Aluminum sand casting for Chenery Gnome Rotary

[albd5a]

A taller sprue increases the velocity of the metal, which is not what you want.
When I started backyard casting, I used very tall sprues, and one of our members (luckygen) illustrated that you don't need a tall sprue extending above the top of the cope at all.
These days, the top of my sprue is at the top of the cope (mold), and I use a 1" tall piece of pipe as a catch ring at the sprue.

I keep the lip of the crucible as close to the top of the spure as possible when pouring, even touching the top of the spure.
You don't want a waterfall effect, since that churns air and slag into the melt.

I heat my aluminum as fast as possible, being careful not to overheat the metal, and also pouring immediately when pour temperature is reached.
If you let the alumimum linger at or over pour temperature, it will absorb a lot of hydrogen.
I don't use any flux with aluminum.
The flux that I have heard that works with aluminum is pool shock, which creates some extremely toxic gas (nerve gas I think), and I would not recommend using that.
I have also see some on ytube recommend using washing soda, but that has no effect on aluminum, and several folks including myself have proven that. If you back the washing soda in the oven and drive off the moisture, then you will see that it just sits on top of molten aluminum and does absolutely nothing. It will not even mix with molten aluminum.

Aluminum castings will not be brittle just because they have some porosity from hydrogen.
Hydrogen porosity shows up as pinholes in the metal surface.
If the casting will be painted, you will not see the pinholes.
Even if the casting is not painted, the pinholes are not very noticeable.

You can use an inert gas bubbled through the molten aluminum to degas it, such as argon I think.
Best thing to do is just heat the aluminum as fast as possible, and pour immediately at 1,350 F.
This is what I do, and I don't use any flux, and I don't have porosity.

I will start a thread to show my aluminum casting gaffes, when I started trying backyard casting in 2011.
There is no need for anyone to repeat my mistakes.
I became an expert and finding every conceivable casting mistake that could be made, before I got it figured out.
.

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?

 

[Fidlstyks]

No, I did not use any flux. I saw somewhere, someone, said that he did not use any. My castings look sparkly clean, but I haven’t mentioned and Aloo the internal areas yet… As far as flux what about borax? Wow, beeswax really I know I saved the water of that somewhere, how much beeswax would you put in for about 2 pounds of aluminum?

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.

 

[albd5a]

Borax destroys crucibles very quickly.
People obsess about using flux with aluminum, and often try to solve a problem that they don't even have.
My recommendation would be to not try to solve problems that you don't have.
I have never used flux with aluminum, and the only problem I had was overheating the melt, and letting it sit for several minutes at pour temperature before pouring, which caused pinhole porosity, but still a usable casting.

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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?

 

[albd5a]

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?

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?

Photos:

 

[GreenTwin]

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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[GreenTwin]

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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