Pot Metal and Chrome

[1929Chrysler]

I've noticed a lot of questions recently about chrome plating but none of the answers I've read have answered my questions, so here it goes.. It's my understanding that pot metal is a mixture of garbage metals to form an alloy that eventually deteriates over time?? Is this correct? Secondly, from what I have read, the part that is made of pot metal is stripped bare of any old chrome, plated in copper, soldered to mend any stress cracks, plated in copper again, then nickel plated and then finally chrome plated to where it looks perfect. So my question is when the process described above is done to a piece of pot metal, does this copper plating and soldering permanently halt the deteriation of the pot metal piece or is it inevitable that given a good number of years the same deteriation will happen to the same piece again?

Is there anything that can be done to stop pot metal deteriation or is it just the nature of the material?

Thanks in advance

Dan

[Guest simplyconnected]

Dan, ALL parts to be re-chromed are stripped down to base metal, whether they are steel or zinc (pot metal). Pot metal is not junk. Zinc alloy is the least expensive metal for making light castings. Steel rusts faster than zinc alloy pits, so in that sense it beats steel.

Everything returns to the earth over time. Zinc oxide turns to a white-ish powder. It breaks through paint and plating to form pits. Before plating again, all oxides have to be removed, which forms huge voids (craters or holes). It happens naturally and cannot be stopped. I have had painted headlight doors from the 50's that never pitted, but the chrome plated eyebrows on those same doors looked like a teenager with bad acne.

Even chrome plated plastic parts pit. Temperature extremes promotes chrome pitting, not moisture alone.

[1929Chrysler]

Perhaps I was misinformed about pot metal. It was explained to me that it is composed mostly of zinc and other metals such as tin, lead, copper, etc. with no specifice percentage of each. It is a fast and inexpensive method to make castings. I have several old U2 carburetors that are made from pot metal that are no good because they are all cracked. Some old U2 carburetors that are pot metal have survived the deterioration. When I asked why, it was explained that since there is no specific recipe for pot metal (percentage of each metal) they are basically mixed into the "pot". What probably happened to the carb that survived is that it had a higher content of a more stable metal when it was originally mixed in the pot. The bad experiances I have had with pot metal has left a bad taste in my mouth which is why I refered to it as garbage.

On a different question regarding plating.. Will copper plated steel stop rust and corrosion such as on water jacket covers?

Thanks

Dan

[Guest Backyardmechanic]

I have seen cooper coated steel that will corrod as copper will turn green if left in water or outside for a given time.

The best way to stop this I have so far found is to coat the water jacket with POR 15 This stuff cures to a hard finish I have a peice of steel treated with por-15 screw to the mail box been there for 2 years now and the road salt hasn't damanage it yet still shinney as the day I install it to the mail box.

Also pot metal will fall apart in time.

Vern

[Guest Backyardmechanic]

I have seen cooper coated steel that will corrod as copper will turn green if left in water or outside for a given time.

The best way to stop this I have so far found is to coat the water jacket with POR 15 This stuff cures to a hard finish I have a peice of steel treated with por-15 screw to the mail box been there for 2 years now and the road salt hasn't damanage it yet still shinney as the day I install it to the mail box.

Also pot metal will fall apart in time.

Vern

[jrbartlett]

What I have read is that pot metal was used originally because it is ideal for casting intricate parts, and accepts plating well. The problem comes with age, as the pot metal eventally deteriorates causing pits to form and the plating to bubble. Of course, this is usually 15 years down the line.

[Guest simplyconnected]

Am I missing something? I've never had a carburetor crack in half. Maybe my carbs aren't as old as yours; mine are from the '50's, but they all work very well, and they aren't coated with anything. I don't do anything special to clean them, mostly use gas on a rag to pull oil and dirt off. I've come across body parts that were cast in pot metal, that were scant (not fully filled at casting). Bondo worked great on that. After paint, nobody could tell the diff.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 1929Chrysler</div><div class="ubbcode-body"> ...Some old U2 carburetors that are pot metal have survived the deterioration. ...What probably happened to the carb that survived is that it had a higher content of a more stable metal when it was originally mixed in the pot.

On a different question regarding plating.. Will copper plated steel stop rust and corrosion such as on water jacket covers?

Dan </div></div>

If the copper plating is on the inside of your water jacket covers, it should be in contact with antifreeze (like a copper radiator), and it should be ok. If the copper is on the outside, I would paint it. Copper plating on steel is a good way to stop rust. Exposed copper should be clearcoated, or painted with anything to keep air away.

Sorry your pot metal is cracking. My experience is, they're still making engine parts out of pot metal, like throttle bodies. They have all along for nearly 100 years. I would think, if pot metal were bad, it would be replaced with cast aluminum.

[1929Chrysler]

Simplyconnected, I should have clarified. I am interested in having some trim re-chromed on my car which is pot metel. There is no coating on my carburetor. I was just using it as an example of the deterioration of pot metal. The Stromberg U2 is famous for cracking at a thin part in the casting and it is blamed on the aging pot metal and the constant expanding and contracting of the heat next to the manifold. There is an outfit in Australia who sells re-cast U2's out of, you guessed it...Cast aluminum. They ONLY go for about $1,200 the last time I checked!!

