Why did these welds fail?

I belong to the local Eagles club and it has been up to me to keep the
popcorn machine working. Recently the flat bottom bowl in which the
popcorn pops fell out of the bowl housing. This is because there is a
disc welded in 4 places to the outside bottom of the bowl and the
welds all failed. There several 8-32 PEM studs coming out of the disc.
Over three of the studs fits a steel plate which clamps the heating
element against the bottom of the bowl. Two of these three studs
penetrate the housing and nuts are threaded on to these studs to hold
the bowl into the housing. So I had to re-weld the disc back into
place. Anyway, all the welds failed by cracking through the centerline
of the beads. So what could have caused these cracks? Could it be the
heat cycling? Or just bad welds? When I re-welded the disc I made
welds larger in cross section than the original welds but I don't know
if the larger welds will be more resistant to cracking. Any thoughts?
The original welds did last for many years so if my welds are at least
as good as the original I will probably never need to do this repair
again. On the other hand if there is something I don't understand
about how the stresses are affecting the weld maybe my repair will
fail in a short time. Any thoughts?
Thanks,
Eric
Reply to
etpm
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Heat cycling and probably the wrong type of filler.
Reply to
Gunner Asch
I rebuilt a popper for my church, and that means total disassembly, and replacement of many parts. One of the most interesting was the wiring for heating the pot. It is a nickel based type wire, and is $9 per foot. It is rated to heat up to some high temperature repeatedly. The one I replaced was original, and just held together by rust and dust.
I would suggest that failure on yours was caused by repeated high heat cycling, and then, there are some people who just leave the pot on all the time. The minimum wage crowd, and those who have no ideas about how things work. This allows the whole thing to get to temperatures that are at the top of the safety range. If you would couple that with improper welding at the start, failure would be imminent. Without close inspection, it is hard to tell if it was Tig, or even CadWeld.
My machine had no welds, so can't be a lot of help.
It was just its time to go. Those things take a beating. I was able to rehab mine for $100, and a new one of that model is $1500, so it was well worth it.
Reply to
SteveB
I'm pretty sure the welds were MIG welds. Coulda been TIG but they just didn't look like it. The popper assembly has a bimetal switch that keeps it from overheating. I would think that keeping it hot all the time would be less harmful than repeated heat cycling. Considering how much the machine gets used I'm really impressed with how long it has lasted. I sure would like to know why it failed, to be as sure as possible why at least, because it's good to know things like that. Eric
Reply to
etpm
How long did the original welds last? 20 years or more?
Reply to
John B.
If this is a stainless steel assembly then I am surprised it lasted this long. Normal stainless steel has very little tolerance for heat cycling and vibration. Once it starts cracking it will run like a zipper.
Reply to
Ernie Leimkuhler
I can't believe in that whole, long, detailed post I forgot to say the parts in question are aluminum. Jeez! Eric
Reply to
etpm
Aluminum can be even worse than stainless for stress fatigue cracking. If they welded it with a harder wire like 5356 it would be more likely to crack over time than 4043. Plus 5356 doesn't like heat.
Reply to
Ernie Leimkuhler
Another thought, was from when a friend brought a VW case to me to weld. I fucked it up royally, and afterward, found out that aluminum actually captures oil, and that it takes a severely good TIG man to know how to boil it out, when it's out, and when to apply filler. Sounds like what your case might be.
Our church found one by the side of the road. For $100, I revived it. Lots of elbow grease, no charge for the near 40 hours of labor. But it sure works good and looks shiny. I'm going to bring it home, and make a big cart for it, and doll it all up like that restoration show on TV.
After getting into it, though, and here's my point ................ look around and advertise for wanted. Yours might just be past that point, and you might be surprised what you can find locally, particularly if you tell them it's for a good cause and you are not going to make money on it. And even if you get a fixer upper, what you end up might be a jewel.
Contact me if you go that route, I can give you some pointers.
Steve
Reply to
SteveB
According to the serial number, mine was made in 1957! All in all, except for the deterioration of the fiber coating around the wire, all else was remarkably good condition. I did replace most of the machine bolts, nuts, and chased the threads. I boiled the pot in a larger pot with some dishwashing liquid, and it came remarkably clean with little effort.
Steve
Reply to
SteveB

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