Which Cast Iron to use

[kylenlord]

Hello everyone,

I've begun working on a Edwards Radial engine and am in the process of collecting metal to work with.

Today I ordered the cast iron to make the cylinder liners. I ordered from McMaster a 1' length of easy to machine Cast Iron. I was thinking that because I would of course be turning it to size that makes sense.

There is however another type called ductile cast iron. I'm guessing not as easy to machine, but I imagine a bit more resilient.

I'm hoping that the easy to machine variety is acceptable, because I've already ordered it... However at $16 a foot and free shipping thanks to my job It wouldn't be that great of a loss if I can't use it.

Is the easy to machine casting iron acceptable for the liners? What about for the piston rings?

Thank you
Kyle

 

[gbritnell]

Kyle,
The grey iron that you ordered is fine for the liners but I would use the ductile for the piston rings. Ductile iron machines fine. It produces a chip much more like mild steel than typical iron does. I use carbide tools to cut both grey and Ductile but have used H.S. tooling also.
gbritnell

 

[Mark Rand]

Ordinary grey cast iron has angular graphite flakes in it. These separate the iron crystals and cause stress raisers, which make it easy to machine because the swarf breaks up easily. Ductile cast iron (or spheroidal graphite iron) is treated with magnesium metal in the ladle shortly before it's poured. This causes the graphite flakes to take a spherical form. This results in a cast iron that's closer to a steel in it's properties. The excess graphite doesn't cause the stress raisers that make grey cast iron brittle and easy (albeit, very messy) to machine. It's also more ductile, hence the name. it can be cold bent, whereas grey iron just breaks. The corollary is that it's not as good a bearing material and it doesn't machine quite as easily.

For cylinder liners either would do the job, higher grades of grey iron will be better than lower ones, because they're likely to have a finer structure. OTOH, for something like a motorcycle centre stand or side stand, the ductile iron is rather better than the grey iron, especially if I'm riding the bike (yes, Triumph stands did bend straight again).

I hope that hasn't confused things even more.

 

[kylenlord]

Great,
Thank you guys for clearing that up. No problem using ductile for the rings, what I order was specifically for the liners and I will be ordering another 1" by 12" bar to make up the rings.

No that is not confusing at all, it makes perfect sense. Thats funny, I never pieced together what a center stand is made from. I know the one I pulled off my cb 750 weighed a metric ton... because its from Japan

I will start a build thread soon, what little free time I have goes into working but I haven't forgotten that I need to make one.

Thank you guys again
Kyle

 

[petertha]

Uh-oh. Do you think this class-40 is equivalent to McMaster 'grey'? http://www.speedymetals.com/s-82-cast-iron.aspx

Can you please provide me a typical MCM part numbers for recommended cylinder CI vs. ring CI material. Somehow this detail evaded me.

And lastly, what would Durabar be more similar to?

 

[rklopp]

I make my piston rings from gray cast extruded bar from McMaster. I follow the Trimble method. I don't think I've broken one yet, out of dozens, that I have installed. They are surprisingly ductile after annealing. I would use gray rather than ductile due to its better friction properties. Here is a link to an example on McMaster.

I believe Durabar offers both gray and ductile iron grades. One thing about ductile is that the chips from turning are HOT! You don't want to get one down your collar.

 

[10K Pete]

This thread is most interesting to me because to the best of my knowledge
the bar from McM, Speedy and DuraBar are all continuous cast grey iron,
what Speedy calls G40, unless stated otherwise. I have a couple of pieces
from Speedy that are intended for a cylinder, rings and a head. I had not
heard or read about using anything except grey iron for those parts so I'm
also questioning my choice!

Keep the info coming, I'm reading!!

