Hydrogen Embrittlement Again

Q: We manufacture parts that have a spring-like action. Our specification calls for zinc plating followed by baking at 375°F for three hours. Many of the parts still suffer from cracking. We outsource all of this work. I should add that when the plating was done in-house we did not have this problem. Can you make any suggestions on how to eliminate this problem? T.T.

 

A: Your question is a good one. It illustrates an issue that seems to occur with great frequency in our industry. The first comment is that when you outsource your plating you must prepare thorough and complete specifications. What might have been taken for granted when the work was done in-house cannot be assumed when having an outside company doing the work. You do not mention in your e-mail whether the work is being outsourced to a U.S. company or being sent overseas. If it is the latter, this becomes all the more important. When plating is sent overseas the issue of language and communications play a major role in success or failure. (I have been involved in a number of situations in the last few years where communications played a major role in plating disasters!)

Some general things to consider in writing specifications for your process are:

• Avoid the use of acids during the pro- cessing of the parts.
• Specify that cathodic, direct or forward eletrocleaning is not allowed.
• Bake the parts prior to the plating step at a temperature that is approxi- mately 100°F lower than the last heat treatment temperature. Too high a tem- perature may affect the temper of the part.
• Specify a high efficiency acid zinc plat- ing bath. These baths are essentially 100% efficient and generate little or no hydrogen.
• Increase the temperature and bake time after the plating step.
• Specify that parts must be baked imme- diately after the final plating step.

You might consider mechanical plating or peen plating as an alternative to a “wet” plating process. Mechanical plating is a mature technology and is used successfully by many companies. Your can find more information about this process by doing a search on www.pfonline.com using the terms “peen plating” or “mechanical plating.”