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Ash

It's all about the crucibles

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Hi all 

 

I'm new here and i'm just starting out doing as a hobby at the moment but also getting in to metal melting as as a plumber i have a lot of scrap copper brass and iron that a bugger to store unless i melt it down but my question is is all about the Crucibles.

i have notices theirs two types 

Graphite  and ceramic

for what i'm melting to be reformed what is best?

i'm a tad bit lost also going on a whim here and hoping that you all know about this

thanks

Ashley

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This isn't an answer to your question but unless you have the appropriate breathing apparatus, don't try melting any brass.  The fumes from the molten zinc in it can be lethal.

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I second Gary on the zinc fumes.  Nasty stuff.

As for crucibles, clay-graphite are the cheapest and work okay once you get used to them.  They must be "tempered" before use, which means put in a cold furnace and then slowly raising the temperature to your planned maximum, holding for an hour, and shutting down the furnace leaving the crucible in place until cold.  They are somewhat fragile, so properly fitting crucible tongs are a must.

Pure graphite is the most expensive, doesn't need tempering before use, and is the sturdiest.  It will be hard to find a pure graphite crucible big enough for your wants at a price that's affordable.

That leaves silicon carbide.  They cost twice as much as clay-graphite, but don't require the tempering step and are less fragile.

What sort of stuff are you wanting to make?

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Gary i'm sporting one of the bad boys https://www.protectivemasksdirect.co.uk/moldex-reusable-half-mask-respirator-protection-moldex-7000?gclid=CjwKCAiA6qPRBRAkEiwAGw4SdgCq5-DiG9XGZzxUax8_GRjQNtxOWTctpylCil1S-zKU_XI80SzrnRoCfvIQAvD_BwE as i'm in roof spaces a lot and the chemical cartridge are £10 a pop and are a 4 week life span so i'm all good.

 

Alan just to start i'm going to melt down copper to get it clean then into ingot to store then the iron may just tinker and see what i can do with it. I have steal thredded bar i may try and make into knife of some sort in the Christmas shut down at work. May also look at casting iron fittings and aluminium

unless there a section for what to make first to text page i have mist would also be interested i would in?

 

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Well, there's a couple of "how to get started" posts here and there, but no real "what to make first" section.  We kind of leave that up to the person involved.  

One thing about pure copper: it LOVES oxygen.  I mean, to the point that in an open crucible it turns almost foamy with holes.  Standard practice if you don't have an inert gas shielded vacuum furnace (no, I don't know anyone who does either ;) ) is to use a lidded crucible and/or a heavy layer of powdered charcoal on top of the charge in the crucible to keep out the oxygen.  

Hopefully Jeroen will see this and chime in, he's a very experienced caster of copper and bronze.  I just do pewter, which is a lot more user-friendly.

Oh, and don't use the same crucible for a different alloy.  In other words, if you do the iron, use a new crucible, not one that's had copper in it.  And vice-versa.  

What's your heat source situation?

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I'm using MAPP gas as my main heat would adding borax to the copper not work the same way? 

also making a small refractory out of an old expansion vessel from work as it is a good fit for what i want just need cutting and a few legs adding  

and thanks didn't know i would need different crucibles for different metal :o

 

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I can confirm that the silicon carbide crucibles are the sturdiest. They can last hundreds, if not thousands of castings. Just don't cool down the metal inside the crucible, but poor it out in ingot moulds. Some people use baking trays, then find out why experienced people use more proper ingot moulds (hot copper or copper alloy dissolves steel). 

If you do have a proper way to protect yourself from breathing in zinc, lead and other nasty fumes, then if you want to melt and cast brass, you must be careful not to overheat it. Same goes for copper b.t.w.  If it's liquid, poor, don't leave it molten for long. In general, the longer you heat it, the more gasses it will absorb. But with brass, it will turn into some sticky dross, that seems to appear faster then you can scoop it out.  And you get a bright white flame, yellow zinc oxide deposits everywhere.

There's not a lot you can do for copper to take up oxygen, except to keep the environment as oxygen free as possible. Like Alan suggests, let charcoal float on top, and keep a lid on it. And keep you furnace environment reducing. I've heard from professional casters that borax doesn't help much in shielding copper. Don't know why though. Probably won't hurt adding it. 

 

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Ok thanks for all the info cant wait to get melting just waiting for everything to get here and then off i go 

if there any other useful pointers i'm all ears 

 

Thanks 

Ashley

 

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A MAPP torch?  Probably won't get hot enough.  A proper burner (see the two pinned burner threads down in the Tools and Toolmaking forum) and a properly insulated furnace are needed for any melt big enough to need a proper crucible.

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Mapp gas burns at 2020 C copper melts at 1080 C i have 2 torches so going to make 2 inlets for the burners one on each side so in theory that should do it  and i'm doing in in a 4 inch crucible just got with 1 inch clearance on each side so not a lot of air to heat around the crucible im using fire cement that going to be 2 inch think and then ceramic fibre around the out side of that  so hopefully will do it if not off to the yard and grabbing the big acetylene torch

 

Edited by Ash

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Oddly enough, acetylene is too hot.  It'll melt the wool almost instantly, and might crack the crucible.  Try the MAPP first.

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I should add, it would be best to do two layers of wool topped by a fairly thin layer of cement.  The wool insulates, the cement just absorbs heat.

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MAPP burns about 30% hotter than propane (and costs about 30% more).  The reason a propane burner is recommended is because you can buy a bigger tank of propane (easier to buy one at least) and build/buy a bigger burner.  Plumbing style soldering torches have a hot enough flame, just not generally a big enough flame.  

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10 hours ago, Gary Mulkey said:

This isn't an answer to your question but unless you have the appropriate breathing apparatus, don't try melting any brass.  The fumes from the molten zinc in it can be lethal.

 

10 hours ago, Alan Longmire said:

I second Gary on the zinc fumes.  Nasty stuff.

Slightly off topic, but this popped into my head when I was looking at the responses. So never made any Mokume Gane, so got to ask, when working on Mokume Gane is this a concern, as well???

I have a real heavy Brass threshold that came out of an old New Orleans style mansion. I have used a piece or two over the years but have thought about cutting up and melting some of it the making of Mokume Gane. 

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No, mokume is never hot enough to worry about zinc fumes.  By the time you got there you'd have a puddle ibstead of a stack. ;)

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