Q. What is the best way to agitate our plating baths? We are in the process of redesigning a number of our plating lines and would like to get the most efficient method of agitation installed. What are your thoughts?—R. L.
A. Many shops grew up with air agitation, cathode reciprocation, mechanical mixing or filtration flow. A paper dating back to 1999, “Exploitation of Eductors Agitation in Copper Electroplating,” by D. R. Gabe, M. Ward and J.N. Crosby, addressed these questions in detail. Using a mathematical relationship the following enhancement factors were determined.
|Agitation Method||Enhancement Factor|
|Natural convection||1 – 2|
|Cathode reciprocation||2 – 4|
|Air agitation||2 – 5|
|Vibratory||3 – 30|
|Turbulent flow||5 – 15|
|Ultrasonics||2 – 10|
As can be seen from the above data, the agitation method used, compared to non-mixing, does make a difference. Surprisingly, the two standard methods, cathode reciprocation and air agitation give similar enhancement factors. The data above also indicates that the vibratory and turbulent flow methods of agitation offer real improvements over the classic methods. The vibratory method is used in the plating industry but not to a great extent; 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. Eductors are inexpensive fitting and are well worth the investment.
Originally published in the July 2015 issue.
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