Been getting into this hobby, and realised that there are a lot of complex parts that can't be machined, so I have a couple of questions on casting! I've seen a number of furnaces ranging for a barrel with concrete, to a couple of grand worth of supplies, something you'd see in a real foundry, so what's good for a beginner on a budget, I got an old blow torch can that be used as a burner? I would still like to be able to melt larger amounts of metal, for future, larger projects, what are some ways I can do this? How should I go about casting more complex geometries? I've seen many people use the lost foam method and dip it in plaster, but I find that the finish looks very rough, and if I use this method for say, an engine block with oil ports, what if there is a defect in one of the ports that I can't get to? I have a 3d printer, and I've also seen people use 3d prints with some type of slurry and get better results? Overall any method decided it seems I need some type of slurry, I've seen people, once again, use plaster, and they say they also mix in silicone, what does that do? I've also see people wrap the object in chicken wire after the first layer of slurry, and then add more slurry, what does that do? So basically, what should a slurry be made of to give the best finish with the least defects, and why are so many different methods of casting something? Are different methods used for different types of objects? And for something like an intake manifold, are there materials that can be in the manifold that can be removed easily after casting that will still provide a somewhat nice finish?
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Rule #1, don't use concrete for a foundry furnace, since it will explode.
There are ytube videos of violent explosions, because you can't get the residual water out of concrete.
The material that looks a lot like concrete that is used with foundry furnaces is called refractory, and it can be slowly dried out completely, so that it does not explode when heated very hot.
Most beginners start with melting aluminum using some sort of propane torch, or in some cases charcoal (I don't recommend using charcoal, that is a very wasteful way to melt aluminum).
Usually beginners use some sort of metal crucible. It should be thick enough to have sufficient strength when hot to contain the molten metal.
Often aluminum cans are melted, and that is not really a good idea, since they often trap moisture, and can explode when heated.
Aluminum cans are not made from the most ideal aluminum casting allow, and extrusions are not really ideal aluminum alloy either.
Aluminum 356 is the alloy that is almost universally used to make aluminum castings, and it can be heat treated/tempered.
The trend these days seems to be propane-fired furnaces sold online that have a ceramic blanket liner.
This is a relatively inexpensive way to make a furnace, but be sure to spray on one or more coats of satanite to seal the ceramic blanket and prevent airborn fibers. Inhaling airborn ceramic fibers can cause lung disease.
Note that a forge is generally a small furnace that is used to heat metal for blacksmith work, and it is often built horizontal like a mini aircraft hangar, with an opening on one end, where you can insert metal that you want to heat. One or more propane burners are generally mounted on the top of a forge.
A foundry furnace is typically round and vertical, with a removable lid.
If you want a more durable furnace, you can use a "hot face", which is typically a thin layer of high temperature refractory, with a backing generally of a few layers of ceramic blanket.
A hot faced furnace (if you use the correct hot face material) will withstand the very abusive temperatures that an iron furnace will see, along with handling the inherent slag that gets splattered when melting iron.
A step above a steel crucible is a crucible made of a high temperature clay-like material, such as clay-graphite.
Clay graphite crucibles are more fragile than a steel crucible, but are considered superior to a steel crucible, since they don't contaminate the aluminum with steel.
Many beginners use either water-based "greensand", or oil-based greensand, and use patterns that are either made from wood, or 3D printed. "Greensand" generally refers to fine sand that has been mixed with clay, to make molds.
The molten metal is poured into the cavities in the molds.
If you are not sure if you really want to get into the backyard castings side of the hobby, then go cheap at first.
I built my first furnace using hard firebricks stacked in a circle, and a steel crucible welded from a piece of pipe.
A weed burner would probably work, but if not, a "Reil" type burner can be made relatively easily.
You may have to use a higher output propane regulator that what is used on just a bbq grille, such as a turkey-cooker regulator.
If molten metal comes in contact with the slightest amount of moisture, and it does not have to be visible moisture, the moisture will superheat, and explode molten metal right into your face, so protective eyewear and a protective face shield is extremely important.
There are a number of videos of people on ytube who melt and pour metal in the backyard, and in most cases, these are excellent examples of what you should never do, so keep that in mind.
Obviously do any metal melting outside and far away from the house, car, and anything combustible.
I have dabbled in casting brass and a few types of bronze, and I must say I despise this alloy because if the metal has zinc in it, the zinc boils out first and creates large clouds of smoke that can make you very sick.
