Zinc Plating on Components with Tight Assembly Tolerances

On the second point, what size is the hole? Would it be hot dip galvanising? Our local galv company gives these clearance figures for moving parts,

Up to 30mm Dia. minimum rad clearance 2.0mm

Over 30mm Dia. minimum rad clearance 2.5mm

Diameter is 30mm. And it is not hot dip galvanizing but electrooplating otherwise achieving those close tolerances will be impossible

Not sure then, think most places give you a minimum thickness rather than a maximum, have you had a look at ISO 2081?

GA

That was my thoughts as well, though I have no personal experience in this area at all.

"You said what I was thinking" mostly sums it up!

I would leave the holes either "uncut" or "not" cut to "nearer" than within final last 3mm (using the average values posted by another here) until after the plating had been carried out. Just to be sure.....

Cutting holes twice would appear to be extra work for no result though....

Also bearings are often secured by being glued in with various different "Glues", but to my mind, such plating is often not even a good base to glue on either....

Locktite I sells such glues (as a name to use).

loctite.co.uk

Yes I would do the same here....

can you please elaborate?

Right now I am machining the specific area where the bearing fits, is that ok?

What about pin and hole assembly? Should I specify max plating thickness on drawing and accordingly keep my tolerances?

To me that is the best way to proceed. Specify your "finished" OD including plating. Normally zinc and other platings are .0003" or less in thickness unless you specify otherwise. Check what the tolerances are on your bearing as well. There are many different types of fit you can specify. Normally bearings are oversized to the specified shaft size, but you can also have size on size, shrink fit and interference fit. All depends on your application.

I think machining away the zinc in one small area to fit machine tolerances (and not allow such a soft metal as zinc to support heavy loads), will be completely acceptable. Remember that in galvanic protection, the metal that is bonded to the sacrificial anode (zinc) is protected (when under water) within the line of sight, essentially. That is a really good rule of thumb taught to me by a world expert. He is presently a retired drip under pressure.

You should use a reamer after plating if the parts come predrilled, and remove traces of zinc in the holes.

Cathodic protection is not rocket science, and neither is it completely a black art. It cannot protect an entire battleship with a one pound anode, but it can protect large objects with only a relative few pounds, and the solutions vary with the type of environmental exposure. Salt air and galvanized is one thing. Salt air and not galvanized is gone.

I know that by dipping your job for a while in Hydrochloric acid you can remove zinc plating. I remember doing that few years back, just out of curiosity, by dipping a zinc plated screw in HCL, within few seconds the plating was gone.

So, here is what I am going to do. Advice me if I am wrong.

The shaft area where Inner ring of needle roller bearing fits, I will suggest either dip it in HCL to remove the plating or remove it by machining such as turning (which is rather difficult considering the setting up) , etc.

The hole area where the needle roller bearing fits, I will have to machine it by reaming, etc. (since applying HCL in a hole is difficult)

The other assembly where the hole and shaft are assembled in location fit (without bearing), I will adjust tolerances considering the 8 to 20 micron thickness (YES! that's the range we usually get) of plating.

But, there is one interesting link I found wherein different trials were performed for masking zinc plating. I guess that could be some useful alternate solution.

Following is the link-

https://www.galvanizeit.org/images/uploads/pdfs/Masking_Materials_for_Preventing_Hot-Dip_Galvanizing,_Bernardo_Duran__Thomas_Langill,_Ph.D_%28Galvanizing_Notes,_2010_Dec%29_.pdf

I strongly advise against using any hydrochloric acid around metals, especially if there is iron containing alloys, or aluminum, aluminum alloys. This will lead to uncontrollable corrosion of the parts later.

Machine off excess zinc, even a specially made tool like a battery post cleaner will work for what you need done, but that will be a unique, small tool to have in your kit, just for cleaning bearing mount pins.

Isn't there any means of inserting the bearing mount pins (hydraulic press) after the plating operation is done?

I agree for any number of reasons.

Thanks a ton for your advice.

So, HCL option is totally ruled out.

I will only stick to the machining or masking option.

If you are pressing the bearing in/on then it will probably remove the soft zinc. Electroplating in holes tends to be thicker at the entrance. I would allow clearance and use Loctite (can hear the traditionalists groaning?), it will also provide a crude electrical barrier, check the temperature rating as it can soften at higher temperatures.

Tony