexpensive and great efficiency, plating speed, easy to manage, than the alkaline plating bath not easy to hydrogen embrittlement, But the crystallization of thicker, shiny poor are poor plating. The alkaline cyanide zinc plating solution to the main component, although more expensive, but the throwing power is good, if properly managed, can have a shiny coating, if the further implementation of chromate treatment can be more bright excellent corrosion resistance coating.

Also used for hot-dip galvanized screws, bolts and nuts of the surface corrosion, hot dip galvanized screws than galvanized screws are the better corrosion resistance, but high cost and high strength structural bolts NA hot dip galvanized, the coating is easy to form hard and brittle because, at high temperatures or high loads may occur when the fracture.

Zinc coating durability in the corrosive environment, a linear relationship between its thickness, or coating thicker the longer they lived, but in the industrial zone containing sulfide is its poor corrosion resistance, while in the maritime and tropical climate China will have a lot of corrosion products from the color to be imposed to prevent the chromate treatment. Zeng Yi in the United States of thin film thickness 0.03mm galvanized pilot specimen was found in the country areas, coastal areas and industrial sites, the average life expectancy of about 3:2:1, that the pollution in the air, galvanized layers prone to corrosion, as in industrial emissions of exhaust from the plant contains a number of sulfur oxides (SOx) and nitrogen oxides (NOx) will destroy the zinc coating. The atmosphere in the coastal regions due to the existence of large salt crystals and liquid particles (chloride) can cause metal corrosion, and relative humidity significantly affected the size of the corrosion rate. Beijing University of Science and Technology Materials Protection, also in the mainland areas for zinc layer Bu Tong Tai Qi exposure corrosion test, test of one year Jieguofaxian Fushi rate Zui Gao's is in the atmosphere of SO2, chloride (salt Li Zi) were the highest and maximum relative humidity of the area. Atmospheric relative humidity which is considered the main factors causing corrosion, and atmospheric pollutants, particularly SO2 and chloride are the major factors promoting corrosion.

Galvanized screws in the production, storage, transport process, the zinc coating may occur white, dark, black and other phenomena, mainly galvanized layer and the corrosive medium and atmospheric moisture, oxygen, carbon dioxide corrosion exposure results. To prevent this phenomenon can be processed in the screw surface state as possible before Xuanyong better material, because of the galvanizing process, the screw surface of the defect tends to acid, alkali, salt etc. correlative corrosive medium penetrate inside, Nan Yi cleaning lead to Fushi. In screw machining to minimize the stress concentration due to stress concentration area, it is easy to produce in the process of pickling rust corrosion. Screws heat treatment to minimize the thickness of oxide film, particularly that fully implements removed before plating the surface of oil and corrosion properties and proper control of pickling time rust, so as not to affect the quality of plating. Electroplating operations should pay attention to choose a good covering power of zinc solution, strengthening bath maintenance, proper control of current density and amount of additives. Fully implements to be washed after plating to eliminate the electroplating solution and the organic coating damage on the other screws to minimize the exposure time in the atmosphere, sealed as soon as possible. Reasonable choice of packaging materials to avoid the use of zinc incompatible with the plastics, packaging materials such as galvanized iron sheet metal the best, the box can be placed in order to reduce the amount of desiccant inside the humidity, the Treasury and the relative humidity to reduce to prevent erosion of harmful gases.