hey guys,
i was just thinking of ways to spend money i dont have and came up with the idea of using titanium in the engine. do you guys think there would be any benefits in using titanium for apex seals or maybe stationary gears? any other ideas you guys think would be cool?
ttyl,
joe

 

-check the temperatures at which Titanium softens and liquifies to ensure it can withstand that level of heat

-check it's dimensional stability across a heat range to see how much it expands/contracts. If it'll be too loose to seal when cold or to tight to allow a rotor to spin when hot, you're screwed

Someone proposed magnesium rotors a few weeks ago, singing the praises of how such a lightweight rotor would improve the engine, without realising that magnesium actually burns quite readily.

 

ok i found somewhere that a certain alloy (they call it alpha alloy) can be treated to resist up to 1000 degrees farenheit. that is also with very little creep. yeah magnesium is a bad idea. my dad used to throw oldd VW blocks made of magnesium into bonfires, run a safe distance away, and watch the show. hehe. anyone else have opinions or ideas on this titanium thing?

 

Spending money you don't have is fun.

 

My Brother owns a factory which makes turbine blades for jet engines and guided missiles all milled from titanium. Thus it is unlikely to be a problem except the cost which even the aviation industry thinks high.

 

titanium has high sheer strength, but poor torsional rigidity.
There I sound smart now

 

Titanium is highly notch sensitive. That means cracks start easily at the slightest nick, gouge, or scratch.

Also, ask anyone who's ever rode a bike with Ti parts... That stuff is flexible as all hell. Ti seatposts, stems, and handlebars make it feel like you're riding a noodle. Solution is to increase the cross-sections for increased rigidity, but this isn't a possibility when dealing with things of a fixed size like in a preexisting design.

 

good stuff guys...thanks this is the sort of input i was looking for. Its fun to learn hehe

 

Hm peejay, you ride mountain?

BUY MY CROSS COUNTRY BIKE!!!

um... oh yeah... ti..... Yeah its great. Really rubbery tho.

Full suspension TI mountain bikes dont need a rear pivot, and they have around 2.5-3" rear travel. REALLLL bendy them's is.

 

What kind of alloy do they use in the bikes? I always got the impression it was much more rigid than steel.

 

They use pure, 3Al/2.5V, and 6Al/4V depending on several factors. (For instance 6Al/4V is incredibly hard to work so it's not used for tubing, but it's good for dropouts and other weld-on bracketry)

Titanium, as well as aluminum, are significantly LESS rigid than steel. However, they are both much lighter, so they can increase the cross section of the metal (huge diameter frame tubing, for example) to increase the stiffness. For parts that must be a fixed dimension, though, such as handlebars or seatposts which must be a standard diameter, you do not have this option and you really feel how whippy the stuff is.

ioTus I've been paring down my collection I went from about 20 bikes to 3 main ones. I stayed away from Ti, because it's really not significantly lighter for the money. My cross country/trials bike weighs about 22lb and is laterally stiffer than plaster, as opposed to my 20-lb 70's Vitus-tubed steel road bike (it's very retro, I felt ashamed for putting clipless pedals on it!) which I cannot hammer uphill on or the frame flex will cause the chain to come off on the front... and my "normal" bike is a 30lb full suspension bike (Schwinn URT "Sweet Spot" design) with fenders and slicks on it - call it a complete mutt and a bit confused about its mission in life.

At my peak I weighed 190lb and I went through parts like I was eating them. I grew to hate titanium. I'll admit, it was nice to feel how my (lighter, weaker) friends' bikes were a tad lighter.

And I'm just about to go back to the garage and straighten the rear wheel on the roadie, again... *sigh* Too worried about theft to ride the valuable bikes to the store!

 

I've often thought about making parts out of 718 stainless steel. I work at machine shop where we make parts for industrial electric generators. Many of the nuclear power plants require that we use 718 stainless in the steam generators, because it maintains it strength up to 1600 degrees farenheit. Might be good for seals and such. Definitely wouldn't use it for stationary gears, the metal is too flexible. As for stationary gears, I think you're just better off with the old gas nitriding method, as I understand, their failure rate is quite low.

 

I once worked in a machine shop that did design prototypes for Sanvic specialty metals. Once in the late 80's we did a prototype all Ti frame for a mountain bike. That stuff is a bear to lathe, even more so to weld. Ti is actually really flamable too, as we accidently found out. You have to take really small passes on the tubes on the lathe, because if you cut too deep it'll warp really easy. Well, we caught all those shavings in a metal garbage can, and some idiot decided to throw a butt in there and that was it. After expending all 5 fire extinguishers we had in the shop we still couldn't put it out. Completely slagged the garbage can. Luckily this was just outside the shop door and not inside.

