Casting Aluminum question

[Morgans[_2_]]

OK, so there has been a lot of talk around here, about casting aluminum for
VW heads. It was here that I first learned that you can not use iron
crucibles for melting aluminum.

So, what if you need to cast a little job for something that does not to be
a pure aluminum part, for a non-aircraft application, where strength is not
very important? Would it be good enough?

My part is a socket (retainer) to go on top of a tractor shift lever. Think
like a donut, with the inside of the hole shaped like would be formed around
the outside of a sphere, or half of it. It has a retainer that screws down
around the outside of the part, holding the shift lever and ball around it,
down onto the transmission.

I believe the metal part that needs to be replaced is/was made out of what
is usually called "pot metal." What the heck is that, anyway?

So, what do you all think? Contamination from a cast iron crucible OK for
this part?
--
Jim in NC

[Charles Vincent]

Morgans wrote:
> OK, so there has been a lot of talk around here, about casting aluminum for
> VW heads. It was here that I first learned that you can not use iron
> crucibles for melting aluminum.
>
> So, what if you need to cast a little job for something that does not to be
> a pure aluminum part, for a non-aircraft application, where strength is not
> very important? Would it be good enough?
>
> My part is a socket (retainer) to go on top of a tractor shift lever. Think
> like a donut, with the inside of the hole shaped like would be formed around
> the outside of a sphere, or half of it. It has a retainer that screws down
> around the outside of the part, holding the shift lever and ball around it,
> down onto the transmission.
>
> I believe the metal part that needs to be replaced is/was made out of what
> is usually called "pot metal." What the heck is that, anyway?
>
> So, what do you all think? Contamination from a cast iron crucible OK for
> this part?

Lots of people cast aluminum using steel pots. I don't -- but I spent
the money on a selection of graphite crucibles long ago and a big
carbide one as well. The steel "crucibles" will eventually fail with a
burn through (so will graphite for that matter , but there is a very
different event horizon).

Pot metal is generally some zinc alloy, like zamac. Decent strength,
easy pour, given to corrosion. Atlas used to make a lot of chrome
plated die-cast zamac parts for their tools, especially their lathe,
which they marketed directly and through Sears & Roebuck. When you
buy an old Atlas lathe, you have to make sure the gears, handles and
other Zamac doodads don't crumble. Sometimes it almost seems like the
chrome is filled with sand.

Seems to me I saw plans for a cupola furnace made out of flower pots
years ago and fired with BBQ briquettes -- no crucible required. Then
again, flower pots can be deadly too.

Charles

[Maxwell[_2_]]

"Morgans" > wrote in message
...
> OK, so there has been a lot of talk around here, about casting aluminum
> for VW heads. It was here that I first learned that you can not use iron
> crucibles for melting aluminum.
>
> So, what if you need to cast a little job for something that does not to
> be a pure aluminum part, for a non-aircraft application, where strength is
> not very important? Would it be good enough?
>
> My part is a socket (retainer) to go on top of a tractor shift lever.
> Think like a donut, with the inside of the hole shaped like would be
> formed around the outside of a sphere, or half of it. It has a retainer
> that screws down around the outside of the part, holding the shift lever
> and ball around it, down onto the transmission.
>
> I believe the metal part that needs to be replaced is/was made out of what
> is usually called "pot metal." What the heck is that, anyway?
>
> So, what do you all think? Contamination from a cast iron crucible OK for
> this part?
> --
> Jim in NC
>

Iron pots or crucibles are often used for melting aluminum. Coat it with a
clay or graphite slurry before each use for best results. Steel will work,
but will not last as long as iron, and coating is a must. Molten aluminum is
very corrosive to clean steel. Rust or blasting will help a clay based wash
adhere to steel or iron, where cast iron is usually rough enough as cast. I
personally prefer to allow new steel ladles to rust outside, then coat
regularly with a graphic based wash. I have never personally used cast iron.
All my crucibles are silicone carbide.

Drying is not terribly important after a wash if you are starting with cold
metal. The time and heat required to melt aluminum will dry the pot or
crucible long before you see molten metal. But if you are coating a ladle to
dip molten aluminum, adequate drying it's an absolute must.

Pot metal is usually just slang for die cast aluminum with high zinc
content. It makes it very difficult, if not impossible to weld, but I'm told
it flows well in high production die casting.