AMETEK Brookfield Page 64
Manual No. M09-1200-F1016
Critical Wall Friction Angle:
The Wall Friction Angle of the powder forming the Critical Arch or the
Critical Rathole. This is determined by taking the Wall Friction Angle at
the corresponding Critical Consolidation Stress.
Effective Angle of Internal Friction
:
Represents the friction between sliding layers of powder, defines the
ratio of the major and minor principal consolidation stresses during
steady state flow.
Failure Locus:
The line of maximum Shear Stress that a powder can support before
flow occurs under various Overconsolidated Normal Stresses. This is
dependant on the Consolidation Level.
Fill Density
:
The Bulk Density of the powder in the trough before any stress is applied.
Flow Factor:
(Arching) Ratio of the consolidation stress in a powder during Steady
State Flow to the stress required to set up a stable arch. This factor
depends on both the flow properties of the powder and the shape of the
hopper.
Flow Function
:
Line of a powder’s Unconfined Failure Strength versus the Consolidation
stress that is applied to it.
Free-Flow:
The powder flows reliably through very small outlet dimensions under
gravity. Arching and Ratholing does not occur. This is indicated in
hopper calculations as “Free Flow” or “0.0”.
Geometeric Spacing
:
Series of values where each value is equal to the previous value times a
constant factor. The factor is chosen to space the values over the entire
range. In this type of series, there will be more values at the lower end
of the range.
Hopper Half Angle:
Maximum angle of the converging hopper wall (from the vertical axis)
needed to ensure Mass Flow. Angles greater (shallower) that this will
produce Core Flow.
Major Principal Consolidation Stress
:
The largest stress acting on the powder during Steady State Flow.
Mass-Flow:
A first in-first out discharge pattern where the powder flows at the vessel
walls and all the material is in motion.
No Flow
:
(Arching) For the given Flow Factor, the powder always arches. This is
indicated in the hopper calculations as “No Flow” or “-----”.
Normalized Flow Function:
A version of the Flow Function graph. The “normalized” flow function
provides a means for comparing powder. The graph plots “potential
arching diameter” against “major principal consolidation stress”.
The mathematics involves dividing the density of the powder at each
consilidation stress into the value for the unconfined failure strength.
This approach analyzes the strength of the powder in the abstract, which
means that the influence of the hopper is not included.
