29 melts ago I placed a pretty clapped-out crucible in my furnace to see how it would work as a plinth. I was going to otherwise toss it and I was curious to see how it would hold up. So, I simply placed it open-side down on the floor of my furnace and held my breath. Well, it worked very well holding up for 29 melts of an average of 1.5 to 2 hours each with my furnace running as hot and hard as I could run it. Considering the durability of other plinths, this was very good. But finally I noticed it was starting to lean a bit. I pulled it after my melt the other day and could see that the flame had eroded the down-edge of the crucible. That is not too surprising given the fact that it was by no means in "new" condition when I placed it. So, then what to do? I had a couple of old A-25's with very thin upper rims but I could tell the main body from about an inch from the top down to the base was still good and thick. Not knowing how a tile saw might do on the crucible, I rented a good one at my local rental place and had at it. Because of the diameter of the crucible I had to remove the sliding table and just hand-hold the crucible and freehand the cut. And that seemed pretty straightforward, The saw did not seem grabby and I did make sure to rotate the crucible cut toward me so that any kickback would be releasing as the blade would be pushed into the cut rather than climbing uncut material. The graphite cut quite easily and cleanly. Here is pic of the results: I plan to set the crucible/plinth rim-down and a bed of Blu-Ram to seal the rim from gas passing under it. The whole works will rest on a 1" thick mullite plate that I had collected some time ago and that I cut into 8" squares with the saw today. I'll update how this works out. I am hopeful that with the new modifications of Blu-Ram bedding and mullite base that this should provide an even more durable plinth. Denis
I have often thought of reusing old crucibles for base blocks....let me know if you figure out how to cut silica carbide
A little follow up on this use of crucibles as plinths. I have now melted 6 times since installing the plinth and have found that it has better stability if placed on a piece of 1/2" thick mullite and grouted in with bubble alumina. I am sure other castable or ramable refractory would also work. But, BA, while spendy, is very moldable and can be fired immediately with no set time and no dry out. The mullite provides a nice solid base and I just happened to have a suitable piece on hand. It also cuts easily with a tile saw. After setting the plinth I noted it was not exactly level on top so I used my 4" angle grinder and a concrete-grinding 4.5" diamond cup wheel that cost ten dollars to level the top of the plinth (bottom of recycled crucible.) Again, it ground easily and I made it just slightly saucer-shaped so that the crucible would sit on it without any wobble. I think having the base of this plinth grouted in will extend its life as it looked like flame getting under the perimeter of the first crucible/plinth may have been a major cause of its eventual failure. Denis
