tailieunhanh - Handbook of Shaft Alignment Part 15

Tham khảo tài liệu 'handbook of shaft alignment part 15', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 670 Shaft Alignment Handbook Third Edition FIGURE Small steam turbine with upper casing removed. Additional Information on Electric Motors Moderate to excessive soft foot conditions have been experienced on virtually every size motor regardless of frame construction design. Uneven air gap problems found occasionally due to improper positioning of end bells or housing distortion due to uncorrected soft foot. Inboard coupling end bearings may run hotter due to misalignment conditions. Excessive vibration may be due to improperly bored coupling hubs. Infrared thermography surveys and motor current signature analysis are very helpful in diagnosing problems. Steam Turbines Steam turbines can range in output from 20 to 100 000 hp with speeds up to 25 000 rpm and therefore become some of the more interesting equipment for OL2R surveys and consequentially some Figure through Figure of the more difficult equipment to maintain and operate properly. Steam pressures can range from 200 to 4000 psig and temperatures from 400 F to 1100 F. Due to the fact that a high-temperature gas is used to propel blades for shaft rotation extensive frame and casing design considerations concerning FIGURE Small steam turbine. Alignment Considerations for Specific Types of Machinery 671 FIGURE Large steam turbine. casing and rotor expansion and contraction are taken into account to minimize excessive positional change of the rotor during operation. However movement of the shaft invariably occurs from OL2R conditions that can range considerably from unit to unit. In addition rotor expansion must be taken into consideration when selecting a flexible coupling to prevent thrust transfer from one rotor to another causing premature bearing or coupling failure. On several occasions the condensing end of the steam turbine has been observed to move downward during operation. The cooler temperatures and the vacuum draw down effect of the condenser may actually move