Résumé
In a wet agglomeration process, inside a low shear mixer, the blade displacement allows for homogenizing the pulverized liquid on the powder surface and promoting the growth mechanisms of agglomerates. The efficiency of this mechanical action is obtained if the blade can apply an adapted stress field in the granular media. Low shear mixers with a vertical arm can cyclically mix the grain bed by alternating dynamic states of the particles close to the blade and static states beyond the influence length of the mobile. As a consequence, the blade displacement alternately disturbs the mechanical profile at equilibrium inside the powder bed and strongly affects the flowing powder properties once the powder is in movement. Until recently, the qualification of the static state of a granular media is essentially described by Janssen’s model, which, under some hypotheses, allows calculating the stress at the bottom of powder column. Recent stress measurements, conducted by some of us, showed that Janssen’s profile is different from the local stress profile.The objective of this work is to experimentally contribute to local stress distribution establishment inside a semi-confined granular bed. Several reactive powders issued from durum wheat were selected to estimate the physical characteristic impact of the particles (size, angle of rest…) on the local distribution of stress which is measured by a force sensor immersed in the powder bed. The results show that the shape of the local stress profiles is similar whatever the powder characteristics. The construction of the local profile is discussed according to a structuration of three layers in the powder bed, which seem to be separated by two characteristic lengths.