You just described carbon apex seals.

 

Im doing my masters in mechanical engineering, the project is material selection and testing for piston seals and chamber coatings in a pivotal engine (rectangular pivoting piston, 2 stroke) one of the seal materials that we are using is kind of an Al alloy, it is called CE7, it is a low expansion aluminium silicon alloy with approx 70% silicon, this material works well in our application but I dont think it would hold up to the temperatures in a rotor, also you would have to look carefully at the stiffness of the material at operating temperatures to make sure that it would not bend and catch on the exhaust port. Interestingly the mazda apex seals appear to have very little carbon/graphite on the wear/seal surface.

 

the problem with rotary seals is that the seal must withstand the brunt of all the forces during a combustion sequence, wehre as the piston ring seals are protected essetially since they are not in the path.



Mazda probably uses some sort of steel alloy with low conc of carbon. As carbon increases the brittleness of metals as it's concentration goes up. But it does make it harder.

 

do you guys really think you can make a better seal then mazda did on your own?

you must have a lot of money, good luck

 

it's cast, the lowest grade of cast iron has more carbon content then the highest carbon steel. the hardning of the steels is what makes it that bittle if you were to temper it it should work alright, you aneal the end of a punch and it takes the same if not more abuse.

 

if some one has enough money, time. and people to help any thing is posable.... and i wouldnt waste my time on casting, i would just make a mold and if the mold is all in spec every thing should be close or if not just good enough as it is.... but i dont think any of us do thes kind of things as a living... but i would also think about using an e.d.m. more then machining thim if its realy all that hard of a aloy



but other then that, its worth a try if your wanting to put the time and money into it.... good luch

 

yeah EDM is definately the way to go.

 

There are definitly plenty of materials out there that would probably be better than the mazda seals, just that there does not seem to be many people experimenting with it. When I get round to putting my motor together I think I will make my own seals purely for cost if I can find a block of something useful ( free EDM wire cutting at the university)

 

Do you have any idea just how many alloys mazda has tested over the years?

 

Aluminum melts at around 1000F. And because of the nature of the beast, mechanical properties are greatly diminished even at around 400oC and starts to soften at 700F-800F.



Choosing a suitable material for them apex seals is one thing.. then there is the question of manufacturing them. Manufacturing process will have to be closely controlled to get a homogeneous seal with no residual stresses(or a uniform state of). There's also a question of cost, performance characteristics like wear, natural frequency etc etc.



I'm not saying that a new high quality seal can be made.. just that there is a whole lot more to the material selection that alot of people think.