Journal Running Positions

Abstract

The classic theory of bearing lubrication propounded by Reynolds and extended by Sommerfeld has shown that when a journal runs in a full bearing with a complete film, the journal center will run opposite the center of the bearing when the journal load acts directly downward against the bearing. The classic theory has, the author believes, also shown that the journal will never rise higher than opposite the bearing center, if the bearing measures 180 deg. long and if the load line bisects that angle.

Consequently the impression has gained ground that under no circumstances will the journal rise higher than the bearing center in any clearance bearing—if the classic theory is correct. The present investigation was therefore undertaken to find out whether that current impression was reasonable. A study of journal running positions was undertaken for clearance bearings whose resultant pressures do not bisect the bearing angle.

The 120-deg. bearing was chosen for the present study because it approximates the bearings widely used in steam turbines. Other angular lengths will be studied later if the results of the present study indicate that an extension of the work is desirable, much of the preliminary work already having been done.

The result of our analysis proves that the current impression is erroneous. The journal may run with its center higher than that of the bearing, if the load, speed, viscosity, clearance ratio, and α/β ratio are compatible therewith. This must be so if the classical theory is correct.

The present analysis indicates that the load direction upon a partial bearing has an amazing influence upon the running position of the journal. It also indicates that no matter how high above the bearing center the journal may run at any finite speed, it will return to run concentric with the bearing at infinite speed.

This study disclosed other interesting phenomena that are explained in the text. Side leakage was neglected. The viscosity was assumed constant. Influence of friction upon the direction of the resultant pressure was estimated. Consequently the present work is readily comparable with that of Reynolds, Sommerfeld, Harrison, and with previous work of the author.