Some of these things are probably the only thing that I’ve done right so far, pouring as soon as completely melted, not touching the dross on top, pouring into an offset basin to the sprue immediately without any great distance and without letting Air gulp into the sprue through intermittent pouring. I have a safety question, how long will the graphite crucible last for? I believe it’s considered an 8 kg. And is it possible to actually crush the crucible with the tongs?
Aluminum sand casting for Chenery Gnome Rotary
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Fidlstyks
Active Member
If you Google and read about Hydrogen Embrittlement, it may enlighten you some. Most concerns alloys.
All I know is that on 15# of aluminum, I toss a heaping table spoon of raw beeswax on at the time of pouring. In dirty aluminum that took longer to melt, I drop some in at 3/4 of a pot.
I do this, then always deslag with steel screen spoon.
The main concern seems to be not pouring in rain, or very high humidity and never let the molten metal set and draw in hydrogen from the air.
Pour it as soon as molten and fluxed with the beeswax. It burns off quickly. I think the burning wax makes anything in the metal burn out, like oil and trapped water.
I think sprue design seems somewhat critical. Going from a 3 inch tall sprue to a 5" makes thinner pieces pour. Size and gate size make it work. I have seen times the sprue was too big and actually sucked back in aluminum rather than filling the casting.
There is some consternation of pouring a foot long stream oposed to as close as one can, as soon as he can. Aluminum does pickup hydrogen from the air.
My tongs with wide tips reach down around below the bilge when lifting, and I set the crucible on a preheated brick with some sand on it, using a ringed pouring handle 4 foot long, with thin slats welded in. The longest on the side of pouring lip to prevent rocking.
Some have a quick flip up latch to keep it in olace.
When I first started, we had a small crucible, we just grabbed the top of the crucible and lifted and poured holding it that way.
It worked till the crucible wore out and was thin.
Buy some CW Amen books, he had knowledge.
I just recovered a very good casting. I see no visible distortion anywhere, including no large porosity. I placed a large riser in the center in addition to my other riser at the end. However, this is the only casting out of about five of them, which has a bit of a bronze color and it does actually have, micro surface porosity. I use the same clean aluminum ingots the same crucible. I am timing the furnace. I let it go full blast for 17 to 20 minutes. That’s what I did with all of them. Not sure why this one is slightly different you’re right those first ones were beauties. However this structurally best one with the overlying porosity had probably the most inconsistent pour. I might’ve allowed a little bit of air to gulp inside the sprue because I have that large opening in the center for that large center riser and I didn’t want some of the metal to enter that at the same time , and your pipe idea would probably have helped. I’m afraid of my hitting that and caving in the investment/sand… Any thoughts about these surface porosities the only one out of five castings? Too much air? Large riser in center? Ashes from paper from lighting gas furnace? Old Petrabond? Low atmospheric pressure? Mold sat overnight before pouring next day?
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I skim the dross off the top of the melt before pouring.
What you don't want to do is stir an aluminum melt.
Those castings look great !
You are a pro.
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What you don't want to do is stir an aluminum melt.
Those castings look great !
You are a pro.
.
I use stops on my lifting tongs, so that the fingers grasp the crucible about 2/3rds of the way down, but cannot apply pressure to the crucible due to the stops.
A Morgan Salamander-Super clay graphite crucible will last a very long time with aluminum.
I have some from 2011 that are still in perfect condition.
Lesser brands of crucibles can fail unexpectedly, and I have seen one of my original off-brands degrade to the point of being unusable in about 3 melts.
There is a huge following of offset pour basin folks out there in the backyard casting world, but some of the best and most prolific backyard casting folks just pour directly down the sprue, which is what I do.
Pour as fast as possible with the crucible lip almost touching the top of the sprue, and fill the spure immediately, and keep the sprue full for the entire mold fill.
The offset basin just churns bifilms, air and slag into the melt, and should not be used.
You can put a short ring made from 2" steel pipe, about 1" tall at the top of the sprue, which is more of a dam to prevent spill.
You don't want a basin at the bottom of the sprue for the same reason you don't want to use an offset basin at the top of the sprue.
It just causes the aluminum to roll over onto itself and trap air, sand, slag, and bifilms.
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A Morgan Salamander-Super clay graphite crucible will last a very long time with aluminum.
I have some from 2011 that are still in perfect condition.
Lesser brands of crucibles can fail unexpectedly, and I have seen one of my original off-brands degrade to the point of being unusable in about 3 melts.
There is a huge following of offset pour basin folks out there in the backyard casting world, but some of the best and most prolific backyard casting folks just pour directly down the sprue, which is what I do.
Pour as fast as possible with the crucible lip almost touching the top of the sprue, and fill the spure immediately, and keep the sprue full for the entire mold fill.
The offset basin just churns bifilms, air and slag into the melt, and should not be used.
