The main reasons for yellowing of rolled galvanized parts include.
Author: Robby
Pre-treatment is not complete: because the piece parts are always close together, degreasing and pickling can not completely remove the oil, resulting in galvanizing process oil entrapped in the plating layer, the formation of fogging phenomenon. This can be done by using tumbling instead of degreasing, the parts are acid cleaned by adding water, sand, sodium carbonate and tumbling for 1 hour, and then cleaned and galvanized by cleaning and activated with 15% hydrochloric acid.
Excessive Current Density: Excessive current density may cause the plating to burnish and form black spots. The thickness of the plating layer can be ensured by reducing the current density and extending the plating time appropriately.
Iron impurity deposition: Iron impurities in the plating solution are deposited on the surface of the plated layer to form black spots. Iron comes from parts dissolved in the plating solution without current. Iron impurities can be removed by regular treatment with hydrogen peroxide.
Cleaning is not clean: In the polishing, passivation and cleaning process, if the parts surface residual polishing liquid, passivation liquid, will lead to the plating layer fogging, yellowing. This can be solved by intensifying the cleaning and using compressed air to agitate the flowing water.
Rust water dripping: Rust water dripping onto the surface of the zinc layer or yellow water inside the local welding seam flows out, resulting in yellowing. The surface color can be repaired by using galvanizing coloring agent.
Insufficient galvanized layer: The galvanized layer of angle steel is insufficient and yellowing after rusting. It can be sanded and descaled to brush the special repair coating for hot-dip galvanizing.
Solution:
Strengthen pre-treatment: use roller grinding instead of electrolytic degreasing, strengthen the cleaning process to ensure that the surface of the parts is free of oil.
Adjust the current density: Reduce the current density and extend the plating time to ensure the quality of the coating.
Regularly deal with iron impurities: use hydrogen peroxide or hydrochloric acid to activate and passivate after the light out, regularly clean the iron impurities in the plating solution.
Strengthen cleaning: Try to shake the surface of the parts and strengthen cleaning in the process of polishing, passivation and cleaning, use compressed air to stir the flowing water if possible.
Repair the surface color: Use galvanizing colorant to repair the surface color.
Ensure the thickness of the coating: After grinding and removing rust, brush and apply the special repair coating for hot-dip galvanizing.