The muffle furnace is a necessary and commonly used electric heating equipment in the laboratories and heat treatment workshops of general enterprises, colleges and universities. Now most of the box-type high temperature muffle furnaces in the laboratory are refractory brick muffle furnaces from a few years ago or even more than ten years ago. Because the refractory bricks are used as the insulation layer, the insulation effect is not good, and the sheet metal shell is only wrapped with a layer of iron, and the shell is very hot, sometimes reaching more than 100 ℃. There is a certain danger...