Flow Property Tests

Flow Property Tests Flowahility of the produc t granules can be charac terized by unconfined yield stress and angle of friction by... 

Temperature Cohesiveness is also affected by the solid s temperature typically, increase in temperature leads to increased cohesiveness. Flow properties testing at various temperatures may be carried out to optimize the right temperature for optimal flow. 

Steady fiow will occur with fine powders if the target flow rate (feed rate through the system) is below the critical flow rate that occurs when the solids stress is balanced by the air pressure at the outlet. The target flow rate is often controlled by a feeder, such as at the inlet to a compression machine (press feed frame). The critical flow rate, and the flow properties tests used to determine it, is described in more later in this chapter. At target flow rates exceeding the critical flow rate, unsteady flow can occur by two different modes described below. 

Therefore, when Jenike developed his methods to mathematically model the flow of bulk solids, he concluded that a bulk solid must be modeled as a plastic, and not a visco-elastic, continuum of solid particles (1). This approach included the postulation of a flow-no-flow criterion that states the bulk solid would flow from a bin when the stresses applied to the bulk solid exceed the strength of the bulk solid. The terms stress and strength are further discussed in this section on cohesive strength tests below. The flow properties test methods discussed are used to obtain the equipment parameters required to provide consistent, reliable flow. 

The applicability of the flow property test used is highly dependent on what the user is trying to capture. As an example, if there is concern that a certain batch of material may arch when transferred into a bin, a shear test may be the most comprehensive QC test. However, a quantitative test such as a shear test may require more time/resources to conduct than is practical, so faster test methods are often desired. One option is abbreviated shear cell testing (1). 

No matter the cause, the effects of temperature rises or cycles can be directly measured by flow property testing with the temperature profile of interest matched during the tests. These results can provide information for the setting of environmental controls during storage and transport. 

Generally these behaviors are unfavorable with respect to material handling, and can be investigated through flow property tests with time at rest described previously in this chapter. The results of these tests may indicate the need for steeper bin walls for unaided flow and/or larger openings to prevent cohesive arching. 

Apparent l scosily of Adhesives Having Shear-Rate-Dependent Flow Properties, Test for (D 2556)... 

Sizing an outlet to avoid cohesive arch formation is not as simple as considering only particle size. Flow properties tests need to be run to determine the material s flow function, which is the relationship between cohesive strength and consolidating pressure. Once this has been obtained, the hopper s ow/actor must be determined. The original source for... 

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