Ball Bearing fit in aluminum housings. 3

[RoarkS]

Okay so I've done a lot of things with R4 and R6 size ball bearings in aluminum housings (6061-T6). Done DO160 and MIL-STD-810... I felt pretty comfortable with that. I would always maintain a light press maybe .0005"

About a month ago I'm playing with something a little bigger... the housing was Ø1.126-1.127 for a Ø1.125 bearings. I didn't design it, but the fella said that low temp (high altitude) storage required that it be that loose so that it wouldn't damage the bearings. Seems weird to me. All the design data said that it should be an H6 I figured up that;s 0 to .0008 for that size bearing.

Anyway the real question... I'm working with a #6314 bearing (150mm)OD. To use as a main bearing for a 250hp ICE engine. I want to use an aluminum housing. Where are some good design guides to look at? Currently going through SKF's info.

Sounds like N6 interference fit on outer ring/housing, f7 loose fit on shaft. Thouhgts?

Thanks!

 

[Tmoose]

With load direction varying all over the place ("indeterminate") every revolution you need interference fits on the ID and OD at all temperatures. Aluminum crankcases need a bunch of room temp interference, or a cast-in steel or iron bushing for the bearing OD seat.

What is your engine configuration with 70 mm main shaft(s)?

 

[WKTaylor]

RoarkS…

Hmmmmmmmm... Your reference to '...DO160 and MIL-STD-810...' is pretty inscrutable to me RE bearing installs.

1. A general rule of thumb is...

[A] 'Plain bearings' are usually installed with interference fit; then the ID measured to ensure it is as intended [shrinkage to a specified diameter range due to interference]… or undersized ID's are line-reamed/bored to meet intended operating Dia [after install].

HOWEVER...

Spherical-Ball, ball and roller bearings should be installed in 'close-reamed' holes... and then swaged** for retention. ANY radial interference that causes the outer-race [OD] to contract [shrink]… or ID race press-fit onto a shaft to expand usually results in interference with the rolling elements and can induce rotating friction drag or 'lock-up' in antifriction bearings.

**the housing hole-edge may be (a) roller-swaged or (b) ring-staked or (c) ball-staked over the edge of the bearing; (d) the bearing outer-race is roller-swaged over the chamfered edge of the hole [grooved-bearings only].

2. Bearings/installation are fairly discussed in...

MIL-HDBK-1599 BEARINGS, CONTROL SYSTEM COMPONENTS, AND ASSOCIATED HARDWARE USED IN THE DESIGN AND CONSTRUCTION OF AEROSPACE MECHANICAL SYSTEMS AND SUBSYSTEMS

NAS0331 BEARING INSTALLATION AND RETENTION BY SWAGING OR STAKING

NAS0332 BEARING RETENTION SLEEVE, GROOVED OUTER FACE …

3. Alternate data sources... if available to You...

3.1 USAF T.O.s

1-1A-8 ENGINEERING MANUAL SERIES - AIRCRAFT AND MISSILE REPAIR - STRUCTURAL HARDWARE

44B-1-2 GENERAL MAINTENANCE INSTRUCTIONS AIRFRAME ANTIFRICTION BEARINGS

44B-1-16 GENERAL INSTRUCTIONS FOR INSTALLATION AND REMOVAL IN AIRBORNE ACCESSORIES

44B-1-18 GENERAL INSTRUCTIONS FOR INSTALLATION AND REMOVAL IN AIRCRAFT INSTRUMENTS - ANTIFRICTION BEARINGS (PRECISION INSTRUMENT BALL BEARINGS)

44B-1-102 MAINTENANCE INSTRUCTIONS - ANTIFRICTION BEARINGS

44B-1-122 MAINTENANCE OF AERONAUTICAL ANTIFRICTION BEARINGS FOR ORGANIZATIONAL, INTERMEDIATE AND DEPOT MAINTENANCE LEVELS

3.2 Most of the major Antifriction Bearing manufacturers have excellent technical data/literature on anti-friction bearing selection, installation, maintenance and removal/replacement.

3.3 Most aircraft OEMs have internal design and process documents, this subject.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[RoarkS]

@WKTaylor re testing specs... I had an engineer WAY north of my pay grade override my fit on that Ø1.125 bearing well beyond what I would consider okay. His justification was the "Low temp storage" portions of testing could damage the bearings from contraction so he left the housing in my opinion SUPER loose. Thus that experience has caused me to doubt myself.

I like the swage/stake situation. Old Jacobs radial engines had taperd pins that somehow acted as a stake. I've only ever read about it... so not sure exactly how it works. I'm trying to avoid a steel sleeve/bushing if at all possible.

Tmoose: I would agree a lot of room temp interference indeed. But elevated temp... engine running or even red line temp would be the design fit dimensions? Do you have a design guide suggesting having both be interference fits? I've never seen that, that I can think of. I'm trying to avoid a Engine configuration is single row radial. These are the main bearings.

I've found a wealth of design information for bearings in typical uses. I've been looking at electric motor bearing design guides... no really much published on using ball bearings for IC engine bearings that I can find.

