Solution Agitation

Q. We want to improve the agitation of our plating solutions. Can you offer any advice on this subject? S.J.

A. There are a number of different ways to agitate plating baths, and in most cases any type of agitation is better than no agitation. I personally like eductors and recommend them in most situations. Using eductors give you much im-proved agitation compared to air or mechanical agitation. Following is a some-what-modified version of what I wrote on the subject a number of years ago.

These questions are addressed in the paper “Exploitation of Eductors Agitation in Copper Electroplating“ by D.R. Gabe, M. Ward and J.N. Crosby, which was presented at the June 1999 SUR/FIN, American Electroplaters & Surface Finishers Society, NASF.org. Using a mathematical relationship (which we needn’t concern ourselves with here), the following enhancement factors were determined: 

Agitation Method	Enhancement Factor
Static solution	1
Natural convection	1 – 2
Cathode reciprocation	2 – 4
Air agitation	2 – 5
Vibratory	3 – 30
Turbulent flow (eductors)	5 – 15
Ultrasonics	2 – 10

 

As can be seen from the above data, the agitation method used does make a difference. Surprisingly, the two standard methods, cathode reciprocation and air agitation, give similar enhancement factors. The data above also indicate that the vibratory and turbulent flow (eductor) methods of agitation offer real improvements over the two classic methods. The vibratory method is not used widely in the plating industry, but the turbulent flow method is used.

The use of eductors will give you a turbulent flow environment and, based on the information in the table, much better mixing compared to cathode recip-rocation or air agitation. An eductor is a specially designed nozzle that causes liquid pumped through the nozzle to exit at high velocity. This in turns pulls additional solution from the surrounding region through the nozzle.

Another paper, “Eductor Agitation for a Nickel Plating Bath” by C. Porter and D.R. Gabe, presented at the 2004 SUR/FIN conference, gives additional data about the advantages of using eductors.

Since you are not bubbling air through the process tank, you will reduce the amount of oxidation of bath components, which in turn will reduce sludge for-mation. This means that consumption of plating bath additives is reduced. Also, heating costs are slightly reduced due to less cooling of the bath. (Don’t forget that air agitation cools a plating bath.)

The cost of installing eductor systems on your process tanks is modest com-pared to the many other costs involved in the metal finishing environment.

More information on the process and vendors who sell the eductor nozzles can be found at PFonline.com.