Page 310 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

290 Major Process Equipment Maintenance and Repair

2. High Oil Level-High oil level will cause overheating due to the
heat generated when the gear teeth run under too much oil. Many
high speed units have an oil level just below the gear teeth, and to
allow these gears to dip in oil causes overheating.
3. Internal Failure or Poor Assembly-Overheating can be caused by
a multitude of things from gear tooth breakage to internal rubs or
even gear teeth improperly meshed.
4. Blocked or Reduced Oil Passages-Many gear designs include ei-
ther cast or machined oil passages and drilled orifices. These pas-
sageways can be blocked by oil deposits, sludge, or excessive
sealants, thereby reducing oil flow and producing overheating.
5. High Ambient Temperature-Overheating can be due to the high
climatic temprature in areas around furnaces, paper machines,
and other machines that radiate heat. This situation can be cor-
rected by external cooling or in some cases by the use of heat
shields.
6. Low Bearing Clearance-Reduced bearing clearance can be
caused by pinching the bearing at the bore split line, by not having
sufficient clearance bored into journal-type bearings, or by having
the wrong clearance in roller bearings. This condition will usually
show up as localized overheating and can be detected with bearing
instrumentation.
7. Housing Coated with fireign Material- A foreign material on the
exterior of the housing reduces the heat transfer to the air, and
many gear designs depend on radiation and convection to the air
for cooling.
8. Internal Rubs-This condition usually results from poor assembly
and occurs when part of a gear rotating element actually rubs in-
ternal piping or housing walls.
9. InsufJiient Miter Flow to the Cooler-This condition can usually
be checked by measuring the water inlet and outlet temperatures.
If the temperature rise across the cooler is higher than the de-
signed rise, insufficient water flow is usually indicated.

10. Malfiurction of Oil Heaters-Oil heaters are used to raise the oil
temperature for start-up or to maintain an acceptable oil tempera-
ture during extremely cold conditions. Should the thermocouples
or thermostats on these oil heaters malfunction, they can overheat
the oil.
1 1. Contaminated Oil Filter-This condition can cause overheating by
reducing oil flow to the gear unit. If the contamination is exces-
sive, the element can collapse and be carried into the oil passages,
reducing oil flow and causing overheating.