Metal Plating, Rust corrosion problems with zinc plating tank

[ajmcforester]

OK I tried to post this on Caswell's site and it would not let me. I know we have some people that use the CopyCad, so I thought I'd post hear, and try to post with Caswell at a later date.

I have been plating with the CopyCad plating system for almost 2 years. Over the last 2.5 months I’ve been noticing a rust corrosion problem near the location I plate. Then 3 weeks a go on Saturday I got great plating of parts. That Sunday I was plating and the yellow-chromate would not adhere properly to the newly plated parts. They came out with a higher shine from the zinc tank than the day before and I didn’t add any brightener to the tank over that weekend.

I cleaned the parts and re-prepped the parts for plating the next week. That same week I wanted to see if the yellow-chromate was good so I took some new fasteners that I wanted to coat with yellow-chromate no problems.

The next weekend I checked the PH (was close to 7) and set the tanks up. This time the plating came out very bright and the yellow chromate didn’t adhere. However this time three days later the parts were rusty with a red oxide powder on the surface. Also steel parts near the tank got very rusty also.

I’m thinking of just setting up a new tank, but I’d like to have an idea what went wrong so I can prevent it or even correct my current tank any thoughts?

[motorman7]

You're question is a bit of a challenge as there are a number of steps in the process, especially after the zinc plate. I have run into what you are mentioning but changing my procedure has helped. I will detail what I am currently doing and what works best for me, and maybe that will help.

Currently I am doing the heated acid bath for 15 minutes or less, then the electro-zinc plating for about 15 minutes. I am guessing you are probably doing this. For the brightener, I put in one teaspoon about every 3 or 4 batches - as needed to get the brightness I am looking for.

Once I am zinced, I use a spray bottle with RO water to clean/rinse the part, then I dip into blue chromate for about 30-40 seconds. You may not be using the blue chromate, but it gives you the nice rainbow effect on the parts plus helps the yellow to stick. Immediately after the blue chromate, I dip the parts into the yellow chromate for about 2 minutes till I get the right shade of 'gold', then I rinse in a bucket of very hot tap water, then light air dry from the compressor (10 -15 psi). The very hot tap water is key. I think if you rinse with cold water it effects the yellow plating. This is what I was running into. Also, I make sure my yellow chromate is heated to about 90 degrees F. This seems to help a lot.

Also, regarding the quick rusting, sounds like you are not getting enough zinc on the parts. I'd crank up the Amps a bit or increase plating time.

Hope that helps.

Rich

Edited July 25, 2011 by motorman7

[240260280z]

Good info here: http://www.finishing.com/Library/chloride.html

I tried a quick and dirty method:

Degrease

Acid wash

Water rinse

Electroplate in electrolyte

For all those who are curious:

Here is a DIY Zinc Plating site: http://www.thisoldtractor.com/gtbender/zinc.htm

Here is more info and examples:

http://www.medial.com/suzuki/zinc-plated/

http://www.vmax4.com/vbulletin/showthread.php?6172-Zinc-Plating...

http://www.britishcarforum.com/bcforum/ubbthreads.php/topics/65506/2

[ajmcforester]

I had no problems with the plating for 1.5 years was working like a champ, I practiced my same routine then things started to fall apart. I've been using a 24 hour soak in vinegar (longer if needed) to remove any rust and contaminates,wiping off and using hot water to rinse. Then I soak in a degreaser 150deg for 10 min and check with distiled water to see if it is clean, and to rince. I'd found I better plating with 4 volts, slightly higher amps, and a shorter plating time about 7-8 minutes or until buildup started on the wires, also kept the tank around 110deg. I don't heat the yellow chromate, I swirl the part very quickly and added .25oz (only once) of light oil and I get the rainbow affect. I set up to air dry for three days. I only added brightener when the zinc plating gets very dark.

Why my tank is rusting stuff is what concens me, I've plated about 90% of all the zinc and yellow chromate parts. Maybe the salts are shot or the sediment at the bottom of the tank is messing up the plating. Also why is the yellow chromate not adhering to the plating from my tank but no problem on new bolts?

[ajmcforester]

GReat thanks for the sights I'm not a big fan of getting help from Caswell's forum, it is a mess

[240260280z]

The finishing.com site mentions temperature being important. Since most heat the electrolyte, the recent high humidity and high temps in NJ may not be the problem. Did you plate in a hotter than normal garage?

Excessive Temperature: The "cloud point" is the temperature at which the primary organic additive, or wetter, is forced out of the bath. Unlike salt in water, chloride zinc additives are inversely soluble with heat. The higher the temperature, the lower the solubility. The cloud point can be influenced by the pH and the chloride concentration. In addition, as the bath ages and builds up impurities and brightener products, the cloud point can decrease. Proprietary brightener systems have cloud points from 90 to 165° F. It is prudent to find out which conditions are routine for your bath and utilize a brightener system with a higher cloud point if you are encountering oilout due to temperature and do not want to increase expenditures for cooling.

The only other culprit I could think of would be an open liquid acid container or a lead acid battery. The fumes make items in the vicinity rust.

[LeonV]

Nice avatar Blue! Although the last word should be автомобиль.

[motorman7]

I do think the outside temp and humidity effect the final product. There are days when things plate perfectly, and others where you really have to work at it and re-do the parts. Weather is my only guess.

It wouldn't hurt to filter your plating tank. I just take an old dress shirt and pour the liquid from one 5 gallon bucket into another using the shirt material as a filter.

Edited July 25, 2011 by motorman7

[240260280z]

Nice avatar Blue! Although the last word should be автомобиль.

The forum engine truncated the message thus the missing bit Good catch Comrade.

[LeonV]

No problem comrade. Lada was tops on my list growing up! Of course I had no idea what a Z-car, or even a Nissan, was back then.

[ajmcforester]

Last year I did have a harder time in this weather, last year I did a 5 minute dip then an flash acid dip and another plate to get good results. This weekend I'll filter the tank and recheck the PH and try again. The tank has never acted this bad before.

Chloride zinc additives are in a suspension. Blue your statement fits my concern that my tank is getting weak. I've done a lot of plating with 1.5 gallon setup. If the levels are low, temp would more impact the chemical's availability to conduct the desired reaction. This is good information to think about.

[240260280z]

I am in Nova Scotia this week enjoying temp in the 70's... I was in nj for the past 3 and is seemed like 100 every day and often very humid. Worked on my s2000 in a south facing garage...like a Finnish sauna.