Home Foundry

[SmithDoor]

Any looking at Muller's
Try this small one it for food too.

https://www.spectramelangers.com/melangers/spectra-11-chocolate-grinder-cocoa-stone-grinders/
Dave

 

[GreenTwin]

The mulling process is very hard on a mixer/muller motor, so depending on exactly how much sand you want to make, I guess that would determine what you use to mull with.

I use bound sand exclusively, and so I don't mull my sand, but rather I mix the binding agent into it.
For small sand molds I use a small Hobart kitchen mixer, and for the larger molds, I use a commercial Hobart kitchen mixer, as shown below.
I made a custom heavy-duty beater bar for the mixer below, since the stock beaters were not strong enough for sand.

I bought the mixer below used, and the salesman asked me if I needed help carrying it out.
LOL, "No" I said, "I can handle it".
Turns out it weighs about 400 lbs, and it took 5 people to get it in the car, and an engine hoist to get it out of the car and into the shop.
I will mix well up to about 3/4 of the bowl full, but more than that and it starts to bog down.

 

[GreenTwin]

I originally tried to use Petrobond (tm) sand, and I used the small Hobart mixer to mull it a bit, with some success, but you have to use a cap over the bowl since the sand will climb up and out the bowl as it mulls.

The art-iron folks use a cement mixer without the internal paddles, and add one or more weights (usually round) as the sand mixes to help with the mixing process.
This works well for the large batches that they mix up, but is a bit on the large size for the small mixes that I make.

I started to build a traditional muller when I was using Petrobond, and got that design about 1/2 complete before I converted to bound sand exclusively.

Most who make their own mullers in the traditional rotating wheel style make common errors in their design, which is to have a spinning head that is not sufficiently rigid to prevent flexing, and so the plows strike the drum, and chaos ensues.
Another common mistake when building a muller is to omit a shear pin the the drive train, and so the muller head flexes, the plow strikes the drum wall (or a small piece of metal in used sand jams the plow), and the muller proceeds to destroy itself (I have seen this numerous times).

And a geared muller is a powerful thing, so an e-stop in an accessible place is a good idea.
Some high-torque machines I have seen have an over-torque feature, which will stop the motor if the torque gets excessive, and will prevent overtorque damage.

For low volume mixing/mulling, a concrete mixing tub and a hoe will work, but requires some physical labor, and does not mull as well as a real muller, although it does mix well.
One person I have seen pours his sand in a tarp on the ground, and rolls the tarp/sand while stepping on it.
There is more than one way to mull sand, and you don't necessarily have to spend much money to do it, but for large quantities of sand, a muller will save a lot of grunt work.

.

 

[GreenTwin]

This is a Simpson muller, which is used at a local art-iron foundry, and it is a workhorse of an industrial machine for sure.
Most mullers have dual wheels, but if the wheel is massive enough, you can use a single wheel, as shown below.

 

[GreenTwin]

Most mullers have two plows.
In the photo below, the right plow scrapes the sand off of the exterior drum wall, and the left plow scrapes the sand up off the bottom of the drum and turns it over.

The wheel compacts the sand/clay mixture, and also works in a horizontal sheering action, which is what is suppose to give good green strength to the sand.
Green strength is the physical property of the green sand to remain in the shape in which it is compressed, and the ability to withstand erosion as the molten metal fills the mold.

Bound sand eliminates the entire green strength requirement, since bound sand becomes rigid once the binder sets.
Bound sand can also be drilled/carved, etc after it sets, which is an extremely useful feature, and there is no concerns about sand erosion with bound sand.
The downside to bound sand is that it cannot easily be reused like greensand.
The upside to bound sand is that it can produce professional results with a professional (excellent) surface finish when ceramic mold coat is used.
Bound sand can also be used to mold complex shapes that traditional green sand may not be able to mold.

And bound sand molds can be made multi-piece, with the pieces joined into an assembly, which is also a very useful feature, especially with complex molds.

 

[Foketry]

The mulling process is very hard on a mixer/muller motor, so depending on exactly how much sand you want to make, I guess that would determine what you use to mull with.

I use bound sand exclusively, and so I don't mull my sand, but rather I mix the binding agent into it.
For small sand molds I use a small Hobart kitchen mixer, and for the larger molds, I use a commercial Hobart kitchen mixer, as shown below.
I made a custom heavy-duty beater bar for the mixer below, since the stock beaters were not strong enough for sand.

