7. MILLILITERS COLLECTED = LITERS PER HECTARE BEING APPLIED
1.6.7. Power Threshers as Precursors of Mechanization
Power threshers played an important role as the forerunners of farm mechanisation in the Western world. The same was true of Japan and is proving to be the case yet again in nations of the developing world.
Western-style or even modern, small Japanese combine harvesters have been shunned by low-income farmers with fields that are often too small or inaccessible for self- driven equipment. Manual threshing is probably the most tedious and least-attractive field activity. Rising labor costs and manpower scarcities for harvesting accordingly have hastened the development of a wide range of power thresher designs across the rice world in the last 40 years. Threshing machines—power threshers—have enjoyed an illustrious history. In the industrialized world they are completely outdated, but in their heyday they
Figure 1.303. The SG 800 stripper-gatherer developed by IRRI in the Philippines for small-area rice farms. The walk-behind rice stripper weighs just 240 kg and is propelled with 11 hp air cooled engine, can harvest one ha/day with a team of seven and a
thresher (25).
were as important as they were large. Antique threshers can still be seen at show days.
They are an impressive sight, especially when connected by an enormous belt drive to a steam traction engine. But they are no more than nostalgic museum or show pieces today.
By contrast, in developing countries, there are places where threshing is still done using muscle power. Hand or foot treading, either human or animal, or manual bundle-beating still goes on. This type of work takes weeks, even months to get through the harvest. The big Western-style threshers were tried in some developing countries, but they were just too costly, too heavy, and ill-suited to small or inaccessible fields. It was only after the 1950s that Japan, South Korea, Taiwan, China, and other Asian countries began to adopt small power threshers. This came about with rising labor costs and harvest labor shortfalls that intensified with rapid industrial growth during reconstruction after World War II.
In Japan threshers progressed from hand-feed to mechanical head-feed, and from stationary to self-mobile machines.
Other Countries in Asia
In some low-income parts of Asian nations, labor costs are cheap enough that the use of the sickle and manual threshing still predominates. But in these places the use of the power thresher is the necessary first step to enhance labor productivity and reduce drudgery—
this might be called labor-intensive mechanization. In the Philippines, for example, 57%
of the people are involved in farming, and rice is the major commodity. Ninety percent of the rice crop is mechanically threshed in that country. There are only a handful of combine harvesters. The recent development at IRRI of small pedestrian-controlled stripper harvesters has raised the level of interest in this approach to the rice harvest, with six manufacturers each turning out a small number of these stripper-gatherers to test the market. IRRI’s SG800 stripper, however, requires a stationary thresher [25].
Chinese Threshers
China, with a 66% rural population, is the world’s largest rice producer, making up a third of the world’s total. Foot-treadle-operated threshers are still to be found in China, but electric motor-driven models of the same type, i.e., hold-on thresher with wire loop cylinder, are widely used. The Chinese have introduced rural electrification to an extent unprecedented in history. It is not uncommon to see in remote fields, far from any buildings, a thresher brigade manhandling their sled-mounted thresher with its electric motor over to a power pole socket connected to the overhead power line.
Many thresher designs have been manufactured in China, such as conical throw-in threshers, twin-drum through-flow types, vertical-shaft as well as horizontal axial-flow and fan-type power threshers. The main factor holding back axial-flow designs has probably been Chinese farmers’ diligence in making use of the whole crop, in which case they did not want to break up the rice straw. The more recently developed axial flow and rotary thresher designs do not leave the straw intact.
IRRI Axial-Flow Thresher Developments
A comprehensive USAID research project funded between 1965 and 1973 precipitated the successful redevelopment and commercialization of the axial-flow threshers at IRRI with designs that were compact, elegantly simple, and intended for small-area farming in Asia. The project placed emphasis on the need for equipment designs that could be manufactured in-country. Outreach engineers on the project sought to popularize the design and had some impact in Indonesia and India. But in the Philippines and Thailand, particularly, the adoption rate of the axial-flow thresher was rapid and extensive. In 1975 Thai manufacturers took the concept from trailer-mounted models through to power- hungry, truck-mounted models, with engines up to 100 kw, complete with power feeders and sacking elevators. In the Philippines, numerous manufacturers fabricated smaller models that could be manhandled on bamboo poles into remote fields, and they also made compact trailer-mounted models with full cleaning systems.
