Why does the muffle furnace need to be lowered to a low temperature before it can be turned on?

Because the temperature difference between the inside and outside of the furnace door is too large when the temperature is high, it is easy to cause the furnace door to crack and affect the service life. Therefore, it is recommended that the user open the furnace door when the temperature is low. This is mainly to protect the furnace and prevent the refractory material from being damaged by the huge temperature difference.