I bought the mixer below used, and the salesman asked me if I needed help carrying it out.
LOL, "No" I said, "I can handle it".
Turns out it weighs about 400 lbs, and it took 5 people to get it in the car, and an engine hoist to get it out of the car and into the shop.
I will mix well up to about 3/4 of the bowl full, but more than that and it starts to bog down.

View attachment 127395

what kind of bonded sand do you use? there are many types of foundry sand binder (phenolic resin, urea resin, etc.) which one works well for your use?
This resin sand is a product for industrial use, can you buy it without difficulty for hobby use?

 

[awake]

Would a ball mill work for mulling sand?

 

[GreenTwin]

what kind of bonded sand do you use? there are many types of foundry sand binder (phenolic resin, urea resin, etc.) which one works well for your use?
This resin sand is a product for industrial use, can you buy it without difficulty for hobby use?

I use LINO-CURE (tm), which is an alkyd-oil three part binder system that works well for large cores and molds. It has a long available work time and strip time with excellent stripping characteristics. It works well with high pH sands such as olivine sand.

Linocure also works well with iron castings.
You can vary the set speed anywhere from perhaps 5 minutes up to an hour or perhaps more.

The smallest amount I have found is a 5 gallon can of the resin, which will bind perhaps 3,000 lbs of sand.

I use OK85 sand, which is a very dry commercial foundry sand.
Sand that is not very dry will not work with resin binder.

An industrial chemical respirator must be used when mixing and ramming resin-bound sand.

Its not cheap, but if you need very high quality castings, resin-bound sand with ceramic mold coat will produce those, assuming your iron is correct.

Edit:
One alternative to resin-bound sand that I am looking at using is sodium-silicate as a sand binder.
It is easier to source, does not require a chemical respirator (still requires a respirator for sand dust).
You can buy it in a one gallon jug, and it works in a similar fashion as any other bound sand.

https://www.budgetfoundrysupply.com/pyrosil-core-binder(Sets with CO2).

Here is sodium silicate
https://shop.clay-planet.com/search.aspx?find=sodium+silicate
or Chembond 4905, which I think is a sodium silicate binder hardened with a catalyst
https://shop.clay-planet.com/chembond-4905-no-bake-binder---5-gallon-bucket.aspx
I have used sodium silicate with CO2 for cores and molds.
I have not used Chembond with a catalyst yet, but plan to try it.


The downside to sodium silicate sand is that it tends to stick to the pattern, and so you need generous wax or other release agent.
Sodium silicate is normally set with CO2, which requires a CO2 tank, regulator, etc.
Note that putting dry ice in a sealed container can cause the pressure to exceed several thousand pounds in a short period of time, and cause failure of the container. I have read warnings about this online.

Sodium silicate can also be hardened with a catalyst, and the standard catalyst that can be found sets the sand in 45 minutes.
There are catalysts that set sodium silicate more quickly, but they can be difficult to source.

I am told that sodium silicate bound sand works with iron, but I have not tried it yet.
I don't know if sodium silicate bound sand works with an alcohol-base mold coat, and have not tried that either.
.

 

[GreenTwin]

Would a ball mill work for mulling sand?

A ball mill seems to be a lot like a concrete mixer with weights in it.
I did mull some greensand that I tested (I did not like the surface finish results of the greensand I tried, and so reverted back to resin-bound sand).

The problem I see is the sand/clay packing against the outside.
With my very slow rotating concrete mixer, when I was mulling some greensand for a test (without the internal mixer blades installed), I uses a boat paddle to scrape the sand off the walls of the mixer.
A rather crude affair at best, and no substitute for a good muller.

.

 

[dazz]

View attachment 127237

I have done some research on burners.

The purpose of a high swirl swirler combined with a cone spray nozzle is to create a low pressure zone in front of the nozzle that draws in a reverse flow of combusting fuel/air. This is rather like holding a blow torch in front of the burner nozzle, and pointing it back towards the nozzle, to create stable ignition.

The burner in the photo above is a low swirl burner. It has a core of airflow around the nozzle. Around that is a low swirl air flow. This is supposed to locate the flame front away from the nozzle and to create a shorter and wider stable combustion zone. Just what you need for a small domestic water heating furnace, or for a home foundry furnace.

The literature is consistent in saying that flame impingement on the furnace walls is a bad thing. Unavoidable for foundry furnace but it could be mitigated.

My intention is to try the low swirl burner as supplied. If it works, I will use it. If not, I will experiment.

