Holley Carb. plating

[dfarning]

Originally Posted by awdmh

What kind of acid?

I have had the best luck with some of the commerical phospharic acid products. Now I am use metal prep from a local autobody shop. In WI phosphoric acid seems to be illegal to sell so it is pretty had to findl.

For some reason phospharic acid works nice and slowly on zinc die-cast. I have also used a 20:1 muratic acid dip at room temp, but you really need to get the part out quickly and dried.

Originally Posted by awdmh

What kind of container do you put the chromate in?

Now I am using a 3.5 gallon plastic tank.

[seanc]

Originally Posted by awdmh

What kind of acid?

Nitric is best, but can be difficult and/or costly to obtain. IF you have to have it shipped, there's a $25 hazmat fee on top of the shipping charges.

Otherwise, muriatic or sulphuric acids work, just not as well.

What kind of container do you put the chromate in?

Polypropylene or polycarbonate. I use paint mixing buckets available from local hardware stores. Pint, quart and gallon sizes are available.

What temperature do you use for the chromate?

80º for yellow. Most chromates specifiy a range, usually 70-90º, but it depends on the particular chromate.

What ratio of distilled water to chromate? The container info was vague.

Depends on the chromate, which do you have? Mine was quite clear concerning mix ratio.

Sean

[awdmh]

What ratio are you using? The yellow crystal chromate says to use .5 - 2 oz per gallon of water. I was wondering what ratio you use, since your pieces look so good. Thanks!

[seanc]

I'm using the 1 oz/gal ratio.

I experimented a little w/the 2 oz mix, but found that either works the same, just depends on immersion times.

eg, 20 seconds in a 2 oz mix and 40 seconds in a 1 oz mix look identical.

The weaker mix just gives me more precision over immersion time.

Sean

[dfarning]

Sean,
Have you tried phophoric acid as an etch and prefer nitric acid becuse you didn't like the results because phophoric it is hard to come by.

Dave

[seanc]

Dave:

No I have not tried phosphoric on die-cast or zinc plate. OTOH, the only "die-cast" part I've worked with is my carb body, which is either NOT zinc die-cast, or contains too little zinc for chromate receptivity.

I do use phosphoric extensively to iron phosphate steel parts (prior to powder coat), but was not aware that it was used for zinc. If this is what you're using, is it possible that the phosphate is causing the smut?

I use muriatic to strip or activate an existing zinc plate. It's downright cheap, and since it's only needed to dissolve the old zinc, it works just as well as any other acid.

I only use the nitric for a "bright dip" prior to chromating. It is expensive compared to either muriatic or sulphuric for this purpose, but the difference is simply astounding. You have to see it to believe it.

Having spent quite a bit of time investigating zinc plating on the web, it seems that most commercial platers use nitric for the post-plate bright dip. Now, having seen it myself, I understand why.

Sean

[dfarning]

Originally Posted by seanc

Dave:

I do use phosphoric extensively to iron phosphate steel parts (prior to powder coat), but was not aware that it was used for zinc. If this is what you're using, is it possible that the phosphate is causing the smut?

The smut is coming from the electocleaning they get acid dipped after cleaning.

Originally Posted by seanc

You have to see it to believe it.

Looks like I'll be picking up some nitric acid tomorrow. What strength do you use?

Dave

[seanc]

Dave:

About 0.5 - 1% for bright dip. Came from chromate maunfacturers recommendation.

Sean

[awdmh]

Sean,

You do phosphating also? Do you use a commerical or homemade? I've done cast iron carb bases with homemade solutions. Doesn't look too bad. I have some commercial solution from ShooterSolutions. Haven't tried it yet.

About nitric acid, I can get some that is weakened, and some that is full strength. You just dilute it in water to about 1%? After the part is zinced, do you just do a quick dip in the nitric acid, or do you time it? Then a rinse in distilled water before the chromate?

Sorry about all the questions, but you people know more about this than I do.

[seanc]

I use Caswells Iron phosphate for hot dip parts, and a product called "ospho" for quick spray on raw steel to prevent surface rust.

Yes, just dilute the nitric to 1% or less. Use distilled/RO/deioniized water.

The nitric dip only takes a few seconds. You will clearly SEE the change, and when it stops changing, pull it out.