A combine harvester typically has two or three threshing drums, which are cylindrical metal cylinders that are covered with small, sharp teeth or bars. The drums are located in the main body of the harvester, between the cutting header and the cleaning system. The size and number of the drums may vary depending on the size of the harvester and the type of crop being harvested.
The first threshing drum in a combine harvester is called the primary or concave drum. This drum is the largest of the set and is located at the bottom of the threshing system. As the crop is fed into the harvester, it is first directed onto the concave drum, where the teeth or bars rotate against a stationary plate, known as the concave. The teeth on the drum grab the crop, and the concave holds it in place as the drum rotates, causing the grain to separate from the straw and chaff. The separated grain falls through the slots in the concave and is then carried up and out of the threshing system.
The second and third drums, if present, are known as the secondary and tertiary drums, respectively. These drums are located above the concave and are smaller in size. They are responsible for further separating the grain from the straw and chaff that may not have been separated by the primary drum. The secondary and tertiary drums work in a similar way to the concave drum, with the teeth on the drums rotating against stationary plates, known as the separator and finisher plates. The separated grain falls through the slots in the plates and is then carried up and out of the threshing system.
The drums in a combine harvester are powered by the machine's engine and are rotated at high speeds, typically between 600 and 1200 revolutions per minute. The speed of the drums can be adjusted to accommodate different crop conditions and to optimize the separation of grain from straw and chaff.
Overall, the combine threshing drums are a critical component of the combine harvester, as they are responsible for separating the grain from the rest of the plant material. Their design and operation are essential to ensure the efficient and effective harvesting of crops.
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