For those women who want to make the transition from straight or wavy hair to curly hair, curling irons are nothing short of miraculous. Curling irons allow the process to be done quickly and easily, without the need for uncomfortable hair rollers.
Curling irons need a source of electricity and come with a plug for an electrical outlet. They have an on/off switch, preset temperature settings and the metallic heating element that actually does the work of curling the hair. Warmer temperatures allow less manageable hair to be curled more easily.
When the curling iron is set to a temperature and turned on, the device transmits electricity through the heating element. The metal that makes up the part of the curling iron that actually gets hot is simply a poor conductor of electricity, which means that instead of the electricity passing through it, it creates heat. To prevent the metal from getting too hot due to an excess of electricity, curling irons have a built in thermal switch that stops the flow of electricity when the metal gets to the preset temperature.
The thermal switch is created in such a way so that when it gets hot it expands, and when it expands to a certain size, it stops the flow of electricity. As it cools, it becomes smaller again, allowing the flow of electricity to start the circuit once again. This cycle continues until the power switch is turned off or the preset temperature is changed.
Curling irons can curl hair because hair is essentially a long string of protein, acting like wood fiber. If you heat wood, it becomes malleable and you can form it and shape it. The process of heating the hair and curling it around the curling iron makes it keep that form until it is wetted, when it once again takes its natural shape. The temperature range that actually curls hair is fairly small, so all curling irons operate with close to the same amounts of electricity.