Avoiding Problems when Casting Aluminum

[GreenTwin]

Here are a few problems I ran into when I was learning to cast aluminum 356.
Aluminum alloy 356 is what is commonly used to make aluminum castings.
Aluminum cans are often seen melted on ytube, but that is not really a good casting allow, in my opinion, and residual moisture inside the can can cause an explosion in the crucible.

I started learning how to cast aluminum in 2011, and a lot of it was trial and error.
You can hopefully avoid these mistakes.
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[GreenTwin]

First Aluminum Pour - 06-20-2012:

I was really anxious to try to melt metal, and so I cobbled together a temporary furnace, and melted some aluminum 356.
I started making a flywheel pattern, and had the spoke pattern ready.
I also cut a simple round disk out of wood.

I used an open-face pour, and as I mentioned, I just wanted to see if I could melt and pour something/anything.
This was my first pour.
Not bad for a first pour, but had a few problems, and surface finish was a bit rough.
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[GreenTwin]

2nd Aluminum Pour - 2012:

This was my 2nd aluminum pour, and I attempted to cast the flywheel for the green twin oscillator in aluminum.
I saw one one of the backyard casting forums that an alcohol-based ceramic mold coat could be sprayed onto the interior of the mold, and burned off.
This type of mold coat is intended for bound sand molds, and perhaps some greensand molds, but definitely not desiged for use with oil-based sand.
Looks good on top, disaster on the bottom.
Lots of flash between the mold halves, perhaps caused by the alcohol flashing when it got hot and vaporized.

I used an absurdly tall sprue, because that is what many on the internet told me to use.
There is a ton of bad casting information on the internet; almost everything that is commonly accepted/recommended is wrong.
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[GreenTwin]

3rd Aluminum Pour - Flywheel Attempt #2:

This was my 2nd attempt to cast an aluminum flywheel, and this produced a usable flywheel.
I gave this flywheel to a friend because I wanted to cast this flywheel in gray iron.

One again I used an absurdly tall spure, because that is what "they" said to do.
This one had a bit more flash than I like to see, but I was able to clean that up.

Some pinhole porosity caused by letting the melt sit at pour temperature for a few minutes before pouring.

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[GreenTwin]

4th Aluminum Pour - Engine Base -2012:

This was my 4th aluminum pour.
I tried using some automobile rims, but cutting those up was extremely difficult.
I ended up purchasing 356 aluminum ingots from a member here.

Nobody told me that the hydraulic forces could cause the cope to lift off the drag, and cause a runout.
I should have had weights on top of the mold.

And I purchased some sand from the hardware store to make the sodium silicate bound core, and it was too coarse.
Hardware store sand often has a lot of moisture in it, and this can cause problems.
Commercial foundry sand such as OK85 is very fine round grain sand, and apparently it is baked to get it very dry.

I did not secure the core to the drag mold, but miraculously it did not float, for some reason.
The mold halved did separate, causing a runout.

The pour temperature was perhaps a bit on the high side, but the top of the casting had pretty decent surface finish.
The interior of the casting had a terrible surface finish.
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[GreenTwin]

5th Aluminum Pour - 2012:

I wanted to make a cast frame for one of my dad's little wobbler engines, and so I came up with this pattern, and cast two of these.
At the time, my engine making skills were very limited, and so I never actually used these frames.
I was learning model engine design, machining, and foundry work all at the same time, and was new to all of it.
This was more of a learning exercise than anything.
I had no clue about the correct way to place the sprue, runner(s), gates, riser(s), etc.
The thin spike was a vent hole out the top of the mold.

 

[GreenTwin]

6th Aluminum Pour - 2012:

My brother's friend wanted to see a casting demonstration, and so I decided to cast a flywheel.
I had done very little casting work, and did not have a good feel for it all yet.
I accidentally reverse the cope mold 180 degrees on top of the drag mold, and so the two mold halves were offset.
I also got a large amount of flash between the molds, probably from reversing the cope and not having an exact fit due to that.

