sunflower threshing

Biosystems Engineering (2002) 83 (4), 413–421doi:10.1006/bioe.2002.0133, available online at http://www.idealibrary.com onPM}Power and Machinery

Effect of Type of Drum, Drum Speed and Feed Rate on Sunflower Threshing

S. Sudajana; V.M. Salokhea; K. Triratanasirichaib

aAgricultural & Aquatic Systems and Engineering Program, Asian Institute of Technology, Bangkok, Thailand; e-mail of corresponding author:[email protected]

bMechanical Engineering Department, Faculty of Engineering, Khon Kaen University, Thailand; e-mail: [email protected]

(Received 15 February 2002; accepted in revised form 15 August 2002)

A study was conducted to develop a threshing unit for a sunflower thresher. The performance was evaluated interms of output capacity, threshing efficiency, grain damage, grain losses, grain and material other than grain(MOG) separation, power requirement and specific energy consumption against different drum types, drumspeeds and feed rates. The sunflower threshing capacity of a rasp bar drum was higher than peg tooth type,both with open and closed threshing drums. The threshing efficiency was found to be higher than 99%. Visiblegrain damage increased with an increase in threshing drum speed and feed rate for each threshing drum. Theminimum specific energy consumption could be achieved with the rasp bar drum at all speeds and feed rates.The rasp bar drum showed reductions in the proportions of MOG passing through the concave compared tothe both peg tooth types, i.e. with open threshing drum and closed threshing drum. The total grain separatedby the rasp bar drum was higher than 99%. At 3000 kg½head� h�1 feed rate and 750 min�1 drum speed, raspbar drum gave higher output capacity, threshing efficiency, lower grain damage and specific energyconsumption. # 2002 Silsoe Research Institute. Published by Elsevier Science Ltd. All rights reserved

1. Introduction

Sunflower (Helianthus annuus L.) is one of the world’smost important oilseed crops. Sunflower oil is consid-ered to be of very high quality (Downey et al., 1989).The oil content of sunflower is 40%, which is higherthan any other oilseed crops (Rizvi et al., 1993). It is oneof the important oilseed crops of Thailand. The areaplanted with sunflower in Thailand has increased rapidlyfrom 11; 984 ha in 1993 to 96; 000 ha in 1999, and it isexpected to increase further (OAE, 2000). This has beenmade possible largely due to the encouragement andestablishment of infrastructure by the government andprivate sectors (Aiamgrasin, 1996). Nowadays, nothresher to thresh local sunflower is available in Thai-land. Farmers in some areas of Thailand threshsunflower using a rice or soya bean thresher. However,the results obtained indicated that these threshers arenot appropriate for threshing sunflower, as graindamage may be as much as 4–10%, cleaning efficiencyonly 87–92%, and grain losses some 3–13%. Somethreshers recorded grain losses of 20–35% (Peeneejdan-gang, 1999). Moreover, at times, no thresher is available

1537-5110/02/$35.00 41

because other crops are being harvested and threshed atthe same time. One of the biggest constraints forincreasing the production area of oilseed crop inThailand has been the lack of suitable machinery duringcultivation and after harvest of these crops.In order to increase sunflower production, the

development of a sunflower thresher has thereforebecome important. The threshing unit plays a key rolein determining the performance of a thresher. Therefore,this study was conducted to study the effect of threshingdrum types, drum speeds and feed rates; to determinethe best threshing drum type, drum speed and feed rate;and to determine the grain and material other than grain(MOG) separation over the length of the threshing drum(Sudajan, 2002).

2. Literature review

Sharma and Devnani (1979) determined the effect ofcylinder tip speed and concave clearance of a rasp barthresher on threshing of sunflower. Threshing trials werecarried out by varying the cylinder tip speed from 4�81

3 # 2002 Silsoe Research Institute. Published by

Elsevier Science Ltd. All rights reserved

Chutes: (1) (2) (3) (4) (5) (6)

