Strona 2_redak - Instytut Agrofizyki im. Bohdana DobrzaÅskiego ...

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96 The Chute Index (CI) is recommended chute angle to eliminate solids build up on a chute at impact points. The index takes value of CI = ASC +10°, where ASC is an angle of slipping friction along the flat surface of the bulk solid sample compressed with the pressure of 4700 N m -2 and unloaded prior to determination of ASC. The Springback Index (SBI) is the percentage of elastic springback after consolidation, and indicates when springy solids (as straw, wood, polymer foam) may arch. SBI is measured by compressing the solid to a pressure of D×BDI , and then noting the percentage change in the sample height when the load is released. Knowledge of material characteristics expressed as values of indices allows for design of technological process as anticipated. Johanson [78] presented an example of use of the indices in design of the process of blending without segregation of components. 3.1.3. Jenike & Johanson powder quality tester Tester of Jenike & Johanson [134] consists of two units: the body containing the sample holder, and the control unit (fig. 13.3). Sample holder of the volume of one US gallon (3.785 dm 3 ), has a cylindrical upper part while its lower part is conical. The upper lip of the holder may be closed with a tight cover housing a connector for supply of compressed air and fixing of the manometer. Outlet of the conical part of the sample holder can be closed with a sliding perforated plate with aperture diameter lower than the dimension of finest particles of tested material. The procedure requires a period of shaking to aerate the sample. $LULQOHW &RYHU 6DPSOH KROGHU 3HUIRUDWHG VKXWWHU 'UDZHU Fig. 13.3. Jenike & Johanson quality control tester [134]
97 The sample holder proper for particular tested material is placed in the body of the apparatus and thoroughly filled. The holder is closed with the cover and prescribed air pressure is applied that is adjusted with the valve and kept constant for 30 seconds. Then the pressure is decreased to zero and the perforated plate removed to open the outlet. The pressure gauge is turned on, and pressure in the sample holder increased till the moment of collapse of an arch when material flow commences. The measurement cycle from consolidation to outflow is repeated four times (at least) for one level of consolidation pressure. Results obtained with the tester were compared with results of the Jenike method for limestone powder and baking soda. Part of the tests showed fairly good agreement of results of the two methods, while another part was in disagreement. The authors concluded that the tester may be successfully applied for comparison of different lots of the same material [134]. 3.1.4. Uniaxial tester of POSTEC Led by premises similar to those reported by other designers of powder testers, researchers of the Norwegian institution POSTEC proposed their own solution. The tester is a type of indirect shear apparatus, namely uniaxial, and its description here is quoted after Maltby and Enstad [102]. In uniaxial compression test a compressive failure strength similar to the unconfined yield strength 1 c may be determined directly as a function of the consolidation stress 1 1 . The measurement is taken in a fraction of time required by other testers. Due to the consolidation procedure used, the tester does not measure the flow function, and therefore should not be used for silo design unless a correction factor is introduced. The procedure used assures the scatter of the results is minimal, which together with the rapidity with which such measurements can be made, makes the test perfectly suitable for quality control purposes. In the POSTEC tester (see fig. 13.4) the sample is confined in a slightly conical die and consolidated by the piston moving vertically down. The flexible membrane is stretched between the outer surface of the piston and inner surface of the lower part of the die. A layer of lubricant is spread between the flexible membrane and the die wall. The die is filled upside down and closed with a tight cover, turned upside down again and placed into the guiding device of the tester. The sample is consolidated by moving the piston until the predetermined value of 1 1 is reached, corresponding to a strain 0 1 . After a predetermined time of sample stabilization the die is raised up and compressive failure strength is measured with the piston moving down. The maximum value 1 c is reached before the sample falls apart. The apparatus allows for direct observation of the forming of failure surface that theoretically forms an angle of . ƒ + 3 with the horizontal plane. More complicated shape of failure surface points indicates that the sample was not tall enough. Using precise procedure for examination of BCR-limestone, Maltby and Enstad
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EC Centre of Excellence AGROPHYSICS
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4 9.3. Factors influencing the coef
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6 BASIC NOTATION c - cohesion [kPa]
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8 Numerous granular materials when
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10 the tensor of plastic strain inc
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12 Fig. 2.1. Yield curves with comp
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14 Stable or unstable behaviour of
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16 In turn, the model of Lade, also
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18 same porosity need not have iden
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20 where: A = ∫ E( β) sin βdβ
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22 (β = 0 o ), positioning the out
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24 grain was poured into the mould
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26 axes of the ellipse characterizi
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28 [176] for the determination of p
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30 A different approach to the desc
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32 where: I - moment of inertia, k
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34 a) b) f s f s m M f n f n Contac
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36 The micropolar model yields resu
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38 Fig. 3.17. Model of shear band f
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40 In the case of agricultural mate
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42 5.2. Density of consolidated mat
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44 (cereal grain, sand, soil), the
Page 46 and 47: 46 Multiple wetting and drying of g
Page 48 and 49: 48 vertical pressure within the ran
Page 50 and 51: 50 of the curve defined by A, where
Page 52 and 53: 52 6. Vertical consolidation refere
Page 54 and 55: 54 poured into the box without vibr
Page 56 and 57: 56 7.2.2. Bulk density Stress-strai
Page 58 and 59: 58 near the box wall and lifted alo
Page 60 and 61: 60 and the upper boundary was 18.5
Page 62 and 63: 62 A -1 5 -1 0 -5 1 0 5 -5 5 1 0 1
Page 64 and 65: 64 Fig. 8.2. Yield locus and effect
Page 66 and 67: 66 in such a way that friction woul
Page 68 and 69: 68 a) b) µ = tg ϕw ϕ w c) d) e)
Page 70 and 71: 70 9.3. Factors influencing the coe
Page 72 and 73: 72 galvanized steel received from d
Page 74 and 75: 74 9.3.4. Velocity of sliding Becau
Page 76 and 77: 76 1+ sinϕ k = . 1 − sinϕ (10.3
Page 78 and 79: 78 N ϕ VLQϕ 3UHVVXUHUDWLRN
Page 80 and 81: 80 10.4.1. Friction force mobilizat
Page 82 and 83: 82 10.4.3. Moisture content With in
Page 84 and 85: 84 Table 10.1. Measured (k s ) and
Page 86 and 87: 86 conventional engineering analyse
Page 88 and 89: 88 a, b - product-dependent coeffic
Page 90 and 91: 90 also be performed as a function
Page 92 and 93: 92 reliable processing and stable v
Page 94 and 95: 94 unconfined yield strength to pow
Page 98 and 99: 98 obtained the maximum deviation o
Page 100 and 101: 100 efficient flow control using op
Page 102 and 103: 102 In the field of experimental in
Page 104 and 105: 104 22. Britton M.G., Moysey E.B.:
Page 106 and 107: 106 69. Horabik J., Rusinek R.: Pre
Page 108 and 109: 108 114. Morland L.W., Sawicki A.,
Page 110 and 111: 110 158. 6WSQLHZVNL$ Influence of m
Page 112 and 113: 112 16. APPENDIX - Physical Propert
Page 114 and 115: 114 16.2. Density and porosity Tabl
Page 116 and 117: 116 Table 16.7. Mean values (±St.
Page 126 and 127: 126 Table 16.16. Cont. 1 2 3 4 Icin
Page 136 and 137: 136 Table 16.25. Cont. 1 2 3 4 Icin
Page 140 and 141: 140 Table 16.29. Cont. Table sugar
Page 144 and 145: 144 Table 16.35. Mean values (± St
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