Some of the bronze alloys have little or no zinc, and people seem to have the most success with this alloy type.
Brass and bronze require a lot more heat in order to reach pour temperature than aluminum.
The Holy Grail of metaldom (in my opinion) is casting gray iron, and that can be done most easily using an oil burner, with a combustion air blower. Molten iron is extremely hot, and so you need heat shields on equipment handles, etc. to keep your gloved hands at a reasonable temperature.
I actually find iron to be easier to melt and cast than brass/bronze, since iron does not contain zinc, and so no zinc fumes.
Aluminum melts can be done easily with a naturally-aspirated propane burner without a combustion air blower.
And if you really want to get a bit crazy, you can pour ductile iron, which is a special process that is done in reaction chamber.
The additive for ductile iron is generally some alloy of magnesium, and so the reaction is exothermic, and sometimes a bit violent.
For good aluminum castings, you have to use quality molding sand of some type, and you have to measure or otherwise be able to accurately predict when you have reached pour temperature.
If you heat aluminum above pour temperature (generally pour temperature is about 1,350 F), you will get a very rough surface finish.
And if you hold molten aluminum at pour temperature for any length of time, it will absorb hydrogen, and that will cause gas bubbles in the casting.
That is about all I know.
.
There are ytube videos of violent explosions, because you can't get the residual water out of concrete.
The material that looks a lot like concrete that is used with foundry furnaces is called refractory, and it can be slowly dried out completely, so that it does not explode when heated very hot.
Most beginners start with melting aluminum using some sort of propane torch, or in some cases charcoal (I don't recommend using charcoal, that is a very wasteful way to melt aluminum).
Usually beginners use some sort of metal crucible. It should be thick enough to have sufficient strength when hot to contain the molten metal.
Often aluminum cans are melted, and that is not really a good idea, since they often trap moisture, and can explode when heated.
Aluminum cans are not made from the most ideal aluminum casting allow, and extrusions are not really ideal aluminum alloy either.
Aluminum 356 is the alloy that is almost universally used to make aluminum castings, and it can be heat treated/tempered.
The trend these days seems to be propane-fired furnaces sold online that have a ceramic blanket liner.
This is a relatively inexpensive way to make a furnace, but be sure to spray on one or more coats of satanite to seal the ceramic blanket and prevent airborn fibers. Inhaling airborn ceramic fibers can cause lung disease.
Note that a forge is generally a small furnace that is used to heat metal for blacksmith work, and it is often built horizontal like a mini aircraft hangar, with an opening on one end, where you can insert metal that you want to heat. One or more propane burners are generally mounted on the top of a forge.
A foundry furnace is typically round and vertical, with a removable lid.
If you want a more durable furnace, you can use a "hot face", which is typically a thin layer of high temperature refractory, with a backing generally of a few layers of ceramic blanket.
A hot faced furnace (if you use the correct hot face material) will withstand the very abusive temperatures that an iron furnace will see, along with handling the inherent slag that gets splattered when melting iron.
A step above a steel crucible is a crucible made of a high temperature clay-like material, such as clay-graphite.
Clay graphite crucibles are more fragile than a steel crucible, but are considered superior to a steel crucible, since they don't contaminate the aluminum with steel.
Many beginners use either water-based "greensand", or oil-based greensand, and use patterns that are either made from wood, or 3D printed. "Greensand" generally refers to fine sand that has been mixed with clay, to make molds.
The molten metal is poured into the cavities in the molds.
If you are not sure if you really want to get into the backyard castings side of the hobby, then go cheap at first.
I built my first furnace using hard firebricks stacked in a circle, and a steel crucible welded from a piece of pipe.
A weed burner would probably work, but if not, a "Reil" type burner can be made relatively easily.
You may have to use a higher output propane regulator that what is used on just a bbq grille, such as a turkey-cooker regulator.
If molten metal comes in contact with the slightest amount of moisture, and it does not have to be visible moisture, the moisture will superheat, and explode molten metal right into your face, so protective eyewear and a protective face shield is extremely important.
There are a number of videos of people on ytube who melt and pour metal in the backyard, and in most cases, these are excellent examples of what you should never do, so keep that in mind.
Obviously do any metal melting outside and far away from the house, car, and anything combustible.
I have dabbled in casting brass and a few types of bronze, and I must say I despise this alloy because if the metal has zinc in it, the zinc boils out first and creates large clouds of smoke that can make you very sick.
