8.15 : Collar Bearings

Collar bearings are essential in various machines designed to support axial loads on rotating shafts. Depending on the specific application and requirements, they can be found with single or multiple collars.

Consider a single collar bearing subjected to an axial load. The total bearing contact area is the region between the external radius and the internal radius of the collar. When the bearing is assumed to provide even support, the uniform normal pressure can be calculated by dividing the force applied on the collar by the total bearing contact area. This value represents the average pressure distribution across the bearing surface.

To further analyze the forces acting on the collar bearing, consider a small, infinitesimal area element on the bearing surface. The force acting on this infinitesimal area is a product of the friction coefficient, pressure, and differential area. Understanding the relationship between these variables is crucial in calculating the moment required for the shaft to rotate.

The impending rotation of the shaft is determined by analyzing the moment equilibrium equation about the rotational axis. This equation considers all the forces and moments acting on the shaft, including the frictional forces generated by the collar bearing.

By integrating the equation, the applied moment needed to overcome all these frictional forces can be determined, which initiates shaft rotation. Finally, to estimate the moment of the shaft, substitute the differential force and area values into the integrated equation.

Integrating this equation over the total bearing area provides a comprehensive understanding of the forces and moments acting on the collar bearing and the moment required for the shaft to rotate.