head button material

[lohring]

The problem with ceramic heads, and some of the other poor heat conduction materials, they would allow run-a-way heat build up in the combustion chamber. The idea is to raise the combustion temperture some to allow for the more effecient burning of the fuel/air mixture while still being able to control the upper temp limit. Too much combustion chamber temp would make the engine go into damaging preignition and detonation. This would raise the temps even more and reduce the RPM's just before the engine lets go. If all you wanted was more head temp, do away with the water cooling and fins. Charles

That's why I'm afraid you would need a ceramic piston and liner, much harder items to fabricate. Then you would need to deal with the fuel issue, but that is easier and has been investigated. One of the easiest ways to increase the thermal efficiency of an engine is to increase the temperature. Our tiny engines suffer from more heat loss than larger engines because they have a lot of cylinder area for their cylinder volume. Ceramics are the most promising materials for increasing the temperatures. It's just that all our backgrounds are in designing and fabricating metals. So far, no big ceramic piston or turbine engines are being built. I'm sure experimentation is going on and little engines shouldn't have some of the structural problems of big engines. I'm stuck in several conventional gasoline engine projecst or I would consider some experiments.

Lohring Miller

 

[Bart Drieghe]

Take a look at http://www.youtube.com/watch?v=i8kGbygny7s&feature=g-hist&context=G2c12c02AHT08bzAALAA for an idea of what dental labs can do. The problem with things like threads is that the zirconia is machined in the sinitered state and needs to be fired after machining. That results in shrinkage that is compensated for in the machining, but I doubt that they are setup to thread mill. Tapping would result in an undersized hole. Zirconia is very strong and I bet accuracies of +-.0005" are routine in the finished product. A 100 mm (4") block like the one pictured costs over $200, though.

For coatings you could try http://www.swaintech.com/

Lohring Miller

The problem with the dental zirconia is that it needs to be fired . While you might think the accuracies are very high , they aren't ...... . And its not that very strong , i'm sure if you would try to "tap" it it would most likely just break like glass . Its strong but can break like glass . I've got no idea how well you can machine it after firing but in my eyes , this isn't an option .

B

 

[dwilfong]

Before firing put a insert in the plug hole?

I have a .21 with ceramic coating on the cylinder bore.

David

 

[lohring]

The flexural strength of dental zircronia is over 1400 mPa (200,000 psi). Silicon nitride (bearing balls) has a flexural strength of around 880 mPa (130,000 psi). 4130 heat treated steel has a tensile strength of 1100 mPa (160,000 psi) depending on the heat treatment. All ceramics are brittle, so it takes different thinking on some design features. Lots of doubters are having their noses rubbed in the sucess of ceramic hybrid bearings in internal combustion engines. Old time dentists like myself are having the same experience with the new ceramics.

The accuracies are reasonably good, the same as precision investment casting, but some parts would need machining after firing. I know that can be done with high speed diamond burs because that's what I use to adjust ceramic crowns. The profit margin is lots higher in dental applications than in model engine building. Cost is the real problem.

Lohring Miller

 

[lohring]

A quote from a manufacturer:

High – precision zirconia balls are available in many sizes. Zirconia balls are most commonly used as check valves in flow control applications. When subject to stress by impact, grinding, or cracking, a zirconia ball undergoes “transformation toughening” which stops cracks from spreading and actually makes the ball stronger in the stressed area than what it was originally.

Lohring Miller

 

[lohring]

More on zircronia by ceramic engine investigators:

Zirconias: These engineering ceramics were once dubbed "ceramic steels" (ref 21) because of their very high fracture toughness among ceramics. Also, zirconia ceramics have one of the highest maximum service temperatures (~2000 C) among all of the ceramics (ref 25) and they retain some of their mechanical strength close to their melting point (2750 C). However, their low creep resistance and their low thermal shock resistance (ΔT ~ 350 C) could pose a problem.

 

Zirconia ceramics have been used in heat engines because of two very notable properties they possess: a high temperature capability and a low thermal conductivity. None of the other ceramics possess a thermal conductivity as low as the zirconias. This means that engines made out of zirconia would retain much of the heat generated in the combustion chamber instead of loosing it to the surroundings (approaching near adiabatic conditions). Thus the need for a cooling system could also be eliminated.

Lohring Miller

 

[dwilfong]

OK so how do you get some in the raw form to mess with. also how dose it need to be fired.

would relay like to try and make a button from it.

Don't know unless you try.

David

 

[Bart Drieghe]

The flexural strength of dental zircronia is over 1400 mPa (200,000 psi). Silicon nitride (bearing balls) has a flexural strength of around 880 mPa (130,000 psi). 4130 heat treated steel has a tensile strength of 1100 mPa (160,000 psi) depending on the heat treatment. All ceramics are brittle, so it takes different thinking on some design features. Lots of doubters are having their noses rubbed in the sucess of ceramic hybrid bearings in internal combustion engines. Old time dentists like myself are having the same experience with the new ceramics.

The accuracies are reasonably good, the same as precision investment casting, but some parts would need machining after firing. I know that can be done with high speed diamond burs because that's what I use to adjust ceramic crowns. The profit margin is lots higher in dental applications than in model engine building. Cost is the real problem.

Lohring Miller

Hi Lohring,

When i said , the accuracies aren't so high , then i meant that the Zirconia needs to be machined precisely after the firing . The % of shrinkage is known yet i don't think you can mill /fire the zirconia that precisely that you can just use it . And even if the fit for the liner is good , you still need to tap it . You'd be needing a special tap ( to counter the shrinkage ) . The insert , not sure how well it will survive the firing but that might be an option .

That aside , i'm sure that there are companies able to machine the zirconia but like you say , the cost will be the issue there as the tools are very expensive to use .

@ David , you can most likely find the Zirconia at a dental supplier , i'm sure that Lohring can help you in that . But in my eyes , you'd better search a dental lab who does work with the Zirconia and can help you to mill , fire( don't forget the shrinkage) the zirconia . It will be like lots of things , trial and error .

B

 

[dwilfong]

One of the guys in are club has a eng with a ceramic button in it.

He said that Garry Preusse made it for him?

David

 

[lohring]

"... you still need to tap it"

That's what I mean by thinking needs to change when you design with ceramics. I don't think threads into the ceramic will be the best fastening method.

I've considered contacting dental labs about making parts. The problem is that they are setup for very specific styles of parts. Long cylinders with slots would take special fixturing on their machines. Conventional mills with high speed grinding spindles would work. The unfired material is fairly machinable. It takes diamond for the fired material. Diamond burs for dental drills cost around $10 each.

In all, building a ceramic engine is a big project. There have been attempts, but no obvious successes. I'm not volunteering

to try.

Lohring Miller

 

[Charles Perdue]

Has anyone done any testing on the effect of different finishes, shiney vs satin vs rough, on the head buttons? Would think that shiney would be better. It would reflect the heat back into the combustion process better.

Charles

 

[dwilfong]

Has anyone done any testing on the effect of different finishes, shiney vs satin vs rough, on the head buttons? Would think that shiney would be better. It would reflect the heat back into the combustion process better.

Charles

Charles

I polish my buttons now and after a run thy come out looking much the same. I also do the top of the piston. Not sure if it help make power. If it dose would be hard to tell with out a Dino to check the result as I think it would be minimal.

But every little bit helps as I see it. all those little bits add up to allot.

David