Cyanide Zinc Electroplating Problems

A. Hi Rajib,
a few decades ago cyanide zinc was the only practical zinc plating method, so barrel plating is certainly possible with cyanide zinc. These days acid zinc and alkaline non-cyanide processes are very practical as well.

300 liters is still rather small, but can certainly be done. But if you are considering 'commodity' plating/pricing you would find yourself not being competitive with barrels of that size. About 800 liter tanks would be required for 14" x 30" barrels, which are about the smallest practical size for commodity plating; but if you can stay in the 'specialty plating' zone, you'd probably be better off :-)
Luck & Regards,


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

Hello, Rajib,

I've been barrel plating small door lock parts for a few years now with cyanide zinc without problems.

There are some points that i've learned with practice that I think you should pay attention to:

-since the current density is usually lower in barrel plating, depending on the shape of your parts you may have problems plating in recesses and sharp edges. Raising the zinc content of the bath has solved this problem for me.

-anodic efficiency is considerably higher than the cathodic efficiency, therefore the zinc content of the bath tends to rise if you are working with only zinc anodes. Alternating between steel and zinc anodes helps controlling this variable (does this happen with rack baths too?).

Kind regards,

A. Thank you for answering, Pedro.

Yes, increasing zinc concentration can happen in rack plating as well. In alkaline non-cyanide plating, "generation" tanks are pretty common (inert anodes are used in the plating tank and a side tank is employed where zinc anodes dissolve into the caustic, and a limited amount of this concentrated zinc solution is metered into the plating tank). I don't know if generation tanks are ever used in cyanide zinc plating.
Luck & Regards,


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

A. Dear Hashem

Try your Zinc Plating process like this
Degreasing - acid (HCl) pickling - Cyanide (NaCN)dip - Zinc plating - Cold rinse - 1% HNO3 dip- Passivation - dry

Hope this will eliminate your problem.

A. Dear Mr Hashem;

Apart from decreasing, acid pickling, in zinc plating metal to cyanide ratio and metal to caustic ratio is most important. ideal composition are metal 34 gm/lit cyanide 90 gm/lit total caustic 75 gm/lit. Also use of good brighteners and purifier will increase the quality of deposit and good brightness. Use good quality anodes, i.e., zinc 99.999% special high grade is must. Regulated current density 25 to 30 amp per square feet is required. To achieve good bright finish plate 20 to 30 minutes at the above current density to achieve 10 micron thickness in rack plating.

A. Hi,

Give a activated zinc dust [on eBay or Amazon] treatment to cyanide zinc bath, also put some purifier in the bath, maintain a medium cyanide bath with little high caustic soda [affil links] , for black passivation you need to build up a good thickness around 7 - 8 microns, use double dip for passivation, I mean dip in passivation made of lower concentration, then a final passivation dip , increase the additive containing silver content, maintain the pH given by your supplier specs.

Regards,

A. Canning is now a part of Macdermid who have an extensive network of technicians. As the brightener supplier they should be able to help you, and should be your starting point.

A. 1. Use a dip of 1% HNO3 after zinc plating and before chromating, rinse before and after.

2. That's normal.

3. Blistering is caused by bad cleaning before zinc plating or too much brightener in zinc-bath, check if you are inside spec.

Good luck,

A. Hi cousin Pankaj. Black spots and color change in zinc plating are such a common problem that we have almost countless threads here about it. Cyanide "bleedout" is a very common cause of spotting and discoloration. But one issue is that "black spots" may mean pits, barrel printout, cyanide bleed-out stains, areas where chromate didn't take, spots in the plating, spots in the passivation, etc. I think a good next step would be to send us pictures of the defective parts to try to reduce the confusion of readers inferring a different meaning from black spots and discoloration than you intended.

Also: are these parts rack or barrel plated? Are the plating and passivation processes proprietaries or home brew? Do you inspect the castings before plating, and have rejection criteria for cold shuts, pits, porosity and other defects? Could packaging materials play a part, or does the defect appear before packaging? Thanks!

Regards,

A. Dear Jon,

If you want to improve your productivity in your line. Improve process cycle time to meet your customer specifications.

If you need to get more output add up one more section in your zinc plating tank. It will reduce the process time.

Example
One Cell Plating cycle time: 30
Two cell plating cycle time: 15
three cell plating cycle time: 10

To achieve 12 barrel per hour your cycle time should be 5 minutes.

It requires 6 cell plating.

Thanks