Copy Cad Plating Questions?

[Inferno]

Hello, I have been plating fasteners to start out with. I was wondering the cause of dark circles on my zinc plate. I am plating with a 300mamp supply with a surface area of about 12. My plate is smooth, it just has a few spots. Is this do to poor agitation?

Also, I am having issues with the yellow chromate it is not sticking. When I rinse it in distilled water after the chromate dip alot of the chromate washes off. What am I doing wrong? The chromated parts have a fresh plate.

Thanks.

[jimcarry]

This could very well be poor agitation what size kit are you working with ?
And what are you using for agitation it can also be poor prep of the part itself

[Inferno]

Thanks for the reply. I am working with the 1.5 gallon kit. I have an aquariam airline ran in the tank. However I am considering adding another as I have another pump available. Is too much agitation ever an issue?

Also, does anyone know or can explain what the dark coating that forms on parts that have been dipped in acid is? Is this just the color of clean steel? If I polish then go to the acid I get the dark coating as well.

Also does anyone know what the problem with the chromate is?

Thanks alot, Ross

[jimcarry]

I think the more agitation the better the solution should appear as if it is boiling .
The darkening from the acid im not to sure about .
But the yellow chromate not adhering is a preparation issue the piece needs to be clean polished
and free from all grease and oil.
Preparation of the parts you are plating is the most important step .
The best finish you start with is the best finish you will end up with !

[Inferno]

Here is my preparation process:

First dip in acid until all the oil zinc is gone
Rinse in DI water
Dry
Polish with a wire wheel
Dip in acid for a couple of minutes
Rinse
SP degreaser
Rinse
To plating bath

If my parts where preped poorly wouldn't the zinc fail to adhere? The zinc seems durable. Is there a film on the freshly plated parts that causes the chromate not to adhere?

I have been going from the plating bath to a rinse then directly to the yellow chromate.

Thanks for any advice, Ross

[seanc]

Ross:

Got any photos of your parts? That would help a lot.

What I'm about to tell you contradicts the instructions, but it works for me:

1) You need more than 25ma/sq-in. (300/12). You'll need at least 50, 80-100 works best. See my Current Density Test Results

2) if you're using the 1.5v/300ma wall wart that comes in the kit, it's impossible to know how much current it's actually delivering unless you measure it with a meter, and it's difficult to get repeatable results from. See my Wall-Wart Characteristics

3) you should dip the part in a mild acid solution after plating/before chromating. The electrolyte leaves a brown film on the part after plating, which might interfere with chromating, (but my guess is that you don't have a good plate due to insufficient current.) See some Sample Parts

4) you don't need a lot of agitation. How much depends on how many sq-in of parts you're plating. The more parts you plate, the more gassing occurs, and the more agitation you'll need. A simple aquarium pump is all I use to circulate the electrolyte. It works well for up to @ 50-sq-in. If I have bigger parts, I put a second pump in. Some Photos & Videos of Agitation

5) How strong is the acid you're using before plating? If the acid is too strong, you may well be dissolving the steel, which will turn the parts black. You only need a mild solution, 2-5%.

6) Do NOT use SP degreaser between the acid dip & plating bath.

I would recommend this procedure (rinse between each step):

a) thoroughly pre-clean and de-rust the parts.
b) if the parts have a pre-existing zinc/cad plate, acid dip until all fizzing stops
c) hot SP degreaser for a few minutes
d) acid dip for 30-60 seconds
e) plating bath
f) acid dip for a few seconds, just long enough to remove the discoloration. You will be able to SEE the brightening action.
g) chromate

This has been working well for me. You can see my results in the link below.

[Inferno]

Thanks seanc,
I will try that method. However I think I will invest in a better power supply. I will look into the 3 amp supply that caswell offers. I would like to be able to plate more at once anyways since I have probably 100 or more bolts to plate.

[Inferno]

I forgot to add that my acid is too strong as well as I am getting a black coating. I think I will look into the Pickle #4 for this though as the acid fumes require that I do the acid part outdoors and the rest is done indoors. The Pickle #4 will allow me to do everything in one area.