Dazz

 

[GreenTwin]

Just what you need for a small domestic water heating furnace, or for a home foundry furnace.

I think it can be a mistake to assume that a foundry furnace will act like a commercial heating unit.
The furnace is round, and the combustion area is narrow and limited, which can be different than a commercial heating unit combustion chamber.

I have read (but cannot prove) that a narrow flame distribution is better for a furnace to prevent flame impingement on the crucible.
Direct flame on the crucible will greatly shorten its life.

My intention is to try the low swirl burner as supplied. If it works, I will use it. If not, I will experiment.

What we do know is that your burner arrangement will work well with a heating unit.
The only difference I see with what I and many others use and yours is the spin vanes.
Some folks use spin vanes and some do not.
Some started out using spin vanes, only to discard them later.
I don't use spin vanes.

I am not sure what angle your nozzle is designed for (the angles vary).

So as you suggest, try your burner unmodified, and if it works well, then your work is done.
If it has problems, it would be easy enough to either cut out most of the vanes on the spin vane piece, or use pliers to straighten them to be almost parallel to the air flow.
I don't think it will requiring much effort/modification (if any) to make your burner work correctly.
That configuration is almost identical to what most siphon-nozzle foundry folks use.

The pressure return line with needle valve is where I think you will need to modify things a bit.
But if it works well without a return fuel line and needle valve (unmodified), then stop right there and use it as-is.

The expression is "don't fix things that are not broken".

Edit:
Here is a test I did on my siphon-nozzle burner, to study the compressed air pressure effect on the way the burner operated.
What I discovered in the test is that under about 30 psi compressed air, I don't get full atomization of the fuel (especially when the burner is attached to the furnace).
If you turn the compressed air down enough, you just get a stream of liquid fuel out the tip.
This test was run on diesel.

Note: Don't turn the burner towards your face during a test on a windy day, or you may singe/burn off your eyebrows as I did at 3:36.
Of course you should have sense enough to have a full facemask on during the test. I think I only had safety glasses on.

Also note that this test does not use combustion air (the blower is off), and so is not an exact test, but an approximate one that allows you to see the atomization that occurs with various compressed air pressures. You can use more than 30 psi compressed air pressure, but more pressure does not make the burner operate hotter, and may actually make it run cooler.
The science of fuel oil combustion is not that simple, and a finer droplet size is not necessarily one that burns hotter.
It is more a matter of getting as much surface area of the very hottest flame around the droplets.

Diesel is rather tame fuel as far as flammability.
Kerosene is noticeably more flammable than diesel.
Kerosene would work just as well as diesel, but for some reason kerosene is about four times more expensive than automotive diesel in this part of the country.

https://vimeo.com/user82094693
.

 

[dazz]

Hi
My reading is that high pressure nozzles have a narrow range of working pressure, centred around 100psi or so. I expect to buy a selection of nozzles to try so I can find the right one.

Preventing flame impingement in a small furnace filled with a crucible is unachievable. I think some things could be done to reduce impingement. eg. Shape the furnace interior so the fuel nozzle is set back to give some volume for "normal" combustion to happen before the flame hits the wall. A short wide flame should maximise energy intensity in the confined space of a furnace.

Combustion is clearly a really complex process subject to a lot of variables that are unlikely to be controlled or measured in a backyard setting.

 

[dazz]

Hi
What to people use for fuel containers???
I am thinking of using metal jerry cans with a modified all-metal pouring spout to create a fire and hot metal resistant fuel supply.

 

[Ed T]

Possibly dragging this further off subject, but here goes. I have been planning to do some casting for some time and I have gathered all the bits needed to do it. AFA burners go, there seems to be a lot effort put into making various kinds, all of which seem to work adequately if not efficiently. Why wouldn't an ordinary fuel oil gun burner work? It seems that it is already designed to do exactly what is needed and comes in a nice compact package and uses readily available fuel which is reasonably priced. There must be a reason that I have never seen it done. Comments?

 

[GreenTwin]

What do people use for fuel containers???

I was using 5 gallon plastic containers for fuel, and I was not that pleased with those.
The new fuel containers have so many safety features on them that the are almost impossible to use.

For bulk transport from the gas station to home, I use these containers.
They can be a bit heavy when full, but I don't need very many of them, and only have to lift them down out of the van to the ground, where I can wheel them around after that with a two-wheeler.

I intend to pump the fuel from these containers (I have two) over to my operating fuel tank for the pressure nozzle, which I will show below, so I don't actually ever lift and pour these containers.

