FREQUENTLY ASKED QUESTIONS

Bulk Material 101

1. What is Bulk Solid ... ?
2. What is the best way to predict how a powder will behave in various processing situations?
3. Why doesn't Bulk Material Flow from a Hopper when it's supposed to?
4. What makes material bridge and rathole?

What is Bulk Solid?

A bulk solid is, by its very nature, a non-homogeneous, non-isotropic assemblage of individual particles that vary in size, shape, surface roughness, moisture content and chemical composition.  Consequently, during testing, we must consider carefully the test conditions and solids preconditioning (including the way the test cell is loaded).

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What is the best way to predict how a powder will behave in various processing situation?

Using the Diamondback Technology® System. Here is Why?  Recent development in characterizing powder flow properties show promise in predicting the success or failure of tableting presses, and related powder processing and handling equipment, with untried formulations.  Derived from basic powder flow properties, the recently developed flow indices quantify various basic powder flow phenomena related to blenders, feeders, chutes, bins and tableting presses.  The indices technique, although developed specifically for predicting flow in hoppers, feeders and chutes, shows great promise in the broader application of characterizing the theological properties of various formulations.  Because the indices area combination of basic properties, they can be extrapolated to predict the success or failure of new formulations in existing processing system.

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Why doesn't Bulk Material flow from a hopper when it's supposed to?

Material has formed a "bridge" i.e., stationary mass.  Suspended above a void area above the product outlet or "rathole" i.e., the bin is empty only in core extending from the bottom outlet to the top of the bin with the remaining material suspended both on the hopper and along the bin walls.  The Arching Index (AI) can self support suspended over the outlet opening of a conical bin.

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What makes material bridge and rathole?

• Material strength which generally increases with time and pressure.  Factors which affect material strength:

  • Moisture-especially with particles which fuse together with moisture. (i.e. cement, salt, sugar)

  • Particle shape

  • Cohesiveness

  • Static Charge

  • Elastic Springback

  • Cycling of Temperature from hot to cold (see item 1)

• Bin Geometry

  • Factors which can adversely affect flow are:

    • Square corners

    • Simultaneously converging hopper sides

    • Shallow hopper slopes

    • Non-movement of material along walls 

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