Ti wouldn't be my choice for bike frames either. I've seen some really nice Aluminum ones, and some great cromoly steel, double and tripple butted. The problem with both Ti and Al is that it has a considerably shorter fatigue life than steel.

 

My dash kit is made of brushed stainless steel facia over lightweight aluminum chassis.

The brushed stainless looks gorgeous.

 

Steam generators are in Presurized Water Reactors (PWR's), but I work at a BWR (Boiling Water Reactor), so we don't have any.

However, while heat and stress are very important for design in nuclear components, neutronics plays a HUGE role. What that means is that radioactive flux from Alpha, Beta, and Gamma play a very large part in the life of a component. Alpha and Beta will actually plate out on the metal surfaces and change the metals grain structure, and gamma has similar effects to thermal stresses.

The largest reason for using high quality stainless is so there is no galvanic corrosion passed to the fuel bundles. Fuel corrosion is a huge problem if it happens, and can contribute to fuel pin failures, which means lots and lots of $$$ to clean up and fix. (It doesn't affect public safety, just the ratepayers costs for electricity)

Electrochemistry in metals under such high temperatures and with such enormous water flow rates are giant headaches waiting to happen. Our condensor is made from admiralty brass, and we've encountered some spalling corrosion with copper deposits on our last fuel cycle (mostly the 4th burned stuff, most people don't realize that only about 1/4th of the fuel is actually replaced during a refueling, the rest is shuffled to achieve optimal performance). No big deal, just something like a couple of hundred million $$$$ to replace the condensor, which is going on 20 years old.

The really ironic thing is that most all coal and gas fired steam electricty producing plants are allowed to run at higher temperatures and pressures than we do. Add the word nuclear to anything and you've trippled or quadrupled the price of a component because it now is way over-engineered to meet the ASME boiler codes for Nuclear, as well as seismic and safety classifications.

 

So let's say I got my hands on some Ti and machined some apex seals...would you use them in your engine?

I get the feeling they would bend and let pressure leak past before they would shatter, and maybe that's a better scenario than with the steel ones?

 

i think it would be fun to buy a cheap motor from a junkyard and try that out. i would totally do it if i had the funds and the time...just run it hard to see what i could stand up to. it is a costly undertaking though.

 

\
That happens quite a bit around here doesnt it

Oh and directly at the exhaust manifold on a turbo rotary its hot enough to crack cast iron. I think Ill keep the regualr rotors

 

I've heard that for bikes, the best material is beryllium, it is 35% lighter than alluminium, and 60% lighter than titanium, and is stiff, elastic(returns to original shape, not soft), and has a melting point of 1500+ K (around 2300 F). Anouther plus, is that it tends to form only covalent bonds unlike magnesium, and titanium, which is why they are flammible'(highly exothermic). the bad part about beryllium is: 1) 86x the cost of titanium 2) highly controlled substance due to its ability to reflect neutrons, making the critical mass of plutonium half of what it would normally be. So it is a key to making small/cheap nuclear weopons.

I've heard that a pair of bikes were made using beryllium, they cost something like $30,000. So.... interesting but impossible to use.

 

Boy, I tell you....engineering is an art. Its all about finding the best solution for the least amount of money. I seriously doubt that anyone here is a good enough rider that they would notice any difference between a beryllium frame and a titanium or aluminum frame. Its like NASA. They spent billions upon billions developing the space shuttle, just so they could have a recoverable launch vehicle. The Soviets looked at it, copied it, built one, said "oh, that's nice", then went back to doing space launches the old fashioned way, build a big rocket, light the fuse and watch it go up. Why? Because its cheaper / faster / easier and does exactly the same thing, and therefore its much better.

Another example of this is the development of the Harrior Jump Jet. The Brits spent like two decades developing it. The original design requirement was to be able to launch an aircraft from a really short flight deck, (STOL). While they were still tinkering around with their designs for 20 years, within a single year we were strapping on rocket boosters to existing aircraft. Problem solved.

Beryllium huh? hmmmm....I think that I would prefer carbon fiber. One thing though. Extreme rigidity is not that desirable in a bike frame. Its better to have a frame that will flex just a little, and the more rigid, generally the shorter the fatigue life.

Since we're dreaming and all, I would like some depleted uranium for loading shotgun shells for goose and duck hunting. That Federally mandated steel shot just doesn't hit hard enough

 

LOL..... Beryllium is just a pipe dream, but could you imagine your rotors, and housings so light,(with all the coolant/oil jackets) that it would float!!!