Pete

 

[gbritnell]

Pete,
I have used what Speedy Metals sells, Schedule 40 iron, and have used it for rings and cylinder liners. When I made the liners for my current project, flathead V-8 engine, I used this material because I had a piece of it left from another job. It machines better than just plain iron, closer to Ductile but not quite the same. When it came time to make rings for my engine I needed to order more material so I did a little investigating and comparing, just for my own knowledge.
First I looked at McMaster's information on both the Grey and Ductile that they sell. I wrote down the specs, carbon, silicon, magnesium etc.
I then did a search for Durabar (trade name). http://www.dura-bar.com/products/index.cfm
I was familiar with the material that they sell listed as 65-45-12 because we had used it where I worked and it was wonderful to work with. Here again I wrote down the specs for comparison sake.
I then went to Speedy Metals and knew that they sold what is listed as Class 40 iron. By the description posted it says that it is a Grey iron but with the inclusion of Silicon it nucleates the the Graphite to change it's properties.
The hard part of actually identifying what Class 40 iron is, at least for me, is because other than the amount of alloying elements the charts get into ASTM numbers and it gets confusing.
https://en.wikipedia.org/wiki/Gray_iron
http://www.versa-bar.com/MetalStockResources/Class40GrayIron
Here is what Wikipedia says about Ductile Iron.
"The common defining characteristic of this group of materials is the shape of the graphite. In ductile irons, graphite is in the form of nodules rather than flakes as in grey iron. Whereas sharp graphite flakes create stress concentration points within the metal matrix, rounded nodules inhibit the creation of cracks, thus providing the enhanced ductility that gives the alloy its name.[5]
If you go back to what Speedy describes as nucleating the graphite and what Wikipedia states as graphite in nodular form it seems to have a similarity. ?????
I can tell you this. Machining Ductile iron as supplied by McMaster and Class 40 as sold by Speedy show differences. Not a lot mind you but some. The one thing that is recognizable is when you make piston rings from both materials.
The rings I used in my flathead engine are .030 wide (to fit in a .031 groove) They are .040 thick and have a diameter of .830. Although I have no trouble with breakage while installing them on the pistons the ones made from Ductile iron will start to bend at some point whereas the Grey rings will snap. This falls under the category of Modulas of Elasticity, I believe.
I guess the bottom line is either can be used for liners and rings. Which is better or preferred I can't say. In the model engine world liners and cylinders have been made from 4140 steel to 12L14 steel to Iron but as far as my research and experience rings have always been made from iron.
I hope this more helpful than confusing.
gbritnell

 

[10K Pete]

George, thank your for that information. Very enlightening. I have done a
small amount of reading on the subject but not to the extent you've done.

I really like the way the G40 from Speedy machines. I've not used the
iron from McM or DuraBar. I have worked CI but it was always whatever
the particular part was cast from.

I've found the G40 to be very tough compared to 'regular' cast iron such as
one receives in the typical kit part. Produces a better finish and is very much
more stable than most other materials I've worked with. And it doesn't seem
to be hard on tools either.

I'll be discovering how it scrapes very soon as I have to make a master
straight edge, a small one 14", with a 60* edge so I can finish scraping
in the ways on my Benchmaster mill. It's all milled out just waiting for
me.

I think I'll not be concerned with using anything else for models!!

Thank you,
Pete

 

[petertha]

Pete,
I have used what Speedy Metals sells, Schedule 40 iron, and have used it for rings and cylinder liners...
gbritnell

Thanks for the info George. I made a test liner using Speedy Sch-40 cast iron. I rather like how it machines, a bit messy but quite controllable. They sent me a mill spec sheet, I should dig that up.
http://www.homemodelenginemachinist.com/showthread.php?t=25163

Last test I want to try is 1144 stressproof just out of curiosity. Pretty soon I'm going to have to pick an alloy from the tester samples & run with it for 5 cylinders. In the back of my mind I was hoping to earmark my remaining Speedy CI chunk for rings. Unfortunately both Speedy & McMaster require extra monetary lubrication to get landed in Kanuckistan. OnlineMetals unfortunately doesn't carry any CI, but they have nice discount sales & good shipping, so I tend to favor them.

 

[kylenlord]

Hey guys,
I got my cast iron rod in today. Clearly labeled on the bar it says dura-bar, it was cut before the class number stamp. All it says is class. I chopped it on the horizontal bandsaw at work into 5 equal lengths. At home it does indeed machine nicely, it break off into many tiny flakes. This weekend I'm hoping to start the boring process.
Kyle

 

[petertha]

Kyle is this what you ordered?

 

[kylenlord]

Yes that is the one that I ordered.
Kyle