Furnace Woes


My furnace failed a few days ago. I’m sad.

I was heating up the furnace to melt some white bronze for a Wonder Woman casting and although it reached at least 930 C (the goal was 1020 C), when I checked it five or ten minutes later, it was down to around 750 C and the temperature was dropping.

This is what happens when the elements fail.

I wasn’t too surprised. I was suspicious that the heating elements were coming to the end of their life. I have been maintaining statistics on my furnace use since inception. I did lose my data after about six months of use, but I do have statistics going back to November of 2014.

I have used the furnace 87 times since November 2014. This is about 2 times a month. My typical operating time for the furnace is about 2 hours.

Back when the furnace was new the furnace would heat to my maximum operating temperature 1070 C in about 1 hour. Once it was hot I would be able to do my work in the next hour. It ran this way for a number of years. Over the last six months I have observed that my operating times are increasing. A few days ago when I ran the furnace up to 1070 C it took exactly two hours and my total operating times are reaching 3 hours, rather than 2 hours. So, my furnace appears to be running slower than it once was.

I ran a linear regression analysis on the furnace data to try and come up with a formula that describes its performance. The dependent variable is time to reach pouring temperature and the independent variables would be operating temperature, crucible weight, and metal weight.

But, the performance is not linear. I think as the elements age the time increases and it probably follows an exponential curve. So I really haven’t got this figured out yet.

Regardless, here are some pictures of my furnace. When the quote come back for repair I will be able to factor in furnace wear costs into my pricing formula. But my best guess right now is that it is costing about $10 – $15 each time I fire up the furnace to do some casting. I really need to factor this cost into my pricing for my bronze works.