Specifications

103
Fig.9.2 - Heating element (type 1) Fig.9.3 - Heating element (type 2) Fig. 9.4 - Terminal and power cord
Working of iron box: When electric supply is given to the heating element using 3-core power
cord, the heat produced in the element will be transferred to the sole-plate which is then pressed
over the cloth to be ironed. Thus the iron converts the electricity into heat at the sole-plate. The
heat at the sole-plate is used to iron the clothes. In Non-automatic type irons, the temperature
is not regulated. As such the user has to switch ON or OFF the electric supply as per the heat
requirement.
9.4 AUTOMATIC IRON BOX:
Automatic Iron box is same as that of Non-automatic type except that it has additional
device called as thermostatic device to regulate the temperature. The simplest form of automatic
type is shown in Fig.9.5
Fig.9.5 - Simplest form of Automatic iron box
Construction: The main parts are 1) Bakelite handle 2) pilot lamp 3) steel cover 4) chrome
plated, cast iron sole plate 5) built in automatic heat adjustment 6) cord
Thermostats: A thermostat is a switch which can be designed to close or open a circuit at
predetermined temperature. One of the simplest and most dependable components in the modern
heating appliances is the BIMETAL THERMOSTAT.
Bimetal thermostat: The principle behind a bimetallic strip thermometer relies on the fact that
different metals expand at different rates as they warm up. By bonding two different metals
together, we can make a simple electric controller that can withstand fairly high temperatures.
The general layout is shown in Fig.9.6
In the thermostat there is a bimetal strip made of two strips of metal with different expansion