The surface finish was ok.
My brother's friend was not impressed.
I was a bit embarrassed since I had never had anyone watch me do foundry work, and at the time, I had very little experience.

The lesson I learned was to use a 1/4" diameter flask pin on one side of the flask, and a 3/8" pin on the other side, so that it would be impossible to make this mistake again.
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[GreenTwin]

7th Aluminum Pour - 2012:

This was the 2nd attempt to cast the green twin engine base.
I used a large weight on top of the molds.

I was using a follower board for this pattern, and someone on a casting forum asked "Why are you using a follower board?".
The answer was that I did not know what I was doing, and so I assumed that I needed a follower board, but actually I did not need it.

I omited the sodium silicate bound core, and molded the underside with oil-based sand.

This time I poured too cool, and so I got a partial mold fill, which I think is called a cold shut.
I discovered that I really needed to keep records of my pour temperature, so that I could figure out what the best pour temperature is for aluminum.
A pour temperature that is too cold gives a partial mold fill, and a pour temperature that is too hot gives a rough surface finish.

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[GreenTwin]

8th Aluminum Pour - 2012:

I upped the pour temperature on this pour, and got the temperature too high, so the surface finish was very rough.
The aluminum started to burn its way into the oil-based sand.

This was a trial-and-error method, with the unintentional emphasis on "error".

I still had no idea about gates, risers, etc.
I should have used one or more knife gates on this piece.
I did get a complete fill.
There was some undesirable flash on the bottom of the casting, as well as some inclusions that left holes in the surface of the casting.

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[GreenTwin]

9th Aluminum Pour - 2012:

This was another flywheel casting attempt in aluminum.
I used another absurdly tall sprue.
The gate leads directly into the mold at the rim, and while I see this often in the backyard casting world, technically, I think it would be better to have a runner shaped like a horseshoe around the flywheel, with a gate into either side.

Lots of flash, I am not exactly sure why I kept getting so much flash.

And the runner is way too long; it could have been 1" long.
The transition from the bottom of the sprue into the runner should have been smooth.
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[GreenTwin]

1st Cast Iron Pour - 2012:

This was my first gray iron pour attempt, and I made the mistake of using oil-based sand, which caused a few sand inclusions.
I later cast this flywheel again using resin-bound sand, and it did not have any defects.
I was so proud of my first iron pour that I filled in the inclusion spots, and used this flywheel on my engine.
I was not really sure if this was a one-time partial success, or whether future attempts would be a failure.

This flywheel machined easily, even though I did not use any ferrosilicon in the melt.
At the time, I was not even aware of the need for ferrosilicon in iron melts, so I got lucky in that this casting was thick enough to not need ferrrosilicon.
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[GreenTwin]

1st Brass Pour - 2013:

This was the first time I tried to melt brass.
This was a plaque for a friend of mine's boat.
I found it difficult to get the brass up to pour temperature without burning out a lot of the zinc.
There were clouds of zinc fumes coming off the melt, with I avoided breathing.

I was not pleased with the results of this attempt, but it was a first brass attempt.

I used another hastily constructed furnace, and it was a very low quality affair that did not last very long.
I had a significant spill onto the concrete driveway, and contrary to popular belief, the concrete did not explode.
I have seen a video where someone spilled an entire large crucible full of brass/bronze onto the driveway, and that did cause a concrete explosion.

The oil-based sand did not work very well with these patterns, possibly because I did not have it mulled correctly.
I was fabricating equipment as I went, and made the lifting tongs, as well as a pouring shank.
I had to make a new pouring shank, since the retainer on this one did not actually retain the crucible very well.
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[GreenTwin]

2nd Brass Attempt - 2013:

This was a 2nd brass attempt.
I am not sure exactly what went wrong, but it was pretty much a disaster.

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[GreenTwin]

3rd Brass Attempt with Sodium Silicate Mold - 2013:

I tried to cast the plaques again, this time with sodium silicate bound molds.
The mold was better, but the casting quality was still pretty bad.
I had discovered OK85 foundry sand at this point, and you can tell what it is because it is white in color.

