Powder Manual Glossary

Angle of Internal Friction
Angle is a measure of how easily a powder can flow under an applied force, such as gravity
Angle of Wall Friction
Represents the frictional interaction between a powder and the wall of a hopper or chute during the onset of flow
Arching Dimension
Critical outlet size required to prevent the formation of stable arches across a hopper outlet in mass flow conditions
Axial Distance
Distance between the lid from the bottom of the trough, indicating the depth of the powder
Axial Load
Vertical load applied to a powder sample during testing to simulate consolidation
Bulk Density
Mass powder divided by its total volume, measured during a test to understand compaction and flow characteristics
Bin Diameter
Maximum internal diameter of a storage vessel, critical in assessing flow behavior within industrial systems
Cohesion
Measure of the internal strength of a powder after compaction under a specific consolidation stress
Consolidation
Process of applying Normal and Shear stress to a bulk solid to move the particles together, to observe any increases in its Cohesion, Bulk Density, etc
Consolidation Stress
Stress applied to compress a powder, influencing flowability and cohesiveness
Core Flow
Flow pattern where material moves through a central channel, leaving stagnant zones near the vessel walls
Critical Arch
Largest arch span that a given powder can support before collapsing under its self-weight

Critical Consolidation Stress
• For Arching: Major Principal Consolidating Stress acting on the powder in the hopper at critical arching dimensions during mass flow
• For Rathole: Major Principal Consolidating Stress acting on the powder in the region of the outlet due to the head of powder in a core flow hopper

Critical Density
Bulk Density of the powder forming the Critical Arch or the Critical Rathole, determined by taking the bulk Density at the corresponding Critical Consolidation Stress

Critical Internal Friction Angle
Internal Friction Angle of the powder forming the Critical Arch or the Critical Rathole, determined by taking the Internal Friction Angle at the corresponding Critical Consolidation Stress

Critical Rathole
Largest rathole diameter a powder can support before collapsing in a Core Flow regime

Critical Stress
Unconfined Failure Strength of the powder forming the Critical Arch

Critical Wall Friction Angle
Wall Friction Angle of the powder forming the Critical Arch or the Critical Rathole, determined by taking the Wall Friction Angle at the corresponding Critical Consolidation Stress

Density Curve
Graphical representation of the relationship between bulk density and applied stress, used to assess materials compressibility

Drive Disc
Rotating platform in the PFT that supports the sample trough during testing

Effective Angle of Internal Friction
Friction Angle derived from the steady-state flow of a powder under consolidation, indicative flow behavior

Effective Stress
Stress distributed among the powder particles, accounting for load and environmental factors

Failure Locus
Curve representing the maximum shear stress a powder can sustain at varying normal stresses before flow occurs

Fill Density
The bulk Density of powder before compaction or application of any external stresses

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
Relationship between unconfined failure strength and consolidation stress, used to characterize powder flowability

Flow Index
Derived value that quantifies a powder’s flow characteristics under defined stress conditions

Friction Angle Curve
Plot illustrating the angle of friction at various stress levels, used to assess wall and internal friction properties

Hopper Half Angle
Angle between the vertical and converging walls of a hopper, influencing whether mass flow or core flow will occur

Mass Flow
Flow pattern where all powder within a vessel is in motion, ensuring first-in-first-out discharge and minimal stagnation

Major Principal Consolidation Stress
Largest stress acting on the powder during Steady State Flow

No Flow
(Arching) for the given Flow Factor, the powder always arches, indicated in the hopper calculations as “No Flow” or “-----"

Normolized Flow Function
Flow function adjusted for density variations, used for comparative analysis of powders

Normal Stress
Stress due to the Axial Load, stress applied perpendicular to the powder bed

Overconsolidation
After Consolidation, reducing the Normal Stress without shearing so that the Bulk Density is high relative to the new Normal Stress

Rathole Diameter
Minimum outlet diameter of a Core Flow hopper needed to ensure that the powder will flow instead of forming a stable rathole

Shear Stress
Stress due to the Torsional Load. It is the stress between parallel layers of powder (Flow Function and Time Consolidated Flow Function tests) or a layer of powder and the lid (Wall Friction test)

Steady State Flow
Continuous powder flow where the Normal and Shear Stresses have reached a constant level

Time Consolidation Test
Compacts the powder at a given Consolidation Level for an extended period (hours, overnight to represent static storage in a hopper) before measuring the Failure Locus

Torsional Distance
Distance that the trough has rotated from its starting position at the beginning of the test

Torsional Load
Rotational force applied during testing to simulate shear conditions within the powder sample

Trough
Container that holds the powder sample during testing, available in standard and small volume sizes

Unconfined Failure Strength
Maximum stress a compacted powder can withstand at a free surface, after it has been compacted to a given Consolidation Level

Wall Cohesion
Measure of the adhesives force between a powder and the wall of a hopper or chute

Wall Friction Test
Test to determine the interaction between powder and wall surfaces, influencing hoper design

For Immediate assistance,

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