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1. Hot-dip galvanized fastener materials 1. The chemical composition of hot-dip galvanized fasteners shall comply with the provisions of GB/T3098.1 and GB/T3098.2. In addition, when the total content of phosphorus and silicon is between 0.03% and 0.13%, high temperature (530 ° C ~ 560 ° C) galvanizing is recommended.
Note: The influence of hot dip galvanizing temperature on product performance should be considered when selecting materials.
2. Surface condition Before immersing in zinc solution, the surface of the fastener should be clean and should not have any contaminants. Otherwise, it affects the effect of galvanizing.
Second, hot dip galvanizing procedures and precautions 1. Eliminate the stress on the fasteners used in important occasions, before pickling and hot dip galvanizing, you can ask to eliminate stress first.
2. Surface cleaning parts should be surface cleaned first. During the surface cleaning process, hydrogen may be substantially absorbed by the steel during pickling. Hydrogen cannot be completely melted into the zinc solution and may cause hydrogen brittle fracture. Unless otherwise agreed, parts with a heat treatment or work hardening hardness greater than or equal to 320 HV shall be cleaned by a combination of corrosion-resistant acid, alkaline or mechanical means. The time to immerse in the corrosion resistant acid depends on the state and duration of the receiving surface.
Note: Suitable anti-corrosion acids can reduce the erosion of steel and the adhesion of hydrogen.
3. Drying If drying is carried out, it should be carried out before the surface activation treatment.
4. Solvent treatment (plating)
Parts should be surface activated and dried if necessary.
5. Hot dip galvanizing Hot dip galvanizing is generally carried out in a plating bath at a temperature of 455 ° C to 480 ° C. High temperature hot dip galvanizing can be used to obtain a smooth and thin zinc layer. High temperature hot dip galvanizing is generally carried out in a plating bath at a temperature of 530 ° C to 560 ° C, and the surface obtained is usually dull. In order to avoid micro-cracks, bolts, screws and studs of M27 and above with a performance class of 10.9 are not suitable for high-temperature galvanizing. Hot dip galvanizing should be avoided in plating baths with temperatures from 480 ° C to 530 ° C.
6. Centrifugation and Cooling Remove the parts from the plating bath and centrifuge immediately, then cool in water or air (determined by size).
7. Special technical requirements for nuts Nut threads or other internally threaded parts should be tapped after hot dip galvanizing, and repeated tapping is not allowed.
8. Most post-treatment hot dip galvanized parts do not require post treatment. When requested by the customer, a post-treatment process such as chromate or phosphate may be applied to prevent white rust (white corrosion) or to facilitate the post-plating spraying process when stored in a humid environment.
Fasteners - hot dip zinc process
Hot dip zinc process