Electric Iron

Electric Iron

Principle: An electric iron is a general household appliance used to press the wrinkles out of the clothes. This work on the basic of heat and pressure combination to remove wrinkles from clothes. The principle of the electric iron is that when current is passed through a coil, the coil gets hot and transfers the heat to the base plate of the electric iron through conduction.

There are two types of Electric Irons. They are:

•          Non automatic electric iron.
• .       Automatic electric iron.

Non automatic electric iron cannot control the amount of heat generated. it generates constant heat depending on the rating of heating element. So, they may reach very high temperatures if kept on for a long time. But automatic electric iron has a bimetallic strip or thermostat which disconnects the circuit by breaking the contacts after reaching the predetermined temperature as show in fig. The screw or control knob can be rotated to adjust the temperature according to the type of fabric.

Construction:

The main parts of automatic electric iron are shown in fig. The function of each parts is given below.

·         Sole or base plate: it is made of cast iron and plated with nickel or chromium to avoid rust. The heating element

·         Heating Element: it is made of flat nichrome wire wound on mica sheet and insulated with mica on both sides which is kept under pressure plate. In automatic iron, 750 or 1000 watt element is used.

·         Pressure (or) weight plate: it is made of cast iron and kept over the element for air tight fitting. It is of the same shape as heating element. Pressure plate fixes and presses the heating element on the sole plate with nuts. It has to be tightly fitted. Any loose connections in pressure or sole plates will damage the heating element.

·         Iron case: It is also chromium plated to avoid rusting. It is used to cover the heating element, pressure plate and other parts.

·         Handle: it is used to hold the electric iron and is made of insulating material such as wood or ebonite.

·         Indicator light: it indicates whether the thermostat is closed or open. The light will glow only when the thermostat is closed. It will not glow even when the power supply is on if the thermostat is open. Other insulating materials such as porcelain, mica and asbestos are used to insulate conducting parts to avoid electric shock.

·         Thermostat: it is mainly used to maintain the temperature at the required level. It is also called as bimetallic strip because it is made by joining two dissimilar metals of different coefficients of thermal expansion. The thermostat is connected in series with the supply and appliance. It is normally kept near the area where heat is produced. After reaching the desired temperature, due to different coefficients of expansion, the strip will bend upon heating and opens or breaks the circuit. After some time, the strip cools down and closes or makes the circuit. Thermostat setting can be changed by adjusting the control knob.

Applications of Thermostat: Thermostats are used in most of the applications which require temperature control. Some of the areas in which thermostat is used are:

·         Air conditioners

·         Refrigerators

·         Ovens

·         Fan control inside lifts

·         Transformer and motor cooling

·         Medical diagnostic systems

Electrical wiring Diagram

In case of non automatic iron heating element is directly connected to the power supply. In case of automatic iron, the power supply as shown in fig.

Steps in Dismantling and Assembling

The following tools are required in order to dismantle and assemble electric iron;

•            40 w test lamp
•            Testing leads or wires 3/22 S.W.G (standard wire gauge) copper wire
•             Mica pieces
•             Asbestos sheets
•             Porcelain sheets
•             Insulated combination, long nose pliers
•            Screw driver
•            Spanner

The steps involved in dismantling and reassembling electric iron are given below:

•          Open the small screw fitted in the knob of heat control system with the help of a screw driver and remove the knob by pulling it upward. Now loosen the nut with a spanner and remove it.
•          The cover of the indication lamp can be opened by removing its screw. Now check the indicating lamp filament.
•         Loosen the screws of the terminal strips with a screw driver and also separate the supply phase, neutral, earth wires and upper cover of iron by holding the handle.
•            Remove the pressure plate and thermostat system by loosening the nuts.
•            Check the heating element for any earth fault.
•             Reassemble each part after checking and testing.

Testing procedure:

Testing of electric iron can be performed by connecting a test lamp in series with the supply and electric iron as show in fig. after turning on the supply the following possibilities may happen:

•   If the lamp glows dimly, then the circuit is working properly and it is known as closed circuit.
•  If the lamp does not glow, it indicates that the electric iron has some internal disconnection and it is known as an open circuit
•   If the lamp does not glow, it indicates that the electric iron has some internal disconnection and it is known as an open circuit.
•   If the lamp glows brightly, it indicates that both the terminals are touching each other and it is known as a short circuit. In order to perform earth testing, connect one wire of testing leads to one terminal of electric iron and another wire to any metal part of iron as show in fig. the possible outcomes are:
•   If the lamp glows, it indicates any part of the element is touching the metal body inside it is known as earth fault.
•  If the spark occurs at metal body and lamp does not glow, it indicates that insulating materials of electric iron are leaking. It is known as leakage fault.

·         Other kinds of faults are disconnection of wire end in plug or connector, broken cleats, breakage in cord etc.,

Repair:

The nature of repair work to be done for different types of faults is given below:

1.   Open circuit fault: Connect broken element or disconnected ends to the respective terminals connect broken or loose wire ends in plug top or connector. Check for any breakage in cord and connect or replace broken wires.
2.    Short circuit fault: If any two live wires or terminals are touching each other, separate and insulate them with mica and insulating type.
3.   Earth fault: if any part of element is touching the metal part of body, separate and insulate them with mica.
4.  Leakage fault: if insulating material has become old, the current may leak from it. In that case, and more insulating material to replace it.
5.  Other faults: if cleats, mica and asbestos are cracked or damaged, replace them. If any iron part gets rusted, clean it with sand paper.

Precautions

The following precautions must be taken while testing or repairing electric iron:

•         Asbestos or mica must be placed carefully between the heating element and the pressure plate to avoid dissipation of heat in the upward direction.
•     The fitting between pressure and sole plate must be airtight or else the heating element will be damaged soon.
•        During testing the operator must stand on dry wood or rubber mat for insulation.
•         Unless the electric iron is ascertained to be free of faults, the supply should not be turned on.