Some of the bronze alloys have little or no zinc, and people seem to have the most success with this alloy type.
Brass and bronze require a lot more heat in order to reach pour temperature than aluminum.
The Holy Grail of metaldom (in my opinion) is casting gray iron, and that can be done most easily using an oil burner, with a combustion air blower. Molten iron is extremely hot, and so you need heat shields on equipment handles, etc. to keep your gloved hands at a reasonable temperature.
I actually find iron to be easier to melt and cast than brass/bronze, since iron does not contain zinc, and so no zinc fumes.
Aluminum melts can be done easily with a naturally-aspirated propane burner without a combustion air blower.
And if you really want to get a bit crazy, you can pour ductile iron, which is a special process that is done in reaction chamber.
The additive for ductile iron is generally some alloy of magnesium, and so the reaction is exothermic, and sometimes a bit violent.
For good aluminum castings, you have to use quality molding sand of some type, and you have to measure or otherwise be able to accurately predict when you have reached pour temperature.
If you heat aluminum above pour temperature (generally pour temperature is about 1,350 F), you will get a very rough surface finish.
And if you hold molten aluminum at pour temperature for any length of time, it will absorb hydrogen, and that will cause gas bubbles in the casting.
That is about all I know.
.
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Do you know anything about slurries? Or a good way to counteract/calculate metal shrinkage? Or anything on casting smaller complex parts?
I have not done investment casting work, but I do know a bit about it.
I will have to dig that out.
Below is a hard rubber mold that I saw at Bob Pearson's shop (the guy who makes Cretors steam engines from the original Cretors patterns).
There is some sort of wax melting pot, and there is a nozzle at the bottom, and you inject wax into the cavities in the mold.
The hardened wax pieces are adhered to a tree (like a real tree), sometimes with a centeral wax stem, and sometimes also with tree branches. Multiple wax pieces are placed on the tree limbs. A tin amount of melted wax adheres the wax pieces to the tree.
The tree is places into a cylindrical container, and investment material is poured into the container.
Once the investment material solidifies, the investment is placed into a high temperature kiln, upsidedown, and the wax is burned out.
This investment mold is then poured I think while it is still very hot, with molten metal, which can be aluminum, brass/bronze, gray iron, steel, or some other alloy.
Steel requires a special process and special knowledge, and so generally commercial foundries only can pour that.
To make the rubber pattern, one would first have to make very accurate and very smooth master patterns, and these patterns have to be oversized by the shrinkage factor of the metal.
I generally use a factor of 1.015 on aluminum and gray iron, and that has always gotten me into a reasonable expected range as far as dimensions.
Some may go up to 1.02 for aluminum (check me on that).
So if you want to make a casting that is 1" diameter round, then the pattern must be sized 1.0" times 1.015, or whatever shrinkage factor you use.
The investment process is generally considered the most accurate process, however, the quality of the castings depends on the quaility of the patterns that are used to make the rubber mold.
Investment casting seems to be the method of choice for making jewelry.
I also recall a vacuum chamber being required and perhaps a vibrating table, so that the air bubbles can be removed after the investment is poured around the wax patterns.
I am not sure if this is a good investemnt casting video or not, because I have not done investment casting.
.
I will have to dig that out.
Below is a hard rubber mold that I saw at Bob Pearson's shop (the guy who makes Cretors steam engines from the original Cretors patterns).
There is some sort of wax melting pot, and there is a nozzle at the bottom, and you inject wax into the cavities in the mold.
The hardened wax pieces are adhered to a tree (like a real tree), sometimes with a centeral wax stem, and sometimes also with tree branches. Multiple wax pieces are placed on the tree limbs. A tin amount of melted wax adheres the wax pieces to the tree.
The tree is places into a cylindrical container, and investment material is poured into the container.
Once the investment material solidifies, the investment is placed into a high temperature kiln, upsidedown, and the wax is burned out.
This investment mold is then poured I think while it is still very hot, with molten metal, which can be aluminum, brass/bronze, gray iron, steel, or some other alloy.
Steel requires a special process and special knowledge, and so generally commercial foundries only can pour that.
To make the rubber pattern, one would first have to make very accurate and very smooth master patterns, and these patterns have to be oversized by the shrinkage factor of the metal.
I generally use a factor of 1.015 on aluminum and gray iron, and that has always gotten me into a reasonable expected range as far as dimensions.
Some may go up to 1.02 for aluminum (check me on that).