You can put a short ring made from 2" steel pipe, about 1" tall at the top of the sprue, which is more of a dam to prevent spill.
You don't want a basin at the bottom of the sprue for the same reason you don't want to use an offset basin at the top of the sprue.
It just causes the aluminum to roll over onto itself and trap air, sand, slag, and bifilms.
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I have never used flux or beeswax, and I have never had any aluminum castings that were brittle.
As I mentioned, you should only correct problems that you actually have.
Don't try to prevent problems that you don't have.
I don't have problems with completely filling molds using a short sprue.
If you need a tall sprue, you are doing your runners and gating wrong.
A tall sprue causes high velocity, which is one of the main things you want to avoid when casting metal.
albd5a is right about not making the sprue diameter too large.
The sprue should preferably be tapered, and should be sized so that it can completely fill almost immediately.
The sprue must be large enough at its base to be able to fill the mold with enough speed that you get a complete fill, but not so fast that you get splashing inside the mold cavity from high velocity.
As I mentioned, you should only correct problems that you actually have.
Don't try to prevent problems that you don't have.
I don't have problems with completely filling molds using a short sprue.
If you need a tall sprue, you are doing your runners and gating wrong.
A tall sprue causes high velocity, which is one of the main things you want to avoid when casting metal.
albd5a is right about not making the sprue diameter too large.
The sprue should preferably be tapered, and should be sized so that it can completely fill almost immediately.
The sprue must be large enough at its base to be able to fill the mold with enough speed that you get a complete fill, but not so fast that you get splashing inside the mold cavity from high velocity.
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Fidlstyks
Active Member
I think the term velocity may look wrong, as turbulance in aluminum is very bad.
My foundry books all say to pour cast iron with like a begining swirl so the iron turns.
When I pour aluminum, I pour fast enough the sprue stays full, till the mold is full. I bottom fill the mold too.
The book on pouring aluminum has much said on gating and pouring techniques, as well as temperature. It leads me to believe there is more science in aluminum than one would think.
Since I do not make critical castings, for temperature control, I just melt all without it setting and pour when the aluminum flips off the slagger. I used a pyrometer at one time. But unless you have new aluminum with known numbers, you won't know what temp to pour at anyway.
The pouring temperature of aluminum is some what critical, as is the speed according to the manual.
With the taller sprue, I mostly pour cast iron and brass, the mold fills better. I do see people pour with a sprue only 3" tall. Once I started using taller sprues, I had more full pours.
When we send patterns to the ductile foundry, they say plated patterns must not have any gating attached.
Believe it or not, gating in ductile and cast iron makes a difference in the way the iron solidifies and changes the chemical make up. Similar to using a chill to create hard surfaces in cast iron castings.
Over heating aluminum and then letting it set to cool off is bad on the metal.
You may have had it too hot. You picked up hydrogen.
If your not interested in the beeswax or pills then Intried and this is all I will have to say.
My foundry books all say to pour cast iron with like a begining swirl so the iron turns.
When I pour aluminum, I pour fast enough the sprue stays full, till the mold is full. I bottom fill the mold too.
The book on pouring aluminum has much said on gating and pouring techniques, as well as temperature. It leads me to believe there is more science in aluminum than one would think.
Since I do not make critical castings, for temperature control, I just melt all without it setting and pour when the aluminum flips off the slagger. I used a pyrometer at one time. But unless you have new aluminum with known numbers, you won't know what temp to pour at anyway.
The pouring temperature of aluminum is some what critical, as is the speed according to the manual.
With the taller sprue, I mostly pour cast iron and brass, the mold fills better. I do see people pour with a sprue only 3" tall. Once I started using taller sprues, I had more full pours.
When we send patterns to the ductile foundry, they say plated patterns must not have any gating attached.
Believe it or not, gating in ductile and cast iron makes a difference in the way the iron solidifies and changes the chemical make up. Similar to using a chill to create hard surfaces in cast iron castings.
Over heating aluminum and then letting it set to cool off is bad on the metal.
You may have had it too hot. You picked up hydrogen.
If your not interested in the beeswax or pills then Intried and this is all I will have to say.
After I cast the aluminum, it takes about two hours to cool off enough to handle without gloves. am I not supposed to let it cool off on its own? Does it need to be quenched with water somewhere along the way.?
One consideration that Bob Puhakka harps on is bifilms in aluminum castings.
For hobby work, perhaps bifilms are not critical, but they are critical for structural aluminum castings.
Aluminum creates an oxide skin as it solidifies, and this oxide film is formed on the outside of the metal as it flows down the sprue, flows through the runner(s), and then through the gates.
The idea is to have the a laminar flow through the system, where you are letting the oxide film form on the outside of the flow, but not churn or fold the flow.
