Blisters and Zinc Plating

Question:

We are having trouble with blisters in our chloride zinc barrel line and our alkaline zinc barrel line.  The substrate is hardened steel. Our lines are traditionally configured, except we don’t have triple rinsing after each step. I can provide detailed line schematics if you like, but I’m looking for some basic advice initially. B. W.

Answer:

It seems that ever since we left classic cyanide zinc plating behind, the problem of blisters has been a major issue in both chloride and alkaline zinc plating. The first place to start when troubleshooting plating problems is with your chemical vendor. Most suppliers have troubleshooting information available and usually have technical expertise to help solve the problems. Assuming you have exhausted this route here are some things to consider.

Let’s start with the alkaline non-cyanide zinc bath. Some common causes of blistering are:

Possible Cause Poor cleaning Brightener concentration high Bath temperature low Metallic contamination Organic contamination Incorrect plating bath chemistry

Action Review cleaning process and upgrade Reduce concentration using vendor recommended methods (carbon treat) Increase bath temperature to recommended value Zinc dust treatment Carbon treat per vendor specifications Analyze bath and make necessary changes

With the chloride zinc plating bath there are a couple of causes of blistering:

Possible Cause Poor cleaning Boric acid concentration low

Action Review cleaning process and upgrade Analyze bath and make necessary changes

In both types of zinc plating, cleaning and surface preparation are the most critical steps.

The Metal Finishing Guidebook & Directory, 2003 edition has a number of chapters on the proper cleaning of surfaces. The Products Finishing web site, www.pfonline.com, also has useful information. Another web site, www.cleantechcentral.com, also has good information on the proper cleaning of materials.