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INDICIZER ADVISOR JANUARY 2004
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Indicizer Advisor January 2004
In this issue of the Advisor we will look at segregation and how using the Indicies produced by the Johanson Indicizers, can indirectly predict segregation.
Johanson Innovations, Inc. will soon introduce details on the next generation Indicizer. All older models produced after January 2003 will be fully upgradeable. The new Indicizer System will feature a more robust electronic platform with enhanced data download capability. Call us for details.
HOW THE JOHANSON INDICES INDIRECTLY PREDICT SEGREGATION EFFECTS
Any attempt to predict solids segregation must relate to the flow properties of both the mixture and individually segregated components. This newsletter considers a bimodal mixture and relates each component�s properties to segregation tendencies caused by the five most frequently encountered segregation mechanisms. The properties used to describe the components include particle size, particle shape and the Johanson Indicies relative to bin flow. All Indicies in this article are for a 10 foot-diameter bin with a one-foot outlet.
SEGREGATION PREDICTORS AND THEIR MEASUREMENT
Particle Size. Although particle size influences other Johanson Indicies, with segregation, the ability of smaller particles to fit between larger particles is critically important. In a bimodal mixture, the size differential between components rather than absolute size governs. A size difference of three or greater in the mean diameter may cause significant segregation.
Particle shape differences. Rough, flat or angular particles tend to have higher bulk internal and surface friction angles. When mixed with smoother or round particles, these materials may segregate in piles from differences in repose angles and from sliding on chutes.
The Arching Index (AI) determines the minimum conical hopper outlet diameter to prevent arching. It indicates if small particles will sift between large particles, stay on large particle surfaces or form agglomerates too large to fit between large particles.
The Ratholing Index (RI) determines the critical rathole diameter necessary to create rathole instability in funnel-flow bins. RI indicates if a finer component will agglomerate during storage before being added to a mixture. Agglomeration changes the component�s effective particle size.
The Hopper Index (HI), which is the recommended mass-flow conical hopper angle measured from the vertical, can predict chute segregation.
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