Page 295 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

Power Transmission Gears 275

vent contact between mating surfaces. Small areas touch each other due
to load and surface irregularities. This results in welding of the two sur-
faces. As sliding continues, these surfaces break apart and particles ad-
here to the surfaces, causing rapid adhesive wear to occur.
Gear lubrication at the present time is not a highly developed technol-
ogy in general industrial applications, and as a result, the ultimate capac-
ity of gearing is partially determined by lubricant load limits. Hopefully,
a much higher capacity lubricant will be developed in the future that will
solve our gear lubrication problems by generating thick films without the
pitfalls now associated with the extremely heavy oils. However, today,
due to the higher prices and disposal problems of lubricating oils, we
must make greater efforts to obtain maximum benefits from the oils now
available.

Inoperative Periods

In new gear units shipped from the factory, the rust inhibitor adhering
to internal exposed surfaces should prevent corrosion of interior parts for
at least six months. Exterior preservatives should last at least six months,
but this protection will depend on handling and exposure to the elements.
A new gear unit should be stored inside if possible, but if not, covered
outside storage can be used. It is always a good idea to use a dry nitrogen
purge during storage to prevent or minimize condensation inside the gear
housing.
When the recommended lubricant is used and the reducer has been op-
erating for a period of time, the lubricating oil should protect interior
parts for inoperative periods up to 30 days since most of these oils have
rust and oxidation inhibitors added.
If additional downtime or storage time is required, one of the following
methods can be used to protect the internal parts of the gear unit:

1. The unit can be operated for a short period of time every 30 days to
redistribute the oil to the nonsubmerged parts and gain another 30
days protection.
2. If extended downtime is expected and it is impractical to spin the
unit, a rust preventative oil should be brushed or sprayed on the
gear teeth and bearings through the inspection opening. Any open-
ing such as breathers or labyrinth seals should be sealed with mask-
ing tape. A quality rust preventative oil should give 12 months pro-
tection against corrosion when applied in this manner. This oil
should be compatible with the operating oil, and it should not be
necessary to remove the rust preventative when the unit is re-