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Agricultural Engineering

Harvesting and Threshing Machines


Harvesting is done by three ways: Man power, animal power and tractor or engine power. In India it is done manually, mostly by sickle. It takes about 170 to 200 man hours to harvest one hectare of paddy crop. Sickle consists of a curved plain or serrated blade of carbon steel, with a wooden handle. The tang of the blade is lightly fixed into the handle with the help of ferrule.

Animal drawn types as cylinder movers, reciprocating movers and reapers are available. Movers were developed for harvesting grasses and forage crops, but now wheat, paddy etc. can successfully be harvested. It consists of mainly wheel, frame, main axle, pitman, cutting mechanism, counted shaft, gear, clutch, crank shaft, crank wheel, levers and grass board. In animal drawn, wheel gives power to the axle, from where the power is transmitted through the gear box. The crank wheel and the pitman are fixed on the outer end of the crankshaft. Reciprocating motion is transmitted to the pitman, which operates the knife (made of high carbon steel) in the cutter bar. There is ball and socket arrangement to connect the knife with the pitman. The operator controls the driving unit with the help of a dog clutch. The height of cut is regulated by the sole of inner shoe. The size of animal drawn moves are generally 1.3 to 1.5m, and it can cover 2 to 3 hectare/day depending on bullock size, sharpness of knives, adjustments of cutting mechanism and crop maturity.

Tractor or power operated movers are horizontal rotary type, gang type and trail type, which are driven by P.T.O. shaft or belt and pulley used for cutting grasses, lucern and berseem. Reciprocating movers are common for forrage crops cutting. In this case the cutting mechanism is driven independently of the forward speed of the mover. A main shaft is connected to the P.T.O. shaft, which drives a ‘V’ pulley with the help of universal joint. The ‘V’ pulley gives power or rotation to another smaller pulley on the crank shaft which is connected to the pitman. Reciprocating motion of pitman is transmitted to the cutter bar. Other basic components of the machine and working are same as that of bullock drawn mover or reaper. The size varies from 1.8 to 2.0 meters, and the coverage varies from 3 to 6 hectare/day. Tractor mowers on attachment basis are classified as trail behind, semimounted, integral rear-mounted, side or central mounted and front mounted.

  1. Pull type or P.T.O. operated type or trailed type

  2. They are small combines pulled by the tractor, at the same time their cutting and threshing mechanisms are operated by the P.T.O. Shaft of the tractor. The large size combines are equipped with a small auxiliary engine, which drives all the mechanism, the tractor in this case only pulls the deadload of the combine. The size ranges form 1.2 to 2.4 meters for small and 3.5 to 6 meters in case of larger combines.

  3. Self propelled type

The combine consists of these parts: The reel revolves in front of cutter bar pushes the standing crops towards the cutter bar, operated like mover or reaper cutter bar, which after cutting pushes the crop toward the conveyor. The conveyor feeds the crop to the threshing drum and concave. After threshing threshed material goes to straw rake. These rakes keep on oscillating and separating the grain. The cleaning takes place on number of sieves with the help of fan. The unthreshed grains pass through trailing auger and go for rethreshing. The clean grains pass through grain elevator and finally go to packing unit. The size of the combine is indicted by the width of cut it covers in the field. It ranges from 1.2 to 6.7 meters. The speed of drum ranges from 2000 to 7000rpm.The field speeds of combine are 2.9 to 6.4 km/hr, while road speeds are 4.0 to 20.9 km/hr.

