Thursday, 24 May 2012

Commisioning and Inspections

Commisioning and Inspections

Gear Inspections

    • Ensure that the steam is off the turbines and the turning gear is engaged.
    • Wipe around inspection doors to prevent immediate dirt ingress
    • Allow sufficient time for the gear case to cool before opening
    • If inspection is non-routine, that is say due to an abnormality ensure extra time for cooling and open doors initially away from the area of concern
    • Guard against items being dropped accidentally into gearcase
    • Use only flame proof lighting
    • Rotate main wheel at least one full turn
    • Inspect all teeth for damage, record defects as appropriate. This normally takes the form of a sheet onto which a sketch showing the size and extent of damage (such as pitting) and a section fo added notes. These sheets are kept as a historic record of the gear allowing judgement on deterioration rate.
    • Observe oil sprays and other internal fittings
    • Look for rusting indicating faulty dehumidifier
Should a fault be found it may be necessary to check alignment, the condition of the flexible couplings, bearings and mounting arrangements.

Checking for mis-alignment

This can be done by blueing one of the teeth then viewing the complimentary mating teeth. Where the blue has transferred this is where the teeth have meshed and this can be compared to the polished area of the on load contact areas.
There will be some difference to the on load polished area as the displacement component tending to push the two centres apart, pushes the pinion up in its bearing. For very accurate aligement this force can be represented by pulling the pinion away from the wheel
If damage to the Bull wheel is suspected , say due to rapid decelleration of the propeller, and the Bull wheel may have slipped its shrink fit then alignment should be checked in a number of positions.

Operation and Maintenance

    A gear set will operate satisfactory provided;
    • It is operating within limits
    • It has sufficient high quality oil supply
    • Close attention is paid to alignement during refits
    • Flexible couplings are maintained
Oils should have anti-rust additives, water content should be kept below 0.2%
Excessive rust and sludge can lead to failure due to corrosion fatigue particularly in gears suffering from pittings
Blued tapes taken on inspection may be kept to record wear
IME recommends inspection periods no more frequent than 6 months to prevent undue contamination.

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