9 replies to this topic

[hydra]

How/where are Keronite coatings used in a modern-day state-of-the-art race engine? Can Keronite coatings be used as anti-wear coatings, e.g. for an aluminum cylinder bore surface, or a piston skirt, or are they better used as a hard coating that resists hammering (e.g. top ring land or maybe even valve seats?)

[McGuire]

Good question. That should be looked into, along with the current state of all the various performance coatings.

[Christiaan]

Keronite is ceramic, therefore would probably not be allowed in F1, however check out this link

[hydra]

That's not necessarily true, as
a) all bare aluminum surfaces contain a passivated "ceramic" oxide layer
b) F1 engines use Nicasil bores, which is essentially a ceramix in a metallic matrix, and
c) F1 engines use ceramic coatings throughout the engine


So it looke like Keronite is a good material for the top ring groove and possibly the piston skirt, but if its as great as they say it is why wouldn't it also be a good material for the piston bores as well? That is my main interest in the process btw.

I was quoted 65 Euros per bore or per piston for the coating btw (pretty expensive for fancy anodizing no? ) , but they have no information on how it would stand up as a cylinder bore material.


Edit: Check this out, its near the bottom of the page..

http://www.keronite.com/motorsport.asp

[Halfwitt]

Originally posted by hydra
That's not necessarily true, as
a) all bare aluminum surfaces contain a passivated "ceramic" oxide layer
b) F1 engines use Nicasil bores, which is essentially a ceramix in a metallic matrix, and
c) F1 engines use ceramic coatings throughout the engine


So it looke like Keronite is a good material for the top ring groove and possibly the piston skirt, but if its as great as they say it is why wouldn't it also be a good material for the piston bores as well? That is my main interest in the process btw.

I was quoted 65 Euros per bore or per piston for the coating btw (pretty expensive for fancy anodizing no? ) , but they have no information on how it would stand up as a cylinder bore material.


Edit: Check this out, its near the bottom of the page..

http://www.keronite.com/motorsport.asp

It's something I think you will have to 'bite the bullet' and try. It bonds very well to aluminium, but I'm not convinced how well it would stand up in an engine. They do offer a polished version which might be OK when honed. As the process is done it looks to have two layers, the inner one quite dense and well bonded to the substrate, and an outer layer which is quite friable and easily removed. This would cause some misery in an engine. I know it is used on piston crowns (mainly to prevent damage due to knock), but I don't know if they remove the outer crumbly layer. I don't know if anyone has ever used it in F1, but my understanding is that they don't suffer a lot with knock at such high speeds.

[hydra]

You sure about the friable outer layer? There was no mention of this anywhere in their literature

I was wondering about the benefits of coating an entire aluminum cylinder head and running it without valve seats or guides (amongst many other things mentioned above)

[Halfwitt]

Originally posted by hydra
You sure about the friable outer layer? There was no mention of this anywhere in their literature

I was wondering about the benefits of coating an entire aluminum cylinder head and running it without valve seats or guides (amongst many other things mentioned above)

Yes, I'm sure that this is the case in the immediately as-treated condition.

It might be OK for a lightly loaded road car, but my inclination would be to fit proper seats and guides. I don't imagine a very hard aluminium oxide is going to be too kind to anything rubbing against it, and I think it mightn't stand too much impact loading. I'd go for tried and tested materials here. There may be some other advantages (some prevention of knock / detonation damage), but I'd wait until they (Keronite) can tell you about definite successes with their treatments in these applications before I went spending my money testing it for them.

[J. Edlund]

Originally posted by hydra
I was wondering about the benefits of coating an entire aluminum cylinder head and running it without valve seats or guides (amongst many other things mentioned above)

The thermal conductivity of aluminium oxide is about 1/8 of that of aluminum. Compared to copper, its about 1/15. That makes these kind of coatings unsuitable for various engine parts such as piston crowns, cylinder heads, valve seats and valve guides.

Ceramics are hard and brittle, therefore they are unsuited to high stress applications. With a ceramic applied to a metal, there is a possebility that high stress causes cracks in the brittle ceramic surface, the cracks can then continue to grow into the substrate.

Valve seats and guides for racing engines are typically made of copper based materials for their high conductivity. Coatings that replaces valve seats seems in general to be made by copper matrix composites, these have a high hardness and conductivity. You would also want the seat to have a certain ductility so it doesn't crack during operation.

