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Plating racks build up with plated metal

 

Q. Nylon coated racks (base material :MS and Spring steel) are used to plate watch cases. Contact tips are heavily built up with multiple layers of Ni,Pd/Ni and gold. Many alkaline and cyanide based strippers (immersion) have been tried. Electrolytic strippers have also been tried. Either its stripping rate is very slow or it attacks the base material of racks itself. Presently we remove it mechanically (cutter). Can anyone suggest an immersion stripper whose rate of stripping is fast and also one which doesn't attack the base material.

Thanks,

Venkat Raja
- Kitchener, Ontario, Canada


A. Are you sure they are nylon coated, Venkat? Nylon offers little resistance to plating chemicals. The racks should perhaps be plastisol coated?

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


 

A. In addition to Ted's comment, I would switch to stainless racks so that the stripping chemicals won't eat the exposed portion of the racks.

Dan Brewer
chemical process supplier - Gurnee, Illinois


 

A. If you use stainless racks with PVC plastisol coating as suggested, then you will be able to strip in nitric acid with a controlled amount of chloride to assist in gold removal(fume extraction essential) or electrolytic in nitrate based strippers but you will also need a cyanide stripper if gold is thick.


Geoff Whitelaw
- Port Melbourne, Victoria, Australia



Q. Thanks to Mr. Ted and Mr. Dan and Mr. Geoff for their reply.

Earlier (3 years back) we used to use plastisol coated racks. As its coating was porous it affected the quality of our products. Hence we switched over to nylon coated racks whose quality was excellent (it was chemical resistant, heat resistant and it was not porous). Also we are not in a position to use bare ss racks as we use acid gold strike baths (pH 0.6 and it's H2SO4 based bath.) And moreover we don't want to coat plastisol over ss because it's costly and the possibility of getting back to old problem is high. With the prevailing parameters please try to suggest a stripper.

Venkat Raja
- Kitchener, Ontario, Canada

A. Hello again, Mr. Venkat. Progress is to be applauded, so if nylon works for you, great! But plating racks have traditionally been coated with vinyl plastisol for many decades, and the reason is that vinyl is resistant to all chemicals commonly used in a plating shop whereas nylon isn't. Thousands of shops around the world have used plastisol coating in thousands of critical applications; so if you experienced porosity, the problem was in the execution, not in the concept.

You have already determined for yourself that you cannot successfully strip the racks with an alkaline solution, nor a cyanide solution, nor electrolytically. Geoff suggests the remaining acid and nitrate options but feels that nylon and steel are incompatible with them. Good luck, and please tell us when you find the solution.

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Pine Beach, New Jersey


To prevent tin coating on jigs and hooks

+++++

Q. I am an electroplater in Chennai.

My question is: we are using copper jigs for mounting components in the tin plating process; along with the components the jig also gets coated. After 4 hours of plating process we are forced to stop work for want of removal of tin coated on jigs. We used to melt the coating and send for reprocess of pure tin anodes. Instead of this, is there any method to avoid coating taking place on jigs. We tried plastic coating on jigs, leaving the hooks. We don't know how to remove tin coating from hooks. Please give me a good solution for this problem.

Mustak Ali
electroplater - Chennai, Tamilnadu, India


+++++

A. Hello Mustak Ali

You can use plastisol coating to coat the plating rack body and exposing only the contact portion of the hook/clip. You can remove the tin coating on the hook by tin stripper either by immersion or electrolytic.

Germie Maravilla
- Laguna, Philippines



thrashing

Nickel is plating onto PVC plastisol coated plating racks

May 31, 2009

Q. Dear sir, we are facing the problem of depositing nickel on PVC coated jigs in ABS plating plant. Kindly let us know the reason (is this is problem of plastisol or something else) and solution.

Jyoti Kamboj
manufacturer - Delhi, India

June 18, 2009

A. I would say either the coating is thin enough to allow a little attraction, and allowing the rack to become "encapsulated" with plate, or there are pinholes in the plastisol. A spark tester will demonstrate if there are voids in the coating, and their location. There is also the remote possibility that the plastic was somehow made "plateable", but this seems pretty far-fetched...

G. Brackett III
- Maine


June 20, 2009

A. We found that we would get 1-2 years of use out of a rack before it started to plate. Normally it happened in an area that had been roughed up or abraded-IE: the smooth surface was not smooth any more.
We would strip and re plastisol the rack in house. Some times we would use a couple of layers of 1" platers tape to get a bit longer life out of it. Now, there are vinyl patch kits available or you can try the vinyl for pliers handles that can be bought in some auto parts stores and some big box stores. It will extend the useful life of the rack until you can find time or money to just recoat the rack.

James Watts
- Navarre, Florida


June 23, 2009

A. We had trouble with a polypro tumbler barrel plating in EN. The problem turned out to be poor rinsing of our parts. The part were ground prior to plating. Fines trapped in a lip on the parts "seeded" the plating barrel, and we got patches of nickel on the more porous parts of the barrel where the metal fines got trapped.

Michael Costello
- Grand Junction, Colorado, USA


July 3, 2009

A. Jyoti, You give us your problem but do not tell us how you got there! It seems to me like the Plastisol jig is becoming suitable for electrodeposition, but the reasons for it are unclear. It could be that the Plastisol has started to break down and is not offering the insulation to the jig that it should, or it could be that you are using the jig in the ABS activation process and as a consequence you have also activated the jig.
The remedies are slightly different for either cause. The initial thing is that you need to strip down your jigs and recoat them. This will solve the problem in the short term. If you are using the jigs to activate the ABS, stop doing so! This will entail you buying or making more jigs specifically for the activation process. You will then need to find a way of transferring the activated ABS parts to other jigs that will not take up metallisation; this could be a tricky step, but since we don't know what you are doing, we cannot offer any guidance from here in.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

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Ed. note: Readers may wish to also view letter 36615 "Our ABS plating rack is getting electroless nickel plated".


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