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Nickel plated sockets are cloudy/milky without a copper preplate

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Q. Hello! I am new here and appreciate any help! This one has us stumped.

here is what we have been dealing with in a nut shell. These are hand tool sockets made from M440 and in some cases 4140 forgings. They are heat treated then tumbled with a chemical called chemtrol 402, then sent on to us for electrolytic nickel and trivalent decorative chrome.
Our typical process is as follows:

- soak in brake clean solvent to cut oil
- rack parts on plating rack
- anodic reverse current in hot alkaline soap 1 minute 180 degrees F.
- thorough rinse
- 1 minute soak in ambient temp 30% muriatic acid
-thorough rinse
-electrolytic nickel plate
-thorough rinse
- trivalent chrome plate

The problem is, without copper cyanide strike or mechanically polishing through the top layer on the part, we end up with a cloudy dull finish coming out of the nickel bath.

I have attached a picture of a part as they come in to us:


Thanks in advance for taking a look at this.

E Rothe
- Cleveland, Ohio
March 17, 2023

A. Hi. I haven't been able to find Chemtrol 402 or Type M440 steel, but it seems that you are saying the sockets plate okay with a copper preplate, but not with nickel plating directly on the substrate. This seems to indicate a reaction between the nickel plating and something on or in the substrate which the copper plating seals away.

It seems possible to me that a 1-minute electroclean at 180 °F and whatever concentration you are holding just isn't enough cleaning. A fairly standard thing to do is to take a number of sockets, scrub them good with a scrub brush and pumice powder mixed into water with a little bit of detergent, and then rack them up for the normal cleaning, activating, and plating cycle. If the cloudiness disappears like it does with a copper preplate, you know that your cleaning just isn't quite good enough. If the cloudiness doesn't disappear with this cleaning but continues to disappear with copper preplating you know that I can't help you beyond suggesting that you copper plate them :-)
Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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