ALIGNMENT OF GEAR TEETH.—Whenthe gear and the pinion are parallel (axes of thetwo shafts are in the same plane and equally dis-tant from each other), the gear train is aligned.In service the best indication of proper alignmentis good tooth contact and quiet operation.The length of tooth contact across the face ofthe pinions and gears is the criterion for satisfac-tory alignment of reduction gears. To static checkthe length of tooth contact, coat about 5 to 10teeth with either Prussian blue or red lead, thenroll the gears together with sufficient torque tocause contact between the meshing teeth and forcethe journals into the ahead reaction position intheir bearings. After you determine the tooth con-tact, remove all the coating to prevent possiblecontamination of the lubricating oil. If tooth con-tact is to be checked under operating conditions,coat the teeth with red or blue Dyken or with cop-per sulphate.SPOTTING GEAR TEETH.—All abnormalconditions which may be revealed by operationalsounds or by inspections should be corrected assoon as possible. Rough gear teeth surfaces,resulting from the passage of foreign objectsthrough the teeth, should be stoned smooth. Ifthe deterioration of a tooth surface cannot betraced directly to a foreign object, give special at-tention to lubrication and to the condition of thebearings. Also consider the possibility that achange in the supporting structure may havedisturbed the parallelism of the rotors.Spotting reduction gear teeth is done first bycoating the teeth with Prussian blue and then byjacking the gear in its ahead direction of rotation.As the gear teeth come in contact with themarked pinion teeth, an impression is left on thehigh part of each gear tooth. Rotate the gearabout 1/4 of a turn to a convenient position forstoning. Then remove all the high spots indicatedby the marking with a small handstone. Normally,it will be necessary to replace the bluing on thepinion teeth repeatedly, since if the bluing isapplied too heavily you may obtain false impres-sions on the gear teeth.A satisfactory tooth contact is obtained whenat least 80% of the axial length of the workingface of each tooth is in contact and distributedover approximately 100% of the face width.Remember that the stoning of gears is usefulonly to remove a local hump or deformation, notto remove deep pitting or galling.Main Thrust BearingsA ship is moved through the water by an ax-ial thrust that is developed by the propeller andtransmitted to the ship’s structure. This axialthrust is transmitted by the shaft through a thrustbearing which is located either at the forward endor at the after end of the main reduction bull gearor in the propeller line shafting aft of the gear.Pivoted-segmental shoe bearings (Kingsbury type)utilize a wedge-shaped film of oil in their opera-tion. The source of lubricating oil for thrust bear-ings depends on the location of the bearings. Insome installations oil is provided by the samesystem which furnishes oil to the reduction gears.In other installations, a separate lubricatingsystem is provided.Kingsbury-type thrust bearings consist of acollar mounted on the shaft and revolving betweenone or more sets of babbitt-faced segmental shoes.The backs of these shoes rest against roundhardened steel pivots which permit the shoes toassume a tilt and change their angle with respectto the shaft collar. Bearings in which the thrustis always exerted in the same direction areequipped with shoes on one side only, but sinceprovision must be made in most marine applica-tions for thrust in two directions, it is more com-mon to find shoes on each side of the collar. Theshoes are free to adjust themselves at an angle tothe collar. Rotation of the shaft collar drags a filmof oil into the space between the shoes and thecollar, and as the oil film forms, the shoes adjustthemselves to the angle most efficient for the loadconditions and the oil viscosity.Additional information on Kingsbury-typethrust bearings and other types of bearings is pro-vided in the NAVSHIPS Technical Manual,chapter 243. Detailed information on allowabletolerances and procedures for taking thrust bear-ing readings can be obtained from the manufac-turer’s technical manual.End play checking of a Kingsbury thrust bear-ing must always be done with the upper half ofthe housing solidly bolted down, otherwise thebase rings may tilt and provide a false reading.Chapter 4—REDUCTION GEARS AND RELATED EQUIPMENT4-7
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