Pot Metal is driving me nuts!

[tgoode]

I am attempting to strike plate some pot metal parts using Flash Copper in preparation for electroless nickel plating. My prep work on these parts has been:

-Sandblast with silica sand paying careful attention to pits to ensure they are free of oxides
-degrease with a soak in naptha (5 minutes)
-degrease with a soak in acetone (15 minutes)

The plating conditions are:

-Dip plating in flash copper @ ~130 degrees
-600 mAh transformer
-2l of solution
-3 square inch anode
-approx 10 to 12 square inches of surface area to be plated
-Anode is approx 4" away from the parts
-Plating time was 10 minutes

I am getting "flowers" of some kind of whitish oxide forming on and growing out of the surface of the parts. Beneath the oxide the part is blackened, pitted, and not plated.

I have successfully plated this alloy using the pot metal primer in the past. I have switched over to Flash Copper with the understanding that it provides a superior strike coat.

Am I doing something wrong?
Is the temperature causing this?
Could this be the result of surface contamination by the Acetone or Naptha?
Would boiling the parts in distilled water prior to plating help?
Should I zincate the parts first?

[48Buick]

Tgoode:
I dont know the make up of the flash copper....but, I do know you will be better off if you just sand blast, blow off your part and start your plating in the strike bath. Try to go into the bath with the power on and at the highest setting it will allow. Back off the amps after a min. of plating. Basically your trying to get the plating on as fast as possible so your base metal wont corrode. IE...Turn black!
I use a neutral nickel bath and have used copper cyanide in the past.
It seems any time you introduce fresh/raw potmetal to anything but air.... you run the risk of reactivating old corrosion deep inside the metal. I have had some parts blister after a month..(depresing!) But, that is the nature of potmetal/zinc alloys.
To me it seems that sandblasting with silica sand is the best way to remove chrome/old nickel/reactivate old nickel and corrosion in one step.
Good luck and keep at it! It takes time and patience...im still learing after 3 yrs!
Also...try and get some type of power supply that you can adjust. Its really the only way to go. Check here for some or E bay for bigger units.
48Buick

[tgoode]

Well, I'm having no luck with the flash copper at all.

I'm switching back to the pot metal primer as I know for sure that it works with this particular alloy.

[mcaswell]

Please post a problem report if you haven't already.

In all our tests, Flash Copper stuck to Pot Metal parts like glue. We had a hard time to even bead blast it off. It's a commercial grade product, used commercially as an alternative to cyanide copper baths by large plating shops.

[slvrlily]

The acetone may be the problem. I've had similar problems with diecast and it stopped when I switched to SP degreaser. I also follow that step with Lava soap (of course, I'm plating little things, don't know how that would work with something bigger). Water sheeting is a pretty good test to see if everything is completely rinsed.

[mcaswell]

If you sandblast a greasy part, you actually POUND the grease INTO the surface.

You should ALWAYS degrease BEFORE sandblasting.

As for naptha etc. These items are really only good at removing OILS, not greases. You need the action of sodium hydroxide (lye) which chemicallly changes the grease into a water miscible soap.

[Coley]

A lot of older zinc die-cast parts had a small portion of lead introduceed to the melt before the die casting run started. This made for a smoother finish in the steel dies. The lead also contributes to the corrosion (pitting) of the metal. Not sure how the copper strike will act on lead....

[fly]

This is what I do and it works every time, make sure you have the part polished and free from those white spots from the pits because that will cause problems. Get some maratic acid and mix about 4oz acid to 10oz of water and after you degrease the part take a brush and brush the mixture over the part until it turns grey and rinse and then go to your flash copper. Don't leave the mixture on the part very long.

[chromepl8tr]

one thing i have not heard mentioned is the importance of a good electrical contact. make sure your parts have a very good contact at the rectifier,buss bar and item to be plated. remember you are using low voltage and high amperage. just like a car battery. bad contact and your car won't start.bad contact and your part won't plate!