hersey: laws of lubrication 543 



Equations (3) and (4) are purely formal and their practical 

 use demands a knowledge of some relation 



f = iPi {p, n, D, I, etc) (5) 



between the coefficient of friction and all the physical conditions 

 governing the action of lubrication; together with some relation 



Po = di, {n, D, I, etc.) (6) 



between carrying power and the various controlling factors. 

 Equations (5) and (6) symbohze the two laws of lubrication which 

 are needed in designing. They may be called the 'law of 

 friction" and the "law of carr>4ng power" respectively. 



2. Assumptions relating to carrying power. In designing bear- 

 ings it is of the utmost importance to decide whether carrying 

 power and speed shall be assumed to vary in the same or in oppo- 

 site directions. The former assumption is the one commonly 

 given in text-books. But the latter assumption appears to 

 represent the practice of the General Electric Company/ and will 

 be shown in this paper^ to be directly deducible from physical 

 facts. 



II. THE DYNAMICS OF LUBRICATION 



3. Scope of the problem and method of attack. This paper is 

 limited to the consideration of horizontal journal bearings lubri- 

 cated with clean oil and running under steady conditions. We 

 exclude metallic contact (very heavy load with very low speed) , 

 also the case of any appreciable thrust due to forced lubrication. 

 With these restrictions, our problem is to map out the laws of 

 lubrication as completely as can be done on the ground of com- 

 monly accepted physical principles. But it will appear that we 

 need not exclude oil-grooves, ring-oiling, eccentric load, worn 

 (i.e. non-circular) bearings, or any other purely geometrical 

 irregularities. Thus, we attack a more general case than could 

 be handled by mathematical reasoning alone. ' 



Under the above limitations we may regard the frictional 

 resistance of a bearing as due entirely to the force required to 

 shear the oil; while the tendency of a journal to center itself at 

 high speeds may be attributed to the wedging action of the oil 



1 Alford, Bearings and their Lubrication (1911), p. 81. 

 - See equation (27). 



