How does an Electric Iron Box works?

 

  The iron box is a small appliance used to remove wringles from cloth. Ironing works by loosining the bonds in the dress, between the long chain polymer molecules in the fibres of the material. While the molecules are hot the fibres are straightened by the weight of the iron, and they hold their new shape as they cool. Some fabrics, such as cotton, require the addition of water to loosen the intermolecular bonds. Ironing may also be used as the germ/ parasite killing hygienic operation.

      The basic principle of electric iron is that when a current is passed through a coil of wire, the coil heats up. This heat is distributed to the soul of the electric iron pro conduction. When the required temperature is reached the electric iron gets automatically switched off. Heat produced per second is i square R.

  There are basically three types of electric irons: (i) Automatic electric iron (ii) Non- Automatic electric iron and (iii) steam irons

   Automatic iron uses a thermostat to regulate the temperature. Non automatic iron has no provision for controlling or regulating temperature.

Parts of electric iron

1. Sole plate

2. Heating element

3. Pressure plate

4. Cover plate and handle

5. Power cord and plug

6. Thermostat

7. Inductor lamp

Sole Plate:

       The sole plate is the tick triangular shaped slab of iron that forms the base over which the electric iron is built up. The bottom surface and edges are chromium plated, to prevent it from rusting. The base plate should hold the iron pressure plate and cover plate in position.

Pressure Plate:

       This plate is called the top plate as it follows the shape of sole plate. The pressure plate is heavy and made of cast iron or a thin sheet of steel. In automatic type of electric iron, the pressure plate has a rectangular hole for heating the thermostat.

 

Heating element:

      The heating element is present between the sole plate and pressure plate. It consists of nichrome wire, wound around a sheet of mica. The two ends of the wire are connected to the terminals of the iron. Mica is a very good insulating material. It can also withstand very high temperatures. There is an asbestos sheet, which separates and thermally insulates the top plate from the heating element.

  Cover Plate:

       The cover plate is made of thin sheet of iron. It is placed on top of the base plate and it coves all the internal parts of the iron. The handle and connector are only attached to the cover plate.

Handle:

     The handle can be made either with wood or with plastic. The handle is attached to the cover plate with the aid of screws.

Thermostat:

      In non automatic iron there is no provision for controlling for regulating temperature. When the iron is hot it is to be manually switched off and when the temperature is less than that required, it is to be switched on manually.

    In an automatic iron thermostat is used to regulate the temperature and there is a indicator lamp. The indicator lamp is on the top of the cover and glows when the heating is going on. The thermostat is a device which makes and breaks the connection when the two points depending on the temperature. It is like an automatic on-off switch. The transition between on and off depends on temperature which can be chosen or set. There is a dial knob by rotating which temperature can be set as per requirement of the type of fabric. If the set temperature is 150 degree Celsius, then when the iron is switched on, the thermostat will act as on switch and will allow current flow through the heating element. As current flows through the heating element, temperature rises. Once the temperature rises above 150 degree Celsius the thermostat acts as a off switch and cuts off current flow through the heating element. Then the temperature gradually decreases. Once the temperature is below 150 degree Celsius the thermostat acts as on switch and allows current flow through the heating element. These on and off conditions continue and the temperature of the iron remains constant approximately  at 150 degree Celsius.

   Thermostat uses a bimetallic strip to operate the switch. A bimetallic strip consists of two different metals bonded together. The two metals should have a different coefficient of expansion. If sucha strip is heated, it starts to curve towards the metal having the lower coefficient of expansion ie, the bimetal strip bends and the circuit opens and the current ceases to flow. On cooling, it straightens and comes back to the normal position to allow the flow of current.

Steam iron:

     In steam iron there is a water resevoir on the cover plate and a steam chamber above the sole plate and the sole plate has slots. As the iron is switched on, heat produced by the heating element boils the water and steam is produced. The steam gets emitted from the slots of the sole plate ensuring better quality ironing.

Trouble shooting and Repair:

       Common problems are break in heating element, defect in power cord for thermostat loose connection and improper earthing. A broken element has to be replaced. Defects in power core and thermostat sometimes can be rectified by adjustment. Loose connection and improper earthing has to be rectified.