Mixer-Agitator Bending Moment and Shaft Deflection

Bending Moment is the Hydraulic Force (FH) acting on a shaft at a length away from the bearings perpendicular to the axis of rotation. Bending Moment causes the shaft to bend away from the central rotational axis and is critical to determine the shaft material, diameter and bearing design. Excessive bending moments or weak materials of construction can lead to catastrophic failures. The bending moment for each impeller is calculated using the applied Horsepower (HP) and impeller distance from the load bearings. The speed of the mixer and diameter of the impeller is also taken into account as well as whether or not the impeller is submerged or at the liquid surface (important for filling and emptying). After the bending moment is established, the amount of shaft deflection can be estimated using the shaft diameter and the material’s Modulus of Elasticity.