Indices Definitions

Symbol

Name

Use

Measurement Basis

AI

Arching Index

(linear)

Sizes hopper outlets, feeder inlets, and predicts segregation potential.

Proportional to the unconfined yield strength/bulk density ratio measures at initial solids pressures and the hopper outlet.

CI

Chute Index

(degrees)

Determines chute angles at impact points and predicts buildup in conveying units.

Derived from the chute surface adhesion after impact from a bulk solid.

HI

Hopper Index

(degrees)

Determines hopper and chute angles for flow and predicts chute segregation.

Derived from the wall surface friction angle determine at either the hopper outlet or at the top of the hopper, whichever has the greater friction angle.

RI

Rathole Index

(linear)

Sizes outlets of funnel-flow bins to prevent ratholing and predicts lump formation in bags, trucks, containers and railroad cars.

Proportional to the unconfined yield strength/bulk density ratio measured at initial solids pressures in funnel-flow bins.

BDI

Bin Density Index

(weight/volume)

Determines bin capacity and loads.

Equivalent to the bulk density measured at uniaxially applied pressures associated with the bin.

FDI

Feeder Density Index

(weight/volume)

Determines feeder capacity and loads.

Equivalent to the bulk density measure at uniaxially applied pressures associated the with hopper outlet.

FRI

Flow Rate Index

(weight/time)

Determines maximum feed rates for deaerated powders, the need for air injection, segregation potential and flooding potential.

Equivalent to the air flow resistance (permeability) measured at the hopper outlet; bulk density and density changes within the hopper.

SBI

Springback Index (percent)

Determines special hangup potential of materials that wind up elastically when compacted during storage.

The elastic bulk modulus measured uniaxially.