 

[BrianE22]

Spherical-Ball, ball and roller bearings should be installed in 'close-reamed' holes... and then swaged** for retention. ANY radial interference that causes the outer-race [OD] to contract [shrink]… or ID race press-fit onto a shaft to expand usually results in interference with the rolling elements and can induce rotating friction drag or 'lock-up' in antifriction bearings.

Not sure I agree with that. Ball bearings are made with various radial clearances. A press fit on the outer or inner race will reduce the clearance. The manufacturer's charts of fits will tell you how much of a press fit you can safely have.

 

[WKTaylor]

BE22... what are Your experiences with aircraft grade bearings?

My experiences... click-on my name. Some quick observations...

Aircraft grade airframe bearings 'tend' to run very tight clearance with low grease fill.

Aircraft grade mechanical component bearings tend run tight clearance with full or partial oil immersion. Grease lubrication is usually limited to low-stress low-speed applications... except where high speed for short duration can be tolerated.

Aircraft recip-engine bearings tend to be plain [solid or split] with lubricant grooves and pressurized-oil delivery... although older slower RPM radials and in-line did run with oil-flooded roller-bearings.

Aircraft turbine-engine bearings are either pressure-oil-flooded plain bearings or [very large] roller-bearings.

In most cases lowest design operating temperatures are either -100F or -65F; however, highest temperatures can range up-to the limit of the grease or oil... which in the case of turbine oils which run really hot. When extreme thermal variations are encountered unique 'devices' or special-design clearances are used to allow for thermally-induced dimensional differences between bearing and housings/shafts.

UNDER NO CIRCUMSTANCES should a bearing ever encounter high friction forces due to adverse mating component 'fits or misalignment' or loss of lubrication or lubricant-lubricity: very bad thing happen.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]

 

[Compositepro]

Tolerance rings are an available option.

http://www.usatolerancerings.com/

 

[RoarkS]

Compositepro that's a pretty interesting product, I'll email them and see what they have to say.

I'm going down the path of deep groove ball bearings because it was explained to me by someone that the forces on a radial don't lend themselves well to typical oil pressure fed tri-metal plain bearings... With that said I couldn't find a single example of a radial with oil/plain main bearings. I've got actual cylinder pressure plots, So I feel pretty comfortable with the basic 6314 bearing selection. Planning on having oil jets spraying probably from the crank... oil system is admittedly not very developed at the moment. But looking for oil operation temps of 140°F to 245°F redline. I would imagine my engine housing is going to be around there also.

 

[Tmoose]

"Currently going through SKF's info."

"Do you have a design guide suggesting having both be interference fits? I've never seen that, that I can think of."

=====================.

https://www.skf.com/us/products/bea.../bearing-interfaces/selecting-fits/index.html

"Direction of load indeterminate refers to variable or alternating external loads, sudden load peaks, vibration or unbalanced loads in high-speed applications. These give rise to changes in the direction of load, which cannot be accurately described. Where the direction of load is indeterminate and particularly where heavy loads are involved, there is a risk of fretting corrosion or wear. You should use an interference fit for both rings."
Not mentioned is creep, where a shaft inside a ring with clearance subjected to a load that varies direction acts like a friction drive with ratio of shaft Ø/bore Ø.

Check out page 21 (smearing) of this SKF_Bearing_faiureandcauses.pdf

https://ec.kamandirect.com/content/resources/2010/downloads/skf_bearing_failureandcauses.pdf

A gentler looking but no less insidious wear can result when fits result in clearance that acts like a creeping friction drive.

https://i1.wp.com/

http://www.hitekbalancing.com/wp-content/uploads/2010/11/hitek8.jpg

One (but not the ONLY) reason for the existence of C3 and other extra internal clearance bearings is to compensate for loss of internal clearance resulting from heavier interference fits required is some arrangement.

Disassemble a typical single cylinder motorcycle engine with vertically split crankcase. I believe you will find the ball bearing main bearings are TIGHT on the crankshaft AND in the crankcase bores.

Check out this old motocross bike's crankcase with steel/iron inserts for the main ball bearings. I believe the intent was in part to provide a better thermal expansion match over a range of temperatures. This make had a reputation for very good reliability, in part due to details like this.

https://i.ebayimg.com/images/g/VyYAAOSwhaBasZyC/s-l1600.jpg

 

[RoarkS]

Thanks Tmoose!

I didn't think of that...I have a friend that blows apart his KTM250 bike pretty regular I'll see what they have going on in there.

 

[RoarkS]

Compositepro,

http://www.usatolerancerings.com/

don't want to play flight critical hardware game

So... I'm machining this thing from aluminum. Best way to "simulate" a cast in steel ring? Bushing? top hat? Anyone done anything like this?

 

[GregLocock]

The car industry went through all this a while back, and the problem of designing good wheel bearing fits into aluminium spindles that were robust and could handle the heat from braking, led to the development of cartridge style bearings, where the bearing pair is in a steel tube that is then fitted to the knuckle using a bit more of an interference fit than the bearing itself could tolerate.

http://www.ntnamericas.com/en/websi...and-literature/catalogs/hub_bearings_4601.pdf

As you can see they've taken on a lot of the functionality from the hub, but that is independent of the basic idea, which Gen 1 demonstrates.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[RoarkS]

GregLocock

Thanks for that.

Sounds like just make a steel press in bushing and call it day.