Interference fit with 6061-T6 Hub mounted on a 4130 shaft

[Breastfed]

Hi,
I'd be interested with any thoughts or concerns regarding an interference fit using Oil Injection to hydraulically mount an impeller for a Water brake machined from 6061-T6 mounted on a 4130 Shaft.

Taper 50:1 (1.15deg Incl)
Shaft Dia = 80mm
Taper Length = 37mm
Pushup distance = ~7mm
Interference = 1/50 = 0.02 x 7 = 0.14mm
RPM 6000
Torque 271nm (200ft/lb)

The Impeller consists of 12 radial Fins with an OD of 325mm and the Hub ID is 80mm x 140mm x 37 wide.
Another consideration is centrifugal force at 6000 rpm where the hub expand and no longer has sufficient interference with the hub and slips.

appreciate any help or thoughts.
Breastfed

 

[hydtools]

Looks like too many axial constraints to being able to dependably imstall the hub on the taper for adequate gripping.

Ted

 

[btrueblood]

You need to consider thermal expansion differences as well, presumably you have done so, and this ruled out a shrink fit (cylindrical)? Agree with hydtools, that the taper makes the precise placement of the endplates/housing more difficult.

 

[Sparweb]

SAE Spline?
It would be a LOT easier to replace a damaged impeller if it wasn't force fit onto the shaft.

STF

 

[tbuelna]

From the sketch provided, it looks like there would be no problem using a bolt flange to attach the impeller to the shaft. Have you considered this approach?

 

[Breastfed]

Thanks for the replies
Apologies for not replying sooner as i had other urgent matters and travel.

I have considered flanges and SAE splines but I feel that the Oil Injection method is rather simple all things considered, I can machine a precision taper in our work shop plus we have all the tooling required for oil Injection. Splines etc both Int & Ext would best be out-sourced.

I'm thinking that a Steel Impeller would be more suitable for Oil Injection on a 4130 shaft, to help combat the rust and corrosion I'm thinking to powder coat the Impeller & stator assy or perhaps even Teflon coated. The powder coating is cheap and done local... mates rates !!

Breastfed

 

[rb1957]

why are a lubrication provision for a "press" fit joint ?

as noted above, be careful about temperature effects, if this thing gets hot, it'll loosen the joint

do you have the taper on both parts ? I don't think so, based on how you've calc'd the interference, and that means the interference is at one end of the hub.

another day in paradise, or is paradise one day closer ?

 

[hydtools]

Do not apply any finish to the pressfit surfaces. The finish material will creep and the joint will loosen.

Ted

 

[Breastfed]

Both Hub and shaft have a taper 50;1
High pressure oil (<= 30,000psi) is used to expand the Hub and another Hyd cylinder is used to pushup the Hub onto the shaft and maintain the seal for pushup.
The Hub is slightly smaller in dia 0.14mm hence the 7mm pushup, surface finish is Rz6.3 as this is also required to form a reasonable seal between the 2 surfaces while oil is injected between the hub and shaft for expansion. After pushup is complete the High Pressure oil is released, the Hyd Cyl remains in place for an hour or so until the oil drains out from between the Hub & Shaft followed by additional time before load is applied.

I don't expect this would get over 60-70 degC provided there is sufficient water flow of course.

Breastfed

 

[Ron]

After the corrosion occurs from the dissimilar materials, you'll never get that impeller off!

 

[BrianPetersen]

I have a motorcycle whose flywheel is secured on the crankshaft with a taper, and a bolt that secures it from the end. There is a keyway, but it is only used to hold initial alignment. The taper is much steeper than 1:50.

That flywheel is an absolute *$^$#%($%# to remove after it has been on there for a couple of years.

The flywheel has internal threads larger than the threads in the shaft that allow a removal tool to be threaded in to push on the end of the shaft while simultaneously pulling on the flywheel. It's still a real pain.

It has been found that blue Loctite applied to the shaft actually makes it easier to remove later, presumably by inhibiting corrosion between the two parts.

 

[MikeHalloran]

Similarly, Borg-Warner/York 2 cylinder ac compressors used a taper (much steeper than 50:1), with a Woodruff key for insurance, and they got tight, and had in internal thread for disassembly.

<tangent>
My then local Ford dealer tried to do some warranty service on mine. There was a delay, so I went out in the shop, and the ace mechanics explained that they didn't have the 'special puller tool'. So I walked to the local hardware store, bought a 5/8-11x2" bolt, and gave it to them.

They let their apprentice reinstall the clutch, and he failed to line up the key with the keyway, so the damn thing wobbled like crazy. Asshole service manager said 'They all do that' and refused further participation, and the dealership owner backed him up.

Took back my bolt, went home, and remounted it. Took 2 minutes.

I was glad to see that dealer go under.
</tangent>

Have you actually worked out the stress in the aluminum part?
Just off the top of my head, it looks like installing it will permanently enlarge the hole and/or crack the hub, negating all your fancy retention plans.




Mike Halloran
Pembroke Pines, FL, USA

 

[Sparweb]

Mike, Brian,
I've had my own fights with tight fitting parts. It's a pretty common experience.
I believe that the OP is objecting to the cost of the other mountings. Don't blame him, if the price of the end product cannot absorb the extra tooling & labour costs of our recommendations.
Do you know of some rough estimates for the different costs for the different attachment mechanisms available? "A wheel on a shaft" is a pretty common joint, and there are 100 ways to do it.
I have some engineering books that show many different ways, but none of them estimate cost, or even labour time to accomplish. I could guess at the costs myself, but is there a more authoritative source?
Clearly a SAE spline (my suggestion) is much more expensive than a keyway+split hub, and I expect a taper is much less expensive than a keyway...

STF

 

[MikeHalloran]

The taper tolerances will have to be ridiculously tight in order to place the installed hub/rotor at the correct axial position between the two ball bearings, because the tolerance on that position can't allow the hub/rotor face positions to vary more than a few 'tenths' in order to have clearance from both end faces of the housing.

I.e. with more or less normal tolerances in the parts and in the taper installation procedure, there will be relatively large variations in the installed position of the hub/rotor relative to the bearings, so 'selective fit' or worse (keep demounting and remounting until it fits) will be necessary.

Better, IMHO, to form a slightly short spline or polygon drive on the shaft, and allow the rotor to find its own axial location between the two end plates, without the location of the male spline or polygon getting involved in defining that axial location of the rotor.



Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

This might be worth looking at:

http://www.skf.com/us/knowledge-centre/engineering-tools/skfoilinjectionmethod.html

 

[3DDave]

Loctite shaft retaining compound is pretty cheap.