Anyone ever used hard anodized pistons?

[Raceboy]

I have thought about it and since I have done DIY anodizing on many components before (mostly brake caliper adapters and the like) and have read about using it on pistons also.

Any thoughts/experience with that? I was thinking about anodizing RS pistons for my 2.5 SS turbo engine so the ring lands etc would be stronger and would get higher mileage out of them.

Come on in & enjoy a 5.4 2011 dry sleeved alloy shortblock build up > - Yellow Bullet Forums

[chris_seven]

The type of anodising you use would have a significant impact on results and you have specifically mentioned hard anodising.

Conventional decorative anodising followed by the addition of a colour during the sealing process wouldn't offer much benefit as the oxide layer is very thin and doesn't give huge improvements in wear resistance.

Hard anodising, when the anodising cell is operated in a different manner to the decorative process, is routinely used as treatment for diesel engine pistons as it improves the thermal characteristics of the piston crown.

I think it is also used in many Turbo and Nitrous Drag race engines for similar reasons.

It is also common practice to hard anodise piston ring grooves as it reduces micro-welding and improves piston life. It doesn't howver, strengthen this area of the piston.

It is less conventional to hard anodise piston ring skirts.

You would need to allow for the growth of the component during processing which would be typically 50% of the oxide film thickness and would affect clearances.

Hard anodisng does cause a roughening of the surface of a component and Aluminium Caliper Pistons that are hard anodised are normally centreless ground after processing to avoid excessive pad knock off.

This surface roughness could be an issue on piston skirts and the best means of avoiding any problems would be to apply a skirt coating after anodising.

It may be possible that the porosity of the oxide film may hold an oil film and eliminate this problem but without some testing I would coat the skirts.

You would also pave to adjust the fit of the pin following anodising or it would be more that likely to jam or gall.

[Spenny_b]

Hi, I was up at Omega Pistons in Birmingham, UK, yesterday. Was chatting with Fred Hadley, the owner of Omega and all-round genius.

When he was describing to me the process of their manufacturing, and the sheer accuracy of what they do, I was astounded. Despite having an engineering background (a long time ago) I was still amazed at the time and effort that goes into every piston they manufacture.

The heat treatment process, apart from being extremely critical in terms of the transition time between heating to treatment, is super critical. The treatment duration is >30 hours, and the accuracy of the process is within 1 degree C.

Frankly, I don't think you'd get anywhere near what you need to achieve, by doing it at home.

(By the way, Omega have manufactured every Ducati Corse piston in MotoGP and SBK for the last 20yrs, currently involved in very secret F1 projects, have done Toyota Indycar pistons, etc, etc....a very very credible manufacturer, and very nice guys to deal with)

[Flieger]

Would the oxide crack as the piston heats up or is it flexible enough to accomodate the metallic expansion (which I assume is greater than the oxide)?

[chris_seven]

Max,

I am not sure this is much of a problem at the temperatures involved for piston crowns.

The CTE of Alumina is typically 8 x 10^-6 per degC compared with around 20 for a 2618 Alloy. The flexural strengthof the coating is about 350MPa.

It is possible that thermal fatigue could cause some spalling of the surface but I don't think there is much evidence that this is a major problem.

The difference in Modulus between the oxide film and the substrate could have an influence on the 'strain sensitivity' of the oxide film. The porosity of the film would have an effect on this type of failure but again I am not sure it is a real issue.

Use of anodising on Diesel engine pistons hasn't shown any real problems.

Keronite which is a PEO treatment also seems quite durable and uses thicker oxide films than hard anodising and the oxide layer has around the same CTE. Keronite tends to have a lower bulk modulus than hard anodised layers.


Gas Turbine blades are routinely treated with oxide based Thermal Barrier Coatings and although differences in CTE are lower (Substrates with CTE of 12-16) the temperatures are much higher (around 1400 degC). and in general they survive very well.