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

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unconfined yield strength to powder density 1 c was used as a measure of flowability,
a low degree of consistence with the direct shear test was observed, particularly at low
range of normal pressure. At higher levels of normal pressure, both the methods gave
fairly close results. The authors [16] performed a ranking of a number of materials
based on the Jenike and Johanson methods and found that the two methods gave
results in a fairly good agreement. In summary, Johanson’s indcizer was found to
be a convenient and repeatable tool to use, but its predicted 1 c values and arching
and rathole diameters did not correlate well with the results of the Jenike cell. For
some materials good agreement of flowability ranking was obtained under certain
circumstances, but the basis for these limiting circumstances could not be quantified.
JR Johanson Inc. proposed investigations of materials in a wide range of
temperature and moisture content. Standard testing has been offered for determination
of density, permeability, strength and angles of friction and adhesion.
Testing of flowability using Johanson’s indices is also offered. Values of parameters
for determination of the indices are measured under pressures and for scale
factors corresponding to the dimensions of equipment applied in the process
under consideration. Some indices have physical dimensions expressed in US
units, as for that market the equipment was meant.
The Arching Index (AI), with a typical range of 0-4 ft (1.22 m), is the conical
hopper outlet required for unaided gravity flow after dropping the solids into an
empty hopper and ensuring arch collapse in a conical bin. The AI is related with
material properties as follows: AI = 2.21 c /, where 1 c i are measured under normal
consolidation pressure of: 3d/2.
The Ratholing Index (RI) – typical range, 0-30 ft (0 to 9.15 m) – is the flow
channel size in a hopper required for a solid to collapse into the hole above the
outlet, if arching did not occur. RI also provides a good indication of lumping
tendency. If, after a time at rest, the solids RI exceeds 10 ft (3.05 m) a lump breaker
may be needed in the system. The RI is related with material properties as follows:
RI = 2.51 c where 1 c DQGDUHPHDVXUHGDWFRQVROLGDWLRQSUHVVXUHRId.
The Hopper Index (HI) is the minimum half-angle of a conical hopper, required
to ensure flow along the hopper walls. Its value is HI = 42 –3where –3 is the
angle of kinetic friction measured at nRUPDO FRQVROLGDWLRQ VWUHVV RI d, or if 3
increases with an increase in stress value of 3 determined at the stress level of D.
The Flow Rate Index (FRI) – typical range 1-12000 lb min -1 (0.5 to 5400 kg min -1 )
is the rate at which the solid will flow through a hopper outlet of diameter d when
totally deaerated. Low value of FRI usually points out to fine, highly compressible
powder. Particles of sizes in excess of 400 m are usually incompressible, very
permeable, and have a high FRI. Variation in the value of the index may be a signal
of segregation or change in composition of powder mixture during processing.