Casting Gray Iron

[CI]

I ran across a website in 2011 about someone who built an oil burner, furnace, and melted the broken parts of an old cast iron stove.
This was the first time I realized that gray iron could be melted in anything other than a cupola.

I built a furnace and oil burner, and while I had some initial success with casting iron, I could not consistently do it, and the Petrobond sand I was using was causing some defects.  I had no concept of how to tune an oil burner, and no idea of what fuel flow rate to use.

I ran across some local art-iron folks who make sculptures and such in iron using a cupola, and they introduced me to resin-bound sand, which is specifically designed to work very well with iron and steel castings.
The resin-bound sand has been a game changer to say the least, and if the runner(s) and gating are correct, this sand basically eliminates casting defects.

A buddy of mine built a furnace after I did, and he was regularly melting iron with it.
I was able to watch him at the Soule engine show, and learned a lot about handling the iron as it was melting, and handling the slag as it was produced.

I made a test stand with multiple valves, so I could quickly test my oil burner at various flow rates, such as 1,2,3,4,5,6,7,8,9 and 10 gallons per hour.
As it turned out, for my furnace dimensions, about 2.7 gallons per hour produced the hottest furnace interior.
I also learned that operating the burner reducing (rich) minimized the slag produced on top the iron.
Initially I though an oxidizing (lean) burn would work better, but that produced excessive slag.

Then I had to learn about ferrosilicon, and why it was needed (to eliminate hard spots in thin sections of iron).
And I had to learn the exact amount of ferrosilicon to use.  Too much caused excessive shrinkage and hot tears.
A very slight amount of ferrosilicon is required.

My first furnace was very heavy, and used dense cast refractory, so it took a long time to heat up.
I built a second furnace with a fraction of the mass.
First furnace had about 300 lbs of dense refractory; second furnace had 70 lbs of dense refractory.
The second furnace allowed me to reach pour temperature with gray iron in about 60 minutes, with a #10 crucible.

And I had to figure out which crucible worked with iron, and turned out to be a Morgan Salamander Super clay graphite crucible, which I use exclusively now.
This crucible is one of the few crucibles that is actually ferrous-metal rated, and rated for iron temperatures (about 2,900 F rated continuous).

Then I had to learn about sprues, runners, gates, risers, etc.
I have adopted modified methods that are from John Campbell's book "10 Rules for Good Castings".
There is a bit of an art to this, but basically you want to eliminate air aspiration, turbulence, high flow velocity, and irregular shrinkage/solidification.

Then I discovered spray-on ceramic mold coat, and that totally stops sand burn-on, and gives a smooth shiny finish right out of the mold, with no cleanup required.

It required quite a bit of sluthing to figure it all out.

At this point I can melt and cast gray iron with not much more difficulty than casting aluminum, and can create commercial-grade iron castings.
Gray iron melts are very hot, and the radiant heat is significant, so shaded goggles are required to avoid IR to the eyes, and full leathers are required.
And heat shields are required on the handles of the pouring shank, etc.

I prefer gray iron engine parts to any other metal, give the wear characteristics, and ease of machining/drilling/tapping, etc.

This year's challenge is to make dutile iron, and I have found some material to use for that.
Ductile iron used a secondary mixing chamber, where the reaction with a magnesium alloy takes place, and I think I have figured out how to build the secondary chamber.
The idea is to cast crankshafts in ductile iron.

Its a fun hobby, and really adds a lot to the engine building process in my opinion.

[CI]

Examples of resin-bound sand molds.

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[ddmckee54]

Is any of the resin bound sand recoverable, or is it all one-use-only?  If it's one-use-only how do you dispose of it?

Don

[CI]

Resin-bound sand is not easily reused; there is some sort of recovery process in commercial foundries, and I think it involves burning off the resin.

I don't recycle mine.
It is considered a hobby discard, similar or even the same as many materials used in pottery.
Residential is allowed to discard X pounds of it each month, I forget the exact amount, but not a huge amount.

I think it is about like discarding epoxy material, or perhaps bondo-like material.

And once the resin is set, it is like plastic, and so it is relatively stable for a long time; not like a liquid that will leach out.

.
Edit:
One thing to remember is that bound sand molds are very strong, and so they do not need to be very thick.
Some of my molds are only 3/4" thick, or less than that in some spots.
And I often block out the interior of my flask around the pattern, to shape-form the bound mold around the pattern, and save a lot of bound sand.

Generally speaking, a bound sand mold can be 1/3 or less the weight of a greensand mold (perhaps 25% of a greensand mold).
Using any more than that is a waste of bound sand and resin.

And the sand used with resin is required (per the instructions) to be very dry.
I use OK85, which is a commercial fine grain sand, and I am pretty sure it is baked, since it is extremely dry; I keep it sealed in 5 gallon buckets.

Edit02:
OK85 sand bound with sodium silicate is a viable alternative to either epoxy or resin-bound molds, and supposedly works with iron and other metals.
Sodium silicate can be hardened using either CO2 (5 second gas only....do not overgas soldium silicate molds or cores), or a catalyst can be used which will cause the mold to self-harden.
Sodium silicate is much more environmentally friendly than epoxy or resin.
It is often seen used for making cores, but it can be used to make the entire mold too in the same manner than resin-bound sand is ued to make molds.

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[pirmin]

Fantastic ! i wish i had a garden for such projects! casting iron is realy something that starts to disapear. when i read old ME magazines i see that many local communitys and societys had someone in their area wich was able to cast iron . Now its a very expensive thing ! here in austria there is no company that offers casting services to private model engineers.

[CI]

One group that still makes gray iron castings on a regular basis are the various art-iron folks in the States.

A local art-iron group are the ones who taught me how to use resin-bound sand, and ceramic mold wash.
They use cupolets (cupola with a lid) to melt their iron, and because they are typically non-profit art groups, they can readily purchase limited amounts of coke (coal heated in the absence of oxygen) as a fuel.
The generally use old radiators as a scrap source, since that metal has phosphorus in it, and thus has very high fluidity.

The local group has several iron pours every year.
They have helped me with learning how to cast ductile iron.

There is another larger group at the old Sloss foundry in Alabama; and many art groups associated with colleges.
The art of casting gray iron needs to stay alive, for many reasons, but especially to make model engines (in my opinion).

A few photos from a local art-iron pouring event.

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[CI]

The art-iron folks all seem to use cupolas/cupolets, and they were very surprised to hear that I could melt iron with an oil-fired furnace.
I brought my furnace to one of their events, and demontrated how to melt/pour iron with a cupola oil-fired furnace.

This is my 2nd furnace, with a 1" Mizzou hot face, backed up with one layer of soft fire bricks, and two layers of ceramic blanket.
It remains cool to the touch on the exterior beer keg surface.  It is actually made of several beer kegs, which were cut and welded to give the same diameter as a 55 gallon drum (I should have just bought a stainless 55 gallon drum, but I did not know they existed at the time I built this furnace).
The Mizzou hot face holds up very well to iron slag and the general abuse that an iron furnace experiences during operation.

Combustion air is provided by a Toro variable speed leaf blower, set to the lowest speed.
The burner is a Delavan siphon nozzle style, with a 10 psi pressurized diesel fuel tank, with 30 psi safety relief valve on the tank.
The PVC valve at the top of the leaf blower is a dump valve that is opened when the burner is first lit, to prevent blowing out the flame, and then slowly closed to provide all the air output to the furnace after the burner is lit.

[CI]

This is my furnace design.
It can be used with a range of crucibles, from very small up to a #20, and with an extension ring, I think I could use a #30 in it.
The Morgan "Salamander Super" clay graphite is the one I use that is rated for ferrous metals and iron temperatures.

This furnace is designed to be modular, so that the hot face can be replaced easily.
I have found a product called "plastic refractory" that is rated 3,800 F, and it basically eliminates the need to replace the hot face, since it can patch any defects.
Plastic refractory is what the art-iron folks use to patch the interior of their cupolets.
.

[CI]

The scrap I use is motor end bells.
There is no need to clean gray iron scrap.
You can melt it with paint, oil, heavy rust, etc. and the impurities all come out in the slag.

Using a consistent quality scrap iron is important if you want quality iron castings.

.

[CI]

The hot face was made using castable refractory (Mizzou), and I rammed it into the upsidedown form using a wood dowel to pack it in 2" layers.
I dried it slowly with a propane burner, and then brought it up to operating temperaure using a temporary flat lid.
I built a permanent domed lid from 1" Mizzou, so that if it every cracks (the lid has not cracked yet), it will self-support like a Roman arch.
Total weight of the hot face is 70 lbs.

The plinth that the crucible sits on top of is also made from Mizzou refractory.
.

[CI]

A few cast items.
The ceramic mold coat completely eliminates any sand burn-in.
The phoenix plaques in the photo have just been turned over out of the mold, with no cleanup work.
.

[CI]

The Delavan oil burner build with a stainless tube.

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[CI]

Delavan siphon nozzle.
Works very similar to a paint sprayer.
Has a small spin vane near the tip (the part not brass).

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[CI]

An oversized Cretors flywheel, and the pattern I made for it.
I carved one spoke from wood, and then cast six more for the pattern.
This piece is in 356 aluminum, and was cast before I figured out how to consistently cast gray iron.

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[CI]

Testing a prototype burner outside the furnace.
Oil burners do not operate outside the furnace the same way they operate in the furnace, and that is something I had to learn by trial and error.
The small propane burner is maintaining the combustion.
Diesel does not like to burn in an oil burner outside the furnace without some combustion source.
When the furnace is operating, the red hot interior of the furnace maintains combustion of the diesel.
.

[pirmin]

Fantastic work !!!!! the little straight edge is so sweet ! but all the other things are nice too. thank you for sharing your knowledge and information. and dont worry that nobody responds, its mid summer, most people are on holidays , its typical for online forums in summer .

Keep us updated please ! this is very valuable information

[Kim]

Very fascinating!   I've never been that interested in foundry work, but all your pictures and work you show here make it look pretty enticing! 

Kim

[CI]

I appreciate the kind comments.
I had some initial success with casting iron, but could not get consistent results.
I had a really hard time figuring out how to set the burner, how and when to skim slag, how to prevent hard spots, etc.

I gave up more than once over about a six year period, and swore I would never figure it out, and would just use aluminum.

I had several folks who encouraged me to keep trying, and that is pretty much the reason I stuck with it long enough to figure out the entire process.
I am anxious to share this information because I would like to see others in this hobby learn and use it.
Casting engine parts in gray iron is not that much more difficult than casting aluminum, if you know exactly what to do and how to do it.

Pat J
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[Alyn Foundry]

It’s been a good 40+ years since I dropped my first 10 pounds of Iron.
We used Propane as the fuel for convenience and its energy density is a little greater than Oil. However enough history.

As the use of chemically bonded sand was prohibitive we favoured the traditional Green sand moulding technique. Yes, the flasks are much more bulky but one major advantage is they hold the heat . This heat retention greatly reduces the risk of chills and hard spots. Another factor is to leave the poured flask alone and break out the following day.

The choice of Iron scrap  will play a major role in the machinability of your castings. Try to avoid thin sections that have a Whitish tinge to them. Look for dark Grey.

If you can get hold of it I would recommend the addition of Ferro Silicon to the melt, just before the pour. We used around a teaspoon full per 10 Lbs melted.Thoroughly rabbled with a preheated Steel rod. A small quantity of finely crushed Limestone can be added to the progressing melt to reduce oxidation.

Home casting can be great fun. It also has its dangers.  As with every thing we do common sense should be our guide.

I will make one point stand out however. Water, even in its tiniest amount doesn’t play well with molten metal. I have the scars to prove it. Always make sure that all the tools are thoroughly dry and preferably preheated before use.

We made several engine kits before deciding it was too labour intensive to carry on, as we were all in full time employment.  Today, my kit lies idle. The advent of CAD and the 3D printer have rendered the Aluminium master pattern redundant.

   Graham.

[MJM460]

Hi Pat, your trials with casting is most interesting, and your persistence is now paying off with such great results.

I can’t contribute to this technology, but I am keenly following your progress.

MJM460

[Dick Morris]

Thanks for writing this up. It was very interesting. Having cast aluminum and bronze, this looks very doable.

[Jasonb]

We made several engine kits before deciding it was too labour intensive to carry on, as we were all in full time employment.  Today, my kit lies idle. The advent of CAD and the 3D printer have rendered the Aluminium master pattern redundant.

   Graham.

That is assumming the person wanting the patterns can use CAD, there are many that have no idea how to produce a 3D model of a pattern and for those owning a 3D printer is limited to printing downloaded toys from the net. Unless they can get someone to do the CAD work for them then traditional methods may be all they can use.

When it comes to master patterns as opposed to the one off home casting there is still a need because the 3D printed pattern is not durable enough, think of the Nattie Flywheel pattern for example due to it's thin spokes I did not even want to make that from wood, a plastic print would be even weaker. An alternative to aluminium are the modern 2 part resins where a 3D print could be used to make a mould and then PU resin patterns cast from that which can be bonded to a match board, often several cast patterns of the same part on one board.

[CI]

I have had some 3D printed patterns break up, especially the ones with thin infill and walls.
I use a small automotive slide hammer to pull patterns from bound sand, and if you don't exceed the strip time, then the adhesive bond between the sand mold and the pattern can be broken with a light tap of the hammer.

I forgot to pull the patterns one time, and left them in the mold overnight.
The patterns were effectively glued into the bound sand mold.
I damaged most of the patterns trying to get them out of the sand that time; destroying about half the patterns.

I have seen the resin pattern casting material, and hard resin master patterns that can be cast from that mold.
I am not really keen in stocking more resin material though, since it will have a finite shelf life.

Since I am set up to melt alumium, and have quite a few 256 ingots, it would make sense for me to cast permanent patterns, such as for the Ball Hopper Monitor.
Aluminum is easy to melt and pour, since the temperatures involved are so low compared to iron.

With cast aluminum permanent patterns, you can always use JB weld to touch up any bad spots, or to add a bit here or there to the pattern.

And you can epoxy additional pieces onto a cast aluminum pattern; I have seen that, where sometimes adjustments must be made after the pieces are adhered to the matchplate.
I am not a fan of matchplates, since they are really not required with bound sand.
I did use some matchplate arrangements for the green twin engine, and that did work well.
It is very easy to add runners, gates, risers, etc. to bound sand after it has set.
If there was a production run, it would pay to create matchplates.

Edit:
One advantage of the poured resin product to create hard plastic permanent patterns is that the resin will exactly mimic the smooth surface of the pattern.
With a permanent cast aluminum pattern, ceramic mold coat will help get a very smooth surface finish, but the aluminum casting will still probably need to be buffed out with a fine ceramic buffing disk.
I am not sure how stable the hard plastic permanent patterns would be, but I would think they would last a long time, and would never oxidize.
.

[bent]

Very cool writeup CastIron, thanks! 

I am in the process of retiring (currently working half time and training a new hire to take over) from being the valve design engineer at my company, where I've been designing bronze and ductile iron castings for production, and then lately forged brass valve bodies too.  I've had the privilege of watching a large foundry here in Washington state operate their jolt-squeeze molding machine and pour our valve castings in ductile iron.  I'm always a bit in awe of real foundrymen, there is a lot of art as well as science to the trade.  We were lucky that for a time, their foundry business was slow, and so for a few years we had them use our parts as fill-in work for their production line.  Then, they got busy with their in-house products again, and we were politely asked to take our products elsewhere. 

 

our local foundry:

https://www.romac.com/foundry

[Mcgyver]

Good stuff!  Thanks for posting it.

[CI]

Thanks to all for the kind comments.

That is a great looking foundry (Romac), with some sophisticated methods, such as the laser guided pours, etc.

I read several casting journals regularly, and there is a good market for ductile iron castings, since they often can meet or exceed the strength of steel, but with a lower cost.

Kory Anderson (150 hp Case guy) uses ductile iron for flywheels and other items, but I really only need ductile iron for crankshafts.

It is exciting to see US-based foundries with high quality products, and this on-shore capability solves the supply chain problems that we have seen in recent years, as well as provides jobs for folks located here.

I am in the wastewater renovation business (electrical side of things), and there is a lot of money involved, given the large size of many plants, and the dedicated operational and repair funding that the EPA requires.

Learning the methods of making ductile iron has been more difficult than learning to pour gray iron, and I have had to pick out bits and pieces of critical information about how to do it on a small scale from suppliers and an occasional person who has worked in iron foundries.
Some folks know ductile iron on a large scale, but can't really give helpful information about how to do it on a small scale.
I think I have it figured out, and I think I have all the materials required to do it successfully, so we shall see.

I feel like preserving the knowledge of how to pour gray iron is critcial to keeping the model engine hobby alive in the US, and pouring iron engine parts is just downright fun.

I hope to get to the point where I can make more iron castings in the near future.

Thanks for everyone's interest.

Pat J
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[Jasonb]

I would have thought you could use Ductile iron on more parts than just crankshafts Pat.

Any cast part that is long and slender will be far more durable and less likely to get broken than if it were made from regular grey iron. Other kit producers use it for things like valve rockers & posts and on the monitor the pivoting arm of the cam follower and the governor weight would be best done in ductile.

[CI]

The ductile iron casting process is more involved than just casting plain gray iron.
The sulphur has to be controlled, and the inoculation process I will use takes place in a lined container, which will be somewhat wasteful just due to the nature of the setup.
And I have a finite amount of ferromagnesium, and don't have a supplier for that.

So there are some challenges ahead, such as verifing the exact process in a backyard setting (I have seen it done, and so I understand how to do it).

For long thin parts, it will require a lot of fluidity, and I have an additive for that too, but again, a finite amount with no supplier.

One of the biggest challenge for me, and I think one of the biggest challenges for hobby casting folks, is finding small quantities of commercial materials.
Generally, one has to know someone in the industry in order to get some of the materials.
I have done a lot of begging to get what I have.

You can purchase materials by the 55 gallon drum, or by the ton (sand), but smaller quantities are very difficult to source.

The ductile iron making process is a volatile exothermic reaction, and the exact volatility depends on the percentage of magnesium contained in the additive.
One wants enough magnesium to give good results, but not so much magnesium that it melts your entire reaction chamber.
I think I can make ductile iron, but I don't think I would want to cast it routinely, especially without finding a readily available supplier.

It is very difficult to find art-iron folks who do ductile iron, and the ones I have found don't really discuss how they do it.
It is a very secretive thing, perhaps just from a general lack of knowledge.

Here is a video of a ductile iron attempt.
It was not an explosion in the ladle, but rather just a very aggressive reaction, and way too agressive in my opionion.
I can't find anyone to even discuss this attempt, but obviously, great caution must be used with this process.

<a href="https://www.youtube.com/watch?v=SQLAdOg6V5g" target="_blank">http://www.youtube.com/watch?v=SQLAdOg6V5g</a>

[CI]

I think a typical small reaction chamber for making ductile iron can be seen in this video at 10:20.
The chamber would need to be lined with 3,800 F plastic refractory, and it must have a pocket on one side for the ferromagnesium.
The reaction is relatively mild, and would be messy without a tall vented chamber.

And if you don't control the sulphur, then you are not going to get ductile iron.

It should be noted that the IR (infrared) coming out of a hot furnace, from the crucible, and from the top of the melt, is very intense, and without wearing shaded gas welding glasses, you can have sunburn in the eyes after a single exposure.

<a href="https://www.youtube.com/watch?v=xrLkm243_-8" target="_blank">http://www.youtube.com/watch?v=xrLkm243_-8</a>