Sangeetha Pulapaka
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Thermostat is an important component of an electric iron that regulates its temperature. The word thermostat is very common due to its usefulness in many home appliances that deals with temperature control. The two words that were coined together to get thermostat are ‘Thermo’ (heat) and ‘statis’(status quo or constant).The main function of thermostat is to keep heat constant in a given setting.

The main function of thermostat in an electric iron is to make sure that the iron doesn’t get too hot if it is left unattended to for a period of time. The mechanism work as follows.

When electric current is passed through a coil in an electric iron, the coil becomes very hot. Through conduction the heat is transferred to the flat base plate of the electric iron which is used to iron our clothes .

However, the heating element continues to get hotter so far there is continuous drawing of electricity from the power supply. This result into a lot of energy wastage, cloths ruin and in the worst scenario, cause nasty accident. At this point, thermostat comes in because it is important that the iron doesn’t heat up to temperature that is hazardous.

Bimetallic Strip

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Bimetallic strip:

The thermostat in iron makes use of bimetallic strip. This bimetallic strip is made up of two different types of metals (Brass and iron) with different coefficient of expansion bonded together. Therefore, in the presence of heat, the bimetallic strip expands differently. The metallic strip is connected to a contact spring through small pins.

The bimetallic strip remain in physical contact with the with contact point at moderate temperature. However, at a temperature of the iron above a certain limit, the strip tends to bend towards the metal with lower coefficient of expansion. At this point, the strip stops to be physically connected to the contact point and current stops flowing because of opening of the circuit.

(a) when the iron is at normal temperature (b) When the iron becomes too hotAs far as the circuit remain open, the temperature of the iron continue to reduce, then the strip goes back to its original position and current begins to glow again. This cycle continues until the power supply is being switched off from the main electricity source. This is the main reason why your iron tends to power on and off on its own when connected to electric source.