To help you detect overheating, use this checklist:
o Visually inspect the gearbox exteriorforsigns of overheating.
o Record temperatures from gearbox thermometers, thermo- couples or resistance temperature detectors(RTDs).
o Measure oil sump temperature.
o For pressure-fed systems with an oil cooler, measure temperature at the gearbox oil inlet and outlet, as well as the cooler water inlet and outlet.
o Estimate gearbox housing and shaft temperatures using water spray.
o Survey the gearbox housing temperature by touching it with the palm of your hand and using temperature-sensitive paint, crayons and labels, or a digital thermometerprobe.
o Check the gearbox housing temperature using an infrared thermometer or infrared imaging camera.
o Analyze gearbox oil for signs of oxidation or thermal degradation using on-site and laboratory tests.
o Analyze gearbox oil using particle counters, spectrometric analysis and ferrography to detect weardebris.
o Inspect internal gearbox components through inspection ports for signs of overheating, misalignment, inadequate backlash, inadequate bearing endplay or oil oxidation.
o Measure gearbox sound and vibration and compare to allow- able limits.
Inspect the breather. The breather should be located in a clean, non-pressurized area away from contaminants. It should include a filter and desiccant to prevent ingress of dust and water. Also, ensure that the breather is shielded from water during wash-downs.
Check shaft seals. Look for oil leaks at the shaft seals. If there are signs of oil leakage, the seals are probably allowing ingression of dust and water. If the gearbox has labyrinth seals, it should have external seals such as V-rings to prevent contaminant ingression.
Examine through inspection ports. Examine the inspection port cover and determine whether all bolts are tight and the cover is properly sealed, or if there is oil leakage. Only qualified personnel should be allowed to open inspection ports; in some cases it is necessary to secure the ports with padlocks to enforce security.
Clean the inspection port cover and the surrounding area. Remove the cover,being careful notto contaminatethegearbox interior. Count the bolts and store them in a separate container so there is nochancetheywillfall intothe gearbox.Observe the condition of the gears,shafts and bearings.
If the gears or bearings are damaged but still functional, management may decide to continue operation and monitor dam- age progression. In this case, the gear system should be continuously monitored. You should also make certain there are no risks to human life.
For critical applications, examine the gears with magnetic particle inspection to ensure there aren’t any cracks that prevent safe, continued operation. If there are no cracks, you should periodically perform a visual inspection and measure temperature, sound and vibration.
Collect samples of the lubricant for analysis, examine the oil filter for wear debris and contaminants, and inspect magnetic plugs for wear debris.
The rule of thumb for installing sample port tube extensions is to keep the end of the tube at least two inches away from any static or dynamic surface.
You will need to flush the entire combination of tube extension, sample port adapter and sample tube before you take your sample for analysis. Flush at least 10 times the volume of all the components prior to taking the sample for analysis. This typically works out to three or four ounces of fluid for a sample port with a tube extension of 12 inches.
To prevent further damage to the gears and bearings from wear debris, replace the filter element and then drain, flush and refill the reservoir with new lubricant. Continue to monitor lubricant properties during operation and repeat the maintenance if necessary.
If cracks are found or the damage is severe enough to warrant removal of the gearbox, measure shaft coupling endplay and alignment before removing the gearbox. Note the condition and loosening torque of fasteners, including coupling and mounting bolts. To check for possible twist in the gear housing, install a dial indicator at each corner of the gearbox and then measure movement of the mounting feet as bolts are loosened. If there’s no twist, each indicator will record the same vertical movement. If there is twist, calculate the twist from relative movements.
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