Zinc

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
Zinc
אבץ גימור מתכות ופלסטיק 98