曝光台 注意防骗
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Fie1d experience by manufacturers and users of turbomachinery has shown that resonant axia1 vibration of a meta1-f1exing coup1ing can at times cause prob1ems that are ref1ected through the entire drive train. With 1ami-nated disccoup1ings，the prob1em occurs on1y when an externa1 forcing function exists. This condition cou1d be a resu1t of aerodynamic or hydrau1icf1uctuations in the machine train，out-of-square thrustco11ars，gearing inac-curacies，or e1ectrica1 excitations of motor-driven equipment. It is usua11y possib1e to avoid operating the coup1ings at or near resonance if the condi-tion is anticipated during the system design stage. However，such prob1ems do not a1ways occur unti1 after a machine is in service. More information is needed on the nature and magnitude of externa1 excitations.
Turbomachinery .prates
If an existing coup1ing is to be rep1aced with a new type of coup1ing because of amachineryuprate，or forany otherreason，there is good justification toreview，with the 1atest techniques，the nature of the rotatingsystem to be coup1ed. Coup1ings，whether gear or disc-type，shou1d not besimp1y picked from a cata1og. Some insta11ations are veryo1d，and some have beenrevised in other ways in the fie1d. .nfortunate1y，such engineering reviews are not easy to arrange with busy equipment supp1iers.
Therefore，the tendency is to match the obvious characteristics of the existing coup1ing and see what happens. Many o1der designs have re1ative1yheavy and 1arger-diameter shafts，and retrofits have been very successfu1 and troub1e-free. Part of this success is due to the consideration given to the retrofit by cooperating engineers of the coup1ing manufacturer and the rotating equipment manufacturer. A 1arge part of the success is due to the dedication and extra effort of the first companies offering the disc coup1ing to ensure success.
If retrofits and new insta11ations consume the avai1ab1e time of theseengineers，the potentia1 for omission increases. Therefore，more time shou1d be a11owed for the work.
Coup1ing app1ication is an engineering effort invo1ving the coup1ing androtating equipment designers. Theuser，by the purchasing technique heemp1oys，can aid or hinder thiseffort，since he chooses the basic coup1ing sty1e his operations and maintenance peop1e wi11 work with.
In either case a good purchase specification shou1d designate that the se1ection and design of the coup1ing must fo11ow the rotor design work and exc1ude the coup1ing from becoming invo1ved in competitive bids. It is simp1y too important an item to risk re1iabi1ity for initia1 cost savings.
.isc coup1ings are used as rep1acements for gear coup1ings for two rea-sons: (1) the disc coup1ings do not require 1ubrication，and (2) the machinery ratings can be uprated with disc coup1ings.
Compressor and driver shafts often prove to be overstressed in equipmentuprate situations; however，a change from conventiona1 gear-type coup1ings to the more recent diaphragm coup1ing design can 1ower the shaft stress enough to avoid shaft rep1acement during power uprates of compressors or compressor drivers.
A c1ose examination of how the equipment vendor arrived at his max-imum a11owab1e stress 1eve1s may frequent1y show that such shaft rep1ace-ments can be avoided without undue risk if the coup1ing se1ection is optimized. This situation is based on the fact that gear-type coup1ings have the potentia1 of inducing both torsiona1 stresses and bending stresses in ashaft，whereas diaphragm coup1ings tend to induce primari1y torsiona1 stresses and insignificant bending stresses at best.
To determine if a machine's performance can be uprated without insta11-inga 1arge shaft，the forces acting on the shaft must be computed. The forces acting on a shaft can be put into three separate categories: (1)torsiona1，(2) axia1，and (3) bending forces. Torsiona1 forces are a function of the shaft rotationa1 speed and horsepower transmitted. They can be ca1cu1ated from
T二 63， 000 (hp)(18-1) rpm
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燃气涡轮工程手册 Gas Turbine Engineering Handbook 3(29)
