The purpose of an agitator is to generate imbalances in a fluid and this causes it to be subjected to various stresses. These efforts are reflected in the following link.

The torque and other forces are absorbed in the first instance by the mobile and the second element to absorb forces is the shaft (torque and bending moment) that will transmit them to the reducer.

All elements must be designed to withstand the corresponding stresses with the appropriate safety index.

The shaft of a stirrer is a solid or hollow metal bar that transmits rotation and power. The shafts operate under a wide range of service conditions, including corrosive environments and high temperatures, and are subjected to varying tensile, compressive, torsional, bending or combined loads. Shafts are manufactured in various materials according to their application, being carbon steels and stainless steels AISI-304L and AISI-316L the most used.

Fatigue is the most common cause of cracking or even breakage of shafts and can arise from metallurgical or design imperfections. Therefore, designing the shaker with the fatigue safety factor in mind is essential.

But, what is fatigue and how does it occur?

The design of shafts subjected to dynamic loads, whose application is repetitive or fluctuating over time, even when the resulting nominal stress is lower than the yield stress, induces changes in the internal structure of the material, originating microcracks that, when propagating, lead to a progressive fracture called fatigue fracture.

Therefore, the fatigue calculation of a shaker is a dynamic calculation of the forces acting on the shaker shaft. Structural fatigue analysis is a tool to evaluate the validity of a shaker design or its durability under normal service conditions and under normal operating conditions. If the results of displacements and stresses are below a certain allowable level, it can be concluded that the design is safe regardless of how many times the load is applied.

A fatigue safety factor of 1 indicates that, if the calculations were completely accurate (which they never are), the shaker would never break down and its life would be infinite. At G&G Ingenieros we always provide this value and we choose this factor of minimum 2.5 as a safety factor in terms of operating conditions and to cover the different inaccuracies that are handled in the design.