Threshing is the process of detaching grains from the ear heads or from the plants.
Principle of Threshing for Crops:
Threshing separates grains from panicles, cobs and pods.
Threshing is based on the principle that when:
1. Some impact or pounding is given on crops; the grains are separated from panicles, cobs or pods.
2. The crop mass passes through a gap between drum and concave, wearing or rubbing action takes place. This separates grains from panicles.
Thus the rupture of the bond between the grains and ears is due to the factors, like:
1. Impact of beaters or spikes over grains and
2. Wearing or rubbing action.
The strength of the bond between the grain and the panicle depends upon:
(a) Type of crop
(b) Variety of crop
(c) Ripening phase of grain and
(d) Moisture content of grain.
The efficiency and quality of threshing depends on:
1. Drum speed
2. Number of beaters
3. Drum size
4. Gaps between drum and concave
5. Quality and condition of plant mass fed to the thresher
6. Direction of feeding and
7. Rate of feeding
Methods of Threshing:
The common methods of threshing are:
1. By Manual Labour
2. By Animals and
3. By Machines
1. Threshing by Manual Labour:
Threshing by manual labour is a slow and labour consuming device. Process of beating the harvests on a floor or beating by stick is the method followed for small quantity of harvests.
2. Threshing by Animals:
Threshing by animals is very common method used in villages. The harvest is spread on a clean threshing space, the animals are tied in line one after the other with the help of a strong pole, fixed in the centre of the threshing space. Animals move round and round on the harvest and trample them continuously till the grains are completely separated from straw. One man drives the animals from the back.
3. Threshing by Machines:
With the increase of mechanization in farms, threshing machines are getting popular day by day. Different types of threshers are used for threshing.
It is mainly a wheat thresher consisting of notched discs placed on three axles, fixed on a wooden or iron frame on which a seat and a platform are provided. This thresher is operated by animal(s).
Olpad thresher is said to have its origin at a small place named Olpad in Gujarat State. This thresher is useful for threshing wheat, barley, gram etc. on a threshing floor. This thresher has three or four wheels to facilitate its movement from one place to another.
Olpad thresher mainly consists of:
2. Disc space (spools)
3. Disc axles and
4. Bearing blocks
Threshing efficiency depends upon following factors:
1. Peripheral speed of the cylinder
2. Cylinder-concave clearance
3. Type of crop
4. Moisture content of crop
5. Weather condition
6. Feed rate
Flow Diagram of a Power Wheat Thresher:
Fig. 17.16 shows a flow diagram of typical power wheat thresher. The harvested crop is fed through the feeding inlet. The grains, after striking the drum fall down on sieves. From the lower most sieves, the grains fall to one side of the frame from where the grains are lifted through the lifting through the lifting device. Finally the grains move to a container or a bag fitted suitably at one side of the thresher.
In this thresher, crop is fed to the threshing cylinder which removes the pods from the vines. A blower is provided to separate the pods from the rest of the material. The thresher is fabricated from steel and mounted on the wheels. It can be operated by stationary power unit as well as by tractor. It is used to remove the groundnut pods from the vines. It can be run by 5 hp electric motor. Its capacity may be 400 kg pods/hr. It is a spike tooth type thresher.
Safety Precautions for Threshers:
1. Do not remove the safety devices.
2. Do not wear loose dress and wrist watch.
3. Do not smoke and light fire near threshing yard.
4. Do not operate the thresher under the influence of liquor, opium etc.
5. Do not stand on the thresher.
6. Do not cross over the belt.
7. Do not keep hand at a close distance from thresher.
8. Do not stand on a bundle of crop or bullock cart or trolley to reach the chute for feeding the crops.
9. Do not make any adjustment before switching off the prime mover.
Precautions and Care in Operation of Thresher:
1. The machine should be installed at a leveled surface as far as possible.
2. The direction of the machine should be set in consonance with the direction of the prevailing wind i.e. the bhusa outlet should be kept in the same direction as that of wind.
3. The machine should be fixed in the ground with the help of suitable pegs or by digging into the ground.
4. The thresher should be operated at the speed recommended by the manufacturer.
5. Suitable size of pulley should be provided on the thresher.
6. The feeding should be continuous and uniform.
7. Bearings and other working parts should always be properly greased and oiled.
8. Before starting the machine, the main pulley should be driven by hand to ensure that there is no obstruction inside the machine.
9. While feeding, care is to be taken that crop should be free from any wooden or iron pieces.
10. It is desirable to dry the crops before feeding, as far as possible.
11. The sieves should be inspected frequently and cleaned from time to time to avoid stucking.
12. While feeding, the operator should not insert his hand deep in the feeding trough.
13. After continuous working for 8 to 10 hrs the machine should be given some rest before it is put into operation again.
14. When the machine is not is use after the threshing season is over, all the belts should be removed and the machine should be kept in a covered place.