We do a lot of weld repair/ build up on tool and die steel sections, 4140 being very common. Al has it right, if you don't preheat properly, weld with correct filler, and post weld heat treat...it will break. Even if you are just welding a small section, pre/ post heat is critical. With a section of that size (18"dia, how long? don't know), I would expect the preheat time would be 8-10 hours in a 450F oven, and welding time would only be an hour or two.
If you take short cuts, your minor grooves will turn out to be major repairs when the shaft breaks.
Good luck,
Mark
If these grooves are where a seal rides, You may be able to use a "shaft saver" such as a "CR Speedy Sleve" I don't know if they make them that big, but they are a stainless steel sleve that provides a smooth surface for a seal to ride on. If doing a PROPER weld job with all the pre & post heating is impractical, and the grooves are were a bearing race goes, I would consider machining a wider and deeper groove and making a 2 piece bushing to restore the original diameter. There are spray welding methods used for the job You are doing. Check with Eutectic-Castolin or Colmonoy [there are others too] for the details, but You still need to do the pre and post heat treatments due to the material.
maurer03 , like al says if you weld you might be looking for a new one and as dave says you can repair those groves they even make epoxies to do that , check with your bearing supplier there is many types available that would work . if you build it up with weld or spray you will have to machine to tolerences needed can you pull off the flywheels and drives without breaking them ? they if available probably cost more than the shaft . check with factory . we have had to spray some and use our portable crankshaft grinder to machine in the field so not to completely disassemble . i don't know where you are but there are people who travel thruout the world that do these repairs many on ships shafts larger and more complex than yours . let us know what you do . good luck . willie
Well after talking with a Lincoln Electric Applications Engineer and a guy who has a PhD in Metallurgy we are going to preheat it for as long as we can stand (suggested 1 hour per 1" of thickness...therefore 9 hours for an 18" dia shaft) to at least 400 F. We'll do our best to maintain interpass temperature and then wrap it and let it slow cool. We'll dye-pen it before and after. Lincoln guy suggested using a wire machine with Lincore 33 ("hardfacing, self-shielded, cored, welding wire") if we couldn't use Lincore BUG with 95/5 Ox/Arg @ 27V, 250 in/min, 0.045 wire (he said this would actually be a spray). Our welder said the Arg shielding wouldn't work because of the wind so we would need to use the Lincore 33.
Also, these grooves are only about 0.030" deep. That rules out the bushing idea. I looked at the Colmonoy and Eutectic Castolin website and they definitely looked promising but these guys (the maintenance guys I'm helping) have apparently done this (resurfacing with a 7018 stick) before...without any of the preheat, pwht, etc and the shaft stood up to the abuse. There is a new sheriff in town over there though and he wants to try to do it right this time, hence me asking ya'll about it!
We are going to do the machining over the weekend and will hopefully do the welding monday/tuesday so I'll try to get some feedback on here next week. I have no idea when the shaft will go back in service though so I won't be able to give you any feedback regarding whether or not it survives...unless you find me on here asking how to weld an 18" shaft back together! Lets hope not.
By mooseye 
Date 11-28-2007 17:22
Edited 11-28-2007 17:25
I hate to tell you but if it has been repaired with 7018 and held up for even 1 minute, it is not aluminum.
I was already questioning the aluminum shaft in a car crusher anyway. I don't think it would stand up to the abuse.
And another thing? I want to see this 6000 hp motor. I saw a 300 horse once and it was half the size of a small house.
Is this shaft a solid round shape? Or is it a tube? If it's a tube, the pre- and post-heat requirements can be calculated from the wall thickness, not the diameter.
And who ever said anything about aluminum???
Right, my bad. To many threads on aluminun latly.
Wow Mooseye, you had me going for a while on that one.
Best regards - Al
You MAY get away with improper pre & post heat treatment due to the size of the shaft. 4140 does not harden deeply, and the softer interior of the shaft may arest the cracking that will form in the HAZ IF the shaft is over built by a great enough margin, or the loading is low enough at the repair areas, but as everyone agrees it is a risky operation. Are You machining this part in place? The bushing requires that a wider and deeper grove be machined to acomadate the bushing. While this may not be a good way for this job, keep it in mind for others.
