There are various electrical inventions used for domestic purposes such as the electric fire, electric iron, and electric water heater that all depend on one common principle; when a current is passed through a piece of wire, the wire heats up and emits heat radiation. This heat is distributed and used for various purposes. Learn more about how this works with information on the electric iron invention. In this article, we will discuss about the various types, parts, and theory of operation.
The Electric Iron
An electric Iron is a general household appliance used to press the wrinkles out of the clothes. This works on the basis that the combination of heat and pressure removes wrinkles. The principle of the electric iron is that when current is passed through a coil, the coil gets red hot and transfers the heat to the base plate of the electric iron through conduction.
In the earlier days steam irons were used, but now the electric iron is preferred over the steam ones. Steam irons have some maintenance issues due to clogging. Steam irons usually have vents through which the water passes. As the steam iron gets used, slowly the minerals from the water accumulate at the vents and blocks the water from passing through. Thus the efficiency of the steam iron is compromised. So the steam iron has to be cleaned and maintained regularly to ensure its proper working. If you live in an area where hard water is used, then clogging is a major problem.
This drawback is eliminated in electric iron as it uses a heating element and there are no vents in it. There is considerably less maintenance in an electric iron when compared to a steam iron.
There are basically two types of electric irons:
There is not much difference between the two types. The former has one regulator to control the temperature of the element and in-turn the temperature of the iron.
Now you may ask, why do we need to control the temperature of the iron?
The answer is simple. Now-a-days we use various types of fabrics such as cotton, silk, linen, etc. So to suit the temperature required for different kinds of fabrics, we use the temperature control.
Parts of an Electric Iron
The sole plate is the thick, triangular-shaped slab of iron that forms the base over which the electric iron is built up. The bottom surface and edges are heavily chromium plated, to prevent it from rusting. The base plate should hold the iron pressure plate and cover plate in position. For this purpose we can see two or sometimes three studs in the base plate. These studs aid in holding the position of cover plate and pressure plate.
This plate is generally called the top plate as it follows the shape of sole plate. The pressure plate has some holes through which the studs form the base plate passes through. We should tighten the nuts on the studs in such a way that the pressure plate and sole plate are pressed tight against each other. In some iron the pressure plate is heavy and made of cast iron while in some other cases, it is a thin sheet of steel, about ¼ cm thick.
In automatic type of electric iron, the pressure plate has a rectangular or circular hole for locating the thermostat.
Parts of electric Iron [contd…]
The Heating Element
The heating element is present between the sole plate and pressure plate. It is pressed hard between the two plates. The heating element consists of nichrome wire wound around a sheet of mica. The two ends of the nichrome wire are connected to the contact strips. The contact strips are connected to the terminals of the iron. There are two reasons for which mica is chosen in the heating material. Mica is a very good insulating material. Besides that mica can also withstand very high temperatures. The entire assembly of mica sheet, nichrome wire and contact strips are riveted together resulting in a mechanically sound and robust construction. There is an asbestos sheet, which separates and thermally insulates the top plate from the heating element.
The Cover Plate
The cover plate is made of thin sheet of iron. It is placed on top of the base plate and it covers all the internal parts of the iron. The handle and connector are only attached to the cover plate.
The handle can be made either with wood or with plastic. The handle is attached to the cover plate with the aid of screws. Studs can also be used for this purpose.
The pilot lamp is housed in the cover plate of the electric iron. One end of the pilot lamp is connected to supply, while the other end is connected to the heating element. A shunt resistance is provided across the pilot lamp which assists in providing a voltage drop. The shunt is designed to provide a voltage drop of 2-5 volts.
When it comes to an automatic electric iron, the thermostat is the most important item. It uses a bimetallic strip to operate the switch which is connected in series with the resistance (or) heating element.
The bimetallic strip is a simple element which converts a temperature change into mechanical displacement. A bimetallic strip consists of two different metals bonded together. The two metals should have a different coefficient of expansion. If such a strip is heated, it starts to curve towards the metal having the lower co-efficient of expansion. On cooling, it straightens and comes back to the normal position.
Now we might wonder why such an element is used in iron. What is the purpose of this element in an electric iron?
The bimetallic strip is attached to a contact spring through small pins. The contact point between the strip and contact points remains closed. When the temperature rises significantly, the unusual expansion causes the strip to curve and the contact between strip and contact spring opens. Thus the supply to heating element is temporarily stopped (until the temperature goes down to normal). A special device called the cam is placed is placed near the contact spring, with which we specify the amount of curving of bimetallic strip required to separate the contact.
Thus using bimetallic strip the temperature is kept constant within certain limits.
The thermostat helps in maintaining the temperature within limits. But frequent making and breaking of circuit damages the contact points and it may also result in interference with radio reception. To avoid this, a capacitor of certain range is connected across the two contact points.
When a current is passed through the heating element which is placed between the sole plate and pressure plate, the element gets heated up and transfers its heat to the sole plate through conduction and in-turn the sole plate also gets heated up. Now to remove the wrinkles in clothing, we should apply heat and pressure. Heat is formed due to the coil and when we press the clothes with iron, the wrinkles are removed. For maintaining the optimum temperature, a thermostat is used along with pilot lamp which serves as an indicator.