Chapter 5- FUNDAMENTALS OF SHIP PROPULSION AND STEERING 



elements. Both roller and ball bearings are 

 made in different types, some being arranged 

 to carry both radial and thrust loads. In these 

 bearings, the balls or rollers generally are 

 assembled between two rings or races, the 

 contacting faces of which are shaped to fit the 

 balls or rollers. 



The basic difference between ball and roller 

 bearings is that a ball at any given instant 

 carries the load on two tiny spots diametrically 

 opposite while a roller carries the load on two 

 narrow lines (fig. 5-9). Theoretically, the area 

 of the spot or line of contact is infinitesimal. 

 Practically, the area of contact depends on how 

 much the bearing material will distort under 

 the applied load. Obviously, rolling contact 

 bearings must be made of hard materials be- 

 cause if the distortion under load is appreciable 

 the resulting friction will defeat the purpose of 

 the bearings. Bearings with small, highly loaded 

 contact areas must be lubricated carefully if 

 they are to have the antifriction properties they 

 are designed to provide. If improperly lubri- 

 cated, the highly polished surfaces of the balls 

 and rollers soon will crack, check, or pit, and 

 failure of the complete bearing follows. 



Both sliding surface and rolling contact 

 bearings may be further classified by their 

 function as follows: radial, thrust, and angular- 

 contact (actually a combination of radial and 

 thrust) bearings. Radial bearings, designed 

 primarily to carry a load in a direction per- 

 pendicular to the axis of rotation, are used to 

 limit motion in a radial direction. Thrust bear- 

 ings can carry only axial loads; that is, a force 

 parallel to the axis of rotation, tending to cause 

 endwise motion of the shaft. Angular-contact 

 bear ings can support both radial and thrust loads. 



The simplest forms of radial bearings are 

 the integral and the insert types. The integral 



SPOT CONTACT LINE CONTACT LINE CONTACT 



77,66 

 Figure 5-9.— Load-carrying areas of ball and 

 roller bearings. 



type is formed by surfacing a part of the machine 

 frame with the bearing material, while the insert 

 bearing is a plain bushing inserted into and held 

 in place in the machine frame. The insert bear- 

 ing may be either a solid or a split bushing, and 

 may consist of the bearing material alone or be 

 enclosed in a case or shell. In the integral bear- 

 ing there is no means of compensating for wear, 

 and when the maximum allowable clearance is 

 reached the bearing must be resurfaced. The 

 insert solid bushing bearing, like the integral 

 type, has no means for adjustment due to wear, 

 and must be replaced when maximum clearance 

 is reached. 



The pivoted shoe is a more complicated type 

 of radial bearing. This bearing consists of a 

 shell containing a series of pivoted pads or 

 shoes, faced with bearing material. 



The plain pivot or single disk type thrust 

 bearing consists of the end of a journal extend- 

 ing into a cup-shaped housing, the bottom of 

 which holds the single disk of bearing material. 



The multi-disk type thrust bearing is simi- 

 lar to the plain pivot bearing except that several 

 disks are placed between the end of the journal 

 and the housing. Alternate disks of bronze and 

 steel are generally used. The lower disk is 

 fastened in the bearing housing and the upper 

 one to the journal, while the intermediate disks 

 are free. 



The multi-collar thrust bearing consists of 

 a journal with thrust collars integral with or 

 fastened to the shaft; these collars fit into re- 

 cesses in the bearing housing which are faced 

 with bearing metal. This type bearing is gen- 

 erally used on horizontal shafts carrying light 

 thrust loads. 



The pivoted shoe thrust bearing is similar to 

 the pivoted shoe radial bearing except that it has 

 a thrust collar fixed to the shaft which runs 

 against the pivoted shoes. This type bearing is 

 generally suitable for both directions of rotation. 



Angular loading is generally taken by using 

 a radial bearing to restrain the radial load and 

 some form of thrust bearing to handle the load. 

 This may be accomplished by using two separate 

 bearings or a combination of a radial and thrust 

 (radial thrust). A typical example is the multi- 

 collar bearing which has its recesses entirely 

 surfaced with bearing material; the faces of the 

 collars carry the thrust load and the cylindrical 

 edge surfaces handle the radial load. 



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