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Shaft alignment is very important for long gear life. Poor alignment can cause unequal distribution of tooth loads and distortion of the gear elements from overhung moments. A 2.0-mil shaft vibration level on the gear unit produced by misalignment is equivalent to a gear pitch-line runout of 2.0 mils.
The gear housing must be properly supported to maintain proper internal gear alignment. When agear unit is installed， the support pads must be maintained in the same plane as used by the manufacturer duringassembly when gear face contact was obtained in the plant. Beforestartup，gear face contact should be checked using high-spotbluing， and rotating or rocking the pinion or lighter element back and forth sharply within the confines of the backlash. Inspection of this blued area should showapproximately 90% face contact. If this contact is not obtained， the gear housing can be shimmed under the proper corner until an acceptable face contact is achieved.
Many large， high-hardness or wide-face width gears are manufactured with helix angle modifications to account for torsional and bending deflec-tion. When the helix angle has beenmodified， good face contact will not beobtained under light load. In thiscase， the gear supplier should furnish data on percent of face contact versus load to be used as a guide during installa-tion and startup. Also， many gears have a short area of ease-off on each endof the teeth to prevent end-loading， and this area usually will not show contact under light load.
The larger the gearunit， the more important this checkbecomes， sincelarge housings tend to be more flexible.Also， the use of baseplates furnished by the original equipment manufacturer does not eliminate face contactproblems， and these inspection procedures should be carried out.
After the gear checks have beenmade， the foundation bolts should be uniformly tightened and the alignment rechecked. It may be necessary to repeat the shimmingand tightening of foundation bolts to obtainfinal， correct cold alignment.
Alignment of high-speed gear units should always be hot-checked and adjustments made as necessary. Temperatures vary so greatly throughout the housing and shafting that it is impossible to calculate a thermal growthaccuratelyand，therefore， an alignment checkmust be made in the hot condition.
When the alignment is complete， the baseplate or bed should be grouted in as close to the gear housing as possible. .ournal bearings are used on the gear shafts and proper oil flow must be maintained. The oil system should there-fore be checked thoroughly prior to startup. The gear lube system is nor-mally flushed prior to any operations. The usual procedure is to seal off thegearbox components to which acid would be harmful， acid flush thesystem， and follow with a neutralizing flush before filling with the lube oil. Gear mesh spray nozzles should be checked to be sure dirt was not pumped through the system by observing the sprays or by introducing high-pressure air into the spray nozzle manifold.
When possible， gears should be run-in on initial startup. Speeds andloads should be increased in percentage increments. Lube oil temperature， and pressure and bearing temperatures should be observed and adjust-ments made to the lube system as required. The number of adjustments made will depend on the complexity of the system. Oil pressure is of primary importance. When an auxiliary pump has beenprovided， oilshould be circulated before the actual start. Ifnot， the pump should beprimed， and the journals wetted with oil. Primer holes are sometimes provided or alternate journals can be oiled through the holes provided for bearing temperature detectors.
It is recommended that warning devices be provided to eliminate as muchhuman error aspossible， and the set points should be checked carefully. Aswith any startup， vibrations should be monitored and recorded. The vibra-tion monitoring system should include at least one accelerometer to detect any vibrations generated at gearmesh frequency. The recorded data should be saved to provide baseline vibration data for future reference.
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燃气涡轮工程手册 Gas Turbine Engineering Handbook 2(104)
