Meehanite or SG for cylinders ?

[ShmbryParticipant @shmbry]

Which grade would be more suitable for 5" gauge cylinders ?

[ShmbryParticipant @shmbry]

[JasonBModerator @jasonb]

Meehanite is a specific grey iron which is used a bit like "Hoover" but other similar ones such as GR17 would do. SG iron is not really suitable.

[Martin KyteParticipant @martinkyte99762]

I would be interested to hear why you think SG iron not suitable Jason. I'm not suggesting it is or isn't so just a genuine question.

regards Martin

[JasonBModerator @jasonb]

To me when machined it has a surface much more like steel and not the slightly porus graphite rich surface of grey iron so probably less likely to be a good sliding surface that will hold some steam oil.

I've not machined anything from GS block or bar but have done several crankshaft castings, axle and various small parts and would not choose it over GR17. It is also not as nice to machine being more like steel and not a particularly free machining one. So to me the SG does not offer anything for cylinders but would be good for longer parts that you don't want to break.

The Americans also use what they call ductile iron of which I've machined plenty of castings as they use it a lot on their hit & miss casting kits. This is somewhere between grey iron being similar to machine and the same sort of texture but is a bit less prone to fracturing than grey iron

Then there is the Smell which can put you off as SG has a nasty whiff about it when cut as does the American ductile iron.

Edited By JasonB on 16/08/2022 13:04:11

Edited By JasonB on 16/08/2022 13:05:12

[Martin KyteParticipant @martinkyte99762]

That sound like a very reasonable reasons Jason. I did have a little google around and pulled this from the Reliance Foundry site:-

https://www.reliance-foundry.com/blog/cast-iron

"Compacted graphite iron is beginning to make its presence known in commercial applications. The combination of the properties of gray iron and white iron create a high strength and high thermal conductivity product—suitable for diesel engine blocks and frames, cylinder liners, brake discs for trains, exhaust manifolds, and gear plates in high pressure pumps."

Compacted Graphite Iron looks not to be quite SG, they talk of adding titanium to prevent the spheres forming. I don't know much about cast irons so I'm interested now the subject has been raised. But as you say for our purposes your logic seems most applicable.

regards Martin

Edited By Martin Kyte on 16/08/2022 13:26:57

[JasonBModerator @jasonb]

Quite interesting reading there.

I note they say of the various ductile irons of which SG is one that the characteristics can be tweaked by various means one of which is heat treatment. Many of the US makers say their castings are heat treated so this may be why it's a bit between the two, also has the bonus of removing hard spots and chill.

I'll just make do with this 20kg of grey iron that landed on the doorstep yesterday along with another little pattern and engine design project

[Martin KyteParticipant @martinkyte99762]

Yes. I just machine what I'm sent and glad there are no holes in it.

regards Martin

[Anonymous]

I'd use GR17, easy to machine and to get a good finish. I would only use SG iron where strength in tension is important, ie, for the crankshafts and front axles for my traction engines. I've also found SG tricker to machine, and it has a propensity to chatter badly.

Andrew

[Clive Brown 1Participant @clivebrown1]

The self lubricating property of cast iron is important for cylinders etc. This is brought about due to the form and distribution of the graphite in the metal. SG iron has a different graphite formation, probably not so conducive to self lubrication.

[Dougie SwanParticipant @dougieswan43463]

What engine will that be Jason?

Dougie

[BazyleParticipant @bazyle]

The point about grey iron is that it has loads of flakes of graphite in it an on the surface that provide a form of lubrication to the piston, and help resist rusting as if the iron turns to rust it just exposes a layer of more graphite. The flakes inside the iron however are effectively cracks ready to grow and break under tension. Ideal for cylinders.
Spheroidal iron (SG) has additives which during heat treatment make the graphite form globules of iron carbide – no more weakening 'cracks' and the spheroids are super tough too making it harder and provide a rather hard surface instead of that graphite lubrication. More wear likely unless you adjust by using a soft (bronze) piston but also rust prone, Not good for cylinders but the strength and hardness make it ok for crankshafts running in soft bronze or grey iron bearings.

Play around a bit with the metallurgy and you can make the graphite form globules of just graphite not carbide. Not so hard and no weakening flakes. As you may know you can stop a crack growing by drilling a hole at the end to reduce the stress concentration. The graphite globules do this too so your material can be less fragile. Mostly used for added strength in a complex shape you want to cast but isn't involved in bearing type duties eg exhaust manifold.

[JasonBModerator @jasonb]

Dougie the castings are for a 1/3rd scale Robinson HA oil (paraffin) engine that I did some of the pattern making for. Flywheel is just over 9" dia, Not sure when I'll get round to this one as I've a couple of my own designs that I want to do after the Otto Flame Sucker. The pattern top left which is probably going as firewood was to be used for a Penultimate Mk11 but I'll start again on that one as it has suffered over time.

Original

First engine from the batch of three sets of castings by Graham Corry and his son

[duncan webster 1Participant @duncanwebster1]

If you're having castings made then the chance of success with grey iron is much higher than with SG. One found an put it to me that liquid grey iron is like pouring milk, SG is like pouring porridge

[ShmbryParticipant @shmbry]

I was enquiring with a view to machining rather than casting.

[JasonBModerator @jasonb]

Yes that's what i assumed just a bit of forum drift. I've made quite a few cylinders for both steam and IC engines from CI bar and block

[Dougie SwanParticipant @dougieswan43463]

So, this might be O T but I am building a Holt 75 and need to silver solder some square sections to the base of the cylinders, would en1a or en1apb be a good choice for the cylinder material

Dougie

[JasonBModerator @jasonb]

Ideally sleeve the steel with iron liners and use the EN1A or EN 3, EN32B, S275, etc as they are a lot easier to solder than CI though it can be done with good effect. I would avoid the EN!Apb due to it's lead content but probably won't be an issue with just propane heating.

Not sure of the Holt's water cooling if it was cored into the original kits or had to be machined cooling but using a sleeve is an easy way to create a water jacket around individual cylinders and something I have done on CI kits as well as fabrications of steel outers and CI sleeves.

Edited By JasonB on 17/08/2022 07:15:00

[noel shelleyParticipant @noelshelley55608]

Grey cast iron for cylinders or liners ! For cooling, a wet liner is the way it is done on many engines, the only hard bit is sealing the liner to prevent water leakage. I would avoid lead bearing metals for soldering or welding ! Noel.

[Mark RandParticipant @markrand96270]

Add to Jason's comment:- Avoid the leaded EN1A not because of solderability, etc, but because it rusts at the slightest provocation. It seems to be about the most corrosion prone steel that there is!

[Howard LewisParticipant @howardlewis46836]

Purely an aside to drift off topic, a bit.

When 71000, Duke of Gloucester was being rebuilt, my colleague suggested using SG Iron for the cylinders; and this was done. It seems to have worked well,(Not sure what the liners were ) but what happens at 1/12 scale may be different

Howard

[ShmbryParticipant @shmbry]

Wish I could get some Duke of Gloucester drawings. I contacted the trust, but no reply.

[duncan webster 1Participant @duncanwebster1]

The DOG people probably got the drawings from the National Railway Museum, if so the agreement is that they shall not be copied to anyone else. The NRM quite rightly need to generate some income to maintain the archive. Contact the NRM direct, but be prepared to reach deep into your pockets.

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