Credit goes to the automatic switch made of bimetal. The bimetallic sheet is made by riveting the copper sheet and the iron sheet with the same length and width tightly together. When heated, because the copper sheet expands larger than the iron sheet, the bimetallic sheet bends toward the iron sheet. The higher the temperature, the more pronounced the bending. The picture on the right is a schematic diagram of the structure of the electric iron. At room temperature, the contacts on the ends of the bimetallic strip are in contact with the contacts on the elastic copper strip. When the electric iron head is connected to the power source, the current flows through the copper sheet and bimetal sheet in contact with the heating wire. The heating wire generates heat and transfers the heat to the metal soleplate at the bottom of the iron. People can use the heating soleplate to iron. The clothes are ironed. As the energizing time increases, when the temperature of the bottom plate rises to the set temperature, the bimetallic strip fixed with the bottom plate is heated and bent downward, and the contact on the top of the bimetallic strip separates from the contact on the elastic copper sheet, so The circuit is broken. At this time, the temperature of the bottom plate no longer rises, and it decreases due to the heat dissipation of the bottom plate; the deformation of the bimetallic strip is gradually restored. When the temperature drops to a certain value, the bimetallic strip and the elastic copper sheet are in contact again, and the circuit is connected again , The temperature of the bottom plate began to rise again. In this way, when the temperature is higher than the required temperature, the circuit is disconnected, and when the temperature is lower than the required temperature, the circuit is connected, and the temperature can be kept within a certain range.