Abstract:

ESDU 94008 presents a method for calculating values of lubricant film thickness in the contact region between a disc cam and a follower (where the contact can be described as either "rolling" or "sliding") at regular intervals during a complete rotation of the cam. The calculation of film thickness is a vital step in the design of a lubricated cam mechanism and is especially useful when selecting suitable materials, surface treatments, surface finishes, lubricants and lubricant additives.

The method involves calculation of the force acting at the cam/follower interface due to follower system inertia, externally-applied load and the action of a return spring. It is also necessary to calculate values of lubricant entrainment velocity and cam profile radius of curvature. These quantities, together with the materials properties of the cam and follower and the properties of the lubricant are used to calculate film thickness. A computer program (ESDUpac A9408) that performs all the necessary calculations is provided with this Data Item. Also provided is a Windows executable interface program (VIEWpac W9408) that allows the program to be run in a user-friendly manner. The program includes an option allowing the user to determine suitable values of spring rate and preload to ensure that contact between cam and follower is maintained.

The Item contains a description of the mathematical model on which the calculation is based together with guidance on the use of the program, including interpretation of the output. Three examples illustrating the use of the program in realistic design situations are presented.