Principle
A washing machine is a modern domestic appliance and is used to wash clothes. Washing of clothes involves soaking, application of soap, stirring and rinsing. Dirt gets removed from clothes when soap water is forced through pores in the clothes. Once dirt is removed by soap water, the clothes are to be rinsed with water several times. Rinsing removes soap water. Factors that determine quality of washing are water, detergent, heat, time and physical motion. Application of physical motion like agitation or scrubbing helps dirt remove. In a washing machine washing of clothes is done in two stages: first stage is called the wash cycle and second stage is called spin cycle for rinse cycle. In wash cycle clothes soaked in soap water are agitated or rotated in a tub till dirt gets removed from clothes. Soap water containing dirt is drained out and clothes are rinsed with the fresh water by spinning the tub. This is the spin cycle or rinse cycle.
When detergent dissolves in water, its surface tension decreases and the solution is able to penetrate into every fibre of the fabric. Detergent separates the dirt from the fabric with the help of mechanical action. The mechanical action to dislodge dirt from the clothes is provided by washing machine.
Classification
Washing machine are classified as (i) Automatic and (ii) semi automatic. Depending on how clothes are loaded, they are categorised as (i) Front loading and (ii) Top loading.
In automatic washing machine once the dirty clothes, detergent and water are given as input and necessary instructions are given by means of control switches, the machine takes control and completes washing. Dirty clothes are to be loaded and washed clothes are to be unloaded and there is no manual work in between.
In top loading machine the clothes are loaded through a door at the top and the tab is vertical. In front loading machine the clothes are loaded through a door in front of the machine and the tub is horizontal.
Parts of washing machine
Major parts of a basic washing machine are:
1. Washing tub
2. Electric motor
3. Pump
4. Control panel and controlling mechanisms
5. Valves
6. Transmission mechanism
7. Sensors
8. Water lines
9. Agitator
10. Heater
11. Accessories
Working
Dry clothes are put in a tub. The tub is cylindrical and is made of aluminium or copper or steel or fiber glass. There are small holes on the tub. In top loading machines, the tub is vertical and is fitted inside a solid outer tub. An agitator is there at the centre of the tub. Agitator is driven by a motor and it stirs and agitators soaked clothes. The action of the agitator cleans the clothes by flashing out dirt particles from clothes so water is drained out and the clothes are rinsed with water several times till they become free from soap. Water is extracted from the clothes by spinning the tub. The spinning speed is between 400 to 1000 RPM when the tub is spinned, water from the clothes come out through the holes to the outer tub due to centrifugal force and is drained out. Top loading models without an agitator undergo pulsating oscillation to agitate the soaked clothes.
The washed clean clothes are taken out and are dried outside. The electric motor is a single phase AC motor. It is an universal motor or a capacitor type split phase motor. The same motor is used to drive the agitator during washing and to spin the inner tub during rinsing.
The pump circulates water to fill the tub during washing and drains out water from the tub after spinning. There are valves for hot water, cold water and for mixing.
Control panel
The control panel of the washing machine contains timer and selector switch. Now a days microprocessor and micro controller based electronic controllers are being used. There are switches for setting various parameters. These are start/ pause switch, timings for wash and rinse water level and temperature, spin time and speed, type of clothes to select appropriate condition ect. A definite set of parameter setting is known as wash programme. Recent models use advanced fuzzy logic based control unit and has features like self diagnostic mechanism. Controlling action is based on inputs from advanced sensors like water level sensor, door open sensor, load imbalance sensors etc.
Domestic washing machine can run on single phase 220 volt AC supply. Models with heater can have power rating of 2kW to 4kW. The capacity of washing machine is expressed in kg and it is the weight of clothes that can be put in the machine at a time for washing. Typical values of capacity of available models are 5.5 kg, 6.0 kg, 7.0 kg etc.
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