Development Of Design Equations For A Square-tube Subbase Supporting A Shaft-mounted Speed Reducer

Abstract

Shaft mounted speed reducers are used in material handling applications, such as conveyor systems for transporting ore out of mine shafts. A subbase joins the reducer with an electric motor, and serves to limit the misalignment between the motor shaft and the reducer input shaft. The entire assembly is supported at two points: the axis of rotation of the reducer output shaft, which is fixed, and a clevis-pin joint under the motor, which prevents rotation of the assembly about the reducer output shaft axis.

In an effort to reduce the production and material costs of subbases that support shaft mounted reducers, Rexnord Corp. is implementing subbase designs that are lighter weight and easier to manufacture than current designs. Impeding the implementation of lower cost designs is the lack of an equation to properly choose subbase dimensions for acceptable values of shaft misalignment. Trial and error in subbase construction may provide designs that give acceptable results for misalignment. Given an equation, however, the weight could be minimized while still limiting misalignment at the coupling location. The project goal is to provide equations that give shaft misalignment as a function of three subbase parameters: tube thickness, mounting strap width, and end cap thickness.

Developing design equations by analytical methods is investigated first. Next, finite element models are used to check the analytical results for accuracy. Finally, finite element models are used to perform design sensitivity studies where needed. The final equations for misalignment are given as functions of the three design variables.