Hex male and female driver with high torque 2

[hrana]

Hi,

I have hexagonal shaft (male) driving agitator with female hexagonal attachment (Torque in 2000 kNm range). Please guide me which will be the best combination of hex (Female and male) material.

Also, if there is heavy load acting in the perpendicular direction of the mating face (including bending moment) what could be the solution to prevent any failure (between male and female hex) or the rounding of the hex?

 

[EdStainless]

Is your shaft strong enough to handle that?
Are you stuck with hex or could you use a spline?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[Jboggs]

For that kind of load you're going to want a ball spline:

They're like a ball screw except they transmit torque instead of linear force.

 

[TugboatEng]

Is this going to be lubricated?

 

[3DDave]

The main cause of rounding is too much clearance, not the material. Next up will be contact pressure - without knowing the size or length of the contact no one knows what pressure there will be. The third is fretting wear, so alignment is also important as is, as Tugboat mentioned, lubrication.

It's unfortunate to be stuck with a hex interface - just about the worst of all possible choices.

 

[EdStainless]

Are you sure about that torque, 2MNm?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[hrana]

Thank you all for the responses. I really appreciate that.

Edstainless:
Yes, the Shaft is strong enough and also we are struck with this hex design. Moving to other designs will need a lot of design change work. Yes, torque is around 2 MN-m.

Jboggs:
Thank you for the suggestion. I was not knowing about this, I will look into the details of this design.

TugboatEng:
No, it is not lubricated.

3DDave:
Yes, you are right rounding is the problem. Sometimes there is clearance observed in the connection and there is Vertical force and moment acting on the shaft that makes it worst. However, Lubrication grasped my attention, this might be adding problems to the design.

Thank you all
Highest Regards
Hrana

 

[EdStainless]

Is there a constraint on the OD of the coupling?
If you can make it thick enough then you don't need to go to material that is stronger than the shaft.
You are going to need a very tight fit. You need every surface to mate except in the very corners.
When we ran hex, we made the hex with sharp corners and put very small reliefs in the corners of the coupling.
The lubrication is to allow assembly and prevent (minimize) fretting in service.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[hrana]

No constraint on the OD of the coupling. Is there a thumb rule that the shaft or female hex needs to be stronger?

 

[EdStainless]

We liked the shaft harder than the coupling, but not by much.
We only used very strong couplings when we had OD size constraints.
What shaft size and strength are you working with?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[TugboatEng]

Without lubrication fretting may become an issue. A galling resistant pair often excludes materials of similar hardness. Making the coupling sleeve out of aluminum bronze might provide longer life against a hard steel shaft. The Nitronic alloys may be better still with higher strength.

 

[EdStainless]

We commonly ran a PH SS coupling against Q&T 4140 shafting.
When we had high strength alloy shafting (cold drawn 625) we would use 718 aged for the couplings, and use Krytox grease.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[hrana]

Thank you so much for your input EdStainless.

 

[TugboatEng]

This forum helped out a lot in my selection of materials for a splined coupling with poor lubrication. Krytox 283AD is probably your best choice of lube for this application but I don't think you'll stomach the price tag. We found better coupling material selection paired with Polyurea EP2 gave very satisfactory life for our pump drive application at $3 per pound vs. $1300. Unfortunately, due to pandemic shortages, polyurea based greases are in short supply.

 

[EdStainless]

Tug, I filled an oil filled submersible motor with Krytox oil once. That was about $10k worth.

The little 100g tubs seem to last forever though. You just need a thin film for it to work.
Just a caution, there are no solvents for Krytox, so when you get it on something it is there forever.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[geesaman.d]

2,000,000 N-m would be the worlds highest-torque fluid agitator by a very large margin. I'm picturing an agitator drive mounted above the vessel and this coupling is between the wetted parts and the drive. Is this accurate?

What thickness is this hex shaft, and what material? What is being agitated?