Yet another foundry boo boo - dangerous!

[creast]

Just a warning to others.
I was doing a second melt of scrap copper pipe and to get the maximum in the crucible I squashed it in a vice and folded it back and forth on itself.
Three or four of these concertina style lumps were placed in the crucible and duly heated.
Part way through the process there was a loud bang and hot debris flew out the furnace exhaust hole.
I am guessing some moisture was present and built pressure up between the folded sections. I could see after that some of the copper had gone back to cylindrical form and I treated it as a potential bomb until fully melted.
Next time I will fully dry and ensure no folded seams.

 

[GreenTwin]

I preheat any metal that I add to the crucible after the burner has been started by holding it in the lid exhaust stream, and getting its temperature up to perhaps 600F.

John Campbell's rule No.01 (if I remember correctly) was to use quality scrap for the melt, no exceptions.
I store my scrap metal indoors, but I still treat it as if it is wet.

I use broken gray iron scraps from electric motor end bells.

When I attempt to make bearing bronze, I will use 8" pieces of straight copper pipe, and again if added after the furnace is hot, I will hold them in the exhaust stream for between 30 and 60 seconds, even if they look perfectly dry.

A single drop of water can explode your furnace, and so I go to great lengths to avoid getting water into a crucible of molten metal (as Rich details in the post above).

Rich's post also underscores the need to keep full leathers on when working around a furnace, and wear a full face shield at all times.
I wear safety glasses under my full face shield.

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