Fig. 1. Sunflower threshing unit

S. SUDAJAN ET AL.414

to 8�17 m s�1 and concave clearance from 4 to 12 mm.All threshing parameters were highly correlated with thecylinder tip speed and concave clearance. The germina-tion percentage was directly proportional to the concaveclearance and inversely proportional to the cylinder tipspeed. Jadhav and Deshpande (1990) developed a pedal-operated sunflower thresher. The manually operatedhold-on sunflower thresher consisted principally ofthreshing, cleaning and power transmission units. Whenfresh heads were threshed, the output capacity, thresh-ing efficiency and cleaning efficiency were about40 kg½seed� h�1, 100% and 96–98%, respectively. Rizviet al. (1993) compared the performance of differentthreshing drums for sunflower threshing. The spike/pegtooth, rasp bar and rubber strip cylinder with theirrespective concaves were used. The study showed thatthe peg-type cylinder with a speed range of 400–500min�1 and a concave clearance range from 25–30 mmcan be used for a sunflower threshing unit. Naravaniand Panwar (1994) studied the effects of the impactmode of threshing on the threshability of a sunflowercrop. The results showed that threshing efficiencyincreased as the impact energy increased at seedmoisture contents ranging from 5�76 to 13�56% wetbasis (w.b.). A threshing efficiency of 71% with 9�7%w.b. seed moisture content at an energy level of 20�6N m was observed. Bansal et al. (1994) evaluateddifferent sunflower threshers. Sunflower threshers basedon axial flow designs were mostly used. It was concludedthat sunflower should be threshed at a cylinder speed of6�5 m s�1 with a feed rate of 1500–2000 kg½head� h�1 ata grain moisture content of 30% w.b. Bhutta et al.(1997) compared the performance of a locally madesunflower thresher and a combine harvester. Thethresher was operated with a tractor power-take-off(PTO). The power-operated sunflower thresher had anoutput capacity of 447 kg½seed� h�1 with a threshingefficiency of 97�3% and a breakage of 4�87%. Thecombine harvester threshing drum consisted of eightrasp bars 1�04 m in length and was 600 mm in diameter.The combine harvester had an output capacity of 1000kg½seed� h�1 with a threshing efficiency of 98�7% andbreakage of 0�26%. Anil et al. (1998) designed anddeveloped a prototype threshing machine for sunflowerseeds, using basic principles adopted for cerealthreshers. Test results indicated that the optimalthresher performance was achieved at 9–13% moisturecontent, 180 kg h�1 feed rate and 500 min�1 cylinderspeed. Sudajan et al. (2001) determined some of thephysical properties of both sunflower seed and head atvarious moisture levels for use in the design of aprototype sunflower thresher. Commonly used sun-flower varieties in Thailand, Hysun-33, Pioneer Jumboand Cargill-3322, were used by them.

3. Materials and methods

The sunflower threshing unit (Fig. 1) operates on theprinciple of axial flow movement of the material. Thethreshing mechanism consisted of a threshing drum,which rotates inside a two section concave. The concavewas made of steel plate, with an elliptical hole of 11 mmby 60 mm. The distance between adjacent holes was11 mm, and between the hole axes was 22 mm. Theconcave clearance was fixed at about 35 mm, which hadproved satisfactory in the preliminary tests. The lengthof the concave of the threshing unit was 0�96 m. Todetermine the separation over the length of the threshingdrum, the concave was divided into six equal sectionsby metal sheets underneath the concave. Sections 1 and2 (feed and threshing section) covered the concaveover the length of the feed opening and threshing;Sections 3–5 were the threshing, separating and convey-ing sections, and Section 6 at the outlet sectionseparated the rest of the concave into two parts. Sixchutes were constructed underneath the concave tocollect the separated material from each section. Aplastic container was used to collect the material ejectedfrom the straw outlet.Three threshing drums used were a peg tooth type

with an open threshing drum a peg tooth type with aclosed threshing drum and a rasp bar type (Fig. 2). Thepeg tooth open threshing drum was constructed using 48pegs arranged in four rows on the surface of thethreshing drum. The pegs were 50 mm in height andwere cut from a 19 mm by 19 mm mild steel square.They were fixed on a drum with the help of nuts andbolts in a helical arrangement. The distance betweeneach tooth was 60 mm. The diameter and length of

Fig. 2. Threshing drum types: peg tooth with an open threshingdrum (left), peg tooth with a closed threshing drum (middle)

and rasp bar drum (right)

