Electric Iron
Introduction
Ironing is the use of a heated tool (an iron) to remove wrinkles from clothes.
The temperature needed for this is usually around 180-220oC depending on
the type of cloth. Ironing works by loosening the bonds between the long-
chain polymer molecules in the fibres of the cloth. The fibres are straightened
by the weight of the iron while the molecules are hot, and they hold their
new shape as they cool. Some fabrics, like cotton, require the addition of
water to loosen the intermolecular bonds. The electric iron was invented in
1882, by Henry W. Seeley.
Introduction
Working Principle
The basic principle on which the electric iron works is that when a current is
passed through a piece of wire, the wire heats up. This heat is distributed to
the sole (base) plate of the electric iron through conduction.
Thermostat
But more interesting part to explore is how does it get automatically switched off
after reaching a certain temperature?
This is done with the help of a THERMOSTAT.
Thermostat
Thermostat
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.
Thermostat
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
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.
Bimetallic strip
Bimetallic strip
Mechanism of bimetallic strip
(a) when the iron is at normal temperature
(b) When the iron becomes too hot
As 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.
Comparison Of Dry Iron Vs Steam Iron
Feature Dry iron Steam iron
Water Tank Unavailable Available
Steam holes are
Soleplate Steam holes are available
unavailable
Spraying Mist feature Unavailable Available
Numerous number of features
Number of Features limited
are available
Cannot function as a
Versatility Can function as a dry iron
steam iron
Weight Lightweight for daily use Heavier
Movement by 360
Unavailable Available
degrees
Auto shutdown Available Available
