Question about Sputter Bearings

[ivymike]

(I initially posted in the bearing design forum, to no response)

Hello,

I've heard a few things in the past that don't seem to fit well together in my mind, and I was hoping that someone could clear up this mystery for me.

1) sputter bearings, like those commonly used at the crankpins in many engines, have higher fatigue limits than other bearing materials for the same application, and can tolerate higher specific loads
2) these bearings have a harder exposed surface
3) these bearings are more resistant to siezure
4) these bearings can tolerate lower minimum oil film thicknesses

To me it seems that #3 and #2 don't fit well together. #1 and #2 do seem to fit together well. #4 seems to fit with #3. How can sputter bearings do all four, if they can indeed?

 

[MikeHalloran]

The last time I was real interested in this stuff, crankpins were hardened, usually with addition of nitrogen, and crankpin _bearings_ were soft, alloys or plated composites of tin/ lead/ copper/ indium/ whatever, so you could renew the bearing system without replacing the crankshaft.

I admit it; I have not heard of sputtered bearings. The closest thing I have heard of is coating aluminum cylinder bores with pseudo- alloys of molybdenum and other unmachinable stuff by exploding wires therein, a crude form of sputtering. For cylinder bores, exotic materials and synthetic macrostructures make sense.

For crankpins and their bearings, the only times when the actual materials involved, and the specific characteristics that you numbered, make a difference is during cranking, or just before a rod comes out the side. I.e., if sputtered bearings make a difference, it's in how the engine dies, not how it lives.

Maybe sputtered bearings are the fashion du jour for racing today, or maybe the magazine writers are yakking about something else already. It's hard to keep up with hype.





Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA

 

[ivymike]

For crankpins and their bearings, the only times when the actual materials involved, and the specific characteristics that you numbered, make a difference is during cranking, or just before a rod comes out the side.

I don't agree with that assessment. Bearing material selection can have a huge impact on engine durability, even if the engine is run almost exclusively at one or two specific operating points. In regard to sputter bearings, I think that their relatively high cost has kept them out of high volume automotive applications, but they're often used in large engines and have been for a number of years.

Examples from the press & mfrs:

http://www.ai-online.com/issues/article_detail.asp?id=396

"Hitherto reserved by reason of high cost to large high- and medium-speed diesels, increasing loads on main and big end bearings now make sputter technology viable in car diesels, KS Gleitlager reports. Currently cylinder pressures are as high as 2610 psi and 2900 psi is in prospect, imposing extreme loads on bearing material. In the period 1990 to 2005, the loads imposed on diesel engine connecting rod bearings will have risen by 37 percent, and by 33 percent in the case of the crankshaft bearings, KS Gleitlager estimates.

http://www.federal-mogul.com/cda/content/front/0,2194,2442_8129,00.html

"Product longevity through sputter coating technology. The most resistant bearing material in the world is produced with this coating technology series. The sputter process gives the highest resistance to wear and fatigue. Glyco products are designed for optimal performance in high-powered engines. Current vehicle applications include Audi, BMW, DaimlerChrysler, Opel, Peugeot and Volkswagen -- plus many others."

 

[MikeHalloran]

Thanks for the links.

Okay, I can see these possible advantages:

- A really thin bearing applied to a hard shell allows the bearing system to be thinner, so you can use a bigger crankpin or a thicker rod in a given engine, and you can uprate the engine a bit.

- IF, in a given engine, more traditional bearings are failing by fatigue of the bearing surface at the loads applied, then a thinner, harder, bearing material might survive better. And it had better wear more slowly, because the actual bearing material is vanishingly thin.

The flackery at both sites sort of glosses over the basic fact that when the engine is running right, the bearing surfaces are not in contact with anything; they're riding on a film of oil. The tribological properties of the bearing material itself become important only when the oil film is not present, e.g., cranking or dying.

Thus, referring to the OP,

(1) is probably true, because the bearing surface is being supported, not by more soft bearing metal, but by the steel backing.

(2) is probably true, though neither site tells what material, exactly, is being sputtered.

(3) depends on the crankpin, too. If the engine is running in a near- seized condition, it's got bigger problems, so I don't see the virtue of a bearing that, to coin a phrase, seizes gracefully.

(4) is probably true, because of a presumed better surface finish. Which should be possible to produce on more traditional bearings, too. I'd guess their typical matte finish is intended to retain oil, e.g. during cranking. Which brings up the question of what happens to the sputtered bearings, or the mating journal, during cranking.

I guess we can continue to respectfully disagree.




Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA