Author Topic: Casting Gray Iron  (Read 14381 times)

Offline Casting Iron

  • Full Member
  • ****
  • Posts: 35
Casting Gray Iron
« on: July 11, 2024, 12:12:05 AM »
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.


Offline Casting Iron

  • Full Member
  • ****
  • Posts: 35
Re: Casting Gray Iron
« Reply #1 on: July 11, 2024, 01:28:03 AM »
Examples of resin-bound sand molds.

.

Offline ddmckee54

  • Full Member
  • ****
  • Posts: 706
  • We're having fun now --- or so I've been told.
Re: Casting Gray Iron
« Reply #2 on: July 11, 2024, 09:17:42 PM »
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

Offline Casting Iron

  • Full Member
  • ****
  • Posts: 35
Re: Casting Gray Iron
« Reply #3 on: July 11, 2024, 11:25:25 PM »
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.

.
« Last Edit: July 12, 2024, 06:24:30 AM by Casting Iron »

Offline pirmin

  • Full Member
  • ****
  • Posts: 161
Re: Casting Gray Iron
« Reply #4 on: July 13, 2024, 09:00:52 AM »
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.

Offline Casting Iron

  • Full Member
  • ****
  • Posts: 35
Re: Casting Gray Iron
« Reply #5 on: July 13, 2024, 09:34:14 AM »
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.

.


Offline Casting Iron

  • Full Member
  • ****
  • Posts: 35
Re: Casting Gray Iron
« Reply #6 on: July 13, 2024, 09:42:34 AM »
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.

« Last Edit: July 13, 2024, 09:45:39 AM by Casting Iron »

Offline Casting Iron

  • Full Member
  • ****
  • Posts: 35
Re: Casting Gray Iron
« Reply #7 on: July 13, 2024, 09:53:48 AM »
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.
.
« Last Edit: July 13, 2024, 10:07:30 AM by Casting Iron »

Offline Casting Iron

  • Full Member
  • ****
  • Posts: 35
Re: Casting Gray Iron
« Reply #8 on: July 13, 2024, 10:01:56 AM »
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.

.

Offline Casting Iron

  • Full Member
  • ****
  • Posts: 35
Re: Casting Gray Iron
« Reply #9 on: July 13, 2024, 10:13:56 AM »
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.
.

Offline Casting Iron

  • Full Member
  • ****
  • Posts: 35
Re: Casting Gray Iron
« Reply #10 on: July 13, 2024, 10:24:42 AM »
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.
.
« Last Edit: July 13, 2024, 10:54:30 AM by Casting Iron »

Offline Casting Iron

  • Full Member
  • ****
  • Posts: 35
Re: Casting Gray Iron
« Reply #11 on: July 13, 2024, 10:29:55 AM »
The Delavan oil burner build with a stainless tube.

.

Offline Casting Iron

  • Full Member
  • ****
  • Posts: 35
Re: Casting Gray Iron
« Reply #12 on: July 13, 2024, 10:33:15 AM »
Delavan siphon nozzle.
Works very similar to a paint sprayer.
Has a small spin vane near the tip (the part not brass).

.

Offline Casting Iron

  • Full Member
  • ****
  • Posts: 35
Re: Casting Gray Iron
« Reply #13 on: July 13, 2024, 10:40:02 AM »
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.

.

Offline Casting Iron

  • Full Member
  • ****
  • Posts: 35
Re: Casting Gray Iron
« Reply #14 on: July 13, 2024, 10:49:04 AM »
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.
.

 

SimplePortal 2.3.5 © 2008-2012, SimplePortal