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D. TAILINGS AUGER. This conveys the unthreshed heads across the rear of the combine into the tailings elevator. The elevator returns the "tailings" 'to the cylinder for rethreshing.
E. SHOE SIEVE. Located below the chaffer, this adjustable sieve permits the grain to fall through it; then the grain moves down the inclined surface of the shoe to the grain auger. The shoe sieve has an oscillating or shaking motion. This aids in cleaning and sifts the grain through the sieve openings.
The position or angle of this sieve in the shoe is adjustable as is the size of its openings. The sieve is usually placed in the shoes with a slight angle downward, toward the fan and grain auger. For cleaning dirty grain, you can raise the rear of the sieve and increase the air blast.
F. FAN. In most designs the blast of air from the fan passes through the shoe sieve, the chaffer, and the chaffer extension and is regulated by doors (blinds) at the fan housing. The air blows the light straw and chaff out of the combine but permits grain to sift through the chaffer and shoe sieve to the grain auger.
VI. Grain-Handling Unit. This power-driven unit conveys the threshed, cleaned grain to the point at which it is taken from the combine. It includes these parts: clean grain auger; clean grain elevator; and grain tank and tank unloader, or bagger and bag chute.
The clean grain auger collects the clean grain at the bottom of the shoe and conveys it across the combine to the elevator.
The clean grain elevator extends upward along one side of the combine. It elevates grain from the auger and discharges it into the grain tank or bagger.
The grain tank retains the cleaned grain until a truckload or wagonload has accumulated. Capacities of grain tanks vary from 18 to 60 bushels or more depending on the size of the combine. A power-driven auger unloads the tank quickly, delivering the grain through an adjustable spout into the wagon or truck.
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Where it is customary to sack the grain, a two-spout bagger attachment replaces the grain tank. One bag is filled while the other is being removed, tied, or sewed. A platform is provided for the operator, and there is a chute down which he slides the full sacks to the ground.
VII. Hydraulic Control. You will find hydraulic power used for many purposes in combine operation. With hydraulic controls you can adjust platform height, adjust the reel (in some models the reel is driven by hydraulic power), steer with hydraulic power, and unload the grain tank hydraulically. And, as in the tractor, you can reach these hydraulic controls easily from the operator's seat.
VIII. Propulsion Drives in Self-Propelled Combine. Most self-propelled combines now in use employ belt-and-gear type transmissions. These transmissions afford a wide selection of forward speeds – from less than 1 mile per hour to a highway travel speed of about 15 miles per hour.
HYDROSTATIC GROUND DRIVES. Manufacturers are providing hydrostatic drives for propelling certain combine models. These employ a hydraulic system to transmit power to the drive wheels. The hydraulic fluid is contained in an enclosed loop and is under high static pressure.
These advantages of hydraulic propulsion were found by engineers from International Harvester Company:
1. Infinite speed control.
2. Forward and reverse with one lever.
3. Dynamic braking.
4. No overloading or shock loading of the engine, transmission, and final drive.
5. Components that last life of the machine.
6. Very little maintenance required.
7. Increased combine productivity.
And the hydrostatic drive eliminates the need for many conventional parts, including the clutch, clutch housing, belts and sheaves, shafts, bearings and control linkages.
Exercises:
I. Answer the following questions:
1. What is the threshing unit intended for?
2. What types of cylinders do you know? Characterize them.
3. What is the concave and its main functions?
4. What are grates intended for?
5. What role does the separating unit play in the whole operation?
6. What mechanisms does the separating unit consist of?
7. What mechanisms does the cleaning unit consist of? What operations do they carry out?
8. What is the grain handling unit intended for? What parts is it subdivided into?
9. What role do the hydraulic controls play?
10. What are the propulsion drives and hydrostatic ground drives? Are there any differences between them?