All metal surfaces in the combustion chamber should be made of a materials that reflects and conduct heat well as that will result in low surface temperatures. Aluminum oxide is a poor conductor and absorb rather than reflect heat.
Valve seats must remain cool, about 120-140 degC in order to cool the valves, aluminum alloy heads should run below approx. 150 degC, higher temperatures will result in aging of the aluminum alloys typically used in heads. A low temperature will reduce knock, pre-ignition and similar problems, but the heat losses increase. Pistons should have a general temperature below 200-250 degC, and piston surface temperature should be below 300-400 degC. To keep these temperatures heat must be able to go from the piston, through the rings and into the liner and finally to the coolant. So, here you don't want a material that acts as a thermal barrier, or at least you want to use such materials as little as possible.

When you have something very hard rubbing against something softer, the hard component must have a high surface finish to prevent abrasive wear on the softer component. On components like cylinder liners a porous surface is important, this to keep the oil where it needs to be. On of the few engine applications of keronite that I can see is for cylinder liners, and the ring land of pistons instead of anodizing. However, before it's used it's performance must be verified. It must also offer low costs, or an increase in performance compared to other options.

Unlike DLC aluminium oxide doesn't have any lubricating friction reducing properties.

In CI engines temperatures are higher, and a thermal barrier can't cause knock lite in a SI engine. On the other hand, CI engines tend to favor cast iron and steel as materials in heads, liners, blocks and pistons. With max cylinder pressures of 200-250 bar, as used in some commerical CI engines, aluminum components would suffer from fatigue failures. With lower pressures used in racing and car CI engines there might be some uses for aluminum oxide, but these are probably similar to that of the SI engine. Since higher combustion pressure also reduce fuel consumption and emissions of for example particles there is also a possebility that combustion pressures will increase in the future.

[hydra]

I don't think that thermal conductivity/brittleness is the problem here, given that the keronite oxide layer is on the order of 100nm. Besides, carbon/soot is similarly non-conductive, and you have a much much thicker layer of that on the piston/CC

If anything keronite valve seats/guides would increase thermal conductivity, due to a) the elimination of the thermal barrier between seat and head, and the fact that most seat/guide bronzes have a thermal conductivity approximately the same as , if not lower than cast aluminum. The problem here it seems would be the friability/abraisiveness of the oxide layer, and the million dollar question is, could they be overcome? Is it even worth the trouble?

[J. Edlund]

Originally posted by hydra
I don't think that thermal conductivity/brittleness is the problem here, given that the keronite oxide layer is on the order of 100nm. Besides, carbon/soot is similarly non-conductive, and you have a much much thicker layer of that on the piston/CC

If anything keronite valve seats/guides would increase thermal conductivity, due to a) the elimination of the thermal barrier between seat and head, and the fact that most seat/guide bronzes have a thermal conductivity approximately the same as , if not lower than cast aluminum. The problem here it seems would be the friability/abraisiveness of the oxide layer, and the million dollar question is, could they be overcome? Is it even worth the trouble?

Brittleness is always a problem with ceramic coatings. Also, for a ceramic coating to be successful, it needs a certain thickness or a substrate material that has a certain hardness. Alumina is for example used in many machine tools today, they are applied on a substrate of cobalt matrix tungsten carbide. It's the alumina that provides the hardness that is needed but you can't replace the tungsten carbide with a softer material. If you do that, if doesn't matter how hard the coating is, it will fail anyway.

It seems that keronite coatings are typically about 10-40 micrometer.

Brush Wellman Alloy 3, used by for example Del West for exhaust valve seats has a thermal conductivity of 240 W/m-K, that's a better than the 109 w/m-K of 319 aluminum alloy and a big improvement over the 30 W/m-K of alumina. The thermal conductivity of alloy 3, used for the inlet valves is similar to that of 319 aluminum alloy. A thin coating will reduce the effect of the low thermal conducticity, but a very thin coating won't work, and with a copper based cermet as a coating, the conductivity will be better.

Soot also have non conducting heat absorbing properties, that why soot in the combustion chamber can lead to pre-ignition and detonation. You don't want soot or thermal barrier coatings in the combustion chamber of a SI engine because of that reason. The amount of soot in the combustion chamber can be reduced by reducing the amount of oil that is able to pass the rings. But soot is also dependant on air fuel ratio and what type of fuel that is used, for example light alcohols produce very little soot while heavier aromatics produce much more soot.

Where a keronite coating could improve thermal conductivity is in the ring land, as an option to iron inserts (which also aren't possible on forged pistons). But there are also other metods to apply ceramics to components, each with its own advantages and disadvantages.