Welcome Guest [Log In] [Register]
Welcome to Bronze Age Center. We hope you enjoy your visit.


You're currently viewing our forum as a guest. This means you are limited to certain areas of the board and there are some features you can't use. If you join our community, you'll be able to access member-only sections, and use many member-only features such as customizing your profile, sending personal messages, and voting in polls. Registration is simple, fast, and completely free.


Join our community!


If you're already a member please log in to your account to access all of our features:

Username:   Password:
Add Reply
What crucibles do you use ?; What do you think is the best crucible
Topic Started: Mar 1 2017, 01:47 PM (206 Views)
Rio van der putten
Member
[ * ]
I am trying to cast bronze for a while now but my crucibles always break. I have a cokes forge wich i use for some steel forging to but i like bronze better. I tried graphite crucibles, a carved out fire brick and a carved out alumina silicate brick. A clay graphite crucible is coming in today. But they keep breaking ! Can somebody help me and/or recommend a certain type of crucible?
Offline Profile Quote Post Goto Top
 
Jeroen Zuiderwijk
Member Avatar
Patron
[ *  *  * ]
Rio van der putten,Mar 1 2017
01:47 PM
I am trying to cast bronze for a while now but my crucibles always break. I have a cokes forge wich i use for some steel forging to but i like bronze better. I tried graphite crucibles, a carved out fire brick and a carved out alumina silicate brick. A clay graphite crucible is coming in today. But they keep breaking ! Can somebody help me and/or recommend a certain type of crucible?

It's not just the type of crucible but also how you heat them. You can't just blast full heat onto a ceramic crucible without it shattering. You'll create very high thermal stress in a brittle material. You have to heat it up gradually and evenly. Particularly a coke forge is about as destructive as you can get.

First of all you need to build a furnace not a forge. A forge is for forging, a furnace for melting and casting. A bronze age furnace is top blown, and uses shallow bowl shaped crucibles. The crucible and furnace type depend very strongly on each other. Later furnaces become side blown and eventually bottom blown, the latter with air inlets around the crucible. This has to be designed properly, or it won't work. And each furnace requires careful fire management, which can take quite a while to learn, particularly if you don't have someone showing how. It all comes down to ensuring the heat distribution is as even as possible all around the crucible, and you don't get cold spots where cold air blows against the crucible.

Back to the crucibles. For bronze age crucibles, you need to use a clay that can withstand high temperatures. This has to be tempered well with grog, sand and possibly a small amount of organic fibers (such as horse dung). This first needs to be fired well. Depending on size, that can take up to a full day to heat it up and fire it. When ready, still heat them up slowly and expect that they have a limited life, about 3 to 30 castings depending on type. Heat them up slowly. Let them warm up near the fire, when they get hot, put them in the fire, cover with fuel and let the fire get up to temperature before you blast air into it. Then carefully start blowing air to raise the temperature further. If the crucible has survived the first casting, place it back in the fire so it doesn't cool down to rapidly. At this point you can heat it up a bit faster, but still don't overdo it.

Modern clay/graphite crucibles are easier to use. But you still have to be gentile when heating them, especially the first time. Modern silicon carbide crucibles are even more forgiving. You can practically get away with putting those in the fire fresh, and with careful bellowing bring up the heat. I've only had one such crucible fail that way. But that was with charcoal, not with cokes.
Offline Profile Quote Post Goto Top
 
Rio van der putten
Member
[ * ]
thank you ! it helped a lot. Especially about hating up the crucible slowly. i have also used charcoal this time. my first cast was a succes but when i started cold hammering it shattered immediatly. when i looked i saw that the grain was huge ! i dont know if this is why it shattered or not. my bronze was actually alumina bronze. it was about 12% aluminium and the rest copper. does this have to do something with it ? and do you also know why the grain is so large? my guess is that it wasnt so smart to dump it in cold water when it solidifyed but i am relatively new to the whole bronze casting stuff so i dont really know how everything works. are you dutch by the way ? because your name seems to be ;) i am dutch anyway
Offline Profile Quote Post Goto Top
 
Rio van der putten
Member
[ * ]
my crucible isnt graphite clay its siliconcarbon. i just saw it on the website. Lucky me i guess ;)
Offline Profile Quote Post Goto Top
 
« Previous Topic · Reconstructing History · Next Topic »
Add Reply