I'm trying to prep a chromed part for powdercoating, but the chrome plating is peeling off. Sandblasting works, but then the chrome flakes clog it. Is there something I can soak it in to strip the chrome but not eat the steel?

The chrome flakes clog what? The blaster?

I just had a set of chrome wheels blasted by the powdercoater, and it worked fine. The chrome was also peeling in my case. Acid dipping is also a common route to remove chrome, though it's expensive.

Yeah, they fall in the sand and clog the pickup. They're coming off in pretty big chunks, but I can't get them to come off with a wire brush. Do you by any chance know what acid is used for that acid dip?

How about just using a belt sander? (assuming the part is big enough)

-Tony

QUOTE (TonyAKAVW @ Jul 13 2005, 05:23 PM)

How about just using a belt sander? (assuming the part is big enough) -Tony

Big enough yes. Convex or flat, no.

Do not use a belt sander. Chrome is hard and if you are unlucky enough to make an impact on it, you will then screw up the finish. Also the acid (and the quantity) is not something to screw around with at home. Bring it to a pro.

try ez-off oven cleaner.

If I remember correctly (it's been 17+ years) concentrated Nitric acid is used to strip copper and nickel flash plating off of steel parts, and I think it will take off the chrome too. As long as the acid is very concentrated it won't hit the steel itself much. If you get any appreciable amount of water into the acid, it will bite the steel very quickly. This really isn't something you want to try without real research and a lot of safety equipment.

The other option is back plating, just like a plating setup except the polarity of the connections is reversed, and probably dummy stainless steel electrodes are used. In this scenario you plate the chrome off of the part and back into the solution.

A lot safer to let a pro do either of these

Harvey

QUOTE (HarveyH @ Jul 13 2005, 05:46 PM)

If I remember correctly (it's been 17+ years) concentrated Nitric acid is used to strip copper and nickel flash plating off of steel parts, and I think it will take off the chrome too. As long as the acid is very concentrated it won't hit the steel itself much. If you get any appreciable amount of water into the acid, it will bite the steel very quickly. This really isn't something you want to try without real research and a lot of safety equipment. The other option is back plating, just like a plating setup except the polarity of the connections is reversed, and probably dummy stainless steel electrodes are used. In this scenario you plate the chrome off of the part and back into the solution. A lot safer to let a pro do either of these Harvey

Yikes. I was hoping it was sulfuric, phosphoric or hydrocloric. There are three acids I won't touch.. Nitric, perchloric and hydroflouric. Now that backplating idea.. I wonder what I'd have to use as an electrolyte..

QUOTE (Dr Evil @ Jul 13 2005, 05:38 PM)

try ez-off oven cleaner.

I don't think that will work.. I've used oven cleaner on a chromed cooktop (yes it's chrome and not stainless.. it's rusting), and it never took off the chrome.

I believe you would use a weak version of the chrome bath used for plating. This raises the problem of chromates, VERY toxic, and VERY detectable by the various regulating authorities. Discharges of chromates to the environment in the parts per billion level are easily detectable and actionable...

As for HF, EXTREMELY nasty. If you look at a reagent bottle of any of the regularly used acids, Sulfiric, Nitric, Hydrochloric, etc., the safety write-up says that if you get it on you, wash well and see a doctor. For HF it says to start washing and keep washing until the doctor gets there.
I used to work in a small plating lab for a Mil aerospace company. The old guy that did the real special stuff was once puting a gold plate on a crystaline garnet substrate for one of the RF development labs. As part of the process he would etch the surface of the substrate in a 50% Nitirc, 5% HF bath. After he took the substrate out of the etchant, I saw him rub a spot on the surface of the garnet with the tip of his finger for less than three seconds. He then put that hand into a running water rinse bath for 30-45 seconds to rinse it off, then continued the preparation process. About a half hour later his finger started to itch. A half hour after that his finger started to hurt. He left work and went to the Dr. treatment for light to moderate HF burns is usually direct injection of Calcium Gluconate to neutralize the acid within the tissue. (For serious burns they start out by cutting away most of the affected flesh) He was out of work for four days, under heavy medication, and when he came back the tip of that finger was 1/4" shorter than it had been.

H.

