Carrs index

The roller compactor s full axial rolls produced compacts in the form of sticks. The unmilled compacts from both machines had the same density, 1.3g/cm. The milled roller compacts produced comparative granules except for bulk density and correspondingly the Carr index values ... 

A common powder flow index includes the Carr Index, calculated as shown in Equation (5). In this index, the ratio of the difference of the tapped versus bulk density to the tapped density is given. This ratio, multiplied by 100 to convert to percent, indicates poor flow when the index equals 20 or greater. 

For example, the use of a shear cell for determination of flow properties (cohesion) has been conducted as shown in Figure 1. Despite some variability, the shear cell values obtained correlated well with the Carr Index. 

Figure 1 Shear cell index versus Carr Index.

The bulk density (/%) of a powder mixture is its mass divided by the bulk volume it occupies. The tapped density (p,) is the density of a powder mixture that has been compacted by tapping or vibration following a specified procedure. Carr57 reported that the more a material is compacted in a compaction or bulk/tapped density test, the poorer its flow properties. Carr index (i.e., compressibility), is defined as ... 

A Carr index less than 21 for a powder mixture indicates good flow, while one between 21 and 25 suggests a marginal flow property. A more commonly used term is the Hausner ratio, which is simply p,/pb, or the tapped density divided by bulk density. This ratio was introduced by Hausner in 1967 to characterize metal powders,58 but is commonly used today for pharmaceutical powders. The higher the Hausner ratio, the poorer the flow. The Hausner ratio varies from about 1.2 for a free-flowing powder to 1.6 for cohesive powder. 

Flow Property Angle of Repose (deg) Carr Index (%) Hausner Ratio... 

The Hausner ratio varies from about 1.2 for a free-flowing powder to 1.6 for cohesive powders. Carr index classifications for flowability [2] are listed in Table 15. 

TABLE 15 Carr Index Classification and Powder Flowability... 

As mentioned in previous sections of this article, the Carr index as well as other empirical tests such as the Hausner ratio continue be used, often in combination with other tests to characterize and predict the flow of pharmaceutical excipients and formulations. In addition to papers already discussed in this article... 

Angle of repose Minimum orifice diameter Carr index Flow rate and... 

Additional test methods A brief review of additional test methods such as the angle of repose, Hausner ratio and Carr Index, and flow rate through an orifice. 

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