21 replies to this topic

[Richard Border]

F1 rules limit crankshafts to steel. What would be better than steel for crankshafts?

[desmo]

I cannot recall even hearing anyone seriously propose a material other than iron or steel as a crankshaft material. The only material I am aware of that might concievably replace ferrous metal in cranks is AlBeMet Beryllium alloy, which is, of course, banned in F1. Titanium isn't stiff enough, the sections would have to be too large. When CF came on the scene, I figured it would find an application for con rods but it never happened. If CF can't make a better con rod, it seems unlikely it is a viable candidate for a crank. Seems like another of many unneccessary technical regulations to me.

[Ray Bell]

At least it cuts out the potential cost of experimentation... or would computer modelling remove that anyway?
Like you say, des, another rule to pack out a book already bulging and looking like a lawyer's nightmare.

[david_martin]

I suspect that Be-Al alloys would not be any good for crankshafts. Although these Be alloys have rather high specific stiffness in compression and tension, they do tend suffer from fairly severe anisotropy problems that would probably make them rather difficult to use in applications with significant shear strains, like a crank. Their fracture toughness is not too great either.

You could certainly use a finite-element method simulation to evaluate the torsional rigidity, localised stress concentrations and effects of thermal expansion of a crank under service loads for different materials. The usefulness of the results will depend on how well you can describe the crank material behaviour.

What is harder to simulate is things like fatigue limits, wear resistance and friction properties, and in-situ thermal behaviour. And fabrication of the crank itself, of course, which with some materials can be the hardest part of all. All that stuff can really only be sorted out by experimentation, whether using small-scale experiments or actually building and running an engine.

[Halfwitt]

I think most rascing cranks are nitrided, which you could not do to an aluminium alloy. Also, nitrinding ehlps with fatigue. Basically, at a low enough level of stress (the fatigue limit) a steel or titanium part will survive for any number of cycles. Only these materials behave like this. Aluminium and its alloys will fail by fatigue at very low levels of alternating stress as it displays fatigue limit for infinite life.

I should imagine CFRP would be poor in compression, and I think thats probably why it isn't much good for con-rods.

[Jaxs]

Have a browse through the Periodic Table, there is a vast array of metals that could be used as a mix to give a stronger crankshaft. But this would again favour the richer teams who could afford the research. The rules help to keep the playing field level.

[david_martin]

Strength is not really the issue here, I think - mass is. Lighter cranks will reduce the total engine mass and make life much easier for the bearings. Finding a robust, lightweight, and torsionally rigid material is the core question.

In reality the range of metals available to form the basis for an alloy which has use in an application like a crank is rather limited, just a small range of the transition elements.

While Nitriding (and carburising for that matter) are very popular ways of improving the sruface hardness without effecting fracture toughness of ferrous alloys, there are several of other techniques for applying surface modifying coatings to many non-ferrous alloys that work well. They are just very expensive to do and more difficult on shapes like a crank.

[Ali_G]

Just wondering guys but does the crankshaft have to be made from some sort of metal. Some sort of Polymers have been created which could take the strain and I am pritty sure take the heat.

Also the rules state either Steel or Iron. But does it state what percentage of carbon is allowable in the steel.

Niall

[david_martin]

The FIA technical regulations on crank materials:

5.5.1 ) The basic structure of the crankshaft and camshafts must be made from steel or cast iron.

The carbon content of the steel is a moot point - the delineation between cast iron and cast steel is usually made on the basis carbon content in any case.

As for a polymer crank, I doubt there is any polymer which has both a sufficiency high elastic modulus and yield strength, and fracture toughness, and sufficiently low anisotropy and creep rate to be of any use in a crank.

[Top Fuel F1]

Originally posted by david_martin

The FIA technical regulations on crank materials:

5.5.1 ) The basic structure of the crankshaft and camshafts must be made from steel or cast iron.

David:

It is my understanding that a good steel racing crank would be a Forged Billet. In simplistic terms the forging process changes the internal structure, which loses it's grainy structure and becomes more fiber like in structure. I think of a casting (cast iron) being something a street car would have. Would you think otherwise? If not, I wonder why the FIA includes cast iron in the rules.

Best Regards;

[Ray Bell]

To cover the bases, I would say. What if some foundry came up with a superior casting technique, the rule might otherwise prevent its use...
Not that they're likely to.

[desmo]

Wouldn't anisotropy in Be alloys be down to the forming technique or is AlBeMet intrinsically anisotropic? Metals generally are isotropic unless that is changed in the forming process like in a forged crank. Would a CNC machining from solid AlBeMet billet show significant anisotropy?

[david_martin]

On the subject of cast and forged cranks:

Phew, this is going to be a hard one to do justice to without presenting a lecture series on ferrous metallurgy. This is definitely not my area of expertise, but here goes nothing....

To begin with, I think we have a bit of a nomenclature problem to deal with. "Cast iron" does not necessarily imply using a casting in its as cast state. Cast iron is really a generic term that encompasses ferrous alloys with more than a certain carbon content (and not enough chromium to be call stainless steel). There are plenty of examples of wrought (ie. rolled or forged or whatever) "cast" irons. Steel, on the other hand, is generally usually used to describe lower carbon content ferrous alloys. Clear as mud?

