The Talking Machine Forum — For All Antique Phonographs & Recordings

Does anybody out there have recommendations to keep pot metal parts from degrading.

Arthur,

In my opinion, there's nothing you can do about it. Maybe keep it away from moisture, but I'm not sure that the internal corrosion is driven so much by moisture as it is by chemistry. I do believe however, that if it isn't crumbled and junk by now, it's not likely to become so. I believe after all these years, what's gonna happen, has happened. Whether or not an item survived with no problems was predestined by the original chemistry of the pot metal recipe used for it. Namely, the amount of lead in the mix. My 1924 Buick has a sun visor over the front window. The brackets for it are made of pot metal. One crumbled and broke, the other is still there, looking good as new. I don't expect it to go bad.

What Jerry said.

Keeping your parts high & dry is good advice... high humidity will accelerate "inter-granular corrosion", if that has already begun.

Generally speaking, "sick" pot-metal will show fine spider-webbing / swelling on its surfaces, often mirroring contour lines, kind of like a topographical map... if that is the case it is "delicate", and there's not much to be done for it.


I have a small collection (dozen or so) pot-metal Orthophonic sound-boxes, ranging in condition from "excellent" to "very bad" (swollen / cracked / split / could probably crumble with my bare hands), and varying states in-between.

The era prior to the Depression was not a good time for die-castings... manufacturers / metallurgists seem to have gotten on top of the issue by the mid-1930's / WW II.

Prayer helps. I was recently handling the tone arm off my big Brunswick and it
shattered in my hand. Bill K Cheers

dutchman wrote:Prayer helps. I was recently handling the tone arm off my big Brunswick and it
shattered in my hand. Bill K Cheers

Were you praying for it to shatter?

Curt A wrote:

dutchman wrote:Prayer helps. I was recently handling the tone arm off my big Brunswick and it
shattered in my hand. Bill K Cheers

Were you praying for it to shatter?

While I was working on it I kept saying please don't break please don't break! Sort of like that last tug on a bolt to make sure
it is tight enough---- SNAP! Bill K

It is possible that the quality of pot metal varied from batch to batch.

Bill

Lucius1958 wrote:It is possible that the quality of pot metal varied from batch to batch.

Bill

I think that is so, based on various examples of Pre-WW II die-castings I have observed, even within same product family / model runs.

I've certainly seen Victor Orthophonic Sound Boxes (pot metal) run the gamut of conditions, from nearly perfect to horribly distorted / almost disintegrated.


Certain die-cast automobile carburetors from the 1920's are notorious for pot metal disease, one of the worst was a particular model of Stromberg carburetor use on luxury V-8 autos (Lincoln L ?) that was noted for warping, cracking, leaking, and dripping raw fuel down onto the hot engine.

So, not only would the carb not function well, it might also result in the immolation of the vehicle !

My father worked as a die caster at GM years ago. In order to speed up production, the supervisor had him alter the injection / pot temperature entering the die. I always wondered if the different temperatures resulted in the variability of product. The problem might be the push for more numbers, and not the engineering of the process in the long term.

Arthur,

Interesting anecdote. General Motors was all about volume production / low production costs, perhaps not as famously as old Henry Ford, but no less cost-conscious.

I think they "needed" their products to be "good enough" to last say 10 years in the user's hands, first as new-car, then as used-car first time around. This builds the rep for "quality / durability", after that... feh.

And if getting widgets die-cast more quickly meant better bottom line for the General, I could definitely understand that.


And all manufacturers are in the business of selling new products, so making something that "lasts forever" may not be in the best interest of the business model.


That said, as a consumer, I want a product to "last as long as I want it to last", especially if it is a big-ticket item. ( This is why I don't buy a lot of "new" stuff... )

Replacing perishable items (belts, hoses, bushings), and/ or normal wear items is one thing, but when structural components self-destruct, that makes me unhappy.

The only pot-metal issue I am aware of with Post-WW II GM die-castings was with their Rochester model B carb, used on Chevy sixes from 1948 into the early 1970's. It might have been as much a design issue as a materials-quality issue, but the top casting for the carburetors tended to warp (compounded by mechanics tending to overtighten the four bowl cover screws), but I have not seen the kind of material degradation (cracking / crumbling metal alloy) that we see with pre-WW II pot-metals.