EN and Plating Out

Q. I have a 150-gal electroless nickel bath, and I am having problems with my 316 stainless steel heaters plating out. This usually happens on the second or third load of parts. The heaters were several years old, so I replaced them with new heaters, but the exact same thing is still happening. I also am having problems with adhesion, dinginess and gray finishes on the parts. I have checked all of my grounds and looked for stray currents. —W.Z.

A. Based on what you have described, it sounds like your electroless nickel plating bath requires a "physical." Here is an abbreviated troubleshooting guide for the problems that you mentioned:

Problem	Possible Causes
Adhesion	1. Improper cleaning
	2. Poor rinsing
	3. On aluminum, poor zincating
	4. Metallic contamination
	5. Organic contamination
Dingy, dull deposit	1. Temperature too low
	2. pH too low
	3. Nickel concentration too low
	4. Metal contamination
	5. Organic contamination

 

The plating out on the stainless steel heaters can be caused by failure to thoroughly passivate the heaters using a 25 percent or more nitric acid solution. If you are doing this now, try increasing the passivation time. A voltage of 0.8 V is recommended. Another issue may be less-than-adequate mixing of the solution. With poor agitation, you can get an increase in temperature around the heaters, causing the rapid decomposition of the solution. Increase your bath agitation.

One last suggestion: make sure you are monitoring your chemistry on a regular basis. If you are unsure as to what tests need to be done, consult with the vendor of your EN chemistry. I also am e-mailing you a troubleshooting chart for electroless nickel.