Thoughts on weld repair of cast gears 1

[KM]

We've got a machine that is almost 100 years old, to be scrapped at most 5 years hence, but to be operational until then. Intermittent service two or three times a month, for a couple of hours at a time, but lots of starts & stops.

The power transmission system is an open spur gear train where many gears have little bits out of them, pieces broken off, and so forth. Mostly on the mitre and bevel gears, the spur gears look mostly OK.

See pic attached. Will post a 2nd one too.

Looks like the original gears were cast, not sure what material, though. In the 1910s could they even do cast steel? I'm guessing it's cast iron.

Some previous repairs were done by welding 5 to 10 years ago, in some type of metal and grinding a new tooth profile. From what I've been reading and from conversations with custom gear fabricators, this is generally a bad idea. Introduces all sorts of weird stress concentrations, possibly micro-cracks leading to sudden failure, etc. etc. They all say this is a repair technique to stay away from.

Yet...the machine has been working. And I only need it to keep working for another 5 years, tops.

So, what kind of risks am I running if I do another weld repair now?

Could we braze-in material rather than weld, and would that be less likely to cause problems?

Constraints are that the machine can only be out of service for about a week to 10 days at a time.

All sorts of thoughts welcome.

 

[mfgenggear]

you know this mechanical assembly is considered an antique. it's over 100 years old. it is amazing, curious how many cycles it has completed.
It would be a shame to scrap such a precis piece of work.

Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[racookpe1978]

Its a gear, so (to be a liitle bit bit obvius) all of the teeth are not only worn and irregular after 100 years of use, but also all are of the same shape.

Model two adjacent teeth sets in "perfect" 3D CAD. Program a 3D milling machine to cut a new gear by duplicating that pattern in a circle to make the gear. Don't try to duplicate the casting itself "perfectly", but only make the raw shape in steel, plastic, or a test material ... or even aluminum; put it in to run a few test turns to verify nothing binds, then run the milling program again on the final steel shape.

 

[chicopee]

Check this site out as the company may have gears to your liking"

http://www.frenchriverland.com"

Also research suppliers of refurbished machine equipment destined for third world countries. One such individual purchased from our company several presses dating back to antiquity. This individual operated from Pensylvania however I have no name and address that you could utilize.

 

[KM]

It's a stoplog lifter on a dam. Prime mover is a 15 hp 875 RPM electric motor. Power goes to two mirror-image gear trains (so each get 7.5 hp). System is reversible and operates a roughly equal amount of time in either direction (log up, log down).

Thanks to all for the further discussion on brazing---obviously a controversial approach. I'll shelve that idea unless something comes back to bite me.

I talked to a custom gear fab shop in the last couple of days. It's relatively expensive, but not insane, to get some replacement gears made from scratch for the gears in worst condition on the machine. Considering it as an "insurance policy," it's actually a pretty good value, so I ended up recommending that approach to my "upper echelons".

And chicopee---that's a great site! Thanks for the link!