motor shaft material 1

[NIDinc]

Looking for a motor shaft steel that can be case hardened and will resist breaking from fatigue/vibration. We've been using 316 pre hardened stainless steel. But I'd like to get something with higher iron content. Leaning toward 1144 or 4140 any input is much appreciated

 

[dArsonval]

A 1999 article published on the subject listed 5 grades of common electric motor shaft materials.
(Not including Monel)

Plain carbon steel (1018, 1045, etc.) Used up to about 500 HP. Can be welded.

Chrome molybdenum steel (4140, 4150) High strength Crusher duty, propeller shafts,
transmission shafts. Do not weld this material.

Resulfurized steel (C1144) Higher strength than C4150. Can be welded successfully.

Nickel chrome molybdenum (C4340) Annealed higher strength than C1144, heavy duty.
Do not weld this material.

17-4PH Magnetic stainless ( 400 series) Used for explosion proof motors that require
magnetic shaft properties.

John

 

[electricpete]

Great info John.

Just curious, why do some explosion proof motors require magnetic shaft properties?

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(2B)+(2B)' ?

 

[dArsonval]

The very first mechanical repair seminar offered by the Electrical Apparatus Service Association at St. Louis in 1991 or '92 covered the subject of two piece welded shafts.
Fifteen years later in 2006, EASA published Tech Note No. 43 authored by Tucker Woodson of Rockwell Automation titled "Making and Installing a New Motor Shaft".
The document described stainless materials used in fabricating electric motor shafts.

I'm not finding an exact explanation regarding "Why" it relates to hazardous duty motors.
It seems to me it would be relevant for any larger two pole motor regardless of application environment.
Perhaps a stainless material offers non-sparking attributes... but that's not necessarily the answer either.

Here's a screen shot portion of the Tech Note document mentioned:

John

 

[electricpete]

Thanks John.

As a side note, I think the reluctance the homopolar flux path (circulating from rotor iron to shaft to bearing housing to frame to stator core and back accross airgap to rotor iron) can significantly change how the motor reacts to eccentric rotor and maybe to unbalanced supply voltages. This could be an additional consideration if switching/choosing between magnetic and non-magnetic shaft materials.

=====================================
(2B)+(2B)' ?

 

[EdStainless]

We used to friction weld the CRA ends onto motor shafts.
If you want stainless then look at some Nitronic 40 or 50 (21-6-9 or 22-12-5 or Aquamet).
Stronger and more resistant to corrosion and fatigue than 316.
The 41xx alloys are commonly used in the through hardened condition, you move to 43xx at larger diameter (say over 2.5").
Use 1040/1045 if you really just want to surface harden them.

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P.E. Metallurgy

 

[NIDinc]

Gentlemen,
Thank you for the valuable input.
The above mentioned article confirms what we learned the hard way some years ago about the problem of using a non-magnetic stainless motor shaft on our two-pole motor. Our amps were 3-4 x higher using a 300 series ss, than when we switched to magnetic 416 ss. We knew it had something to do with the way the steel interfered with the magnetic flux of the rotor but we thought it had more to do with the small diameter of our motor. This article clarifies that it is because of the 2 poles, which makes more sense. Thanks for posting this info.

We may need to look at building a two part shaft as described above in the future for maximum corrosion resistance. For now we are getting by with nickel plating the shafts.

I need to manufacture another run of shafts soon and am debating on using 4140 vs. 1045. In either case I would like to case harden the bearing journals and threads on the shaft. This is a small shaft, approx. 7/8" x 11" It is subject to harsh industrial 24/7 use with some vibration. I want to make sure that it doesn't get brittle and break, as is a problem with our competitor's motor. The 416 pre-hardened ss has worked ok for us in the past but I want something more magnetic and maybe cheaper. We have seen the amps increase approximately .4 amps on these shafts after they are heat treated. I theorize that something changes in the steel and is interfering with the magnetic flux once they are hardened and a more magnetic material will help.

1045 vs. 4140 steel? Which will case-harden higher? Which machines better? Any thoughts? Thanks and happy new year!