Agglomerate strength prediction

Fig. 2.6. Comparison of strength of moist agglomerates with predictions from capillary theory (data of Newitt and Conway-Jones [10] from compression testing and of Pietsch et al. [11] from tensile testing).

It can be assumed that, depending on porosity, up to saturations of = 20-40970 the liquid in moist agglomerates is present in the form of discrete liquid bridges at the coordination points between the particles forming an agglomerate. The tensile strength of such agglomerates is predicted theoretically by equations (13) and (45), respectively. 

Section III. Bonding Mechanisms in Agglomerates Adorjan, L. A., Theoretical prediction of strength of moist particulate materials, in Agglomeration 77 (K. V. S. Sastry, ed.), p. 130. Am. Inst. Min. Metall. Pet. Eng. Trans., New York, 1977. 

All methods for the determination of tensile strength described above are too complicated and time consuming to be suitable for routine industrial quality control applications. In those cases it is the task of the test procedure to determine a specific characteristic of the agglomerate easily, quickly, and reliably. The results must only be reproducible and comparable within the own organization and a relation to theoretical predictions is normally not required comparisons with results from other plants are often not necessary or, in case of competing products, not desired. 

The diagram shows that the relationship at - 1/x is fulfilled. Values lower than those theoretically predicted are mostly due to the fact that the structure is not as uniform as assumed in the model and that the agglomerates were not fully saturated when the tensile strength was determined. The liquid saturation was actually between 60 and 80% in this range liquid bridges are partially contributing to the overall strength. 

However, in practice it remains difficult to predict the tensile strength of sintered agglomerates because the primary particles are normally non-spherical and exhibit various geometries. Furthermore, the tensile strength of the viscoelastic bridges also depends on deformation speed, which makes it difficult to define and determine a stability parameter. 

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