Roller Bearings 1

[enginesrus]

Anyone here that works in that industry? I would like to know what sort of case hardened depth is usually found and Rc surface hardness on the rollers and races of most taper roller bearings found in automotive applications?

 

[TugboatEng]

64 HRC hardness and no case. The bearings are small enough through hardening is possible.

 

[bobjustbob]

We do make TRB's that are case hardened. The case depth depends on the part design.

 

[TugboatEng]

You're talking much larger bearings than would be seen in automotive applications?

 

[bobjustbob]

Nope, we have made TRBs for auto applications that are case hardened.

 

[TugboatEng]

I'm curious what the benefit would be?

I'm honestly curious as in my industry others like to blame spalling on the hard case flaking away and I don't believe that to be true. I've resisted the idea of case hardened bearings and gears as a result. I understand through hard is not feasible on larger geometries.

 

[arunmrao]

I had the opportunity to visit bearing manufacturers for their heat resistant steel parts and accessories.It was always through hardening for automobile and general engineering purposes.

 

[EdStainless]

I have seen even small rollers done both ways. If they through harden they typically start with an alloy like 52100.
When they case harden it is usually combined in the HT process, and often nitro-carberize using an alloy with 80 C.
It is easier and less expensive to work with the lower C material, but it is also more processes and process control.

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

 

[Tmoose]

The required case depth can be figured from the loading and thus hertzian stress. The "hardness" and thus high fatigue strength has go deeper than than highest Herzian stresses that are subsurface.
.06" effective case depth is enough for pretty highly loaded ball, roller and needle bearings.

That is why the various forms of nitriding, which it typically quite shallow, is in-appropriate for rolling element bearings and hard working gearst.
Case crushing and other failurs like the hard candy shell actually sliding of the softer core of an M$M candy are the result.

Similarly chrome plated gears and rolling element bearing components have only relatively wimpy bonding strength a little below the working surface so are only suitable for light loads at best.

 

I can't see them case hardening elements in something like an automotive wheel bearing. Too small and too expensive.

Take one apart and you'll quickly realize that wearout is more likely caused by the skimpy quantity of substandard lubricant. My regimen is to break it open, purge it of butter, and repack with a known quantity like Mobil.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[EdStainless]

They case harden the pins in roller chains which are a fair bit smaller.
They have to HT anyway, if they can incorporate the case hardening in the HT cycle then it is a minimal addition.

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

 

[bobjustbob]

We had several part numbers that went into automotive applications that were case hardened. All of these are smaller parts, less than 4" OD. We still make some parts with even smaller section thicknesses that are case hardened.

 

[swall]

Aircraft wheel bearings I have worked with have all had case hardened rollers. Base material was 8617.

 

[WKTaylor]

SAE aircraft bearings typically have statements like this...

MATERIAL: RINGS AND ROLLERS: SAE 52100 STEEL PER AMS6440.
HARDNESS: HEAT TREAT RINGS AND ROLLERS TO 60 TO 65 HRC AND STABILIZE FOR OPERATION AT 250 °F.

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]

 

[Tmoose]

From Timken Engineering catalog

page 27 - radial cylindrical ROLLER BEARINGS - 5200 Metric Outer rings are made from bearing quality alloy steel. The inner
rings are deep-case hardened to accommodate the hoop stresses resulting from heavy press fits.

From Engineering-Manual-Metals-Catalog_10668 -
Page 26 - - These bearings are traditionally through-hardened but Timken also offers the bearings with casecarburized components for applications where shock loading is a particular concern.

Page 65 - as above - All AP bearings feature case-carburized rings and rollers that offer higher
fracture toughness than through-hardened material.

page 84 - as above - The a3l factor ranges from a maximum value of 2.88 to a minimum of 0.20 for case-carburized bearings and 0.13 for throughhardened bearings. The maximum lubricant-life adjustment value represents a high film thickness and minimal asperity contact. The minimum a3l factor is a function of the material core condition because through-hardened bearings may produce lower bearing life in thin film conditions when compared with case-carburized bearings given equivalent surface finishes.