Hello I purchased an old Hoskins induction furnace model fd 104 5 inch bore 5 1/2 inches high.I have searched fro some information regarding the proper size crucible  I have  silicone graphite a5 bell crucibles, but after a couple of pours from a crucible I tempered melted some cans; it is destroyed and unsafe to use with cracks.  I need to know if you place a small stand or buffer from the bottom of the induction furnace? I have read that silicone graphite crucibles are best,but would like someones opinion on the proper size of crucible type for this specific model, I confess that the model is fairly archaic had to replace a power cord.  Also should I build a cover to achieve higher temperatures if so vented non vented?

 All in all happy i didn't hurt myself having read up on proper procedures and having used safety equipment.  I have a few aluminum bars for my effort, thanks for any help from a partial neophyte on this subject.

Welcome aboard... Sorry I can't help with the furnace question, however this will help you get the best out of the forum. READ THIS FIRST  It is full of tips like editing your profile to show your location because many answers are dependent upon where in the world you are located.

I know this is an old thread, but was the crucible the one that came with the furnace or a new one? The issue is that induction furnaces generally don't heat evenly and portions of the crucible are glowing while others are just getting heated up. This depends on the geometry of the coils and the frequency of the furnace. Is this a 10kW or larger furnace? I know you said A5 crucible which is like 15 lbs of metal right? A pure graphite crucible should handle the thermal shock, has a much higher maximum temperature and will heat much more evenly in an induction furnace due to the internal resistance of the graphite to the induced easy currents.this is all assuming you are melting non-ferrous metals. Graphite would be expensive, but I cannot imagine the furnace was all that cheap.

 

And yes. Making an insulating refractory cover, while not usually used in industrial furnaces, will help the metal melt faster.