With CF technology getting more common for hight temp applications (e.g. brakes), I was wondering if anybody has looked into CF compressor wheels (rather than Ti, Al, etc) to reduce inertia/spool up? Once the initial mold is done, they could be very cost effective, but thermal expansion may be an issue.

I have access to a fabricator for aerospace grade braided CF parts, suitable for a compressor wheel type desgin. What would the cost and weight savings for this have to be for people to be interested?

 

Of course there will be people "interested", but that type of manufacturing gets ludicrously expensive quick. I don't know that it could be viable for the dollar.

 

Isn't CF little to fragile for a compressor wheel? Even carbon fiber brakes are known to shatter ever now and then.

 

It's an interesting idea but, I don't think it's practical for that application. I would be willing to bet by the time you got the structure needed the aerodynamics and weight would be worse than a Ti unit probably worse than stock. Balancing is a whole other issue.

Not to mention laying up something that intricate would be a holy nightmare and bonding it to some type of hub that is going to see lots of thermal cycles is asking for failure. Unless you are talking about the same carbon material rotors are made from but, I don't know how you would mill that to shape without sacrificing structure and eating up a lot of tooling.

If it were possible I'm sure Audi or Porsche or some race team would have pursued it. If they have I've not heard about it.

 

the tune for a car running a turbo with a CF compressor wheel would have to be strict, in that if you exceeded the flow capacity of the turbo and ended up with surge, the reversion of air back into the compressor would probably sheer the wheel apart very quickly. most tunes are designed with a safety margin, where you may overboost without hurting anyhting, here that margin would be ever greater, and there would be more performance loss. carbon fiber has great strength but its relatively fragile when it comes to sheering strength. if it was a full blown race team who could afford to replace engines everytime a blade came off the wheel and got chewed up by the engine, no biggy, but for the more typical evo owner, the cost to replace such a wheel, and the potential to run through these wheels quickly could be a big problem. its been a long day, i hope i got all that out correctly ...

 

thanks for the feedback guys - I work on aerospace parts for a living, and have been talking to one of our manufacturers (also a gear head) who specializes in complex braided CF parts. He thinks a compressor wheel is doable with lower than Ti or Al weight, a hot-side is questionable though (it would be very expensive). The only concern he has is different rates of thermal expansion for the wheel and the housing unless both are made from CF. The unit cost would be low (<$100), but the initial cost would be high (for the design and mold). So I'm trying to get a feel if it's economically viable to pursue the idea (how much they could be sold for and how many need to be sold to break even).

I was also wondering if anybody else had done it yet, but I really do think it's technically doable (we do some pretty crazy CF stuff), just a question of economics though. Especially from a reliability / testing / warranty standpoint. So I was trying to gauge how much money people would be willing to spend on just faster spool, since it won't be more peak hp really.

 

a CF compressor housing would be so awesome. i could stare at it all day. but im still concerned with reversion back into the wheel. your friend and your self are for more knowledgable about CF properties than i am, but from my limited reading in assembly, and how that effects its strength, it would seem to me that if the cf wheel is designed for strength in a particular rotational direction (which to my understanding is why you bond different layers in various angles to each other), then it wouldnt be able to handle a backflow? just to further my knowledge of the subject, could you pm me, or publicly, explain how to counter the generally fragile and brittle nature of CF in an application such as this? im guessing you are making it all from one piece, not bonding each blade to a central hub piece, therefore that would reduce the risk of a blade snapping off. but the leading edges would seem to be so succeptable to damageif the expansion ratios were incorrect (as you pointed out). also another thing that comes to mind, and im presuming it would be made from prepreg cf, if there were any inconsistencies in the resin's application, there could be some vibration produced? all just thoughts popping in my head. hit me up i love this stuff.

 

Less CF, more ceramics...

 

LOL - ceramics would be sweet for a hot side, but just as brittle as CF.

vrex - to answer some of your questions, the key to get the load distribution right is the braid pattern of the CF fibers. The hub/blade interface is tricky (the hub would have to be a metal part), and the resin needs to be tightly conrolled to get the wheel balanced as closely as possible right from the start. Brittlenes is a concern - if you suck in a small rock into your intake the wheel could shatter. Making it out of Carbon-Kevlar would help with that, but makes it heavier.

I don't know if this is going to turn into reality, but it shure would be fun. Maybe we'll experiment with a compressor housing first (less challanging and needed anyway to solve the thermal expansion problem).

 

i think it would cause uncontrollable compressor surge and probally resulting in distruction of the wheel because of its weight and being so brittle. they had that problem with the buschur 20g8 TME the wheel was so light that it surged like crazy.

 

^ that is because it was a poorly matched wheel for the turbo.

a cf wheel, i've dabbed with the idea. lotta my concerns were already addressed. i didn't think you could get the cf to stay stable at 1600f. i thot the resin would boil or the resin would burn off or something.

that said i didn't think cf expanded that much, i thot it expanded less than most metals, but that would still pose a certain tolerance problem. you'd have to make things awkward ratios of thickness which may not be conducive to the already existing wheels that you seek to replace. if you built the turbo from the ground up it would be less of a problem.

just how much could cf of the thickness of a compressor blade take? would it shatter with a grain of sand going at 100mph? cuz i know aluminum doesn't, it just bends. shattering could be very very bad as that gaurantees a catastrphic engine failure, where with al there is no such concern unless you REALLY bugger something up.

 

woa - that's hotter than I thought, does it really get that toasty on the "cold side" of the turbo? I was thinking no more 1000F?

 

i was referring to this

no it doesn't get that hot on the cold side

but you can make the cold side out of magnesium, would cf beat that in terms of weight?

 

Depends on the type of carbon and the processing technique. You can make carbon shapes from just about anything. You can even make them from wood. And, almost anything you can make into carbon you can also make into ceramic. This logically leads to NASA's Ecoceramics: http://www.grc.nasa.gov/WWW/RT2001/5000/5130singh.html

I've seen carbon pistons before. So I guess it can't hurt to try making a compressor wheel out of it. Personally, however, I'd rather see a Beryllium compressor wheel paired with a UBE Tyrannohex ceramic turbine wheel and a TiAl shaft. That would be badass.

Tyrannohex is a pretty neat material. It's about the same strength and density as aluminum, but retains its strength to extremely high temperatures, making it stronger than even the best superalloys at temperatures above 2,000*F: http://www.matweb.com/search/Specifi...assnum=CUBE252

 

Here's were i will shine.

I design furnaces that have the ability to go to over 4000f.

We also made ceramic exhaust wheels for the largest turbo maker. they make almost every wheel for every turbo you can think of. The ceramic wheels are super feather light the only problem they are super brittle but very strong. The only way to damage these wheels are during assembly just tap them and they break but they hold up in cars with almost no therm expansion.