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topic 52598

Nodular buildup at edges with chrome plating.

adv.     u.s chrome

A discussion started in 2009 but continuing through 2018

July 14, 2009

Q. Gentlemen,

We are an aerospace company that utilizes the services of the plating industry very frequently. We have always had trouble with nodular build up at the edges of parts when hard chroming was called for. Is there a particular type of edge prep (chamfer, radius, etc.) that we could employ to reduce or eliminate this issue?

Rick Ramseyer
Manufacturing Engineer - Kulpsville, Pennsylvania, USA

simultaneous July 16, 2009

A. Generous radius and chamfer will help. Ultimately, you probably will have to look at shields or robbers to reduce the high current density areas.
If the parts are amenable, conforming anodes can be tweaked to put on a uniform covering over the entire part. You also get much faster plating with less problems. An additional benefit is less grinding.

James Watts
- Navarre, Florida

July 17, 2009

A. Mr Ramasayer.

Nodular Build up in hard Chrome is a specific defect in Hard Chrome Plating that may occur under the following conditions.

1) An out of balance Chrome solution?
2) A part which is Racked wrongly without " Current Robbers" to avoid very high currents reaching the sharp edges.
3) Too high a Current density for the specific component.

Usually nodules occur as a combination of the 3 factors above or at times a fourth factor.. Too low working bath temperature but that's a lesser possibility.

I hope this helps.

Asif Nurie
- New Delhi, India

With deep regret we
sadly advise that
Asif passed away

on Jan 24, 2016

July 17, 2009

A. Rick,

It is the nature of the beast with hard chrome plating. The plating process is very low efficiency, you have to put a lot in to get a little out. The extremities are what we call high current density areas and consequently you get uneven growth of plating over the part. When you call up the higher thicknesses the extremities will form these nodules.

The problem can be mitigated, but not eliminated, using "robbers" or with a change in anode configuration, with orientation in the bath and with tight controls on the operating parameters. You can also try reducing the thickness called up.

What usually happens is that you call up greater than the final thickness you require and then grind back to size.

Brian Terry
aerospace - Yeovil, Somerset, United Kingdom

July 17, 2009

A. Edge area having high current density. So normally hard chrome will built up more faster on this area.

Using same attachment to connect on the edge to move out the high current density area.

Hard Chrome plater - - Selangor, Malaysia

July 28, 2009

thumbs up signI thank all of you who have responded and now I'll go to my supplier and discuss these conclusions. A little knowledge can be dangerous.

Rick Ramseyer
- Kulpsville, Pennsylvania, USA

April 23, 2013

Q. Current robbing when electroplating large and small exposed areas. Can anybody give me an idea of what is current robbing? How does it influence uniformity of thickness over a large substrate? How to minimize this effect?

Ravi E
- Corvallis, Oregon, USA

April 25, 2013

A. Hi Ravi. Please tell us YOUR situation. Who told you something about robbing and why? "Robbing" can be a good and deliberate thing; it can be an accidental and bad thing as a result of poor racking. In either case it involves something stealing some of the current and thereby depriving another area of current: again, this is often a good thing. What is going on in your situation?


Ted Mooney,
Teds signature
Ted Mooney, P.E.
Pine Beach, New Jersey

January 31, 2018

"What usually happens is that you call up greater than the final thickness you require and then grind back to size".
Brian Terry

Q. We are currently working on a piston which has an chamfer with radius on both ends. chrome plating is required till the starting point of chamfer. We have done the plating like Mr. Brian Terry suggested above. We are facing problems with blending the radii of the chamfer and the chrome plating since sharp edges are forming after grinding it to required size. We are looking for an edge polishing method to blend the radius. Please suggest any solutions to edge polish the chrome to blend it to the convex radius of 1 mm.

Joshia John
- Hosur, Tamil Nadu, India

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