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:
|Anodically electroclean.||Temperature 90°C
Current density 65-70 asf
Time 1-2 min.
|Etch anodically in etch bath.||Sulfuric acid 205 mL
Water 795 mL
Current density 100-250 asf
Time 0.5-1.0 min.
Smutted parts must be desmutted.
|Sodium cyanide 40 g
Sodium hydroxide 40 g
Water to 1L
Current density 70 asf
Time 1–2 min.
Parts are anodic.
|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.
|Dip in a 30-35 g/L
sodium cyanide solution.
|Zinc plate.||Current density 20 asf|
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.