Aluminium zylinder coating options wanted

[rweber]

Dear forum,

I'm currently thinking about coating options for aluminum cylinders. Wouldn't it be nice to not have to install a cast iron liner? What should definitely work is hard chrome plating. However, this is not something you can do by yourself and requires a professional company. But what about hard anodizing? What you read this can be used to create layers of 50 to over 200µm. Eloxal layers are very hard and extremely temperature resistant. Has anyone had any experience with this?

regads,
Robert

 

[Nerd1000]

Dear forum,

I'm currently thinking about coating options for aluminum cylinders. Wouldn't it be nice to not have to install a cast iron liner? What should definitely work is hard chrome plating. However, this is not something you can do by yourself and requires a professional company. But what about hard anodizing? What you read this can be used to create layers of 50 to over 200µm. Eloxal layers are very hard and extremely temperature resistant. Has anyone had any experience with this?

regads,
Robert

What is often used industrially is nikasil. It's electroless nickel plating with embedded silicon carbide particles.

I have looked into it, however there are quite a few issues with DIY hard coating of any aluminium parts:

1. Dangerous/difficult to get chemicals are needed. How bad this is varies depending on what you do, but even hard anodising requires use of nitric and sulfuric acid. Nikasil additionally requires the use of HF, which is infamously dangerous, and hard chrome can only be done using hexavalent chromium which is very carcinogenic.

2. Special tooling is needed to hone the bores. Most of these hard coatings have hardness comparable to tor greater than he aluminium oxide stones of a normal cylinder hone. Diamond honing is required.

3. Much experience and trial and error is needed to get a good result.

So I'm sticking to metal liners. I do think that there are possibilities to run uncoated bores successfully, e.g. aluminium grade 7075 is as hard as mild steel or a low grade cast iron. So we could use that to make the cylinder, just need a compatible material for piston and rings. Al piston on Al cylinder is a poor match but a cast iron or steel piston could be successful, as could an Al piston with some kind of compatible coating.

 

[Toymaker]

I have some small experience with hard anodizing (type 3) aluminum, but not with engines. I built my CNC bench top mill using mostly 6061 T6 1/2" aluminum plate for the frame and in keeping with the all aluminum theme, I used a 1" thick slab of aluminum fixture plate for the bed (table), which, after I milled in the T-slots, I had type 3 anodized. The mill has been well used as a hobby machine for 10 years now and except for a few places where I accidently drilled a little too deep, the surface still looks new, not a single scratch. Type 3 anodize is very resistant to scratches.

Type 3 surface is also very slippery against all other materials I've clamped onto the table, even without lubrication. Two type 3 surfaces placed together are even more slippery. Type 3 surfaces are also slightly porous and retain oils within their surface.

I believe you should hone the cylinder before you anodize it and allow for a slightly smaller cylinder diameter due to the added wall thickness of the aluminum oxide coating; you will end up with a mirror-like cylinder wall. If you also anodize the piston, you should have a very wear-resistant engine.

I payed a local anodizing shop to coat my mill table; I suspect you'll be able to find a shop to do your parts too. But, if decide to go the DIY route, I recall the shop cautioning me to allow the freshly anodized table to thoroughly dry overnight before using it. The porous surface would not be fully hardened until all the rinse water had evaporated.

 

[ChazzC]

Use a high Silicon Aluminum alloy like Reynolds (now Alcoa) supplied for the Vega blocks (dating myself again): I visited the Richmond, VA facility in the 70’s and interviewed the Product Manager about this material. He told me about a Vega with a cracked block had driven ~250 miles on I95 with no coolant and there was not measurable wear on the cylinders (the pistons were blue, so it got plenty hot); Reynolds was doing some testing on some finished blocks for Chevrolet and got permission to swap one of these for the cracked block.

IIRC, the machined cylinder bores were etched so that the wearing surface would be Silicon and then honed with special stones.

 

[rweber]

Thank you very much for your detailed answers! I had already thought about 7075, but unfortunately it couldn't be anodized, ans this is important to me. I think I'll go for hard anodizing. I already have a "normal" anodizing equipment in the workshop and I can get the additives for hard anodizing. I'll try a few things and will see If it works. If it doesn't work within a reasonable amount of time there is still the option of a gray cast iron liner.

 

[Jasonb]

Jim Allen gives quite a bit of info in this long thread about how he chromes the cylinders of his engines.

https://www.modelenginemaker.com/index.php/topic,3890.msg71374.html#msg71374

 

[Toymaker]

Thank you very much for your detailed answers! I had already thought about 7075, but unfortunately it couldn't be anodized, ans this is important to me. I think I'll go for hard anodizing. I already have a "normal" anodizing equipment in the workshop and I can get the additives for hard anodizing. I'll try a few things and will see If it works. If it doesn't work within a reasonable amount of time there is still the option of a gray cast iron liner.

Don't forget that you also need a method to cool the anodizing solution as the current requirements are higher than typical anodizing and will overheat the solution if not cooled.

 

[rweber]

Vergessen Sie nicht, dass Sie auch eine Methode zum Kühlen der Eloxallösung benötigen, da die aktuellen Anforderungen höher sind als beim typischen Eloxieren und die Lösung überhitzt, wenn sie nicht gekühlt wird.

I know, i have some active colling installed.

 

[SmithDoor]

Dear forum,

I'm currently thinking about coating options for aluminum cylinders. Wouldn't it be nice to not have to install a cast iron liner? What should definitely work is hard chrome plating. However, this is not something you can do by yourself and requires a professional company. But what about hard anodizing? What you read this can be used to create layers of 50 to over 200µm. Eloxal layers are very hard and extremely temperature resistant. Has anyone had any experience with this?

regads,
Robert

The best I read was nickel cast iron for liner (there are othe names for iron)
Is this for a hobby or a real engine?

Dave

 

[rweber]

Das Beste, was ich gelesen habe, war Nickelguss als Auskleidung (es gibt andere Namen für Eisen).
Ist das ein Hobby oder ein echter Motor?

Dave

Its for a real Hobby Engine