Has anyone seen this with their crucibles? This is a #4 from PMC Supplies that I’ve only used to cast silicon bronze (95% Copper 4% Tin 1% Silicon). It started bubbling the first time I used it, and the bubbling has gotten more intense for each subsequent cast. I was more curious than cautious so I’ve used it for 6 pours with no issues whatsoever - just a bunch of extra dross to scoop off and a chunk in the bottom of the crucible that’s mostly not bronze (as far as I can tell) that won’t budge. I took a video but can’t seem to upload it so hopefully the bubbles are visible enough in the photos. Inside the crucible is a chunk of half-melted bronze as well as some of the gunk oozing out of the crucible. I built my furnace myself out of a beer keg and some rockwool coated in refractory cement - it gets up to 2000F in about 15mins once I add a leafblower behind the burner. The gauge on my propane tank reads 2PSI consistently throughout the heat. I’m not sure if any of that info helps? Thanks!
it looks like you did not follow the break in instructions , the first use they have to be dried, heated to 250F and held at that heat for several hours or overnight, then they need to be slowly brought up to melting heat, for a hobbiest the best way i have found to do that is to place it inside your furnace after a use as the furnace cools , in about an hour fire up the furnace and bring it up to a melt temp and let it cool as slow as you can. this is not the best method, but unless you have some sort of electric oven you can place it in to bring it up to 1000F only method i have available ... use it till it begins to spall V/r HT1
inside yes , outside no, it does look like his furnace might be underpowered, and he burnt off some of the alloying elements. its really important that copper based alloys get from molten to pouring as quickly as possible. V/r HT1 P.S although the alloy he used is very stable and forgiving, unlike brass and tin bronzes
Good tip, I never thought of that way to slowly heat up a crucible. I needed to make sure the oil line and needle valve etc. for my Moya burner are all still good to go anyway, and dry out the oil furnace as well, so I dragged it all out and gave it a go... All good, but the burner in diesel drip mode was harder to get going really good than I remembered. It's been a few years. And it's still the same diesel, maybe that's part of it. And I was also using the oversized Moya, which I haven't played with too much yet. I think maybe it's just too big, (2-1/4" exhaust tubing for the burner tube with a 5 gallon bucket sized shop vac blower plugged into a dimmer switch) Once the furnace was hot, in went the Morgan A12 that I baked for 3 hours in the kitchen oven at 250F yesterday. Bricked up the vent and stuffed a wad of kaowool in the tuyere and set my alarm for 1 hour. After dinner I came back out and found the crucible and furnace both glowing red/orange. This time I used the standard 1" black pipe Moya burner and it was easier to get it running on straight diesel, but difficult to get the furnace really super hot like I'd hoped. Used up most of the rest of that old diesel, so I'll get some new fuel and use the standard Moya burner again for the next heat, and hopefully it'll go a little better. But I did get the crucible prepared for use. Glowing hot furnaces mess with cameras, both pictures don't really show the brightness or colour of the hot glow accurately. Although I was wearing my new green face shield, so maybe I wasn't seeing the colours accurately myself either. The crucible is sealed up inside the furnace again now, slow-cooling overnight. I'll try and remember to report back with some pictures of the crucible before and after I use it. Jeff
We tend to get too far into what's perfect and forget that our purpose is to melt metal. Tap it with a three-quarter inch open end wrench. If it rings like a bell, you're good to go. If it goes "clunk" you better watch out. That said, it's best to buy quality crucibles from reputable dealers. I use Starrbide silicon carbide crucibles. Richard
