Power line communications (PLC) is a critica9.1 DEFINITION
An Electric Iron box is a heating device in which the electrical energy is converted into heat
energy. This heat energy is concentrated on a smooth, flat bottom surface which is pressed
over the cloth to be ironed.
9.2 TYPES OF IRON BOX: 1) Non-automatic Iron box 2) Automatic Iron box 3) Steam Iron box
9.3 NON-AUTOMATIC IRON BOX :
In non-automatic type, the temperature is not regulated. The user has to switch ON or OFF
the iron as per the heat requirement.
Constructional details: The principal parts of the iron box is shown in Fig. 9.1
Sole Plate: It is made up cast iron and it is generally chromium-plated. The transfer of heat
from the heating element to the material ironed is done through sole-plate.
Heating element: There are two types of heating elements. One is made of ribbon shaped
Nichrome (resistance) wire wound around a sheet of mica. This type of element is placed on
the top of the sole-plate as shown in Fig.9.2. Other type is made up of round resistance wire
coiled on a ceramic form and cast directly into the sole plate as shown in Fig.9.3. The flat type
element is replaceable whereas the cast type heating element has to be replaced along with the
sole-plate only. In this type of irons, a pressure plate is not necessary.
Fig. 9.1 Parts of Iron Box
Terminals and power cord: The ends of the heating
elements are connected at the points called as terminals as
shown in Fig.9.4. The electric supply is given the coil terminals
through 3 core power cord.
Pressure plate: It is made of cast iron and the purpose
is to keep the heating element firmly against the sole-plate.
The pressure plate is insulated from heating element by
asbestos sheet of same shape. The asbestos sheet is placed
just above the heating element to prevent the heat developed
in the element traveling upward due to conduction and radiation.
Cover: It comes above the pressure plat. This part covers
the heating element’s internal connections of the iron. It also
serves as a shield to protect the user’s hands from the
generated heat and the electric terminals.
Handle: It is made of Bakelite or ebonite because it offers
high resistance to flow current and it can withstand more heat.
The indicator lamp and power socket are fixed in the handle.
Heel plate: The purpose of the heel plate is to enable
the iron to stand when the iron is tilted back on the rear of its
handle.
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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
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rates welded together. The metal strip expands when heated and contacts when cooled. One
metal in the bimetal strip has a high rate of expansion when heated and the other has a low rate.
When a bimetal strip is heated both the metals in the strip expand but the one at the bottom as
shown in Fig.9.7, with a high rate of expansion, expands faster and forces the upper half to curl
up or bend away from the contact point. The strip curls or bends enough to break the contact,
i.e. opening the circuit. As the strip cools, it straightens and restores contact with the stationary
point. The bending of the bimetal strip on heating is towards the side that has smaller expansion
rate. By adjusting the size of the gap between the strip and the contact, you control the
temperature. A simplified sketch of Adjustable Thermostat is shown in Fig.9.8l energy control networking technology