ASTM standards flowability

There is, of course, a direct way of testing flowability by measuring the time for a standard amount of powder to be discharged from a specified funnel or hopper. This is sometimes referred to as free flow time , as for example specified by an ASTM standard method40 for testing metal powders the funnel used is the same as in the International Standard ISO 3923, Part 1. The ASTM method was used in measuring the flow time of sands in a study of particle morphology (see Ref. 10, Chapter 17). 

Plow chaiacterlstic.s. Angle of repose and flowability are measurable charac teristics for which standard tests are available (e.g., ASTM Test B213-48, Flow Rate of Metal Powders, etc.). A steeper angle of repose would indicate less flowability. The term Hubricity has sometimes been used for solid particles to correspond roughly to viscosity of a fluid. 

Compressibilities in excess of 20% tend to create particle bridges in hoppers while powders with a compressibility percentage greater than 40% are difficult to discharge (Table 1.6). At present the Hausner ratio is used more widely than compressibility, although Carr (1965c) used his parameter extensively to classify various types of powder into categories of excellent or very poor flow. The Carr approach to flow has now been subsumed into a standard test method for bulk solid flowability (ASTM D 6393-99 1999). 

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