IRRI Engineers continued research and promotional efforts on axial-flow thresher developments. A German GTZ project has assisted with a study of crop movement
Figure 1.304. Axial-flow and rotary threshers have been around for over two centuries, but what the IRRI team was able to achieve in some developing countries was to popularize an axial design that was well-matched to small-area farming conditions and that could be locally
fabricated at modest cost. This photo shows a TC 800 axial flow thresher, the 0.5 t/h unit which is used in
conjunction with the SG800 Stripper-Gatherer (B Douthwaite, IRRI photo).
around the thresher rotor by using magnets and induction sensors. The straw may travel from 4–11 times around the rotor (Fig. 1.304). Considerations of straw flow lead to a Vietnamese design which utilizes less teeth and can thresh rice bundles that are dripping wet from flooded fields. By 1990, the government estimated that there were 1000 thresher manufacturers in the Mekong Delta of Vietnam alone, and that they had built over 50,000 units (Fig. 1.305). Following the popularization of power threshers in the Mekong, Vietnam joined the top three rice-exporting nations, with most of Vietnam’s export grain coming from the Mekong Delta.
Throw-in Threshers That Chop the Straw for Stockfeed
Many farmers in Asia want cereal straw—wheat straw in particular—to be chopped up fine for use as animal feed. In some seasons chopped wheat straw has almost as much
Figure 1.305. Trailer-mounted threshers are the most popular style in Vietnam, some are mounted on a self-driven chassis; this unit from Cantho is powered by a locally made, 15 hp water-cooled diesel and has a capacity of up to 2 t/h of cleaned paddy. The thresher is driven down the road to each pile of rice bundles stacked there ready for threshing, near a canal on the Mekong Delta. The
road is also used as a paddy-drying surface when the sun shines. (GR Quick photo).
value as the grain. Indian threshers achieve a simultaneous threshing and straw-chopping action: all of the crop material is forced through the concave and the rotor is equipped with chopping blades similar to those on a hammer mill. Often a fan is mounted integrally on the rotor axle to provide the air blast for the cleaning system underneath the concave, along with heavy flywheels to maintain the momentum required for chopping.
Where wheat and paddy are grown in rotation, such as in Egypt, parts of China and in India, farmers need threshers capable of use in either crop with a minimum of modification. An adapted thresher with a set of adjustable louvers inside the cover of the thresher drum can be fixed at 90◦to the rotor axis and the straw outlet blanked out for threshing wheat in the beater mode. The louvers are set at 75◦to the rotor axis and the straw outlet door opened for separated straw discharge for threshing paddy.
A Quantitative Assessment of Power Threshers
Information from commercial sources from eleven countries across the rice world was accumulated to calculate power versus throughput and, in the case of axial-flow threshers, throughput versus rotor width. Least-squares regression yields the result that for this group of machines as a whole, specific power (power requirement per unit of throughput, also measured by slope of the regression line for the dataset) was 6.125 kWãh/t of rough rice grain throughput.
For the axial-flow thresher data subset only, the slope coefficient of the trendline for throughput versus rotor size was 4.79 t/h per meter of rotor length. Head-feed threshers were found to require only half the power of the other types as a whole. This type of compact power thresher was not intended for capacities much above 1 t/h, because the feed tray is usually loaded by hand, which restricts feed rate.
Capacities above 2 t/h of grain throughput for throw-in or whole crop power threshers are possible in rice with a power feed mechanism. Power feeders add safety. Unless the feed apron is of sufficient length, there is always a risk of the operator getting a hand or arm pulled in to the drum or rotor of manually fed threshers. The Indian milling type threshers are the most hazardous in that regard and Indian standards have been established to try to minimize injuries to operators feeding the thresher.
There are still huge numbers of power threshers made in Asia. In China for example, a 1992 estimate was that there were 5.9 million threshers on farms and 200,000 were produced (over sixteen times the annual combine production); in India the estimate was 2.2 million on farms with an annual production of around 60,000; while for Japan the peak number of power threshers was 3.3 million in 1967 and production peaked the next year at 372, 263 units. In 1996, annual production of Japanese power threshers was 12,400—less than one-fifth of the shipment of combines that year.
The average contract charge rate for use of a power thresher has been about 4%–5%
of paddy value on farm for the Asian countries surveyed.
Summary
Local demands for threshing equipment have encouraged unprecedented produc- tion of power threshers in many developing countries. The thresher has proven to be a precursor to mechanization and a needed item that can launch indigenous manufacturing capabilities in low income countries.
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Forage Crops