My chemical vendor has recommended using eductors to agitate my plating solutions. Can you tell me more about this agitation process? Is it expensive to install? How does it compare to air agitation? M. A.
Your vendor is giving you good advice. Using eductors gives you much improved agitation compared to air or mechanical agitation. I addressed this question in an earlier Plating Clinic column. At that time, I wrote the following:
A paper, Exploitation of Eductors Agitation in Copper Electroplating, D. R. Gabe, M. Ward and J. N. Crosby, presented at the June 1999 Sur/Fin, American Electroplaters & Surface Finishers Society, www.aesf.org, addresses these questions. Using a mathematical relationship, which we needn’t concern ourselves with here, the following enhancement factors were determined.
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 also indicates that the vibratory and turbulent flow (eductor) methods of agitation offer real improvements over the two classic methods. The vibratory method is not used in the plating industry; however, 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 reciprocation or air agitation. An eductor is a specially designed nozzle that causes liquid pumped through the nozzle to exit at high velocity. This in turn pulls additional solution from the surrounding region through the nozzle. Since writing this response, 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 formation. This means that consumption of plating bath additives is reduced. Also, heating costs are 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 compared 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 PF Online.
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