SUNFLOWER THRESHING 415

threshing drum were 280 and 920 mm, respectively. Thepeg tooth drum with a closed threshing drum wasconstructed in the same way. A rasp bar, closedthreshing drum had four equidistant stationary barsbuilt on the periphery of the drum in a parallelorientation. Four threshing drum speeds of 550, 750,950 and 1150 min�1, equivalent to peripheral velocitiesof 8�0; 10�9; 13�9 and 16�8 m s�1, respectively, wereused. The thresher was powered by tractor PTO (Series40 Tractor; Model 6640) and the speed was set bytractor engine throttle. The power from the tractor PTOwas transmitted to the threshing drum by use of pulleysand V-belts. The four feed rates, 1000, 2000, 3000 and4000 kg½head� h�1, were used for testing. The indepen-dent variables studied were feeding belt speed and feedrate. Material was loaded on the belt conveyor and fedinto the hopper. The drive to the belt conveyor wasprovided and controlled from a 5�6 kW variable-speedelectric motor.The commonly grown sunflower variety, Hysun-33,

was used for this experiment. It was harvested by thetraditional method. The moisture content of the grain,head and straw was determined by the oven-drying meth-od (ASAE, 1983). The average moisture contents of seedsand straw were 7�26 and 13�05% w.b., respectively. Theaverage ratio of seed to straw was 1�25 on dry basis (d.b).Threshing drum speed was measured using a proxi-

mity switch. The torque transducer was used to measurethe torque in this experiment. The strain amplifieramplified the output signals received from the transdu-cer and recorded. The torque transducer was calibratedin static condition. The power requirement was calcu-lated by using the formula given by Kepner et al. (1978)and Hunt (1995).The following performance indicators were used for

the evaluation (RNAM Test code, 1995): output

capacity, threshing efficiency, grain damage, grain loss,power requirement, grain and MOG separation andspecific energy consumption. The performance of thedeveloped threshing unit was analysed against differentthreshing drums, threshing speeds and feed rates byusing a randomised complete block design (RCBD) of a3 by 4 by 4 factorial experiment with three replicationsin each treatment, and comparison between treatmentmeans by the least significant difference (LSD) at the 5%level (Box et al., 1978; Gomez & Gomez, 1984).For each threshing performance test, sunflower heads

were fed to the threshing unit at a particular combina-tion of threshing drum type, drum speed and feed rate.After the test run, the samples collected from chutes 1–6were cleaned to determine grain and MOG separationover the concave length. The samples of threshed grain,broken pieces of head, the straw passed down throughconcave openings and the material ejected from thestraw outlet were collected and separated. After mixingthe grain from chutes 1–6, visual analysis of graindamage was conducted.

4. Results and discussion

4.1. Effect of type of threshing drum, drum speed

and feed rate on capacity

The analysis of variance showed that the threshingdrum type (A), drum speed (B) and feed rate (C)significantly affected threshing capacity (Table 1). It wasobserved that the effect of drum type was the mostsignificant, followed by drum speed and feed rate.Among the first-order interactions, the order ofimportance was AB, AC and BC, all being significantat the 1% level of significance. Among the second-orderinteractions, ABC was highly significant.

Figure 3 shows the effect of drum speed on thecapacity of individual threshing drum and four feedrates. The results indicated that the capacity of the raspbar drum was higher than both peg tooth typesthroughout the range of drum speeds and at all feedrates. At 1000 kg½head� h�1 feed rate, the capacity of therasp bar drum increased from 531–577 kg h�1 as drumspeed increased from 550 to 950 min�1, and it decreasedslightly when the drum speed increased to 1150 min�1.At 2000, 3000 and 4000 kg½head� h�1 feed rates, thecapacity of the rasp bar drum increased rapidly withdrum speed variation from 550 to 750 min�1, thenshowed little difference with further increases of drumspeed from 750 to 950 min�1. It slightly decreased whenthe drum speed increased to 1150 min�1 except at 4000kg½head� h�1 feed rate. The capacity of the rasp bardrum at 2000, 3000 and 4000 kg½head� h�1 feed rates

Table 1Analysis of variance of the results of the performance of the sunflower threshing unit

Sourceof variation

df F-value

Capacity Threshing efficiency Grain damage Grain loss

Replication 2Drum type (A) 2 441:379* * 4:629* 44:455* * 20:611* *Drum speed (B) 3 71:067* * 2.643ns 66:946* * 2:455*Feed rate (C) 3 46:586* * 0.133ns 7:390* * 40:576* *AB 6 24:983* * 7:681* * 3:308* * 6:070* *AC 6 12:229* * 3:607* * 0.889ns 2:522*BC 9 9:664* * 2:751* * 3:246* * 0.735nsABC 18 3:371* * 1:943* 2:091* 1.054nsError 94

* *Highly significant at 1% level; * significant at 5% level; ns, non-significant; df, degrees of freedom.


