ASTM B633 defines zinc plating on iron and steel. It sets a service condition class by zinc thickness and a chromate type for the conversion coating on top. Your drawing names the class and type, and we plate to it.
Service condition classes
The class fixes the minimum zinc thickness for the service the part will see:
- SC 1, mild: about 5 microns of zinc
- SC 2, moderate: about 8 microns
- SC 3, severe: about 12 microns
- SC 4, very severe: about 25 microns
Chromate types
The type names the conversion coating over the zinc:
- Type I: zinc with no chromate
- Type II: a colored chromate such as yellow
- Type III: a clear chromate
- Types V and VI: trivalent, RoHS compliant equivalents of the colored and clear coatings
We run trivalent chemistry for the RoHS types and hexavalent where a drawing still calls for it.
How we plate to B633
Rack and barrel lines both plate to B633. We set the zinc thickness to the class and apply the chromate type your print names. A plater watches the work at the tank, parts are inspected by hand, and the order ships kraft wrapped. Typical turnaround is about seven days. Tell us the salt spray hours to white or red rust you need and we plate to hit the class.