Principles of naval engineering - Historic Naval Ships Association

9Chapter 12- PROPULSION STEAM TURBINESMain lubricating oil systems are discussed inchapter 9 of this text; the theory of lubricationis discussed in chapter 6.Turning Gears47.1 5XFigure 12-18.— Integrally forged turbine rotor(without blades).All geared turbine installations are equippedwith a motor-driven jacking or turning gear.The unit is used for turning the turbine duringwarming-up and securing periods so that theturbine rotor will heat and cool evenly. Therotor of a hot turbine, or one that is in theprocess of being warmed up, will become bowedand distorted if left stationary for even a fewminutes. The turning gear is also used forturning the turbine in order to bring the reductiongear teeth into view for routine inspectionand for making the required daily jacking of themain turbines. The turning gear is mounted ontop of and at the after end of the reduction gearcasing, as shown in figure 12-22. The brakeshown in figure 12-22 is used when it is necessaryto lock the shaft after the shaft has beenstopped.STEAM TURBINE PROPULSION PLANTSINVERTEDCIRCUMFERENTIALDOVETAILPINE TREEDOVETAILSTRADDLE-TEE147.97Figure 12-19.— Methods of fastening blades toturbine rotor wheels.operateranges.withinLubrication Systemstheir most efficient rpmProper lubrication is essential for the operationof any rotating machinery. In particular,the bearings and the reduction gears of turbineinstallations must be well lubricated at all times.The two principal types of steam turbinepropulsion plants now in use on naval ships arethe geared turbine drive and the turboelectricdrive. Direct drive installations, once in commonuse, are now practically obsolete; however,it is possible that an occasional application fordirect drive could again develop in the future.CLASSIFICATION OF PROPULSIONTURBINE UNITSNaval propulsion turbines are classified asClass A, Class B, and Class C turbines accordingto the type ship for which they are designed.Class A turbines are designed for use in submarines.Class B turbines are designed forusein amphibious warfare ships, surface combatantships, mine warfare ships, and patrol ships.Class C turbines are designed for use in auxiliaryships.Naval propulsion turbines are also classifiedaccording to design features. The six majortypes are:Reduction .gears are not used in ships having turboelectricdrive. In these ships, speed reduction isaccomplished electrically.1. Type I (single-casing unit).— The Type Ipropulsion unit consists of one or more aheadelements, each contained in a separate casingand identified as a single-casing turbine. Each333