Cyanide Zinc on Cast Iron

What would be the correct process for plating zinc on cast iron parts?


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Q. I use a high-cyanide zinc plating bath for plating steel parts, both in barrel and rack lines. I have an opportunity to plate cast iron parts for one of my customers. What would be the correct process for plating zinc on these parts?—G.R.

A. The porosity of cast iron tends to make any type of plating more difficult. This doesn’t mean that the base material cannot be plated, however. Here is a classic procedure that will give you decent results: 

Procedure Comments
Anodically electroclean. Temperature           90°C
Current density       65-70 asf
Time                      1-2 min.
Rinse thoroughly.  
Etch anodically in etch bath. Sulfuric acid           205 mL
Water                    795 mL
Temperature           25-30°C
Current density       100-250 asf
Time                       0.5-1.0 min.
Rinse thoroughly.  

Smutted parts must be desmutted.
(If etched properly, surface has a gray
ppearance and no smut.)

Sodium cyanide      40 g
Sodium hydroxide   40 g
Water                     to 1L
Temperature           Room
Current density       70  asf
Time                       1–2 min.
Parts are anodic.
Rinse thoroughly.  
Strike in a stannate tin bath.
(A cyanide copper bath at 15 asf
or 3 min. can be used instead.)
Current density       50 asf 
Time                       0.5–1 min.
Rinse thoroughly.  
Dip in a 30-35 g/L
sodium cyanide solution.
Zinc plate. Current density       20 asf
Rinse thoroughly.  

This is not a simple process, and some experimentation is necessary. Unless there is a large amount of business for you in doing this, I would decline taking the job. One of our readers may have a simpler process to suggest.