How to determine the selection of reducers and frames for kettles

Thread Content

The torque is usually borne by the bearings of the two output shafts within the reducer. For mixing operations with low rotational speeds and short cantilever lengths, the diameter of the shaft can be determined solely based on torque. If the cantilever length is large, the bending moment will be high; as a result, the diameter of the reducer’s output shaft and the bearings inside the reducer must also be increased. Reducers equipped with reinforced bearings will have a significantly higher price. An external bearing can also be installed to prevent the bending moment on the shaft from being transmitted to the reducer; this approach is known as a single-support frame. A bearing capable of withstanding radial forces is installed within the frame to handle the radial loads on the shaft; this reduces the reaction forces on the reducer bearings as well as the bending moments acting on the reducer’s output shaft. As a result, it becomes possible to specify the reducer based solely on torque and axial thrust. After setting up a single-pivot frame, the distance between the frame bearings and the reducer bearings is large. As can be seen from the bearing reaction formula, a larger distance reduces the load on the bearings. However, the deflection of the shafts between bearings as well as that of the cantilever shafts increases, and this increased deflection leads to poor gear meshing and accelerated wear. Excessive deflection at the sealing areas causes premature wear of the seals. A greater problem with single-support frames is that there are three bearings on a rigid shaft; centering a multi-support system is difficult, and improper installation can lead to eccentricity, which increases bearing wear and causes vibrations. Therefore, great care must be taken when choosing a single-point frame. A more feasible approach is to add another thrust bearing, resulting in a double-support frame. Both the axial and radial forces of the shaft are borne by the bearings on the frame, and the reducer can be selected based on torque. In situations where the stirring shaft is very long, resulting in high bending moments, or where there is a strong reaction force from the fluid along with high pressure inside the container, if the bearings of the reducer are used to bear these forces and torques, a larger-sized reducer is required; whereas, by using a double-support frame, a smaller gearbox will suffice. Another advantage of the double-pivot frame is that the reducer and the frame shafts are connected using elastic couplings, which solves the problem of poor alignment associated with single-pivot frames. However, due to the increased rack height, attention must be paid to the rigidity of the rack and the impact of its swinging on the tank body. Therefore, it is necessary to carefully evaluate the economic comparison between the reducer and the frame, conduct a detailed analysis of the bearings in the reducer, and in special cases, using the frame is more cost-effective. Looking at the usage of reducers and frames abroad, in Europe and the United States, gear reducers are used, with bearings generally not installed in the frames ； Japan uses gear or cycloidal reducers, with a two-support frame as the main structure ； The Soviet Union mainly used cycloidal reducers combined with single-support frames. From a rationality perspective, the design in Europe and America is the most reasonable.