MACHINERY SYSTEMS IN TROPICAL AGRI-FOOD CHAINS. Francesco Garbati Pegna

Transcription

1 MACHINERY SYSTEMS IN TROPICAL AGRI-FOOD CHAINS Francesco Garbati Pegna

2 Lesson 9e Tropical agri-food chains 1 (staple)

3 Mechanization of rice cultuivation

4 HARVEST

5 Harvesting It is the process of gathering a crop. For rice, this generally refers to the cutting and gathering of panicles attached to the stalks. Once the plants have reached full growth (approximately three months after planting) the grains begin to ripen, the tops begin to drop and the stem yellow; at this moment the water is drained from the fields. As the fields dry, the grains ripen further and harvesting is commenced. Depending on the size of the operation and the amount of mechanization, rice is either harvested by hand or machine.

6 Harvesting Is the process of collecting the mature rice crop from the field. Paddy harvesting activity includes: Cutting Stacking Handling Threshing Cleaning Hauling

7 Harvesting It is important to apply good harvesting methods to be able to maximize grain yield, and minimize grain damage and quality deterioration. Harvesting can be done manually using sickles and knives, or mechanically with the use of reapers or combine harvesters.

8 Harvesting Systems Manual harvesting and threshing Manual harvesting is done by hand using sharp knives or sickles; makes use of traditional threshing tools such as threshing racks, simple treadle threshers and animals for trampling Manual harvesting and machine threshing Rice is manually harvested, then cleaned with a machine thresher. Machine reaping and machine threshing A reaper cuts and lays the crop in a line. Threshing and cleaning can then be performed manually or by machine. Combine harvesting The combine harvester combines all operations: cutting, handling, threshing and cleaning.

9 Manual harvesting Manual system is the most common method of rice harvesting in Asia. This method includes cutting the rice crop by simple hand tools like sickle for cutting cm above ground level, and simple hand-held knives for cutting just below the panicle. Often the harvest is put together in bundles to improve handling and then dried in the field. The manual system of harvesting is very effective in lodged crop conditions, however it is labor intensive. Manual harvesting requires 40 to 80 man-hours per ha. It will take an additional labor to manually collect and haul the harvested crop.

10 Manual system using manually operated tools harvesting Tools for harvesting

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12 Threshing Threshing is the process of beating paddy plants in order to separate the seeds or grains from the straw. To maintain the high quality of the harvested grains, rice should be threshed immediately after harvesting. Avoid field drying and stacking for several days as it affects grain quality due to over drying. Stacked grains of high moisture content results in discoloration or yellowing. Threshing can be done manually or mechanically. The manual methods of threshing are treading by feet, flail method, and beating stalks against tubs, boards or racks. Mechanical threshing removes rice grains from the rice plant, speeds up threshing (thus reducing losses), and reduces labor requirements. Threshing is one of the many tasks a combine harvester performs, along with harvesting the plant and cleaning the grains.

13 Threshing by hand The most common method for threshing by hand is separating the grain from the panicle by impact. This can be done by hand beating, treading. Hand beating methods are normally used for threshing of rice that easily shatters. Rate: kg/h

14 Threshing by impact (with racks) The farmer holds the crop by the sheaves and beats it against a slatted bamboo, wooden platform, or any other hard object such as a steel oil drum. This is very labor intensive.

15 Threshing in sacs (flailing) Rate: 40 kg/h

16 Threshing with rotating drums A less tiring way of hand trashing is holding the crop against a rotating drum with spikes or rasp bars

17 Threshing in cases Avoids collecting grains from the floor after trashing. Can be done in the field also with obstacles such as water or stalks

18 Threshing by trampling This involves the use of bare feet or animals to thresh the crop. The crop is spread over a mat or canvass and workers trample with their own feet or use their animals. Animal treading or trampling is normally carried out at a designated location near the field or in the village. In some regions, animals have been replaced by tractors. After animal treading, the straw is separated from the grains and cleaning of the grain is done by winnowing, with or without the aid of an electric fan. Threshing rate: kg/h

19 Motorized threshing Given the high labor requirements of manual threshing, in many countries threshing of paddy is now mechanized by use of small portable or stationary machine threshers. Machine threshing is generally done in the field, or near or at the field side. Many threshers for paddy have peg-toothed threshing drums, however threshers fitted with wire-loop or rasp-bars are used as well. Most threshers are of the feed-in type (e.g. entire crop is fed through the thresher) which ensure high throughput. Hold-on threshers (only panicle is fed into the machine) generally have a lower capacity than feed-in threshers and are primarily used in areas where rice straw is bundled and stored for later use. Large stationary thresher are fitted with additional cleaning devices such as an oscillating screen, centrifugal blower, and windboard, and threshed grain can be handled without further cleaning. In many regions, machine threshers are owned by individuals who offer custom operations to farmers. This requires that farmers schedule harvesting dates depending on the availability of the thresher. Many threshers are mounted on trailers or trucks which enables the operator to quickly move from field to field.