increased from 532 to 879, 450 to 1038 and 416 to1015 kg h�1, respectively, with drum speed variationfrom 550 to 750 min�1. However, the mean capacities ofboth peg tooth types showed little difference at all drumspeeds and feed rates. The capacities of the peg toothwith an open threshing drum and the peg tooth with aclosed threshing drum were between 354–541 and 338–575 kg=h�1, respectively. The highest threshing capacitywas obtained from the tests carried out with the rasp bardrum, which had a rough surface (corrugated bar) onthe periphery of the drum. Roughness on the rasp barmay have produced more rubbing and shearing betweenthe rasp bar and the material being threshed than forother drum types. On the other hand, threshing materialstruck by a peg tooth can bounce off in any direction,depending on the angle of the strike. Owing to thedistance between each tooth and the space between thepeg tooth and the concave clearance in the upper part ofthe threshing unit, no coherent crop mat moving aroundthe drum was found. The movement of the crop in anaxial direction was not continuous, with the crop oftenmoving back axially in the direction of the feed section.Figure 4 shows that, as feed rate was increased, thecapacity generally increased at 750, 950 and 1150 min�1

drum speeds for all threshing drums. The capacity of therasp bar drum rapidly increased as the feed rateincreased from 1000 to 4000 kg½head� h�1. From theabove results, the best capacity ð1038 kg h�1Þ wasrecorded with the rasp bar drum at 3000 kg½head� h�1

feed rate and 750 min�1 ð10�9 m s�1Þ drum speed.


and feed rate on threshing efficiency

Table 1 shows that drum type affected the threshingefficiency significantly at the 5% level. Among the first-

order statistical interactions, the order of importancewas drum type and drum speed (AB), drum type andfeed rate (AC), and drum speed and feed rate (BC), allbeing significant at the 1% level. Among the second-order interactions between threshing drum type, drumspeed and feed rate, ABC was significantly different atthe 5% level. Comparison among treatment means usingLSD showed that at 2000, 3000 and 4000 kg½head� h�1

feed rate with 750 and 950 min�1 drum speed, thethreshing efficiency of the three types of drums did notdiffer significantly. Test results indicated that threshingefficiency was within a narrow range of 99�77–100%, forthe range of variables studied. This was because, for allthreshing drums, drum speeds and feed rates, the energygiven to the ear head and grain sufficiently increasedsunflower threshing. This might be due to sunflowerseeds adhering loose to the flower head at the low seedmoisture content. The attaching force between seed andflower head might get reduced and hence seeds might getseparated easily. This might have resulted in a higherthreshing efficiency.


and feed rate on grain damage

Table 1 indicates that the analysis of variance of themain effects of the type of threshing drum, drum speedand feed rate significantly affected grain damage at the1% level. The effect of drum speed on grain damage wasthe most significant, followed by drum type and feedrate. Comparison between treatment means using LSDshowed that at 1000 kg½head� h�1 feed rate with the raspbar type, the grain damage at 550, 750, 950 and 1150min�1 speeds did not differ significantly for either typeof peg tooth drums. At 2000 kg½head� h�1 feed rate withthe rasp bar drum, the grain damage at 750, 950 and

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Fig. 3. Effect of drum speed and drum type on capacity atdifferent feed rates (^, rasp bar drum; &, peg tooth with anopen threshing drum; 4, peg tooth with a closed threshing drum)

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Fig. 4. Effect of feed rate and drum speed on capacity atdifferent threshing drums (^; 550 min�1; &; 750 min�1;

m; 950 min�1;�; 1150 min�1Þ


1150 min�1 drum speeds was not significantly differentfrom the other two types. The other pairs of interactionsshowed statistically significant difference. At 3000 and4000 kg½head� h�1 feed rates with the rasp bar drum, thegrain damage at 750, 950 and 1150 min�1 drum speedswas significantly different from that found for otherdrums. The mean grain damage by the rasp bar type at550, 750 and 950 min�1 drum speeds did not differsignificantly from 1000 to 3000 kg½head� h�1 feed rates.The mean grain damage by the peg tooth with an openthreshing drum did not differ significantly from 1000 to4000 kg½head� h�1 feed rates at 550, 750 and 950 min�1

drum speeds. The mean grain damage by the peg toothtype with a closed threshing drum did not significantlydiffer from 1000 to 4000 kg½head� h�1 feed rates at eachdrum speed.

