Electro Cleaners Series - Part 4

Reverse and Direct (and Reverse?)
Electrocleaning Explained!

Electrocleaner Part 4:  Reverse and Direct Electrocleaning Explained

Finally!
 

Did you read my Electrocleaner parts 1, 2 and 3?  Well…  Click below if you missed them!

So today we are going to talk about reverse and direct electrocleaning and after that I'll explain REACH to you.  If we're doing the impossible we might as well go all out!  

Actually Reverse and Direct Electrocleaning isn't quite as hard to unravel as determining if the products you plate are REACH compliant.  Slightly easier anyway if you're doing it right but…  

Let's start with the easy stuff:

Reverse Electrocleaning is when the part is Anodic.
Direct Electrocleaning is when the part is Cathodic.  

Typically when we plate, the work piece is cathodic meaning that the ions are moving "to" the part or "direct".  Reverse therefore is when the part is anodic (think anode) and the ions are moving away from the part, or, the "reverse" of plating.  
 

See it's simple!  Thanks and next week part 5:

"Don't Stick Your Hand in the Hot Tank".    

Oh…  You wanted to know when you go direct and reverse?  What alloys do you never want to go reverse with?  Which one makes the part more ready to plate?  Well then here we go…  
 

Reverse = Anodic Electrocleaning

For steel you definitely want to clean in reverse with the part anodic.  This helps remove the metallic smut and prevents the deposition of other particles onto the surface.   As the parts gas, oxygen is generated at the surface and the scrubbing action, much like we see in the nickel strike tank, removes oxides and scale.  

When you should you not use reverse/anodic cleaning?  Brass and bronze for sure.  If we're in reverse we'll "de-plate" the zinc or the tin right out of the alloy.  Ever come out of an electro cleaner and that yellow brass is actually pink?  You removed the zinc from the surface.  Magnesium and any other materials that can be etched should not be cleaned in reverse.  And I'm pretty sure I don't need to say not to put aluminum in the electrocleaner right?  Right?!?  
 

Cathodic = Direct Electrocleaning

In direct cleaning the work piece is negative and any positively charged ions in the electrocleaner are moving towards the part.  Instead of creating oxygen at the surface we are creating hydrogen at twice the volume.  So we get a lot more gassing at the surface.  Direct cleaning can deposit smut onto the surface so you have to be sure to remove that before going on to the plating process.  

Two things to remember here…  You are best finishing the part electrocleaning in reverse rather than direct.  That way materials are coming off the part not remaining on the part.  And you need an acid activation step after to remove any smut remaining.  

Why would you use direct cleaning?  You may use it on brass or bronze so you get the scrubbing action of the gassing without depositing a smut onto the surface.  

You should use direct on any alloy that would form a tough oxide like a stainless steel.  If you cleaned stainless in reverse you'd form a tough nickel oxide making the part very passive.  Great if your passivating the stainless, not so great if activating and plating is next.  So stay in direct for stainless steel if you're plating it.  

So these are the very basics of Reverse / Direct cleaning.  Typically you'll find your electrocleaner parked in "reverse" as most of the work is run through it.  If we're running copper, brass or any copper alloy you'll stay in there for a very short time, enough to get some gassing and then move on.  Same with stainless steel.  

And if you refer to your process sheets, you may see that your copper alloy and stainless steel processes allow you to skip the electrocleaner all together.  But… only if the process sheets say you can!  Check 1st!  

 We do occasionally like to do both reverse and direct cleaning of a part and then of course we have "Periodic Reverse" Cleaning.  Why don't we save that for another day.  Say next week?  

Thank you!   

I have appreciated the compliments on these emails and to those of you who hate them, thank you for reading this far and keeping your comments to yourselves!