20 Mechanical thresher

21 Principles of threshing Some threshers have a cleaning system where larger and smaller impurities are separated through sieves, while light and heavy ones by air blast

22 Principle of feed-in type axial-flow thresher Harvested crop is loaded onto the tray and fed into the opening between the cylinder and the concave at one end of the machine. The pegs on the threshing cylinder hit the material separating the grain from the straw, and at the same time accelerating them around the cylinder. The majority of the grain is threshed during initial impact but further threshing is performed as the material moves axially until the straw is discharged at the opposite end. Threshed grain, including impurities such as leaves and short pieces of straw, pass through the openings in the concave and fall on the oscillating screen where large impurities are separated.

23 Thresher output: t/h power need: 20 HP weight: 1,700 kg

24 Thresher output: t/h power need: 15 HP weight: 1,150 kg

25 Classification of threshers

26 Mechanized cutting followed by machine threshing Mechanical cutting using reapers is the first level of mechanical harvesting. Cutting and laying the crop on a windrow is done using a reaper, threshing by a thresher and cleaning either manually or by machine. Most reapers lay the crop in a windrow, which allows easy pick up of the harvested crop. A reaper with a cutting-width of 1.5 m can operate at a rate of 2 to 4 ha per day. A leveled field is important when reaping as it is difficult to reap lodged crop that is lying on the ground.

27 Reapers Reaper - binder

28 Combines The combine harvester combines all operations: cutting, handling, threshing, and cleaning

29 Combine harvester (Head-feeding combine) The combine harvester simultaneously performs reaping, threshing, and separating operations, contributing to easing labor requirements and improving efficiency in the harvesting of rice, traditionally the most labor-intensive aspect of rice growing. A driver's cabin may be installed in large and mid-sized combine harvesters, ensuring a comfortable operating environment. Conventional-type combine harvester Currently, a large variety of farm products are produced throughout Japan. Kubota conventional-type combine harvesters have played important roles, on a nationwide basis, in harvesting farm products including wheat, legumes, rapeseed, blister, millet, and Japanese millet.

30 How a combine works

31 Combines come in different configurations either with standard (conventional) threshing cylinders and straw walkers for grain separation or as axial flow combines using the same threshing and straw separation principle as the axial-flow thresher. The figure below shows the schematic diagram with the components of a standard combine and the crop flow through the machine.

32 Most Combine harvesters consist of several major components: the cutting section, the thresher, devices for separating the straw, a cleaner and a grain collection system. The cutting section usually consists of straw lifters especially for lifting lodged crop, a cutter bar for cutting the straw above the ground, a reel for feeding the cut crop into the conveying system and conveyors for transporting the crop to the threshing components.

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34 The thresher consists of one or more threshing cylinders and a concave. The threshing unit can be conventional but in most cases rice combines have axial-flow threshing and straw separation units, which are better in handling wet straw and do not require straw walkers for separating the straw. Other advantages of the axial flow concept are higher throughput and gentler treatment of fragile seeds like Basmati, which are often cracked by the faster rotational speeds of conventional combine threshing cylinders.

35 A conventional combine has a set of straw walkers for separation of the grain from the straw because the crop passes the concave very quickly and a lot of threshed grains are therefore still contained in the straw. On the straw walkers the remaining grains are separated from the straw by gravity. All combines contain a cleaner in which chaff, immature grains and small straw particles are separated form the grains. The cleaner consists of a blower and several oscillating sieves.

36 For grain collection the combine either has a grain tank or is equipped with a grain bagging station. For transporting the grain and other fractions inside the combine and for unloading the grain tank there are several conveyors, which can be bucket elevators or screw conveyors.

37 Different types of combines

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39 Mini combines

40 Cleaning Grain cleaning after harvest is important as it removes unwanted materials from the grain. Clean grain has a higher value than grain that is contaminated with straws, chaff, weed seeds, soil, rubbish, and other non-grain materials. Grain cleaning will improve the drying, the storability of grain, reduce dockage at time of milling, and improve milling output and quality. Seed cleaning will reduce damage by disease, and improve yields. Following are some general guidelines for cleaning grain and seed.

41 Winnowing Refers to the removing of foreign matter from rice grains (bulky straws, chaff weed seeds, leaves, pods, sticks, stones, metal..). Cleaning principles are based on the size, shape, specific weight and surface characteristics of the material to be removed Hand winnowing 1.5-3% losses doesn t remove heavy impurities Fan assisted winnowing

42 Mechanical Winnowing

43 Winnower Holds 2 or 3 oscillating screens, driven by an eccentric gear, and a fan. The grain drops from the hopper on the first screen (large mesh) witch holds the large impurities but not the small ones ore the rice that drop on the second screen (small mesh) which holds the rice but not the smaller impurities. At the same time the fan blows away lighter impurities. The vibration of the screens together with a light inclination moves the large impurities and the rice towards the edge where they fall in the respective containers