So if you want to make a casting that is 1" diameter round, then the pattern must be sized 1.0" times 1.015, or whatever shrinkage factor you use.
The investment process is generally considered the most accurate process, however, the quality of the castings depends on the quaility of the patterns that are used to make the rubber mold.
Investment casting seems to be the method of choice for making jewelry.
I also recall a vacuum chamber being required and perhaps a vibrating table, so that the air bubbles can be removed after the investment is poured around the wax patterns.
I am not sure if this is a good investemnt casting video or not, because I have not done investment casting.
.
Attachments
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A variant of the lost-wax method is the shel method (I am not exactly sure what the correct terms are), or what I call the lost-filament method, where a pattern is 3D printed, then dipped in multiple coats of ceramic slurry.
The filament is then burned out of the shell in a kiln, and molten metal is poured into the shell while it is still hot.
Here is a video illustrating that method in gray iron.
These castings were easy to machine, with no chills or hard spots.
Here is an investment casting video by Ransom and Randolph.
Be sure you don't inhale any dust or fine particles when handling foundry sand.
The investment slurry has a finite shelf life, perhaps a year.
Again, I have not used that product, but am repeating what I have heard from others.
The filament is then burned out of the shell in a kiln, and molten metal is poured into the shell while it is still hot.
Here is a video illustrating that method in gray iron.
These castings were easy to machine, with no chills or hard spots.
Here is an investment casting video by Ransom and Randolph.
Be sure you don't inhale any dust or fine particles when handling foundry sand.
The investment slurry has a finite shelf life, perhaps a year.
Again, I have not used that product, but am repeating what I have heard from others.
And we have our member "Foketry" who is casting a 1/2 scale Triumph motorcycle engine, shown at this thread.
https://www.homemodelenginemachinis...s-castings-with-petrobond-and-lost-pla.36970/
Apparently he is using plaster as an investment material, and is 3D printing patterns (with a shrinkage factor), using a special filament that is suppose to burner out cleanly.
I am still studying his investment methods, and don't understand them fully.
You can read his thread where he describes his method.
.
https://www.homemodelenginemachinis...s-castings-with-petrobond-and-lost-pla.36970/
Apparently he is using plaster as an investment material, and is 3D printing patterns (with a shrinkage factor), using a special filament that is suppose to burner out cleanly.
I am still studying his investment methods, and don't understand them fully.
You can read his thread where he describes his method.
.
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I have seen a lot posted in the last few years, where someone makes various full-sized automotive intake manifolds using hardware store pink foam, and the lost-foam process.
While this one individual does make some impressive manifolds, the problem is that each pattern he makes is sacrificed in the process.
So if it takes eight hours to make a pattern, and you want two castings, then it requires sixteen hours, etc., ie: the pattern is not reusable; it is a one-time use only.
I have not been impressed with the pink foam casting method for several reasons, as follows:
1. In the commercial casting world, the lost foam method uses polystyrene beads that are expanded inside of a metal mold using steam. This foam has different characteristics than pink hardware store foam, and is designed to vaporized and burn out cleanly.
2. The ceramic slurry coating for the lost foam method must be porous enough to allow the gasses/vapors from the melting foam to permeate the coating. If you coating does not allow the gasses to escape, then you will have some very dreadful castings which are full of holes.
3. The fill rate for lost foam castings is very slow, since the molten metal must melt/burn its way down the foam pattern.
I suspect that this slow fill rate causes cold joins, and other defects that may not be visible on the surface of the casting, but would eliminate the posibility of the casting having any significant structural strength; in the case where you may want a structrually strong engine part.
4. The melting hardware store foam produces a lot of black smoke that I suspect is toxic, so use caution if you happen to try this method.
5. The surface finish of the casting is limited by the surface finish of the mold.
In the cast of some automotive engine blocks, you can actually see the expanded bead pattern in the casting surface.
In some cases, this surface roughness can be buffed out with a ceramic sponge, if you can reach it.
6. I know of one individual who tried gray iron with a pink hardware store foam pattern, and it was a total disaster, with a casting full of huge holes. The ceramic shell/lost PLA method in the video above did work very well with gray iron.
I personally will not be trying the pink lost foam method, based on what I have seen.
.
While this one individual does make some impressive manifolds, the problem is that each pattern he makes is sacrificed in the process.
So if it takes eight hours to make a pattern, and you want two castings, then it requires sixteen hours, etc., ie: the pattern is not reusable; it is a one-time use only.
