Agglomeration tensile strength

A second popular approach is measurement of the main impeller torque, which reflects the increasing cohesive force of the powders via addition of liquid and agglomerate tensile strength. This requires strain gauge installation on the impeller shaft, retrofit installation is more involved than power instrumentation, yet it has the distinct advantage of a direct link to the impeller load and thus the status of the granulating powders, and it is not impacted by mixer conditions. 

Theoretical Strength of Agglomerates. Based on statistical-geometrical considerations, Rumpf developed the following equation for the mean tensile strength of an agglomerate in which bonds ate localized at the points of particle contact (9) ... 

When the void space in an agglomerate is completely filled with a Hquid (Fig. Ic), the capillary state of wetting is reached, and the tensile strength of the wet particle matrix arises from the pressure deficiency in the Hquid network owing to the concave Hquid interfaces at the agglomerate surface. This pressure deficiency can be calculated from the Laplace equation for chcular capillaries to yield, for Hquids which completely wet the particles ... 

For an agglomerate of equal-sized spherical particles (Rumpf, loc. cit., 379), the tensile strength is... 

FIG. 20-65 Theoretical tensile strength of agglomerates. [Adapted from Rumpf Strength of Granules and Agglomerates, in Knepper (ed.). Agglomeration, Wiley, New York, 1962.]... 

Although measurement of the compressive strength of agglomerates is certainly more convenient for routine checking and quality control, the tensile strength is a more fundamental property, since in theory it can be... 

The tensile strength of the agglomerate in the pendular state is readily obtained by combining Eqs. (4) and (12) ... 

Figure 5.2 Tensile strength of agglomerates. From Smith, P.G., Introduction to food process engineering, Kluwer, 2003, figure 13.22. With kind permission of Springer Science and Business Media.

Tensile strength of moist agglomeration, i.e., green granules Due to... 

Betz G, Junker Biirgin P, Leuenberger H. Power consumption profile analysis and tensile strength measurements during moist agglomeration process. Int J Pharm 2003 252 11-25. 

Fig. 7.25 An axisymmetric particle freely rotating in a simple shear field. The force F exerted hy one half of the particle on the other is zero when the main axis is perpendicular to the flow direction it reaches a maximum tensile strength at 45° and it drops to zero at 90°. Then at 135° it will reach maximum compression and return to zero at 180°. If the ellipsoid is at a certain angle to the direction of shear, the same phenomenon takes place, except that the tensile and compressive forces will he smaller and the particle will rotate and wobble. If the agglomerate is spherical it will smoothly rotate and a maximum tensile strength will be generated along an axis at 45° to the direction of shear.

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