Combine harvesters: threshing systems, classes and the largest machines

A combine harvester "combines" four operations: cutting the crop with a header, threshing grain from the ears, separating grain from straw and cleaning it of chaff, before storing it in a grain tank. Modern combines harvest wheat, barley, canola, soybeans, corn (maize), rice and many other crops with the right header.

Threshing and separating systems

• Conventional (walker) combines use a transverse threshing drum and straw walkers. They are gentle on straw, which matters where straw is baled.
• Rotary combines use one or two longitudinal rotors to thresh and separate by centrifugal force. They have high capacity and simplicity, and dominate in North America. Examples: John Deere S-series, Case IH Axial-Flow, New Holland CR (twin rotor).
• Hybrid combines use a transverse threshing drum followed by rotary separators. CLAAS LEXION is the best-known example.

Combine classes

The North American industry groups combines by power and capacity, from Class 5 (around 200 hp) to Class 10 and above (over 600 hp). The largest machines today exceed 750 hp and carry grain tanks of 18,000–20,000 litres (500–570 bushels).

Headers

• Draper headers with belts for cereals and soybeans, up to 15 m (50 ft) wide.
• Auger (platform) headers for cereals.
• Corn heads with 6 to 18 rows.
• Pick-up headers for windrowed crops.

Technology

Yield mapping, automatic settings adjustment, grain-quality cameras, auto-steering and automatic unloading coordination with grain carts help operators get the most from these very expensive machines.