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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