 

[GreenTwin]

For my siphon nozzle burner, I used a new 40 lb propane tank (never cut into a used propane tank); the new tanks are empty and clean.
The siphon nozzle fuel tank runs with diesel and operates with 10psi on it, and has a 30 psi safety valve in case of air regulator failure (I know of one person who had a regulator failure and it overpressurized his fuel line and blew the fuel line off the fitting. He had a big inferno in just a few seconds.

I am going to retire my siphon nozzle burner, so that I don't have to operate an air compressor anymore, and will transition to a pressure nozzle burner, which is almost exactly like dazz's above.

This is the fuel tank I will use with the pressure nozzle burner, and it will not be pressurized.
It will have a supply line from the tank to the burner, and a return line from the burner to the tank.

 

[GreenTwin]

Possibly dragging this further off subject, but here goes. I have been planning to do some casting for some time and I have gathered all the bits needed to do it. AFA burners go, there seems to be a lot effort put into making various kinds, all of which seem to work adequately if not efficiently. Why wouldn't an ordinary fuel oil gun burner work? It seems that it is already designed to do exactly what is needed and comes in a nice compact package and uses readily available fuel which is reasonably priced. There must be a reason that I have never seen it done. Comments?

When you say "fuel oil gun burner", I assume you are talking about a packaged burner unit like the Beckett unit below?

I have seen one person use a packaged burner system with their furnace for a while, and then they changed to a more traditional burner tube / nozzle arrangement with remote mounted gear pump.

Packaged Burner Assemblies:

There are several problems I see with using packaged burner with a foundry furnace, as follows (I have not used a packaged burner):

1. A packaged burner is a rather bulky assembly, and that would make getting the burner tube in exactly the right place at exactly the right elevation would be far more difficult than just a burner tube.

2. The output tube appears to be about 4" diameter, which is really too large for many/most furnaces used for hobby work.
I guess the output tube could be changed to a 2.5" diameter tube?

3. All furnaces sooner or later will leak hot gasses past the burner tube at the tuyere (the tuyere being the entrance low in the furnace).
When the tuyere leaks, and generally before you notice that it is leaking, anything that can be ruined/melted in the vicinity of the tuyere is melted/ruined, such as a packaged burner unit.

4. When a furnace is open, and the crucible is pulled out and set on the ground, the radiant heat is very intense (this is especially true for an iron furnace).
The radiant heat will melt plastic 10 feet away, so I tend to think that over time it would ruin a packaged burner unit.

5. My general rule is that anything in the furnace area (say a 20 foot radius around the furnace) should not be plastic; this includes wheels, and anything else.
There are a lot of furnace photos out there with melted plastic wheels, and melted plastic burner parts/gauges, etc.
The only thing that is plastic/rubber in the furnace vicinity is the fuel line, and that is somewhat at risk.
I intend to slide a piece of flexible metal conduit over my fuel line, to give it mechanical protection, and also to give it heat protection from spilled metal/slag.

Comments on hot-tube burner designs:

The burner tube should remain cool to the touch along most of its length, except perhaps right at the furnace end, which may get a little warmer, but not really hot. There is a school of thought that the burner tube should be operated red hot, and a type of burner that uses a flame impingement out of the side of the furnace and onto the burner tube, I guess with a drip-style burner, to assist with atomization of dripped fuel.
I think that for a typical backyard foundry application, there is no need to run a hot-burner-tube design, and many many reasons why you should not run a hot-burner-tube design.

The main reasons that a hot-burner-tube design is not desirable is that it tends to cook whatever is inside the burner tube, and build up varnish on the hot surfaces, and the burner tube steel will degrade over time, even if it is stainless steel.
But the #1 reason why I don't use a hot-tube-burner design is that it does not work any better than a cold burner design, and I have seen some folks have a lot of problems with their hot-tube burners.
Why introduce new "features" to a burner that are known to cause problems? (Short answer: Because you can get millions of views and likes on ytube featuring all sorts of Rube Goldberg burner deigns).

There are folks out there who make burners and such seemingly only for the purpose of proving that they can make a better (new and improved better mouse trap) burner, and so there are droves of burner styles that actually will melt metal well, and they are almost universally of a bad design from the standpoint of providing a maintenance-free burner that operates consistently every melt without the need for adjustment during the melt.