You can see porosity in the casting, and some brass/bronzes must be degassed.
I did not degas this melt.
It was at this point I decided that brass/bronze casting work was not for me.
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[GreenTwin]

1st Cast Iron Pour using Resin-Bound Sand - 2013:

This was my first attempt at casting gray iron in resin-bound sand.
The local art-iron folks used resin-bound sand extensively to make iron castings, and resin bound sand is specifically designed to work well with iron and steel castings.

I did not know about the limitations of runner length, and so I just put all the pieces into one long mold.
The problem with a long mold is that gray iron can only be heated to perhaps 2,500 F in an oil fired furnace, and that is not really hot enough to fill a very long mold like this.

I got a usable flywheel from this attempt, and a few bits and pieces.
I also discovered that thin gray iron castings will be "chilled", ie: they have the hardness of tool steel, and a certain amount of ferrosilicon must be added to the melt to avoid this condition.
I took the teeth off of a new Portaband blade trying to cut some of these thin pieces.

I was not sure if I would ever discover all of the endless ways to fail at making castings, but I was very new at it.

The flywheel turned out very well.
The 1st and 2nd flywheels I cast are pictured side-by-side.
The surface finish on some fo the castings was not good; I am not sure exactly why; perhaps I did not compact the sand well enough.
I used sodium-silicate cores on the cylinder, and those gassed (since I did not bake the cores to dry them) and caused large gas holes.
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[GreenTwin]

1st Red Brass Casting - 2013:

I decided to try and make permanent metal patterns of the green twin flywheel pattern halves, since the patterns were fragile.
I purchased some red brass, since it does not have the zinc boil-off issues that brass has.
Everything seemed to go well, but I did not use risers, and so I had a lot of shrinkage, which ruined these pattern halves.

I used an oil burner for this melt, instead of a propane burner, and while I got a much faster melt time, I think I also melted my furnace lining.
This mold was made I think from sodium silicate bound sand.
The surface finish was pretty good.
Sprue was still way too tall.

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[GreenTwin]

3rd Cast Iron Attempt - 2014:

This was my 3rd attempt to pour gray iron.
I got really serious about mold making, and used resin-bound sand for the entire mold.
I added runners on either side of the pattern, and used knife gates.
I clamped the mold halves together.
Unfortunately my poorly designed lid lifter failed in mid iron melt, and I could not get the furnace opened.
I saved this mold for later use with aluminum.
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[GreenTwin]

10th Aluminum Pour - 2014:

This was the mold from the iron melt attempt in the previous post.
I ended up pouring this in aluminum 356 allow.
The casting quality turned out pretty good in my opinion.

I used a round ceramic filter at the base of the sprue, and this flowed sufficiently to get a complete mold fill.
I have since begun using runners that end in a spin trap, and thus have eliminated the need for the ceramic filter.

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[GreenTwin]

11th Aluminum Pour - 2014:

I decided to back off a bit on the pour temperature, to try and get a better surface finish, but got an incomplete mold fill.
The only way to learn is to try things, and find out what does and does not work.
The pour temperature that I use for aluminum these days is 1,350 F.
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[GreenTwin]

12th Aluminum Pour - 2014:

I poured another base (I made two sets of castings for the green twin).

I was told by someone on a casting forum that I did not need to vent the top of the mold, and so I assumed that was correct information.
While you may not need to vent greensand due to its porosity, you do need to vent the high points of a resin-bound sand mold, as I found out.
I had a large trapped gas bubble in this casting, which was repairable, but I don't like to restort to repairing castings.
It is best to just make castings that do not have any defects.

The surface finish was good.
I cemented the two mold halves together with furnace cement, and that cement failed.
I still got a usable casting since the entire mold cavity was in the drag.
Lots of flash was created when the mold halves separated.

Luckily I was using a drain pan, and so did not get metal on the driveway; not that my driveway is worth conserving; its just the principle of not spilling molten metal all over concrete.
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