Mechanized threshing of foodgrains for sustainable agriculture in NE
- Part 1 -

Yumnam Jekender, RK Tiwari & SK Chauhan *

Trampling of paddy under feet, beating shelves of rice or wheat crop on hard slant surface, beating crop with a flail, treading a layer of 150 to 200 mm thick harvested crop by a team of animals are traditional methods followed by farmers depending upon capacity, lot size and situation. Threshing by bullock treading is practised on a large scale in the country but it is also time consuming and involves drudgery. Tractor in many places is now used in place of animals for treading.

In all above methods, the threshed materials are subjected to winnowing either in natural wind flow or blast from winnowing fan for separation of grain from straw. Threshing by traditional method involves drudgery and takes more time to obtain required quality of stovers, straw, bhusa. Due to these, mechanical threshers are widely accepted by the farmers. Threshers are generally designated according to the type of threshing cylinder fitted with the machine.

In case of wheat threshing farmers want not only clean grain but also need fine quality of bruised straw (bhusa) for cattle feed. This requirement of quality 'bhusa' makes combining unattractive to small farmers. Drummy type, hammer mill type and syndicator type threshers are suitable for threshing wheat crops only and can produce fine quality of 'bhusa'. Rasp-bar type, wire-loop type and axial flow type threshers are suitable for paddy and they do not make fine straw.

Rasp-bar type threshers can be used for threshing other crops but farmers do not prefer this machine because it does not make fine 'bhusa'; and cost is very high due to its bulky size. Though the hammer mill type threshers can produce fine quality 'bhusa' its use is decreasing day by day due to high power requirement. Portable wire loop type pedal operated threshers are widely used by farmers in paddy growing areas.

Spike tooth type thresher can thresh wheat crop and can produce fine quality of 'bhusa' . This thresher can be used for threshing other crops if the blower is mounted on a separate shaft so that the cylinder speed can be varied independently. Majority of farmers prefer spike tooth type threshers because of their simplicity in design, low cost and their ability to make fine 'bhusa'.

Nearly 90% of power threshers are spike tooth type and majority of them are operated by a prime mover of 3-4 kW. Therefore these crops require lower cylinder speeds to minimize grain loss including seed viability. Spike tooth threshers are commonly used by farmers for threshing due to its simplicity in design, low cost, low energy requirement and lower percentage of grain damage while producing bhusa of satisfactory quality.

The machine factors which affect the quality and efficiency of threshing are feeding chute angle, spike shape, size and numbers, cylinder type, cylinder diameter, concave size, shape and clearance. The intensity of the impact of the pegs of the cylinder on the crop depends on the rotating speed of threshing cylinder which affects the threshing efficiency, grain damage and power requirement. Proper selection of a power thresher is important for low operational cost and accident free operation of the unit.

The selection criteria includes the capacity, type, safety aspects, availability of spare parts, facilities for repair, source of prime mover and suitability for different crops. The spike tooth cylinder type threshers are more acceptable than others due to their compact design, less energy consumption and less percentage of grain crackage.

In this thresher, feeding is done radially. The tip of the spike rotates with a peripheral speed of 20-25 m/s. The spike tooth thresher was found to be less accident prone (1.29%) and accidents in syndicator type threshers were maximum During late sixties AAI power thresher (3.7 kW) was designed and developed.

The spike tooth type thresher had threshing cylinder of 456 mm diameter and 300 mm length. Forty-five spikes (bits) of 12.5 mm diameter and 75 mm length were fitted in nine rows. The thresher delivered threshing capacity of 208 kg/h and total grain losses of 0.5% for wheat. Pantnagar multi-crop thresher consisted of peg tooth type cylinder of 680 mm diameter and 1400 mm length.

The spike teeth (120 no) of 18 mm diameter and 150 mm length were fitted. During field test, the thresher gave threshing capacity of 312 kg/h for wheat and the labour requirement was 1 man-h/q. PAU Wheat cum paddy thresher of 3.75 kW consisted of a spike tooth cylinder with eight rows of staggered spikes, the cylinder had three distinct portions.

The machine had a threshing cylinder with round spikes arranged in 8 rows. The grain output of the thresher reported for wheat was 2 q/h. The CIAE multi-crop thresher of 3.75 kW, suitable for wheat and paddy, consisted of spike tooth cylinder, aspirator type blower and sieve shaker. The threshing cylinder diameter and lengths were 500 and 584 mm respectively.

In the thresher ninety-two flat spikes of size 25x8x80 mm were provided. The threshing cylinder was fitted with forged spikes mounted on 8 bars in staggered fashion.

For wheat, threshing and cleaning efficiency were respectively 99.84% and 99%, at threshing cylinder speed of 19.3 m/s. Total grain losses, broken grain output capacity and power consumption were 0.82%, 0.35%, 276 kg/h and 3.4 kW, respectively. It saved 26-39% labour and operating time and 22% in cost of operation.

CIAE multi-crop plot thresher consisted of spike tooth cylinder of 250 mm diameter and 250 mm length suitable for precision threshing of wheat. The results indicated 99.3% threshing efficiency, 93.4% cleaning efficiency and 29.5 kg/h output capacity. At 1100 rpm broken grain, grain recovery and power consumption were 0.02%, 99.83% and 0.65 kW, respectively.

CIAE semi axial flow multi-crop thresher had threshing cylinder diameter of 540 mm and length of 740 mm. Seventy-two spikes of length 80 mm and 1.6 mm diameter were provided on threshing cylinder. At cylinder speed of 21 m/s, wheat output capacity was 350 kg/h. CIAE High capacity (15 kW) multi-crop thresher consisted of spike tooth threshing cylinder of 700 mm diameter and 1100 mm length.

It was provided with 3 aspirator blowers, cleaning sieves and automatic feeding and bagging systems. At 14.6 m/s threshing cylinder speed, the threshing efficiency, cleaning efficiency, output capacity and power consumption were 99.9, 99.1, 1380 kg/h and 12.5 kW, respectively.

ANGRAU power thresher consisted of threshing cylinder of 500 mm diameter and 610 mm length. It is suitable for threshing of wheat and other crops including paddy. During testing, the thresher gave cleaning efficiency of 98% and labour requirement of 9 man h/q.


To be continued ....