stress relief vs annealed 1040

[Tmoose]

Our spec for a big rotor shaft (9 inch diameter, 100 inch long) is annealed 1045.
A string of 1 inch keyways will be milled down one side, and some diameters are reduced several inches, and we expect to maintain shaft "straightness" of < 0.003 inch TIR relative to bearing journals at the end.

Does the annealing process (850C/~1600 F, furnace cooled) reliably serve to stress relieve (~1200F, soak for 1 hr/inch, still air cool) as well?

thanks,

Dan T

 

[unclesyd]

Are you talking about re-annealing the shaft after machining in lieu of a lower temperature stress relief? The stress relief mentioned would be adequate.

Some points.
Your annealing temperature (850C/1600F) is a little high according to my charts. My charts show 1450F and furnace cool at 20F/hour until 1200F.

A full anneal would rid the shaft of all stresses.

If I may ask s what happened to the previous shaft?

 

[swall]

Yes, but--if any straightening was done to the annealed bar at the mill, it will have some degree of residual stress present. So, you may get some benefit by performing a stress relief after some rough machining prior to cutting all of your keyways and reduced sections.

 

[mfgenggear]

low temp Stress relieve after machining is fine.
My opinion annealing after final machining is bad.

anneal prior to finish machining, otherwise you will lose your straightness & TIR readings.

even at 1450 F there is a chance this shaft is going to move. Your shaft will may distort big time.

 

[Tmoose]

Most of the facts are lost to antiquity.
My current belief is the material is bought annealed, then all machining done.

I was mostly wondering if annealing also accomplishes stress relief, since the basic anneal spec did not mention a 9 hour soak, although still air cooling sounds quicker than a furnace cool

 

[CoryPad]

Yes, annealing accomplishes stress relief.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[arunmrao]

Why do you need to use a 1045 grade in annealed condition. Atleast you can try normalized and tempered condition to improve toughness.

Chocolates,men,coffee: are somethings liked better rich!!
(noticed in a coffee shop)

 

[Tmoose]

1045 anealed is the existing spec.
Yesterday I found one of the drawings on this series of machine that was issued in 1930.

I assume normalized and tempered would add some $$ ?
How straight can I expect a normalized and tempered shaft to be after keys or other assymetrical machining is done on a shaft that was machined with less than 0.003 inch TIR ?

Thanks,

Dan T

 

[dbooker630]

Normalized and tempered may be a less expensive heat treatment than annealing as far as furnace time is concerned. I have changed some practices for 4340 from cycle or subcritical anneal to N & T while still maintaining machinability.

 

[mfgenggear]

How straight can I expect a normalized and tempered shaft to be after keys or other assymetrical machining is done on a shaft that was machined with less than 0.003 inch TIR ?

same as annealing very bad after final machining? will distort.

in my opinion from practical experience, N & T is better than anneal. it homogenizes the material remove stresses
condition the material for post machining, annealed material is harder to machine because the hardness is to soft.makes it's more difficult to obtain a good finish.

 

[Tmoose]

Sorry for the confusion.

My question is what starting material condition would be less likely to distort during/after key milling.
Or, which one can be expected to distore/bend as a result of keyway milling?

Thanks,

Dan T

 

[mfgenggear]

with out viewing the actual part it is difficult to advise.

however if there is minimal machining on the parts stresses will be minimal, if the machining is heavy & aggressive residual stresses will be induced then it must be stress relieved after rough machining. "if not stressed", how much distortion will appear is difficult to advise. it could distort out of spec for sure.

Hope this helps.

 

[Tmoose]

I have experience with shafts in the 1 to 3 inch diameter range made from non-stress relieved material bowing because milling a string (or even worse, a full length) keyways removes residually stressed material. I compare that to cutting a few bicycle spokes from one side of the wheel. The tension in the opposing spokes no longer is "balanced," so the the wheel rim leans away (is pulled away)from the missing spokes. The keyway in a formerly straight 2 inch shaft >>WILL<< become either the low or the high spot depending upon the nature of the shaft's stress state.

Yes, machining always creates "some" stress, and it is possible to induce stresses from aggressive machining directly, or even to pump enough heat in to locally upset material and create enough residual stress to cause permaantent distortion that way.

In the case of hundreds of these 9 inch diameter shafts made over 50 years no intermediate stress relief (after rough machining) has ever been specified, and generally things work out OK. In the last 3 or 4 years a few rogue shafts have had problems, and checking shaft runout has not been consistently done even in those cases either when new or when trouble starts brewing, as far as I can tell (today).

I just want to recommend next time and forever we start with material that is less likely to be inherently laden with residual stress just waiting for the chance to pull things out of line.

 

[mfgenggear]

Tmoose
Normalize or Anneal either way it needs to be straighten, right, then machined to fit bearings and so on.

The straightening and machining will induce stresses right.
so I believe stress relieving your shafts is a cheap proposition.

I also have worked with thousands of parts, but with addition of post heat treat, through hardening, case hardening and so on. There is no magic just experience.
That is what makes or breaks you in making good parts
you have to know your product line,

So normalize your shafts then stress relieve after rough machining. thats it.