Electric soldering iron is divided into two types: external heat and internal heat:
External heating electric iron consists of iron head, iron core, shell, wooden handle, power lead, plug and other parts. Because the iron head is installed inside the iron core, it is called external thermal electric iron. The iron core is the key part of the electric iron. It is composed of the heating wire wound in parallel on a hollow porcelain tube. The mica in the middle is insulated, and two wires are led to connect with 220V AC power supply. There are many specifications of external heat electric soldering iron, commonly used are 25W, 45W, 75W, 100W, etc. The higher the power, the higher the temperature of the iron head [1].
The internal heating electric iron consists of a handle, a connecting rod, a spring clip, a soldering iron core and a soldering iron head. Because the iron core is installed inside the iron head, the heat is fast and the heat utilization rate is high. Therefore, it is called internal thermal electric iron. Internal heat electric soldering iron commonly used specifications for 20W, 50W several. Because of its high thermal efficiency, 20W internal heat electric iron is equivalent to about 40W external heat electric iron. The back end of the internal heat electric iron is hollow, used to be connected to the connecting rod, and fixed with a spring clip. When the iron head needs to be replaced, the spring clip must be withdrawn first, and the front end of the iron head must be clamped with pliers, and pulled out slowly. Remember not to exert too much force, so as not to damage the connecting rod
