190 



AGRICULTURAL ENGINEERING 



Coefficient of friction of various surfaces. 



Fig. 100. A plain 

 bearing. 



*Approximate values; coefficient of friction varies with speed and load. 



Bearings. The bearings are the parts of a machine which 

 contain the rotating parts. When the bearings are a sepa- 

 rable part of the machine they are often called boxes. 

 Bearing should be designed, first, from 

 material which will give a low coefficient 

 of friction; second, so that the surfaces 

 may be thoroughly lubricated; third, from 

 materials that will resist wear or which 

 can be easily replaced; and fourth, in most cases they 

 should be adjustable for wear. 



A bearing which is made in one piece and is separable 

 from the rest of the machine is styled a solid box. A bearing 

 supported on pivots or in a socket 

 which will permit its axis to be moved 

 easily is called a self-aligning bearing. 

 The rotating part which comes in 

 contact with a bearing is usually desig- 

 nated as the journal. The journal is 

 generally made of a harder material 

 than the bearing. Thus the journal 

 is usually made of steel and the bearing of brass, bronze, 



Fig. 101. A self- align- 

 ing bearing. 



