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Crucible Sizes?



 
 
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  #1  
Old July 14th 09, 05:14 PM posted to rec.crafts.jewelry
Muso
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Posts: 10
Default Crucible Sizes?

Hello, folks. The last time I posted here, I was casting zinc arrow
heads. Recently, I have been hanging out with lead bullet casters.
And now it looks like I need to learn how to cast brass. The reason
is because I want to build a bottom-pour pot.

I already know from experience that when working with zinc, I need to
deal with the dross in one way or another, and, when working with
lead, I guess I will run into the same problem. Anyway, I have
decided to try to build a bottom-pour pot, in order to deal with the
dross problem.

What I have in mind is to melt some brass, and then to pour it into an
open mold, the bottom of which will be the bottom of my cast-iron
melting-pot, on the out side of the pot. The sides of the mold will
be something like a tinker's dam, I guess you could say. I will clean
the bottom of the pot first, because, of course, I want the brass to
stick to the bottom of the pot.

After I've got a big lump of brass which is stuck to the bottom of my
melting pot, I will then drill a couple of holes through it, to give
me my spout, and my valve (with a bolt, to finish the valve).

Okay, so the problem is that I will need to select a crucible which
will be the right size for me to melt the brass, and then, by the way,
I will design a furnace to fit the crucible. I will be firing with
charcoal.

Okay, so can somebody give me an idea about crucible sizes? I really
don't have a clue!

Two states have already outlawed lead wheel weights, and I want to get
some lead casting in while I can.

Mike Mandaville
Austin, Texas
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  #2  
Old July 14th 09, 05:27 PM posted to rec.crafts.jewelry
Peter W. Rowe[_2_]
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Posts: 115
Default Crucible Sizes?

On Tue, 14 Jul 2009 09:14:20 -0700, in rec.crafts.jewelry Muso
wrote:


Okay, so can somebody give me an idea about crucible sizes? I really
don't have a clue!


Um, not to state the obvious, but your crucible needs to be large enough to hold
the amount of brass you're melting...

Since you've not given us that information, how can we give you more?

This isn't complex. Crucibles don't come in millions of sizes. Find a supplier
of the types of crucible you're planning to use, and pick a size from their
offerings that is large enough...

Many crucibles sold for jewelry melting will specify their size in capacity for
a certain weight, of a given metal. To convert that to capacity for a different
metal, like brass, divide the original capacity figure by the specific gravity
of the metal they're using as the specification, and then multiply that result
by the specific gravity of the metal you will use (brass). The result is the
crucible's capacity in a weight of brass.

Beyond that, you need to choose a crucible material. Choices include solid
(machined) graphite, a clay/graphite mix (black crucibles, but not machined,
more like a clay pot in how they're made) or various sand/clay mixes, or the
higher temp fused silica ceramics. I'd guess one of the cheap clay/sand types,
or clay/graphite ones, would work fine.

Also. If you wish your poured brass to fully adhere to the iron pot, you'll
need to do more than just clean it. molten brass poured onto cold iron will
seperate again, because of thermal shrinkage as the brass cools. Even with good
bonding from the brass "wetting" the iron, this may be an ongoing problem in
use. But with a good active soldering flux on the iron (after cleaning), and
preheating the iron before pouring the brass, the two should braze together. You
may wish to experiment a bit with a small piece of cast iron first, to be sure
this will work. It's not as straight forward as it may seem. Cast iron can be
tricky stuff to bond to. One potential solution, maybe, would be to not rely
totally on metal/metal bonding, but rather, to also drill and tap a couple screw
holes from inside the pot into the brass, and hold the two together with a
couple screws too.

Or, you could just go and buy a bottom pour crucible... They're not all that
expensive, last time I looked. Which was a while ago...

Peter
  #3  
Old July 15th 09, 03:34 AM posted to rec.crafts.jewelry
Abrasha
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Posts: 298
Default Crucible Sizes?

Muso wrote:
Hello, folks. The last time I posted here, I was casting zinc arrow
heads. Recently, I have been hanging out with lead bullet casters.
And now it looks like I need to learn how to cast brass. The reason
is because I want to build a bottom-pour pot.

I already know from experience that when working with zinc, I need to
deal with the dross in one way or another, and, when working with
lead, I guess I will run into the same problem. Anyway, I have
decided to try to build a bottom-pour pot, in order to deal with the
dross problem.

What I have in mind is to melt some brass, and then to pour it into an
open mold, the bottom of which will be the bottom of my cast-iron
melting-pot, on the out side of the pot. The sides of the mold will
be something like a tinker's dam, I guess you could say. I will clean
the bottom of the pot first, because, of course, I want the brass to
stick to the bottom of the pot.

After I've got a big lump of brass which is stuck to the bottom of my
melting pot, I will then drill a couple of holes through it, to give
me my spout, and my valve (with a bolt, to finish the valve).

Okay, so the problem is that I will need to select a crucible which
will be the right size for me to melt the brass, and then, by the way,
I will design a furnace to fit the crucible. I will be firing with
charcoal.

Okay, so can somebody give me an idea about crucible sizes? I really
don't have a clue!

Two states have already outlawed lead wheel weights, and I want to get
some lead casting in while I can.

Mike Mandaville
Austin, Texas


After about 30 seconds of searching I found you a bottom pour melting
pot for $56.95 at http://tinyurl.com/m9zedt

Do you really think that you can make your own melting pot, by way of
making your own furnace first to melt the brass, for less than $56.95

The materials alone will cost you more. And how many hours are you
willing to waste to get you a result that will not work nearly as well
as that pot I just showed you?

As you said yourself, you really don't have a clue.

Oh, and to answer your question re. the size of the crucible. Have you
possibly considered for a moment, that it should be big enough to hold
the amount of brass that you plan to melt.

--
Abrasha
http://www.abrasha.com
  #4  
Old July 16th 09, 05:33 PM posted to rec.crafts.jewelry
Mr G H Ireland[_2_]
external usenet poster
 
Posts: 16
Default Crucible Sizes?

In article , Abrasha's reply
included, from anothher poster:

"Two states have already outlawed lead wheel weight"


So I ask, slightly off topic: What are using,then, uranium?

Regards to you all, G.H.Ireland

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/ \._._ |_ _ _ /' Orpheus Internet Services
\_/| |_)| |(/_|_|_ / 'Internet for Everyone'
_______ | ___________./ http://www.orpheusinternet.co.uk


 




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