I have not been impressed with the pink foam casting method for several reasons, as follows:
1. In the commercial casting world, the lost foam method uses polystyrene beads that are expanded inside of a metal mold using steam. This foam has different characteristics than pink hardware store foam, and is designed to vaporized and burn out cleanly.
2. The ceramic slurry coating for the lost foam method must be porous enough to allow the gasses/vapors from the melting foam to permeate the coating. If you coating does not allow the gasses to escape, then you will have some very dreadful castings which are full of holes.
3. The fill rate for lost foam castings is very slow, since the molten metal must melt/burn its way down the foam pattern.
I suspect that this slow fill rate causes cold joins, and other defects that may not be visible on the surface of the casting, but would eliminate the posibility of the casting having any significant structural strength; in the case where you may want a structrually strong engine part.
4. The melting hardware store foam produces a lot of black smoke that I suspect is toxic, so use caution if you happen to try this method.
5. The surface finish of the casting is limited by the surface finish of the mold.
In the cast of some automotive engine blocks, you can actually see the expanded bead pattern in the casting surface.
In some cases, this surface roughness can be buffed out with a ceramic sponge, if you can reach it.
6. I know of one individual who tried gray iron with a pink hardware store foam pattern, and it was a total disaster, with a casting full of huge holes. The ceramic shell/lost PLA method in the video above did work very well with gray iron.
I personally will not be trying the pink lost foam method, based on what I have seen.
.
I 100% agree with your opinion on the lost foam method, I believe that it does waste a lot more material and time to produce unsatisfactory results once. I am intrigued on the wax method as this does sound more simple, re-useable, and more cost effective for someone like me. I am also interested in the lost PLA method and the slurry used in it, as I have a 3d printer and it seems doable, the only factor I find limiting would be the slurry, as the comercially available slurries cost a couple hundred dollars, and I've seen people make their own using plaster and silicon. Any thoughts?
I have so far avoided using lost wax and/or ceramic shell methods, since I can to a lot with bound sand.
Sand foundry molds do have their limits though, and if you get into very complex shapes, sometimes a ceramic shell method is the only thing that will work.
I have seen one individual out west make some very impressive motorcycle racing cylinders (full size) for his racing bike, and he actually uses these castings under rigorous racing conditions and high temperatures.
He uses bound sand (I think the same that I use, or perhaps similar).
https://www.homemodelenginemachinis...se-casting-motorcycle-racing-cylinders.35502/
With bound sand, you can spray on an alcohol-based ceramic slurry, and then burn off the alcohol, and this gives a very fine finish to gray iron or aluminum castings.
Example below is a gray iron casting that has just been removed from the mold.
The slight amount of adhering sand can be brushed off with a dry paintbrush, giveing a shiny, clean, smooth surface finish.
.
Sand foundry molds do have their limits though, and if you get into very complex shapes, sometimes a ceramic shell method is the only thing that will work.
I have seen one individual out west make some very impressive motorcycle racing cylinders (full size) for his racing bike, and he actually uses these castings under rigorous racing conditions and high temperatures.
He uses bound sand (I think the same that I use, or perhaps similar).
https://www.homemodelenginemachinis...se-casting-motorcycle-racing-cylinders.35502/
With bound sand, you can spray on an alcohol-based ceramic slurry, and then burn off the alcohol, and this gives a very fine finish to gray iron or aluminum castings.
Example below is a gray iron casting that has just been removed from the mold.
The slight amount of adhering sand can be brushed off with a dry paintbrush, giveing a shiny, clean, smooth surface finish.
.
Attachments
As I mentioned, our member Foketry uses plaster.
You will have to read his thread carefully to see exactly how he does it.
I think he mentions some sort of pre-coating of the filament before investing.
When in doubt, try things on a small scale, and make sure you can get the results you want before spending a lot of money.
He also uses "Petrobond" (tm), which is an oil-based greensand that is often used with aluminum, with excellent surface finished, if you do it correctly.
https://www.homemodelenginemachinis...s-castings-with-petrobond-and-lost-pla.36970/
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I would recommend using the simplest and least expensive casting method you can find that gives you the surface finish and structural quality that you want/need.
There is no sense using a complex and expensive process if you can find a less expensive and easier method that produces the same casting results.
.
There is no sense using a complex and expensive process if you can find a less expensive and easier method that produces the same casting results.
.