QUOTE (HarveyH @ Jul 13 2005, 06:17 PM)

I believe you would use a weak version of the chrome bath used for plating. This raises the problem of chromates, VERY toxic, and VERY detectable by the various regulating authorities. Discharges of chromates to the environment in the parts per billion level are easily detectable and actionable... As for HF, EXTREMELY nasty. If you look at a reagent bottle of any of the regularly used acids, Sulfiric, Nitric, Hydrochloric, etc., the safety write-up says that if you get it on you, wash well and see a doctor. For HF it says to start washing and keep washing until the doctor gets there. I used to work in a small plating lab for a Mil aerospace company. The old guy that did the real special stuff was once puting a gold plate on a crystaline garnet substrate for one of the RF development labs. As part of the process he would etch the surface of the substrate in a 50% Nitirc, 5% HF bath. After he took the substrate out of the etchant, I saw him rub a spot on the surface of the garnet with the tip of his finger for less than three seconds. He then put that hand into a running water rinse bath for 30-45 seconds to rinse it off, then continued the preparation process. About a half hour later his finger started to itch. A half hour after that his finger started to hurt. He left work and went to the Dr. treatment for light to moderate HF burns is usually direct injection of Calcium Gluconate to neutralize the acid within the tissue. (For serious burns they start out by cutting away most of the affected flesh) He was out of work for four days, under heavy medication, and when he came back the tip of that finger was 1/4" shorter than it had been. H.

Yikes. I think I'm going to use a mechanical method of removal. Probably continued sandblasting, as tedious as it is.

I'm a technician at a university, and I once caught a student brushing hydroflouric acid based glass etching stuff on his project WITHOUT GLOVES! I made him put some on.

The stuff is even dangerous for the pros.

a little sulfuric or hydrochloric will do the trick, or battery acid. nice

QUOTE (914GT @ Jul 13 2005, 06:30 PM)

The stuff is even dangerous for the pros.

it seems like once a year you hear about the accidents that kill a few of these guys....one falls into a tank, the guys trying to rescue him parish as well.....scary stuff....

I, picked up a set of headers that have been chrome plated, I did want it removed untill I went to a chrome shop, for the price of removal, they said $180, I said I'll live with thw chrome.

Local Cali chrome shops that offered stripping (up thru '80s) used potassium cyanide. Gee I wonder why you don't find this service available anymore--but possibly in Beijing
MF

FYI, Hydrofloric Acid will absorb into your skin and attach the calcium in your bones. If you do not get the calcium gulconate shot asap it will be too late reverse the effects. The next morning you will wake up with your bone eaten away and basically gone. It will also bind to your DNA and that ain't good.

I work in the semiconductor industry and have played with HF on many occasions. It is one of those materials where you where the maximum amount of personal protection equipment available and still take it slow...while keeping the calcium gulconate in plain view.

-Britain

Complex metal-cyanide salts (i.e. Potassium Gold Cyanide) are used in a lot of plating applications, particularly for precious metal (gold and silver) plating. In most plating applications, a metal salt is dissolved in the bath and sacrificial anodes of the metal being plated are hung in the sides of the bath to replenish the metal as it is deposited onto the plated part. For high value metals like gold or platinum, stainless steel anodes are used and the metal content of the bath is depleted as parts are plated. This requires that the bath be analyzed regularly and additional make-up salts be added to keep the concentration at the required levels. Even so, a precious metal plating bath is very expensive. When I worked in the lab, we had two 11 gallon gold plating baths and an 11 gallon gold strike bath, and these contained quite a few thousand dollars worth of gold salts. If I remember correctly (here's old-timers disease again) a plating bath held 1 to 1-1/2 ounces of metal per gallon of solution, and the strile bath held about 1/2 oz/gal.
A strike bath is normally a low metalic concentration bath used to get the first flash of plating onto the work surface. These are usually used at high current and will activate the surface of the part to produce a good adhesion of the first layer of metal onto the surface. Even copper plating will use a copper cyanide strike bath for the first flash plating in a lot of applications.

Harvey

Harvey

Interesting stuff.


M

I haven't heard anyone offer this one,bu8t I'll throw it out.

I don' know,how big your part is,but if it's not to big,your answer is on the shelf at your local grocery store

At about a dollar and a half a bottle,get yourself some blue Lysol toilet bowl cleaner.

Read the label,it IS hydrochloric acid.

I have watched it strip chrome,rust,anything on a metal surface.It'll usually take an overnight soaking,but it will work.

Your metal will come out as clean as a new nickel.The only downside is that the material almost always flash-rusts as soon as you remove it from the solution.You gotta treat it very soon.



Just M2CW
Ron

Thanks for all the suggestions and warnings. I have come to the conclusion that any method that dissolves the chrome will leave me with a solution of dissolved chromium. I don't want to be anywhere near that. (Ever seen Erin Brockovich?)