Zinc is a bluish white lustrous metal used for the galvanization of steel. Zinc combines with oxygen and other non- metals and reacts to dilute acids in a process which releases hydrogen.
Galvanizing
Electrolytic zinc finishing- cold galvanizing, is known as one of the most common finishing types used in the industry. This type of finishing provides excellent anti- corrosive protection. Due to the electrolytic zinc finishing aesthetic appearance, it can be used both for engineering and decorative finishing.
Finishing Types
From engineering prospective, the thickness of the zinc coats and the passivation process are what determines the differences between the zinc coating types. These variables determine the zinc coating’s electrical properties, corrosion resilience and appearance:
- White passivation and blue passivation
These types of passivation are commonly used in the electronic packaging industry. - Yellow passivation
This type of passivation is primarily used for engineering purposes and for the protection of items residing in corrosive atmosphere. - Black passivation
A Passivation designed for items which contain a black shade used to prevents reflection of light. - Olive green passivation
A passivation suitable for items that require a particularly strong protection (Resistance of 168 hours in the salt chamber).
As the passivation layer thickens, the item’s resilience to corrosion grows and at the same time, its electrical conductivity decreases. Therefore on the one hand, black passivation and green passivation hold exceptional corrosion resistance but on the other low electrical transmission capacity.
Classification according to standard ASTM B633
Classification table according to TYPE and passivation
Type | Passivation Type | Salt Chamber Resilience |
---|---|---|
Type I | No passivation | |
Type II | Zinc plating with yellow, black or green chromate finish | 96 hours – white corrosion |
Type III | Zinc plating | |
Type IV | Zinc plating with toneless chromate finish | 12 hours – white corrosion |
Type V |
Phosphate Finish Zinc is mainly used in preparation for paint |
|
Type VI | Toneless (sheer) passivation- ROHS suitable | 72 hours – white corrosion |
Type VII | Passivation colored in different shades- ROHS suitable | 120 hours – white corrosion |
Passivation according to Class
Classification according to coating thickness and item atmosphere
Class (SC) | Terms | Required coating thickness |
---|---|---|
Fe/Zn 25 | Very severe atmosphere (SC4) | At least 25 microns |
Fe/Zn 25 | Severe atmosphere (SC3) | At least 12 microns |
Fe/Zn 25 | Moderate atmosphere (SC2) | At least 8 microns |
Fe/Zn 25 | mild atmosphere (SC1) | At least 5 micron |
Classification according to standard QQ-Z-325
Classification according to passivation Type
Type | Passivation Type |
---|---|
Type I | No passivation |
Type II |
Zinc plating with yellow, black or green chromate finish 96 hours of salt chamber resilience- white corrosion |
Type III |
Phosphate Finish Zinc is mainly used in preparation for paint |
Classification according to coating thickness
Class | Service Terms | Required Coating Thickness |
---|---|---|
Class I | Severe atmosphere | At least 12 microns |
Class II | Moderate atmosphere | At least 8 microns |
Class III | mild atmosphere | At least 5 micron |