Chapter 12- PROPULSION STEAM TURBINES 



47.1 5X 

 Figure 12-18.— Integrally forged turbine rotor 

 (without blades). 



INVERTED 



CIRCUMFERENTIAL 



DOVETAIL 



PINE TREE 

 DOVETAIL 



STRADDLE-TEE 



147.97 

 Figure 12-19.— Methods of fastening blades to 

 turbine rotor wheels. 



operate within 

 ranges. 9 



their most efficient rpm 



Lubrication Systems 



Proper lubrication is essential for the opera- 

 tion of any rotating machinery. In particular, 

 the bearings and the reduction gears of turbine 

 installations must be well lubricated at all times. 



Reduction .gears are not used in ships having turbo- 

 electric drive. In these ships, speed reduction is 

 accomplished electrically. 



Main lubricating oil systems are discussed in 

 chapter 9 of this text; the theory of lubrication 

 is discussed in chapter 6. 



Turning Gears 



All geared turbine installations are equipped 

 with a motor-driven jacking or turning gear. 

 The unit is used for turning the turbine during 

 warming-up and securing periods so that the 

 turbine rotor will heat and cool evenly. The 

 rotor of a hot turbine, or one that is in the 

 process of being warmed up, will become bowed 

 and distorted if left stationary for even a few 

 minutes. The turning gear is also used for 

 turning the turbine in order to bring the reduc- 

 tion gear teeth into view for routine inspection 

 and for making the required daily jacking of the 

 main turbines. The turning gear is mounted on 

 top of and at the after end of the reduction gear 

 casing, as shown in figure 12-22. The brake 

 shown in figure 12-22 is used when it is neces- 

 sary to lock the shaft after the shaft has been 

 stopped. 



STEAM TURBINE PROPULSION PLANTS 



The two principal types of steam turbine 

 propulsion plants now in use on naval ships are 

 the geared turbine drive and the turboelectric 

 drive. Direct drive installations, once in com- 

 mon use, are now practically obsolete; however, 

 it is possible that an occasional application for 

 direct drive could again develop in the future. 



CLASSIFICATION OF PROPULSION 

 TURBINE UNITS 



Naval propulsion turbines are classified as 

 Class A, Class B, and Class C turbines accord- 

 ing to the type ship for which they are designed. 

 Class A turbines are designed for use in sub- 

 marines. Class B turbines are designed foruse 

 in amphibious warfare ships, surface combatant 

 ships, mine warfare ships, and patrol ships. 

 Class C turbines are designed for use in auxil- 

 iary ships. 



Naval propulsion turbines are also classified 

 according to design features. The six major 

 types are: 



1. Type I (single-casing unit).— The Type I 

 propulsion unit consists of one or more ahead 

 elements, each contained in a separate casing 

 and identified as a single-casing turbine. Each 



333 



