It's all about the crucibles - Bladesmith's Forum

Hi all 

For more information, please visit Foshan Osno.

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

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?

Gary i'm sporting one of the bad boys https://www.protectivemasksdirect.co.uk/moldex-reusable-half-mask-respirator-protection-moldex-?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?

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?

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 

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. 

Mapp gas burns at C copper melts at 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 December 7, by Ash

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.

If you are looking for more details, kindly visit Silicon Carbide Graphite Crucible.

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. 

When it comes to crucibles for melting metals, two common types are clay graphite crucibles and silicon carbide crucibles.

These crucibles differ significantly in their material composition, thermal properties, and durability.

Understanding these differences can help you choose the right crucible for your specific needs.

4 Key Differences Between Clay Graphite and Silicon Carbide Crucibles

1. Material Composition

Clay Graphite Crucibles: These crucibles are made from a mixture of clay and carbon powder.

Typically, they contain 30-50% clay and 50-70% carbon.

The clay provides structural integrity, while the graphite enhances thermal conductivity.

However, the presence of clay limits their maximum temperature resistance and overall durability compared to silicon carbide crucibles.

Silicon Carbide Crucibles: These crucibles are composed entirely of silicon carbide.

Silicon carbide is a compound that combines silicon and carbon.

It is known for its high strength, hardness, and thermal conductivity.

This composition allows silicon carbide crucibles to withstand higher temperatures and resist chemical erosion more effectively than clay graphite crucibles.

2. Thermal Properties

Clay Graphite Crucibles: These crucibles have good thermal conductivity due to the graphite content.

However, the clay component can limit their performance at extremely high temperatures.

They are suitable for a range of non-ferrous metal melting but may not be ideal for applications requiring very high temperatures or prolonged exposure to corrosive environments.

Silicon Carbide Crucibles: These crucibles excel in high-temperature applications due to their high thermal conductivity and resistance to thermal shock.

They can handle all kinds of non-ferrous metals and even medium carbon steel, making them versatile for various industrial melting processes.

3. Durability and Service Life

Clay Graphite Crucibles: Their service life is generally shorter than that of silicon carbide crucibles.

This is primarily due to the limitations in material composition and resistance to high temperatures and chemical erosion.

Silicon Carbide Crucibles: Known for their long service life, which can be 3-5 times longer than clay graphite crucibles.

Silicon carbide crucibles are more resistant to wear and tear from high temperatures and corrosive environments.

This makes them a more cost-effective choice in the long run for applications that require frequent or prolonged use at high temperatures.

4. Applications

Clay Graphite Crucibles: These are more economical and suitable for less demanding applications where high temperatures and corrosive environments are not significant factors.

Silicon Carbide Crucibles: These are superior in terms of thermal performance, durability, and service life, making them more suitable for demanding industrial applications.

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