544 hersey: laws of -lubrication 



film as it is dragged under the journal at the point of nearest 

 approach. Let the film thickness at this point be x, while c 



X 



denotes the mean radial clearance. Call the ratio - the relative 



c 



film thickness. Then if it be granted that all bearings are equaUy 



safe when running with the same relative film thickness, we may 



conveniently define carrying power as that bearing pressure 



which reduces the relative film thickness to some prescribed 



value ( - ) ■ The determination of/ and po as indicated in equations 



(5) and (6) therefore demands a physical analysis of the effect 

 of various conditions on F and x respectively. 



4- Physical conditions governing the action of lubrication. 

 Temperature is evidently a governing factor, and will in turn de- 

 pend in some complicated way on the speed. But temperature 

 can influence friction and film thickness only indirectly, through 

 its effect on the clearance and on the viscositj^ of the oil. The 

 problem may therefore be simplified by treating the dynamics 

 of the case separately from heating effects. 



The dynamical factors on which F and x may depend will 



evidently include the size and shape of the journal and bearing, 



/ c 

 which may be specified by D, — , — > and such other length-ratios 



r' , r" , etc., as may be needed to fix the shape of the oiling ar- 

 rangements, deviation from circular section due to wear, etc.; 

 the load, -L, and its line of action, specified by length-ratios r'",, 

 etc. ; the speed of the journal specified by the number of revolutions 

 n, per unit time; the relative oil supply, specified by the ratio, 

 S, of the volume of oil in the bearing to the whole volume of the 

 clearance space; and the mechanical properties of the lubricant, 

 the viscosity ix being usually the only effective property. // 

 the foregoing list includes all the determining factors we may 

 write symbolically 



F = ^2 (n, L, M, D, ^, ^, S, r j (7) 



X = xPi (n, L, M, D, ^, -, S, rj (8) 



