PRINCIPLES OF NAVAL ENGINEERING 



position with very close tolerances permitting 

 freedom of movement and quiet operation. In 

 view of these requirements, good bearing mate- 

 rials must possess a combination of the follow- 

 ing characteristics for a given application. 



1. The compressive strength of the bearing 

 alloy at maximum operating temperature must 

 be such as to withstand high loads without 

 cracking or deforming. 



2. Bearing alloys must have high fatigue 

 resistance to prevent cracking and flaking under 

 varying operating conditions. 



3. Bearing alloys must have high thermal 

 conductivity to prevent localized hot spots with 

 resultant fatigue and seizure. 



4. The bearing materials must be capable of 

 retaining an effective oil film. 



5. The bearing materials must be highly re- 

 sistant to corrosion. 



Classification 



The reciprocating and rotating elements or 

 members, supported by bearings, may be subject 

 to external loads which can be resolved into 

 components having normal, radial, or axial 

 directions, or a combination of the two. Bearings 

 are generally classified as sliding surface 

 (friction) or rolling contact (antifriction) bear- 

 ings. 



Sliding surface bearings may be defined 

 broadly as those bearings which have sliding 

 contact between their surfaces. In these bear- 

 ings, one body slides or moves on the surface 

 of another and sliding friction is developed if 

 the rubbing surfaces are not lubricated. Exam- 

 ples of sliding surface bearings are thrust 

 bearings and journal bearings (fig. 5-8), such 

 as the spring or line shaft bearings installed 

 aboard ship. 



Journal bearings are extensively used aboard 

 ship. Journal bearings may be subdivided into 

 different styles or types, the most common of 

 which are solid bearings, half bearings, two- 

 part or split bearings. A typical solid style 

 journal bearing application is the piston bearing 

 (part A of fig. 5-8), more commonly called a 

 bushing . An example of a solid bearing is a 

 piston rod wristpin bushing such as found in 

 compressors. Perhaps the most common ap- 

 plication of the half bearing in marine equip- 

 ment is the propeller shaft bearing. Since the 

 load is exerted only in one direction, they ob- 

 viously are less costly than a full bearing of 

 any type. Split bearings are used more frequently 



GUIDE BEARING 



SOLID TYPE JOURNAL 

 BEARING (BUSHING) 



SPLIT-TYPE JOURNAL BEARING 



SPLIT-TYPE COMBINATION 

 JOURNAL AND THRUST BEARING 



147.50 

 Figure 5-8.— Various types of friction bearings, 



than any other friction-type bearing. A good 

 example is the turbine bearing. Split bearings 

 can be made adjustable to compensate for wear. 



Guide bearings (part B of fig. 5-8), as the 

 name implies, are used for guiding the longi- 

 tudinal motion of a shaft or other part. Perhaps 

 the best illustrations of guide bearings are the 

 valve guides in an internal combustion engine. 



Thrust bearings are used to limit the motion 

 of, or support a shaft or other rotating part 

 longitudinally. Thrust bearings sometimes are 

 combined functionally with journal bearings. 



Antifriction-type, or rolling contact, bear- 

 ings are so-called because their design takes 

 advantage of the fact that less energy is required 

 to overcome rolling friction than is required 

 to overcome sliding friction. These bearings 

 may be defined broadly as bearings which have 

 rolling contact between their surfaces. These 

 bearings may be classified as roller bearings 

 or ball bearings according to shape of the rolling 



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