Any abrupt turns in the sprue/runner system should avoided, and there should be no abrupt changes in section.
A pour temperature of 1,350 F is a good starting point for aluminum 356 alloy.
You can then tweek the temperature slightly higher or lower for unique situations, such as large thin parts that need a hotter melt in order to fill completely.
If the velocity of the metal is not controlled, then you can have the aluminum shoot into the mold like a spraygun, and bounce off the back wall, which churns air, slag, sand, and bifilms into the metal. You can see this in the mold fill simulations on ytube.
Gray iron is infinitely easier to cast in my opinion than aluminum, since it does not seem to be susceptible to porosity/gas issues, and I have never been able to overheat/superheat iron with an oil burner.
Gray iron does take a lot more heat to get to pour temperature than aluminum.
Aluminum is somewhat forgiving as far as exactly how you set things up.
I have seem some pretty odd and unorthodox spure/runner/gate configurations that worked fine.
On the other hand, there is no reason why you can't fully understand the process, and only use the arrangement needed for the casting to succeed.
Sometimes it is hard to generalize about things like spure height without having an exact application.
I have seen our member luckygen (what is his screen name here ?, ironman ? I forget), and he casts all sorts of shapes and sizes with a low sprue, and I do the same.
Not to say you will never need a tall sprue, but it makes you wonder if they can use a short sprue, then perhaps you may be able to do it to if you follow their method.
There is really no one-size fits all in the casting business though; much of it is finding something that works for your particular application.
With gating, generally you want the gate at the thickest/largest part of the casting, or in the cast of a plaque, you use a long thin knife gate or gates.
The risers will dictate what parts of the casting solidify last, if risers are used.
I use an oversized runner, and in that case, the gates can act a bit like a feed from a riser.
The gate will generally freeze and block a riser though, if the gate is too small.
I like to bring in a very large gate from a riser, generally a large circlular gate, like 3/4" diameter if possible.
You should not try to fill a thick mold cavity section from a thin section; fill the large cavity first, and then fill the thinner sections.
John Campbell has a good section in his 10 rules for good castings, and it discusses solidification, and how solidification must progress across a casting in a uniform and controlled manner, else you will have two molten setions connected with a solid section, and the casting will pull itself apart when cooling.
One key to machinable iron castings is to cool them as slowly as possible.
Some will actually place insulating blankets over the molds, to slow the cooling, and to maximize dispersion of the graphite evenly throughout the casting.
As far as degassers and additives, you can always try anything.
Beware of the pool shock fumes; those are deadly.
I and others tried the washing soda for a degasser, and the person who was pushing that on ytube was absolutely convinced beyond any doublt that the washing soda was degassing his aluminum.
I and several others experimented with heating the washing soda to drive off moisture, and we all found that washing soda has no affect on degassing aluminum.
There is nothing wrong with trying something like beeswax, but I highly recommend doing a comparison of identical melts/pours, and if you don't notice any difference in the castings, then don't waste your time on beeswax.
If the beeswax does work, post the results here so we can learn that trick too.
.
For hobby work, perhaps bifilms are not critical, but they are critical for structural aluminum castings.
Aluminum creates an oxide skin as it solidifies, and this oxide film is formed on the outside of the metal as it flows down the sprue, flows through the runner(s), and then through the gates.
The idea is to have the a laminar flow through the system, where you are letting the oxide film form on the outside of the flow, but not churn or fold the flow.
Any abrupt turns in the sprue/runner system should avoided, and there should be no abrupt changes in section.
A pour temperature of 1,350 F is a good starting point for aluminum 356 alloy.
You can then tweek the temperature slightly higher or lower for unique situations, such as large thin parts that need a hotter melt in order to fill completely.
If the velocity of the metal is not controlled, then you can have the aluminum shoot into the mold like a spraygun, and bounce off the back wall, which churns air, slag, sand, and bifilms into the metal. You can see this in the mold fill simulations on ytube.
Gray iron is infinitely easier to cast in my opinion than aluminum, since it does not seem to be susceptible to porosity/gas issues, and I have never been able to overheat/superheat iron with an oil burner.
Gray iron does take a lot more heat to get to pour temperature than aluminum.
Aluminum is somewhat forgiving as far as exactly how you set things up.
I have seem some pretty odd and unorthodox spure/runner/gate configurations that worked fine.
On the other hand, there is no reason why you can't fully understand the process, and only use the arrangement needed for the casting to succeed.
Sometimes it is hard to generalize about things like spure height without having an exact application.
I have seen our member luckygen (what is his screen name here ?, ironman ? I forget), and he casts all sorts of shapes and sizes with a low sprue, and I do the same.
Not to say you will never need a tall sprue, but it makes you wonder if they can use a short sprue, then perhaps you may be able to do it to if you follow their method.
There is really no one-size fits all in the casting business though; much of it is finding something that works for your particular application.
