Determination of the Strength of Consolidated Powder Materials with a Pull-Based Tester

Abstract

In recent years, there has been increasing interest in the agglomeration of bulk materials. New methods are being sought to improve the measurement of bulkiness in food powders. This study aimed to design a new measuring device to assess the phenomenon of caking as well as the degree of strength of free-flowing powders. Wheat flour and potato starch have been used in the experiment and loaded into a perforated container. A steel or polypropylene measuring rod has been placed in the middle, and 5 kPa and 10 kPa were loaded, respectively. The new method is based on measuring the force through a sensor when pulling out measuring rods from the powder sample. It was shown that higher strength values have been obtained for powders loaded with 10 kPa and that groove depth has not been significant for wheat flour. Additionally, a significant difference in the evolution of the pulling force with time has been observed for wheat flour and starch, revealing a slip-stick phenomenon in the latter one. The pull-based tester is characterized by fast measurement and easy analysis of the results. The tests performed for potato starch and wheat flour have provided significantly different temporal evolutions of the pulling force.

Time of Consolidation and Humidity Influence on Properties of Food Powders

“…The more intensive water absorption by starch particles at higher ambient humidity resulted in an extended sliding time of starch particles in con-tact. Wajs et al [20] did not observe such a trend for potato starch with a moisture content of 9.5%. These authors reported that, regardless of the consolidation load, the number of oscillations was 40 and 30 for the rod made of steel and polypropylene, respectively.…”

“…Measurements were conducted using a pull-based tester specifically designed for assessing the strength of consolidated bulk materials. A detailed description of the tester with figures and measurement methods is presented in detail in the work [20] and patents PAT.241621 and PAT.241622. The pull-based tester consisted of a perforated cylindrical vessel with dimensions of 24 mm in diameter and 30 mm in height, featuring a mesh diameter of 1.5 mm.…”

“…Many bulk solids of plant origin exhibit this peculiar behavior, including wheat flour, maize starch, potato starch, and milk powder [23][24][25]. It was found that the slip-stick response is affected by, among other factors, shear velocity, coefficient of interparticle friction, stiffness of the material, and its compressibility [20,[26][27][28].…”

“…This is likely due to the presence of additional components in wheat flour, such as proteins, which can interact with adsorbed water [31]. The presence of these components and the lower content of crystalline structures may contribute to the instability of the material during the initial phase of the experiment [20].…”