Recommended interference fit for 3000 RPM Generator couplings
Recommended interference fit for 3000 RPM Generator couplings
(OP)
I have a 3000 RPM, 18 MW generator with the shaft dia of 228 mm at the coupling seating area. The rigid coupling (with a flange and a hub) has four circumferential round key pins and four radial round key pins. All the eight key pins equally spaced around the circumference. What would be the recommended bore dia for this coupling?
I have seen interference values from 0.003 to 0.00075 inches per inch of shaft diameter being recommended for keyed couplings. Any tips from end users?
I have seen interference values from 0.003 to 0.00075 inches per inch of shaft diameter being recommended for keyed couplings. Any tips from end users?
Muthu
www.edison.co.in





RE: Recommended interference fit for 3000 RPM Generator couplings
It might be worth contacting the coupling manufacturer and discuss the application with them.
“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein
RE: Recommended interference fit for 3000 RPM Generator couplings
Johnny Pellin
RE: Recommended interference fit for 3000 RPM Generator couplings
Thanks JJPellin - Thanks. I am thinking of 1/700th of the shaft dia (0.33 mm) as interference.
Muthu
www.edison.co.in
RE: Recommended interference fit for 3000 RPM Generator couplings
http://www.amesweb.info/InterferenceFit/Interferen...
http://www.amesweb.info/FitTolerance/FitTolerance....
I have also used Machinery's Handbook for guidence as well, in my version about page 650
Hope that helps, MikeL
RE: Recommended interference fit for 3000 RPM Generator couplings
Muthu
www.edison.co.in
RE: Recommended interference fit for 3000 RPM Generator couplings
Regards, MikeL.
RE: Recommended interference fit for 3000 RPM Generator couplings
Also, increasing the hub outside diameter, does not change this factor of safety for the hub yield. I thought a thicker hub will increase this factor.
Muthu
www.edison.co.in
RE: Recommended interference fit for 3000 RPM Generator couplings
Increased hub OD without any change to hub ID, shaft size, or interference will result in higher hub safety factor and lower shaft safety factor- because the hub will be stiffer, thus experiencing less strain and imparting more strain into the shaft.
This behavior is obvious if you load the calculator that Mike linked- open the webpage, and don't change any values except hub OD and watch how the output values for safety factor change.
With regard to stress concentration factor- this value needs to be a 'real' value. If your goal is a hub design that will have long life and will perform well, you can't just guess.
There are several resources out there that will allow you to determine what the stress concentration factor should be.
I'd start here:
http://allaboutmetallurgy.com/wp/wp-content/upload...
RE: Recommended interference fit for 3000 RPM Generator couplings
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RE: Recommended interference fit for 3000 RPM Generator couplings
Thanks CouplingGuru. This is a '80's Japanese machine design, so they could have overdesigned the shaft and the coupling, especially, when they put in four axial keys and four radial keys.
This is a 3000 RPM, 15000 KW generator running smoothly (no vibratory loads), but the load (hence torque) changes be quick and large. The coupling hub length is about 291 mm and the hub OD is about 370 mm in the straight portion and 660 mm in the flange portion. The flange width is about 90 mm. I have uploaded the coupling drawing in the link below. Look forward to your calc.
Muthu
www.edison.co.in
RE: Recommended interference fit for 3000 RPM Generator couplings
RE: Recommended interference fit for 3000 RPM Generator couplings
When it comes to couplings we are always here to help.
WWW.PSCCOUPLINGS.COM
RE: Recommended interference fit for 3000 RPM Generator couplings
RE: Recommended interference fit for 3000 RPM Generator couplings
Great points, it seems as if the shaft will easily handle those torque spikes. At 9" in diameter with (4) 37mm diameter keys even with a 1.5 million in-lb torque spike those keys would only see 6410 psi shear. Depending on material, they may be able to handle in excess of 30ksi. That is assuming the dowels provide no help at all.
When it comes to couplings we are always here to help.
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RE: Recommended interference fit for 3000 RPM Generator couplings
RE: Recommended interference fit for 3000 RPM Generator couplings
Muthu
www.edison.co.in
RE: Recommended interference fit for 3000 RPM Generator couplings
0.23mm is a lot of interference, That is more that 0.001" per inch shaft diameter. I would highly recommend cutting that value in half. And I would re-dress the shaft and measure it to verify you can get good uniform contact, especially if it was scored.
When it comes to couplings we are always here to help.
WWW.PSCCOUPLINGS.COM
RE: Recommended interference fit for 3000 RPM Generator couplings
Yes, the shaft has been turned down and grind finished to 228.50 uniformly from original 230.00 mm per pic below. Small blemishes are ignored since to remove them would mean more dia reduction.
Since the original interference was 0.35mm (for whatever reason) and it's been time tested, I do not want to reduce the interference too much and am going with 0.001" per inch shaft diameter thumb rule.
Thanks for all your valued tips. Much appreciated.
Muthu
www.edison.co.in
RE: Recommended interference fit for 3000 RPM Generator couplings
Since you did a great job truing up the shaft, did you also take into account the tapered key pins relative location to the hub bore has changed because of the shaft reduction? Since those are tapered pins, may have to compensate for that in the hub.
When it comes to couplings we are always here to help.
WWW.PSCCOUPLINGS.COM
RE: Recommended interference fit for 3000 RPM Generator couplings
Muthu
www.edison.co.in