Dan

[Curti]

Modern zinc die cast or pot metal is mostly zinc and aluminum. There are other elements copper tin and iron added in for strength and longetivity. The formulation of potmetal has done nothing but get better over the years. Old die cast from the 20's & 30's is a plater’s nightmare. And yes carburetors and other castings will form cracks and brake in half. I am not sure what conditions exacterbate the deterioration of old die cast other than prolonged exposure to old mother nature.

[Guest AmerMidChrome]

Hello Dan,

There is a trick in chrome plating and polishing, the only one you will ever really need to know. The trick is to find a polishing and plating shop that has highly experienced employees. Once you find that shop, bring you parts in and let the experts tell you what to expect and quote you a price. No one can really tell you any honest answers without seeing the parts.

I agree with all the dialog that mother nature rules and will due her part over time. If you really think about it, that happens to everything in the world. Nothing can bypass her.

I own a chrome polishing and plating shop.

If you are local to the Chicago area, stop buy with your parts, we would be happy to give you a quote and tell you what to expect. If you are not local you can ship in and we will call you with the quote.

Wish you the best on your project!

[Guest Anthony Avila]

What is the best repair of pot metal hood ornament that has chrome plating blistering?

[Guest AmerMidChrome]

Hi Anthony,

Strip, polish, copper, copper buff, nickel, chrome. There are many washes in between process and very tedious work involved. If you are local (Chicago, Illinois) and can bring your part in, we can quote you a price. The pictures are not a good way of doing business.

Hope that helps and I am sorry for not getting back to you sooner, my password was locked up all this time, I just now got back on line. Thank you very much. American Midwest Chrome

[Guest simplyconnected]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Anthony Avila</div><div class="ubbcode-body">What is the best repair of pot metal hood ornament that has chrome plating blistering? </div></div> Blistering as in, the chrome is just peeling off, or as in, it looks like a teenager with bad acne?

If you have pits, the rot must be removed. After copper plating, the pits must be filled, polished, re-coppered, buffed, nickle plated, then chromed (with a lot of wash steps in between as stated).

A good plating shop jumps through lots of hoops to produce a beautiful shiny creamy-chrome masterpiece. Lots of custom hand-work is involved. That's why it is expensive.

[Guest palosfv3]

Back to the original question . What can be done to slow the deterioration of plated die cast ?

This seems to be an ongoing problem with plated parts over the years. This issue also can be applied on some new plated replacement parts.

A simple remedy is to soak and rinse the newly plated part ina baking soda solution. It seems the backside of the plated part , which is not usually finish plated, retains some of the acids from the plating tanks . Simple condensation from temperature change ( dew point ) will provide enough moisture to keep the acids active. Some platers are good about completing this step but some dont. Takes a minute to do on your part to ensure you get the maximum life out of your plating.

The other best practice is to apply a good coat of wax to the entire plated part before installing, as well as waxing all chrome regularly. It is amazing how many people forget this important step .

[Guest simplyconnected]

My plater tells me, temperature changes play a major roll in pitting.

I have kept badges in my (temperature extreme) Michigan garage, and identical badges in the basement. After years, the ones in the garage all show pits (even chrome plated plastic). The expansion coefficient of each plated metal is different.

Therefore, if your chrome is kept outside, better use a temperature controlled garage.

[Guest AmerMidChrome]

Everything weathers with time.

As mentioned, keep the metal clean and polished and it may preserve a little longer.

[HarryJ]

Dan, simplyconnected is right. Zinc and most of it's alloys are excellent choices for use in fabricating rigid parts requiring strength and high detail; however, zinc alloys of the past contain lead which causes internal granular disentergration (crystalizion). No matter what you do to the old part today it will continue to crystalize, leading to a brittle/fragil state. I have heard you can coat the original part with ceramic, fire the ceramic and then remelt the piece inside and restart the crystalization process; which only delays the ultimate outcome. Reproducing the parts is as far as I can see the only answer to this problem. I have been studying this issue for some time, as my '28 Chrysler has door and window hardware diecastings that have severly deterioted. It looks as though a modern form of investment casting coupled with laser scanning technology (see Big Dog garage re: next engine) may be the answer. More anon.

[Guest]

I hadn't had any problem with my "pot metal" door handles and window cranks until the other day. All my pieces are original and have been on the car for almost 79 years. I had never opened the quarter windows on my car and thought I would see how well they worked. No one has been in my back seat for years and I havn't looked at the quarter window cranks in twenty years. When I touched them the disintegrated totally. I hadn't even tried to turn them. They looked okay but the years had taken their toll.

[HarryJ]

Exactly,,,,,,,,,,even if you plate the pieces and they look perfect; the crystalization is there. These handles were made by the Ternstadt Co. They may have added the lead to the alloy to make it cast easier. I don't think they were planning for these to last 79 years!

[Guest Anthony Avila]

If I were to ship this item to you with return shipping if it could not be done, could you give me a price. I live in California.

Cheers

AnthonyA@mjavila.com

[Guest Anthony Avila]

Teenager with bad acne.

[Guest Anthony Avila]

Thank for the info. This will help.