The Home Machinist!

Thanks to all who offered suggestions when my first pouring of an aluminum sundial failed miserably.
In doing my second test pour, I made the following modifications:
1. Made a batch of green sand.
2. Opted not to try and cast the gnomen (triangle top part) at the same time.
3. Liberally vented with a piece of 1/16th hanger wire.
4. Use a 2" square peg for the pouring hole.
5. Used a pipe 'funnel' to pour the molten aluminum into the hole.
6. Used a digital thermometer, and only poured when the aluminum reached 1400 degrees.
NEW problem: How to remove the 2" pouring sprue on the back of the dial...

Chet
That looks real nice!! I guess you did not use foam this time or did you?
To get the spruce off a hack saw or coping saw will do it. I think my hack saw has 18 teeth per inch and will eat through the spruce fast.
More teeth per inch for thin things and less teeth for thick things works good.( I had it backwards so I corrected it, got it right this time on the teeth count))
A small die grinder with a sanding pad will clean off whats left of the saw marks. If you have a wood rasp that will help clean off boogers on the casting.
Norman

Yes, it's still the foam, but just plain foam... No drywall mud.
I should have mentioned that!!!!

Whatever you did, apparently worked well enough. Top temps for Aluminum is around 1600, beyond that it tends to radically alter the finer additions of the alloy. Rule of thumb is 50 to 75 degrees over fluid temp, with minimum hold time. Melt fast, pour fast. A trial run as you have will tell you if you need more temp or not. Usually the problem is with thin sections or webs freezing out.

As far as cutting the sprue, or head, a recip saw on a strip of sheet with a long flexible wood blade can do a quick job on aluminum with a little patience to get the blade laying right. Dont rush it, it can jam on the pull stroke. You can get pretty close and finsh with a hand belt sander.

Looks nice by the way.

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Big Dave

Be Alert! The world needs more Lerts.

That is reversed, more teeth for thin, fewer teeth for thick.

Rule: minimum of three teeth in contact with metal, to avoid overloading the tooth strength.

Fewer teeth allows a deeper gullet to store swarf/chip with out overloading gullet during cutting stroke.

Ray

yep, 3 teeth, like granma. Or was that my first dates Mother? Never mind.

Uh forgot to mention, overheated aluminum that gets where it goes before cooling in the runners shrinks like crazy and causes sinks in the heavy or double thickness of the castings, because the aluminum gets slushy early and will not flow down to fill the shrinkage.

If you run into the problem of shrinks at webs or other junctions, try a diferent metal type or even move the web joints apart a bit, to limit the shrink. Depends on what you are doing.

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Big Dave

Be Alert! The world needs more Lerts.

The first aluminum foundry I worked in, we would try to pour at 1440 deg.

Exactly the point. Low fluidity can be from low silicon or high iron content, neither can be overcome by higher temperatures.

Home guys have the problem of wild scrap, and bolts and rivets, that disolve into the melt. No foundry I know of would use general scrap for its pours, only bar metal with analysis. Then temperature control is more critical and beneficial.

Thanks for the input.

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Big Dave

Be Alert! The world needs more Lerts.

Streamin10 I have worked in 4 foundries and in the last 3 years in owning my own shop, I am in and out of foundries a few times a week. I think it all depends on the castings you are making. If you need a specific alloy then we would use specific bar stock. But a lot of times if you are pouring something that you dont need to machine or its not structural, I have seen a lot of scrap go into a furnace. When I worked for Ford Mo. Co. in there foundry, they would put train loads of scrap in the furnace.Each batch would be tested ,but when you are melting thousands of pounds of metal you cant help but use scrap.

Not the same. Any large production foundry has the ability to make additions for chemistry according to analysis. Small foundries do not have that ability, and just pour numbered bar metals. (Ingot stock). What home guy has the ability to tell me he has any numbered alloy, by looking at it. It was not really the point of this thread.

We have a guy trying to pour some stuff at home, and his first try was a learning experiment. He is much like I was some time ago. I offer what I learned the hard way.

I would ask you how Ford an other major cyclers of aluminum control the iron content.

Were they using permanent mold or sand processes? Which sand process?

I never worked in an aluminum or brass foundry. Just my home shop.

A pair of freight trucks in 7.5 gauge are structural, aren't they ?

Do you make any patterns for steam engines? If so what?

I have many questions. In hand pouring, are round runners better, than cubic?

Contact me offline if need be.

_________________
Big Dave

Be Alert! The world needs more Lerts.