Combine Harvester: Components and Working Principle

A combine harvester is a complicated agricultural machine used to harvest a wide range of grain crops. The name “combine” refers to how this equipment combines three harvesting operations—reaping, threshing, and winnowing—into a single process.

This mechanisation transformed farming by saving time and labour while lowering grain losses. Crops that the combine harvester can handle include wheat, barley, corn, soybeans, rice, and oats.

Key Components of a Combine Harvester

1. Header:
   • Function: The header is the front attachment of the combine harvester, responsible for cutting the crop and directing it into the machine.
   • Types: Different crops require different headers. For example:
     • Grain Header: Used for wheat, barley, and oats. It has a reel that gently pushes the crop toward the cutter bar, which slices the stalks.
     • Corn Header: Equipped with snapping rolls to pull the corn stalks down while cutting the ears off.
     • Draper Header: Uses belts to convey the cut crop, improving efficiency in some grains.
2. Reel:
   • Function: The reel, located at the front of the header, revolves to help feed the crop evenly into the cutter bar. The tines of the reel force the stalks towards the cutting mechanism.
3. Cutter Bar (Knife Section):
   • Function: This is the main cutting element of the header. The knife section moves rapidly back and forth, slicing through the stalks of the crop just above ground level.
   • Mechanism: It consists of serrated blades that operate in a scissor-like action to cut the crop.
4. Auger:
   • Function: After cutting, the crop is conveyed to the center of the header by the auger. It uses a rotating helical drum to move the crop inward toward the feeder house.
5. Feeder House:
   • Function: The feeder house connects the header and the main body of the combine. It has a conveyor chain that transports the crop from the header to the threshing mechanism of the combine.
6. Threshing Drum/Cylinder:
   • Function: The threshing drum or cylinder is used to separate the grain from the stalks. As the crop travels through the drum, it is rubbed, beaten, or impacted, causing the grains to fall out of the ears or pods.
   • Concave: A concave is a curved metal grating that sits beneath the threshing drum and traps the grain while allowing smaller detritus to pass through. To maximise threshing efficiency, the clearance between the drum and the concave must be adjusted according to the crop.
7. Separating Mechanism:
   • Straw Walkers: Following threshing, the residual material (straw and grain) is transported over a series of straw walkers. These oscillating racks shake the straw to separate any leftover grain. The straw is then expelled from the back of the machine.
   • Rotary Separators: In some modern combines, rotary cylinders are used instead of straw walkers. These rotate at high speed, increasing the separation efficiency of grain from straw.
8. Cleaning System:
   • Function: After separation, the grain still contains chaff and other impurities. The cleaning system, consisting of sieves and fans, filters out the lighter materials like chaff and dust.
   • Sieve System: The grain passes over a series of vibrating sieves with different-sized holes. The smaller grains fall through the sieves, while larger impurities are discarded.
   • Fan System: A fan blows air through the sieves, lifting away lighter particles like chaff, leaving clean grain.
9. Grain Tank:
   • Function: The clean grain is conveyed to the grain tank, which stores the harvested grain until it can be unloaded. The tank capacity varies across models, and once it’s full, the grain is transferred to a waiting trailer or truck.
   • Auger: The grain is transported into the tank by an auger, a screw-like mechanism that moves the grain upwards.
10. Unloading System:
    • Function: The unloading auger transfers grain from the combine’s tank to a trailer or grain cart. It swings out to the side of the combine and discharges the grain via a conveyor system.
11. Straw Chopper/Spreader:
    • Function: This component chops and spreads the straw and chaff evenly across the field, which can be beneficial for soil fertility and future crop growth.
    • Chopper Mechanism: Blades cut the straw into small pieces before it’s spread back on the field.
12. Cabin:
    • Function: The operator operates the machine from the cabin, which is outfitted with advanced controls, monitoring systems, and, in certain cases, GPS technology to improve harvesting efficiency.

Working Principle of a Combine Harvester

1. Cutting (Reaping): The machine moves through the field, and the header cuts the crop near the ground. The reel directs the chopped crop towards the cutter bar. The auger subsequently transports the cut crop to the feeding house.
2. Feeding and threshing: The feeder house transports the crop to the threshing drum. As the crop travels through the drum and concave, the grain is separated from the stalks and husks. The larger straw particles travel forward, while the smaller grains descend down into the concave.
3. Separation: The straw walkers (or rotational separators) keep shaking and moving the straw, allowing any leftover grains to fall through.
4. Cleaning: The grain runs through a cleaning system that includes sieves and blowers to remove any leftover chaff, dust, or debris. Clean grain is gathered and transferred to the grain tank.
5. Unloading: Once the grain tank is full, the unloading auger transfers the grain into a truck or trailer.
6. Straw Management: The remaining straw is either distributed evenly across the field with a straw spreader or collected and baled.

The combine harvester’s ability to perform multiple operations in one machine revolutionized the efficiency of crop harvesting. It reduces labor, minimizes grain losses, and enables large-scale, timely harvesting.

Frequently Asked Question (FAQs)

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