Crankshafts ! ! !

[CleviteKid]

Reference: NO OIL IN ENGINE (http://forum.thedieselpage.com/ubb/ultimatebb.php?ubb=get_topic;f=2;t=002697) ! !

Doc,
I got a chuckle out of your response to my post about nitriding. It is tough not to get excited since everything we talk about in my classes (fluid power, thermo, mat. science, statics and dynamics, etc.) somehow has an application "under the hood."

Question: What is the carbon content on the crank, and what other alloying elements are present? I understand if you haven't rushed down to the lab, crankshaft in hand, and tested the part's makeup. Generally speaking though, what kind of composition can we "get away with" without sacrificing strength, wear resistance, and low cost?

I'm becoming more interested in metallurgy as I progress through my degree (welding science is next), and so I have come away from each of my materials class sessions with more than a few questions. Therefore my post on TDP sounds perfectly reasonable to me (a gearhead), but even my girlfriend read it saying, "David, isn't this going a bit far?"

"Of course it is," I replied.

Thanks,

David

* * * * * *

Hey David,

Glad I could make you chuckle.

Without looking it up, our cranks would be a high grade of nodular iron, meaning a carbon content of around 3%, magnesium and nickel under 1% each to give the carbon the nodular structure, not flakes as in ordinary gray cast iron, some manganese ( .5 --> 1.5%) that is in almost all iron and steel alloys, and some silicon (less than 1%, I think). Any thing else is just a tramp contaminant, and sulfur and phosphorus would be held to very low levels, since these embrittle iron and steel. The UTS is probably over 100,000 psi (do you use metric megaPascals, or old fashioned Christian units there?) and the ductility is probably around 5% elongation.

Metallurgy is an underappreciated discipline, but it sure is important to industry.

Dr. Lee :cool:

[Dieselboy]

It's a 50/50 deal between English units and SI, though most of the student and professors here think in terms of psi, lbf, and so on. It's the easiest to relate to.

Next:
Prior to being nitrided, what would be the grain refinement process for this cast iron?

After all my hours of studying; if I had to guess, I would say that it there was little or no grain refinment needed. When the crank was cast, it was probably furnace cooled to prevent large pearlite or cementite grains from forming. Then it was machined, went through stress relieving, and finally was nitrided. Either that or it was fully annealed.

By the way, this is the kind of detail that can't be found on other diesel sites or message boards. Just one more reason why what we have here is so special. smile.gif

Gig 'em! http://forum.thedieselpage.com/ubb/icons/icon14.gif

[Bobbie Martin]

Doc,
This is not Diesel related, but should be right up your alley, so I hope you don't mind. A friend and I both have Mini Coopers (the real ones). These are Cooper S engines and they have (35+ year old) nitrided EN40B cranks. As you know, the bearing supply is not what it use to be. Usually we can get Vandervell, but sometimes Glacier - though anymore I'm not sure there is any difference. However its very hard to find the VP2 lead indium bearings. Usually its the reticular tin bearings. My question - for a road going car (6000 RPM regularly, 7000 occasionally) is there enough of a difference to matter?

[CleviteKid]

Since Glacier, Vandervell and Clevite have all been bought and sold multiple times, there is no rhyme or reason in the bearing industry anymore.

For street use, the reticulated tin is OK, but will fatique sooner than the lead-indium overlay on cast copper bearings. So you may be inspecting and replacing them more frequently. Remember, bearings are cheap compared to finding good crankshafts for your engines ! ! !

The Clevite Kid :cool:

[Bobbie Martin]

Originally posted by CleviteKid:

Remember, bearings are cheap compared to finding good crankshafts for your engines ! ! !
Thanks, thats about what I thought. New EN40B cranks are about $1600. Can't get nitrided ones anymore though.

[bio-diesel]

Dr. lee you don

[CleviteKid]

Nitriding, carburizing (a.k.a. case-hardening), carbo-nitriding, burnishing, shot peening, flame hardening and induction hardening are all surface treatments, in that their effect is limited to a zone near the surface of the metal component being treated.

Why use these surface treatments on things like axles, Colt revolver frames, leaf and coil springs, typewriter (remember them?) keys - the ones that push the ribbon against the paper, not the ones your fingers push, crankshafts, u-joints, gear teeth, roller bearing races, etc. etc. ? One reason is for added wear resistance from other components rubbing against them. But do you think Col. Colt really was worried that drawing and reholstering your revolver was going to wear it out? If so, why not case-harden the barrel too?

The main reason is for added strength at the surface. In either bending or torsion, the major loading modes for most real structures (crankshafts are loaded in BOTH bending and torsion) the highest stresses are at the surface. It is well-known that fatigue resistance is proportional to ultimate tensile strength and hardness, for any given surface roughness. Ductility is not a concern for fatigue, where no macroscopic deformation is involved anyway. All these treatments listed above make the surface layer of a metal harder and stronger, and many of them also create favorable compressive residual stresses to better resist the initiation and propagation of fatigue cracks.

In particular for crankshafts, the fillets adjacent to the cylindrical journals are nitrided, shot peened, roller burnished, etc. for added fatique resistance. The bearings never touch the fillets (except during bearing failures !) so wear resistance of the fillets is not an issue.

Dr. Lee :cool: