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Protection of silver-coating

 

We manufacture nuts in ss 316,which are silver coated. We want silver-coat on internal threads only. We want to protect silver-coat on hex-face of nuts, which get unnecessarily deposited during the silver-coating process. Please suggest some soln.

Sharadj Pawar
Fluid Control - Mumbai, India

Not knowing your pre treatments this may not work as anything too hot removes the tape - try one or two and see what happens.

Electrical wiring tape - the sort of thing you wrap round wires in a car if you fitted a radio - wrap this round the outside of the nuts.

The cost of doing this may be more than the cost of the silver saved.

If the customer requires only silver in the thread see if they can accept silver all over.

Otherwise try masking the thread with a rubber plug (cheap,fast and reusable) and stripping.

Martin Trigg-Hogarth
surface treatment shop - Stroud, Glos, England
 

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I don't know whether it would be worth the effort, but you could fabricate a threaded PVC tube that you could screw these nuts onto. The tube could be perforated, and could have an anode wire running through its center. Then you could pump solution through it, and plate only the threaded area of the nuts.

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

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Hi Sharadj,

Ted gave me an idea ... on the premise that one idea often generates another.

For what it's worth, please consider this ... but it would have been easier had I known the nut sizes!

l. Get a plate/strip of PVC plate ideally the thickness the nut plus about 1/8".
2. Drill holes the size of the nuts' internal bore (it could be larger but the hole size 'area' has to be LESS than the nuts 'outside' area). Accurately stagger these holes, let's say @ 2" centers for argument's sake.
3. Heat up the nuts ... to around 400 degr. F.
4. Press into the holes but less, say, the l/8" thickness mentioned in # 1.
5. Withdraw the nut(s) to leave essentially a recess that the to-be-plated nuts can be 'forced' into & will fit into.
6. Get a thin(ner) strip of PVC with holes @ 2" centres (see # 2).
7. Locate the to-be-plated nuts into the recesses and also position the # 6 strip over them (accuracy is necessary).
8. Go PLATE !

This is a swaging process and should work OK. The secret is maybe to make that 'hole' a shade smaller than the nut so that it will not be too difficult to force out the material to fit around the nut.

Food for thought if nothing else.

Freeman Newton [deceased]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).

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Hi Sharadj:

Not knowing the size and quantity of nuts is a problem, but you might stack them together in small lots (4/5?)and wrap the outside with platers tape. Cyanide silver has an excellent throw and will plate the inside of an ideal number of nuts in the stack. If they are big enough (say 1" or more) and in small quantity (say dozens or even hundreds, not thousands) you might consider a similar approach as Ted proposes, that is mounting them in a rotary device and brush plating the inside only. Brush plating is for low qty. and difficult to reach areas. One advantage, less silver gives the specified thickness. Disadvantage, higher solution cost.

Guillermo Marrufo
Monterrey, NL, Mexico