Shear impact
Shear stress refers to the mechanical stress exerted on powders, granules or bulk materials by tangential forces. These forces lead to relative movements between the particles or between the particles and the surfaces of the equipment. They occur in particular during mixing, conveying, agglomeration, comminution or dosing.
For bulk materials, the Coulomb approach is frequently used, which relates the shear stress to the normal stress and to the internal friction angle of the powder.
In powder technology, shear stress significantly influences the particle structure and product properties. It can lead to deagglomeration, comminution, dust formation, surface activation or structural changes in granules. Sensitive products react particularly sensitively to high shear stresses.
For mixing and powder processes, the specific shear energy is highly practical.
Es = Pm˙
- Es is the specific shear or mixing energy in J/kg
- P is the input power, with the unit W=J/s
- m˙ is the mass flow rate, with the unit kg/s
Shear stress can be precisely adjusted using powder mixers. Often, intensive mixing is desired without damaging the particle structure or product quality. In other cases, the opposite is desired: Agglomerates are to be broken up and particles rounded. The precision mixers from amixon® meet both requirements with a single unit. One and the same amixon® mixer can mix both extremely gently and intensively and deagglomerate, whilst always delivering an ideal mixing quality.