Figure 5 shows the effect of drum speed on the graindamage of individual threshing drum at four feed rates.The results indicated that the grain damage increasedwith an increase in drum speed for all drums and feedrates. This increase was due to higher impact levelsimparted to the crop during threshing at higher drumspeeds. The grain damage by the rasp bar type washigher than that caused by the other two types. The

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Fig. 5. Effect of drum speed and drum type on grain damage atdifferent feed rates (^, rasp bar drum; &, peg tooth with anopen threshing drum; n, peg tooth with a closed threshing drum)


reason for this is in line with the findings explained inthe above section (rough surface on the rasp bar). At afeed rate of 1000 kg½head� h�1, the grain damage by alldrums slightly increased from 1�24 to 1�83, 0�80 to 1�18%and 1�20 to 1�26% with an increase in drum speed from550 to 950 min�1. The grain damage increased from 1�83to 3�42, 1�28 to 2�49 and 1�26 to 1�86% with an increasein drum speed from 950 to 1150 min�1. At a feed rate of2000 kg½head� h�1, the grain damage by all three typesslightly increased from 1�23 to 1�93, 0�56 to 1�52 and 0�84

to 1�49% with an increase of drum speed from 550 to1150 min�1. At a feed rate of 3000 kg½head� h�1, thegrain damage for the rasp bar type increased graduallyfrom 0�98 to 2�52% with increases in drum speed, while itincreased slightly from 0�74 to 1�67 and 1�17 to 1�75% foropen and closed peg tooth drums, respectively. At a feedrate of 4000 kg½head� h�1, the grain damage caused bythe rasp bar drum rapidly increased from 0�92 to 2�08%with an increase of drum speed from 550 to 750 min�1,and it slightly increased with further increase in speedvariation from 750 to 1150 min�1. From the aboveresults, it can be observed that the grain damage was lessthan 2% when the drum speed increased from 550 to950 min�1 (8�06 to 13�93 m s�1Þ and 1000 to 3000 kg½head� h�1 feed rate. The recommended parameters arethose at which the visible grain damage should be within2% (King & Riddolls, 1960; Sharma & Devnani, 1979;Vejasit, 1991) to maintain better storage qualities.


and feed rate on grain losses

Table 1 shows the analysis of variance of the maineffects on grain losses. Test results showed that the effectof feed rate was the most significant, followed by drumtype and drum speed. Comparison between treatmentmeans of grain losses using LSD showed that the grainlosses did not differ significantly at 2000–4000 kg½head�h�1 feed rate for all threshing drum types. Grain lossesat 1000, 2000, 3000 and 4000 kg½head� h�1 feed ratesshowed a similar trend. Grain losses when drum speedincreased from 550 to 1150 min�1 did not differsignificantly among the three drum types. Test resultsindicated that the grain losses were between 0�15 and1�22% for all drum types, drum speeds and feed rates.


and feed rate on power requirement and specific

energy consumption

The type of threshing drum, drum speed and feed ratesignificantly affected the power requirement and specificenergy consumption at the 1% level of significance. Theeffect of drum speed was the most significant on powerrequirement, followed by feed rate and drum type. Thetype of drum affected specific energy consumption mostsignificantly, followed by drum speed and feed rate. Thepower required by different threshing drums at differentdrum speeds and feed rates is shown in Fig. 6. It wasobserved that the power requirement of the threshingunit increased as the speed of threshing drum wasincreased. The power requirement of drum increasedwith drum speed because of the increased feed rate

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Fig. 6. Effect of drum speed and drum type on power require-ment at different feed rates (^, rasp bar drum; &, peg toothwith an open threshing drum; 4, peg tooth with a closed

threshing drum)

Fig. 7. Effect of drum speed and drum type on specific energyconsumption at different feed rates (^, rasp bar drum; &, pegtooth with an open threshing drum; 4, peg tooth with a closed

threshing drum).


which accounted for the extra energy required forthreshing the material. The increase in feed rate requiredgreater compression of the material as it passed betweenthe threshing drum and concave causing an increase inpower requirement. The average power requirement forthe rasp bar type at 3000 kg½head� h�1 feed rate wasbetween 1�80 and 4�00 kW, when the drum speed wasincreased from 550 to 1150 min�1 (8�06 to 16�86 m s�1Þ.For the two peg tooth drums, these values were 1�82–4�00 kW (open drum), and 2�17–3�45 kW (closed drum).