Threshing Implements

Threshing is the process of loosening or removing or separating grain from pods or straw or plant. It is done by (i) Machines (ii) Animals (iii) Human. Threshing by manual labour is a slow and time-consuming laborious process. It is done by rubbing between two palm hands or between two legs or beating by sticks or striking the plant against a hard object. In India the indigenous method is bullock treading in which the crop is spread on threshing floor in a circle, and bullocks are made to walk on it in circular path. The repeated trampling under the bullock feet results the threshing. On an average 4 quintal per day can be threshed by a pair of bullocks. With the advancement, farmers started the use of dragging devices like rollers, wooden planks, disc harrow and finally olpad thresher. Olpad thresher consists of 14 to 21 plain or serrated disks mounted on a rectangular wooden or iron frame in three axils with bearings. An operator seats on the top is provided. The design is such that on operation it goes round and round behind the bullocks. About 6 quintals of grains can be threshed per day, with Rs. 3.00 to 3.50 per quintal cost of threshing, which is almost the cost of bullock trampling.

The Japanese pedal rotary thresher introduced in rice growing tract has not proved very popular, because it has given less quantity than beating. It has wooden beating drum with loop type pegs (teeth) staggerly arranged to have better threshing. The drum is mounted on angle iron frame, covered by steel sheet from all sides. It is pedel operated through gears. One man can thresh about 1.5 to 2 quintals per day, with threshing cost or Rs. 2.50 to 3.50 per quintal.

Power thresher is machine, which threshes the crop, prepares bhusa, and separates grain from bhusa with or without bagging arrangements. It can be used as multi crop thresher after attachments or detachments of certain parts. The power threshers are becoming increasingly popular, as operated by 5 to 10 bhp stationary engine, electric motor or tractor. The thresher consists of seed and frame. The crop to be threshed is slowly pushed on to the feeding trough (channel in shaped made of sheet metal) to reach to the threshing drum, cylindrical in shape. The drum rotates at 600 to 700 rpm and are of peg type, loope type, angle iron type, raspbar type and hammer mill types. Most common are peg types in which bolts are used on the periphery of the drum. The crop is threshed by the impact and rubbing action between the drum and concave. The threshed bhusa and grain falls on the screen through slide plate, but bhusa being lighter is sucked by the blower and thrown out. The shaking or oscillating action of the screen along with stream of air separates and cleans the grain. The clean grain is collected and elevated to required height for bagging. The thresher can thresh different crops like wheat, barley, gram, pea, jowar, bajra, mustard etc. by little adjustments or replacements. The power threshers of different sizes are available to suit different H.P. to engines, electric motors and tractors.

Winnowing Implements

Winnowing is the process of separating grain from the mixture of threshed straw (chalf) and grain in an artificially or naturally stream of air. The following are the common devices used for the above work:

  1. Winnowing basket

  2. Winnowing fan

  3. Winnower.

Winnowing fans, either manually operated or mechanically operated, are mostly used,

Where the wind velocity is not adequate, and where artificial means are used to create a sufficiently strong air blast. There are many firms manufacturing winnowing fans, but first indigenous winnowing fan was developed at Allahabad Agricultural Institute by Mr. Masor Vaugh. It consists of frame either made up of wood, angle iron, welded steel or combination of the two. The number of blades of different shapes and sizes are either three or four mounted on an impellor. For required speed various driving mechanisms are used, namely sprocket and chain, belt and pulleys, and single or double reduction gears. Hand operated, pedal operated and power operated winnowing fans are from 0.90 to 1.25 m in diameter, the speed varies from 210 to 320 rpm and cost Rs. 500 to 1500.00.

Winnower the most efficient, quick, easy and effective machine has been designed. It consists of frame, sieves, blower, set of gears, handle, hopper, and occilating mechanism. A man is used to operate the handle, thereby rotates the set of gears, which gives rotation to the blower, at the same time it also gives occilation to the sieves which are three to four in numbers. Two men are required to keep the supply of threshed material into the hopper always. From hopper it drops down due to gravity on the different size sieves. The grain and foreign material being heavy passes through different sieves and straw being lighter is carried out by the blower breeze current. The grain is finally collected near the grain outlet, while bhusa is thrown away from winnower. The cost of winnower comes out to be Rs. 2,000 to 5,000. The capacity is about 8 quintals of threshed material/hr or 2.5 to 3 quintals of grain/hr by 3 men working with the machine.