Principles of naval engineering - Historic Naval Ships Association

PRINCIPLES OF NAVAL ENGINEERINGposition with very close tolerances permittingfreedom of movement and quiet operation. Inview of these requirements, good bearing materialsmust possess a combination of the followingcharacteristics for a given application.1. The compressive strength of the bearingalloy at maximum operating temperature mustbe such as to withstand high loads withoutcracking or deforming.2. Bearing alloys must have high fatigueresistance to prevent cracking and flaking undervarying operating conditions.3. Bearing alloys must have high thermalconductivity to prevent localized hot spots withresultant fatigue and seizure.4. The bearing materials must be capable ofretaining an effective oil film.5. The bearing materials must be highly resistantto corrosion.ClassificationSOLID TYPE JOURNALBEARING (BUSHING)SPLIT-TYPE JOURNAL BEARINGGUIDE BEARINGSPLIT-TYPE COMBINATIONJOURNAL AND THRUST BEARINGThe reciprocating and rotating elements ormembers, supported by bearings, may be subjectto external loads which can be resolved intocomponents having normal, radial, or axialdirections, or a combination of the two. Bearingsare generally classified as sliding surface(friction) or rolling contact (antifriction) bearings.Sliding surface bearings may be definedbroadly as those bearings which have slidingcontact between their surfaces. In these bearings,one body slides or moves on the surfaceof another and sliding friction is developed ifthe rubbing surfaces are not lubricated. Examplesof sliding surface bearings are thrustbearings and journal bearings (fig. 5-8), suchas the spring or line shaft bearings installedaboard ship.Journal bearings are extensively used aboardship. Journal bearings may be subdivided intodifferent styles or types, the most common ofwhich are solid bearings, half bearings, twopartor split bearings. A typical solid stylejournal bearing application is the piston bearing(part A of fig. 5-8), more commonly called abushing . An example of a solid bearing is apiston rod wristpin bushing such as found incompressors. Perhaps the most common applicationof the half bearing in marine equipmentis the propeller shaft bearing. Since theload is exerted only in one direction, they obviouslyare less costly than a full bearing ofany type. Split bearings are used more frequently147.50Figure 5-8.— Various types of friction bearings,than any other friction-type bearing. A goodexample is the turbine bearing. Split bearingscan be made adjustable to compensate for wear.Guide bearings (part B of fig. 5-8), as thename implies, are used for guiding the longitudinalmotion of a shaft or other part. Perhapsthe best illustrations of guide bearings are thevalve guides in an internal combustion engine.Thrust bearings are used to limit the motionof, or support a shaft or other rotating partlongitudinally. Thrust bearings sometimes arecombined functionally with journal bearings.Antifriction-type, or rolling contact, bearingsare so-called because their design takesadvantage of the fact that less energy is requiredto overcome rolling friction than is requiredto overcome sliding friction. These bearingsmay be defined broadly as bearings which haverolling contact between their surfaces. Thesebearings may be classified as roller bearingsor ball bearings according to shape of the rolling94