The relationship between specific energy consumptionand the speed of the threshing drum is shown in Fig. 7.It was observed that specific energy consumption forsunflower threshing was lowest for the rasp bar drum atall feed rates and drum speeds. The specific energyconsumption of the rasp bar drum was lowest at about750 min�1 ð10�9 m s�1Þ drum speed and at 3000 and4000 kg½head� h�1 feed rates. The specific energy con-sumptions were 3�01 and 2�91 kWh t�1 at 3000 and4000 kg½head� h�1 feed rates, respectively.

(1) (2) (3) (4) (5) (6)

Chute section no.

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Fig. 8. Cumulative percentage of separable grain and materialother than grain (MOG) versus the length of the concave with3000 kg½head� h�1 feed rate and 750 min�1 drum speed (^, raspbar drum, grain separation; &, peg tooth with an open threshingdrum, grain separation; m, peg tooth with a closed threshingdrum, grain separation; }, rasp bar drum, MOG separation; &,peg tooth with an open threshing drum, MOG separation; 4, peg

tooth with a closed threshing drum, MOG separation)


4.6. Effect of the threshing drum length on grain

separation

Figure 8 shows the relationship between the length ofthe concave and cumulative separable grain and MOGat a feed rate of 3000 kg½head� h�1 and drum speed of750 min�1. In Sections 1 and 2 (feed and threshingsections, the concave length of these sections was 320mmÞ of the concave, more than 65% (65�14–67�86%) ofthe grain was separated when both peg tooth drumswere used, while less than 3�5% (2�82–3�05%) wasseparated in Section 6 (outlet section). The percentageof the total grain separated by the concave increasedrapidly from 0 to 84�37% for the peg tooth open drumand 0 to 88�34% for the peg tooth closed drum as thelength of the concave increased from 0 to 480 mm(chutes 1–3). For the rasp bar drum, the percentage oftotal grain separated increased gradually from 0 to82�64% as the length of concave increased from 0 to 640mm, and it increased from 82�64 to 99�65% when theconcave length increased to 960 mm. The total grainseparated in the outlet section was about 7�11%. On theother hand, the percentage of the total MOG separatedwas almost the same in all six sections. The percentageof MOG separated by the concave (through theconcave) for the rasp bar type in each section was lessthan that for either peg tooth types. The percentage ofMOG separated increased from 0 to 44�3% for the raspbar type, 0 to 61�0% for peg tooth open drum and 0 to66�4% for peg tooth closed drum. It increased with the

increase of the concave length. This means that thepercentage of total MOG separated at the straw outletwas about 55�68% for the rasp bar, 38�96% for peg toothopen drum and 33�55% for peg tooth closed drum. Thereason for the low MOG separated by the rasp bar drumwas the rubbing and cushioning effects which did notmake fine straw. These findings are in conformity withthose reported by John Deere Service Publication(1973); Klenin et al. (1986), Majumdar (1986) andPandey et al. (1997). The important observations at thestraw outlet indicated that the rejected material by raspbar type was greater than both type of peg tooth drums.This indicated that threshing of sunflower with the raspbar drum could reduce the MOG on the cleaningsystem. However, the percentage of grain losses was lessthan 1% for all threshing drum types.

5. Conclusions

The type of threshing drum, drum speed and feed rateaffected the output capacity, threshing efficiency, graindamage and grain losses during sunflower threshing. Thecapacity of the rasp bar drum was higher than the pegtooth type with an open threshing drum and the pegtooth type with a closed threshing drum at all drumspeeds and feed rates. The threshing efficiency was foundto be in the range of 99�77–100% for all threshing drums,drum speeds and feed rates. The lowest specific energyconsumption was by the rasp bar drum at all drumspeeds and feed rates. The percentage of material otherthan grain (MOG) separated through the concave by therasp bar drum was lower than for the other two types.This means that the rasp bar drum could reduce MOGload on the cleaning system. The rasp bar drum gave thebest sunflower threshing performance. The outputcapacity, threshing efficiency, grain damage, grain lossesand specific energy consumption at 750 min�1 drumspeed and 3000 kg½head� h�1 feed rate were 1038 kg h�1,99�99%, 1�39%, 0�36% and 3�01 kWh t�1, respectively.

Acknowledgements

This work was supported by grants from the AsianInstitute of Technology, Bangkok, Thailand; KhonKaenUniversity, Khon Kaen, Thailand and the NationalResearch Council of Thailand, Bangkok, Thailand.

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