With gating, generally you want the gate at the thickest/largest part of the casting, or in the cast of a plaque, you use a long thin knife gate or gates.
The risers will dictate what parts of the casting solidify last, if risers are used.
I use an oversized runner, and in that case, the gates can act a bit like a feed from a riser.
The gate will generally freeze and block a riser though, if the gate is too small.
I like to bring in a very large gate from a riser, generally a large circlular gate, like 3/4" diameter if possible.
You should not try to fill a thick mold cavity section from a thin section; fill the large cavity first, and then fill the thinner sections.
John Campbell has a good section in his 10 rules for good castings, and it discusses solidification, and how solidification must progress across a casting in a uniform and controlled manner, else you will have two molten setions connected with a solid section, and the casting will pull itself apart when cooling.
One key to machinable iron castings is to cool them as slowly as possible.
Some will actually place insulating blankets over the molds, to slow the cooling, and to maximize dispersion of the graphite evenly throughout the casting.
As far as degassers and additives, you can always try anything.
Beware of the pool shock fumes; those are deadly.
I and others tried the washing soda for a degasser, and the person who was pushing that on ytube was absolutely convinced beyond any doublt that the washing soda was degassing his aluminum.
I and several others experimented with heating the washing soda to drive off moisture, and we all found that washing soda has no affect on degassing aluminum.
There is nothing wrong with trying something like beeswax, but I highly recommend doing a comparison of identical melts/pours, and if you don't notice any difference in the castings, then don't waste your time on beeswax.
If the beeswax does work, post the results here so we can learn that trick too.
.
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Aluminum is different than gray iron when cooling.
The rule is to cool gray iron as slowly as possible, unless you deliberately want a hard casting, such as for high abrasion/wear conditions.
Aluminum can be removed from the mold as soon as it is solid, and can be quenched in cold water with no ill effect.
Perhaps one consideration is that a cold water quench may cause a bit of distortion, but I have not noticed that.
The process for tempering 356 aluminum to an aporoximate T-6 level is to heat it to about 1,000 F for 8 hours, then immediately quench it in water (hot or cold), then an hour or two in the oven at about 400 F.
The T-6 temper gives a harder aluminum that is not nearly as prone to loading up tool bits.
I really like the T-6 temper I have used, but one really needs a digital kiln control to accurately do the first stage of a T-6 temper, and it is a bit of added work.
Edit:
Some report getting a bit of hardening of the aluminum casting with just a quench right out of the mold, when the casting is still hot.
It is worth trying an immediate water quench, just to perhaps get a harder casting, and not have so much tool bit loading.
If you quench a hot iron casting, you probably will not be able to machine it, even with carbide toolbits.
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You can have severe shrinkage problems in gray iron if you use too much ferrosilicon.
Excess ferrosilicon causes hot tears in the iron as it cools, from excessive shrinkage.
It takes a very exact small amount of ferrosilicon in gray iron to make thin parts machinable, and to avoid hot tears.
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Excess ferrosilicon causes hot tears in the iron as it cools, from excessive shrinkage.
It takes a very exact small amount of ferrosilicon in gray iron to make thin parts machinable, and to avoid hot tears.
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Fun fact: from what I can remember, gold seems to behave in an opposite fashion. If you quench gold after casting, while it is a dull red in the dark with water, the atoms, freeze and become irregularly aligned rather than in a strong lattice type of structure. This renders the gold, more malleable and ductile…
Copper can be annealed (softened) by heating it.
I am not sure what quenching does to copper.
I try to stick with a very narrow set of metal types, since you have to learn the quirks of each.
I use Class 40 gray iron, lead-free bearing bronze, and 356 aluminum.
I pretty much know what to expect from casting those.
Any other metal type is a wildcard for me, with unpredictable results, and so I generally avoid anything but these three types.
I do have a significant amount of boat shaft bronze.
It machines like steel, and makes the worst bearings material possible due to the very high stiction factor.
I don't know what to do with the boat shaft bronze, but I feel the need to use it for something; a boat anchor perhaps.
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I am not sure what quenching does to copper.
I try to stick with a very narrow set of metal types, since you have to learn the quirks of each.
I use Class 40 gray iron, lead-free bearing bronze, and 356 aluminum.
I pretty much know what to expect from casting those.
Any other metal type is a wildcard for me, with unpredictable results, and so I generally avoid anything but these three types.
I do have a significant amount of boat shaft bronze.
It machines like steel, and makes the worst bearings material possible due to the very high stiction factor.
I don't know what to do with the boat shaft bronze, but I feel the need to use it for something; a boat anchor perhaps.
.
After you pour a casting, there is usually some aluminum remaining at the bottom of the crucible. Do you keep that there for the next heat up/pour or do you remove that and put fresh aluminum in the crucible?