Your point about forging is pretty much spot on. I am pretty sure cast iron is just a hangover from the "good old days". Mechanical work on a casting (whether a billet or a "near net" cast shape, which is also common) does several rather important things which dramatically improve the material's mechanical properties. Most castings have a few rather bad features which effect strength, ductility and fatigue life - internal porosity, dendritic microstructure and segregation being the worst. Mechanical work helps break up the as cast microstructure (think a 3D network of snowflakes or pine needles and you would be on the right track) into something much stronger, tougher and more ductile (think a bowl of rice crispies). It also help annihilate internal porosity, which tends to act as intiation sites for internal fatigue cracks. So using a forging step to shape something like a crank is really beneficial, and I am sure just about every serious racing engine would be using a forged crank.

I would guess F1 engines would be looking for strength over toughness in a crank material because of the relatively short service life of most engine components and the absolute focus on weight reduction. And as cost and tribological (wear and friction) considerations are also not such big issues, most of the advantages of having free graphite in the microstructure (for self-lubrication during cold running) are nullified. All this probably means fine grained, forged alloy steel with some kind of surface modification (probably shot blasting and nitriding) to increase the surface hardness without effecting toughness or fatigue life of the part.

[Timm]

How about a fibre-reinforced ceramic crank? Can the material experts offer an opinion?

[david_martin]

Originally posted by desmo
Wouldn't anisotropy in Be alloys be down to the forming technique or is AlBeMet intrinsically anisotropic? Metals generally are isotropic unless that is changed in the forming process like in a forged crank. Would a CNC machining from solid AlBeMet billet show significant anisotropy?

If the last post was on the limits of my expertise, then exotic light alloys are right off the map. I will happily admit to not know a great deal about light metals, but once again, I can't resist..

To be honest, when I mentioned anisotropy I was thinking more about plastic, rather than elastic anisotropy - which, on reflection, is reasonably irrelevent. After all we would hope there is no macroscopic plastic deformation occurring in an engine!

All common crystallographic unit cells found in metals have some degree of orientation dependent properties that will lead to anisotropic mechanical behaviour. Extrapolating from single crystals to bulk material really depends on what and how much of the various orientations are present, which as you point out, is largely a function of the deformation history of the material. Depending on how they are done, things like forging, rolling and extrusion can induce anisotropy - sometimes it is desirable, sometime not.

As for milling a solid BeAl billet, the degree of anisotropy in the crank will depend entirely on what the billet was like in the first place. I suspect the most important point is that there probably is not such a thing as a solid billet of BeAl. My understanding is that powder metallurgy is the most common method of fabricating parts from BeAl. Powder will be hot isostatically pressed and sintered to produce near net shape parts. The near net shape parts will then be machined to final dimensions

[Type61]

While I have no idea of as to the intent of the rule, perhaps the F.I.A. was thinking of bi-metal or multi-metal applications. With the thought being to reduce rotational mass (the proper word for this escapes me). A very expensive proposition no doubt.

[Halfwitt]

Originally posted by david_martin
So using a forging step to shape something like a crank is really beneficial, and I am sure just about every serious racing engine would be using a forged crank.

That is what I would have thought until I read an article on a company called Doug Kiddie Engineering from England, who make F1 cranks. They are all machine from solid billets of nitriding steel. No forging at all involved. I would think forging tools and equipment for a V10 crank would be extremely expensive. I had a tour of Triumph Motorcycles a few years ago(about 1995), and saw the equipment for the 3 cylinder cranks which are forged and then hot-twisted to give the 120 degree configuration. I would think a V10 has a 72 degree crank, and the equipment to forge and then put the many twists int this would be prohibitively expensive.

[desmo]

Here's an unspecified F1 crankshaft.

[Halfwitt]

Bloody Hell! Not much to that is there? I would think it is pretty hard to make that from solid without it distorting. How unspecified is 'unspecified'. Is it unspecified as in desmo doesn't know what engine it is from, or is it unspecified in that he isn't letting on??

[david_martin]

Originally posted by Halfwitt

They are all machine from solid billets of nitriding steel. [/B]

Perhaps I was a little ambiguous in what I said. When I talked about forging steps for shaping, I meant that it could include forging (or even rolling) the as cast billet to introduce mechanical work and refine the microstructure. The result could still be a semi-finished shape (like a round, octagonal or square billet), or a near net shape (like a rough crank shape). The important point is that the feed stock for the crank milling or machining steps is not a raw casting - it has been hot worked in some fashion to improve its internal structure and mechanical properties. In your example (which given the small volume of production of something like and F1 crank is probably how it is done) the billet used will undoubtedly have been forged or rolled before milling.

[Halfwitt]

If it is anything like the steel bar we get at work, it is generally hot rolled in the larger sizes.

[Richard Border]

Desmo's picture of the v-10 crankshaft made me think of
another question about crankshafts. Where is the
"proper" place for the oil holes on the crank throw?
Assume that the engine is facing you with the cylinders
vertical, and the engine turning counterclockwise.