There are folks out there who embark on multi-year Don Quixote type quests to design and build the ultimate foundry burner.
The problem is their quest never seems to lead to a functional new burner type, or if the burner does function, it functions in a highly unreliable way that often will not melt iron.
There are numerous burner folks out there in videoland, and many/most never cast anything, or anything of any value other than a lump of metal.
For the professional burner builders, its not about foundry work and casting usable parts; it is about endless burner experiments, and maximizing ytube views.

I have done my share of burner experiments, and have done enough to have a good feel for what works for an oil burner.
When it comes to oil burners, I can say that a cool burner tube and proper atomization of the fuel are what is important to good burner operation.
Beyond that is just a matter of how you want to assemble the parts.

I have never gotten a drip-style oil burner to operate or control correctly, or burn cleanly at all output levels, and so I don't use that style.
A siphon nozzle burner will burn cleanly and control precisely at any fuel flow level within its designed operating range, which is a very wide range of outputs.
A siphon nozzle burner will operate without combustion air (it will naturally aspirate if the combustion air tube is left open), for smaller melts, and most folks are not aware of this function.

Summary:

My siphon and pressure nozzle burners weigh perhaps 5 lbs, and their critical components are located far away from the furnace, out of heat range and spilled metal danger.
It is easy to support my burner tube at the tuyere, and easy to adjust the height of my burner tube to work with multiple furnaces (I have more than one furnace, and the tuyere heights are not the same).

Everyone has their favorite burner and melting methods.
I can't say what works best for others, but I can say what has proven to work well for me.
To each their own, but in my mind the real proof is in the quality of the castings created.
"Show me the castings" as they say, and then we talk about burners.

Edit:
I do know of folks who make very good castings, and use very problematic burners.
They use the fact that they can make very good castings to justify using their problematic burner style.
I make quality castings, and my burner is maintenance-free, and does not require adjustment every.
I see no justification for using equipment that is problematic. Would you drive a car that breaks down constantly? Some do; I am not sure why.

.

 

[GreenTwin]

Furnace heat stratification is an interesting topic with home foundry burners.

The general consensus is that once the furnace interior is up to its maximum operating temperature, then fuel/flame stratification is not important.
I am not sure I agree with this consensus, but I can't prove it to be incorrect either.

I have been told by many that once the furnace interior is up to temperature, you cannot puddle fuel in the bottom of the furnace, since it would vaporize immediately.
I know for a fact that you can indeed puddle a lot of fuel in the bottom of a furnace when it is red hot, and this is a dangerous thing, since the fuel could flash and cause a lot of problems.
Fuel puddling inside the furnace means that your burner is not atomizing the fuel correctly, or your nozzle tip is too far up in the burner tube, and so the spray is impinging on the side of the burner tube and dripping into the furnace, instead of being injected into the furnace via an atomized spray.

Many backyard casting folks (myself included) elevate the crucible in the furnace as high as possible on a plinth, because the top of the furnace is hotter than the lower portion.

If you think about it (you can also directly observe this inside the furnace) the fuel/air mixture is entering the furnace at ambient outdoor air temperature, and so the region in front of the burner tube is at ambient air temperature (approximately).
You can see the effect in the photo below.
The green arrow indicates the coolest part of the flame, and it is what I call the pre-combustion region.

 

[GreenTwin]

The hottest part of the flame I think is the brilliant yellow region, but that region is basically limited to 1/2 the furnace.

A dual 180 degree burner arrangement solves the uneven flame distribution problem, and I have tried a dual 180 degree burner previously, as shown below.
Where the dual 180 degree burner arrangement works better for the average backyard melting person is a topic of discussion.
Most backyard folks successfully use a single-tube burner like the one in the previous post, and they work well in this arrangement.

This is a view of the interior of a furnace operating on two siphon nozzle burners at 180 degrees.
The flame is even around the crucible, and the combustion air velocity is divided by 1/2 for each burner tube.
The lower combustion air velocity helps keep the flame low in the furnace, and reduces the tendency of the flame from striking the back wall of the furnace opposite the burner tube and then climbing upwards towards the lid.

At some point I will probably transition back to a dual 180 degree burner arrangement.
At the time I was experimenting with the dual burner setup, I did not know how to melt iron, and so I was unable to gauge how the dual burner worked compared to a single burner.

 

[GreenTwin]

Here is a good example of the wall climbing affect that happens with a single burner tube.
The wall climbing does not seem to adversely affect the furnace operation, but it makes me wonder if I could save a bit of time with a dual burner 180 degree arrangement that did not wall climb.