Technical handbook for the paddy rice postharvest industry in ...

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48 POSTHARVEST INDUSTRY HANDBOOK3.5. Correct method ofbolting the bucket to thebelt.the belt in meters per minute depends on the head pulley speed. The recommendedhead pulley speed depends on the pulley diameter. A properly designed bucketelevator driven at the correct speed will make a clean discharge directly into thethroat of the head liner ensuring only slight paddy damage and little or no backleggingor downlegging. If the head pulley speed is too slow, the buckets spill thepaddy into the legs. Paddy breakage occurs when the paddy is tumbled within thepulley and re-elevated, as shown in Figure 3.6(A).The optimum speed is shown in Figure 3.6(B). The buckets fill and carry optimallyand discharge the paddy directly into the throat — no spillage, no breakage.If the head pulley speed is too fast, paddy is damaged by rough and fast handlingand the buckets will not fill properly. The buckets lose all their holding and dischargecontrol (Fig. 3.6(C)). The result is inefficient operation as well as excessive breakageand undue head wear of the elevator top.For optimum centrifugal discharge, the speed of the head pulley is calculated bywhere R is the radius of the wheel plus one-half the projection of the bucket inmeters. Experience has shown that for paddy and most lightweight grains, a moreTable 3.1. Dimensions and capacities of elevator buckets.Bucket size Capacity (cm 3 )(mm)when filled toline x-xLength Projection Depth in Figure 3.4Normalspacingon belt(mm)761021271521782032292542793053056470891021141271521521521521786476951141271401591591591591841422835668501416198231153398368139645380102102127152165178203203203203229
49 CONVEYING3.6. Elevator discharge atdifferent bucket speeds:A, too slow; B, optimum,C, too fast.satisfactory operational speed is 80 to 85% of the theoretical speed. Table 3.2 showsthe recommended elevator speeds for different pulleys.Thus, elevator capacity may be calculated from 1) bucket capacity and recommendedspacing found in Table 3.1, and 2) belt speed found in Table 3.2 as follows:Elevator capacity (m 3 /h) = (bucket capacity in m 3 /1,000,000) × (number ofbuckets per meter of belt) × (belt speed inmeters/ minute) × (60 minutes/ h);Table 3.2. Recommended elevator speeds for different size head pulleys.Pulley Average Head pulley rpmPulleycircum- bucketdiameterference projection Cal- Recom-(cm)(cm) (cm) culated mended30 94 10 6641 129 10 6051 160 10 5461 192 13 4976 239 15 4491 286 18 40122 383 20 36a Belt speed (m/min) = (3.1416) × (pulley diameter in meters) × (recommended rpm).56514642313431Recommendedbeltspeed a(m/min)536513808998119
Page 1 and 2: Chapter 3CONVEYINGIn the paddy post
Page 3: 47 CONVEYINGTypesBucket elevators a
Page 7 and 8: 51 CONVEYING3.7. Elevator head show
Page 9 and 10: 53 CONVEYING8.11. Boot section desi
Page 11 and 12: 55 CONVEYING3.15. Elevator with pla
Page 13 and 14: 57 CONVEYINGments vary with segment
Page 15 and 16: 59 CONVEYINGHorsepower requirements
Page 17 and 18: 61 CONVEYING3.24. Standard hangerbe
Page 19 and 20: 63 CONVEYING3.28. Drive arrangement
Page 21 and 22: 65 CONVEYINGWhen the auger is opera
Page 23 and 24: 67 CONVEYINGExample: Determine belt
Page 25 and 26: 69 CONVEYINGeither side of the belt
Page 27 and 28: 71 CONVEYING3.40. Self-aligning cam
Page 29 and 30: 73 CONVEYING3.44. Wing-type pulley.
Page 31 and 32: 75 CONVEYING3.47. Cross section ofc
Page 33 and 34: 77 CONVEYINGMost spouting is straig
Page 35 and 36: 79 CONVEYING3.54. Five-way distribu

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