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drain times & carry over



A common reservation (barrier) to increasing drain time on parts going 
through an immersion process line (e.g. a plating line), is that increased 
drain time increases production time and cuts production capacity (if the 
line operates near full capacity).  The cost of reduced production capacity 
can dwarf  the savings in chemicals and water.

This could be addressed by cutting hold times in the bath to compensate for 
additional drain time.
I have thought about the theoretical trade off's (see below),  but does 
anyone know of:
1.  studies looking at compensating increased drain time with decreased 
hold time?
2.  an expert who might have experience with this?
3.  work to identify optimal hold times for different immersion 
operations/chemistries?


Theoretical analysis
On the positive side,
- Contact time with the chemistry or rinse remains constant.
- Drainage flow will induce some turbulence and in-film mixing that should 
enhance the movement of contaminants away from the  surface or active 
chemistry to the surface.
- the longer the tank hold in standard practice, the less the effect of 
reducing hold time.

On the negative side
- access to fresh solution is reduced
- increased drain time can enhance channeling on the surface, and 
differences between the top and bottom of a part that could create uneven 
surface effects (should be minimal in rinses)
- the stronger the tank agitation is, the greater the possible effect 
lengthened drain time

Sincerely,
Karl DeWahl
MnTAP / University of Minnesota
612-624-4645
dewah001@tc.umn.edu