The Johanson Indices
The Johanson Indices are derived from measured consolidation pressures, time at rest and atmospheric conditions that simulate a plant's actual operating environment and test sample surfaces that simulate material handling equipment.
The Indices safely and accurately answer the most common material handling and equipment design questions including
- How large should the hopper outlet be?
- What hopper angle do I need?
- What happens to material inside a bin if I use vibrators or air cannons? Where do I place them?
- Do I need a hopper with flow at the walls? If so, what type?
- Can I use a partial mass-flow hopper?
- Do I need air injection to prevent limiting flow rate hangups?
- What chute angles do I need?
The following table provides a brief description of the eight Johanson Indices.
| 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 (linear) |
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 (degrees) |
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. |
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Diamondback Technology, Inc.
3851 McKay Drive
Langley, WA 98260
(360) 303-7763
info@diamondbacktechnology.com
