Letter 3000

Problems in Gold plating 

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We have been doing Nickel and Gold plating, for some time now.It is for Brass Watch cases. Normally we are asked to do about 6 microns Bright nickel and an over coat of 2-3 microns of hard Gold. We have been using Acid gold bath with Gold Concentration of about 2-3 g/l and pH 4.2 Recently we shifted to a new premises and the solutions were transferred in Carbouys and later transferred to our plating cell (Natural PP). As it is normal, we did Activated Carbon treatment of the Gold bath because we wanted to eliminate any sort of contamination due to diffusion of particles from the HDPE carbouys. Suddenly we find that the cases are too dull after Gold but does not have any such dullness in Nickel. Did some hull cells but no haze in the operating region of 2 ASD. Any suggestions ?? Chandrashekar.

Chandrashekar
- BANGALORE, INDIA

Sounds like the carbon treatment removed all or most of the gold brighteners. I'd do an analysis of the gold bath and determine brightener levels, or contact the bath manufacturer and advise him of the problem. I'm sure a simple replenishment of brightener will address the problem. .........BOB

Bob Denney
avionics - Tampa, Florida

From personal experience I have found activated carbon treatment to cause similar problems, a dull finish. We filter our baths to help eliminate contaminations but generally stay away from the activated carbon. Also we have found that even slight adjustments in PH will make a major difference in appearance. Try lowering your PH to 4.0 or 4.1.

Michael Noel
- Newville Pa

We are doing gold plating on watch cases in acid base bath having concentration of gold 3 to 4 grammes per liter. we require to plate in the range of 0.1 to 3.0 micron thickness of gold. For this we run the show on assumption only keeping in mind aproximate surface area of the article and then calculating the aproximate weight of gold required to be deposited in achieving the required thickness.Is there any system that works automatically in the line and take care of the area to be plated and allow the required current to flow in the bath and switch off by itself after the required thickness is achieved. Thanks.

Rajveer singh
- New Delhi, India

We think the active carbon treatment which you have given to your gold bath is a bit heavy. You should give 0.5grams carbon per litre of gold solution, as your gold bath is cobalt hardened you need to replinish it with nickel standard solution so as to get the required shining, this nickel standard solution is easily available with your vendor, always keep the PH of the bath between 3.5 to 4, check it twice a day while work is going on.

Rohan Jaipal
- Rajkot, Gujarat, India

Dear Chandrasekhar,
There is nothing strange, replenish your electrolytes with brightner and additives as specified by the supplier. Initially, please increas your bath density by increasing GPC concentration, and adding density correction salts.
Good Luck

Shafiuddin A. Mohammed      metal coating shop - Dubai, UAE