Page 308 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

288 Major Process Equipment Maintenance and Repair

10. Pitch Line Runout-Pitch line runout is a form of tooth spacing
error where each tooth is not an equal distance from the axis of
rotation. This usually shows up as a cyclic noise with a frequency
equal to the shaft rotation speed.
11. Excessive Backlash-Excessive backlash can only cause noise
when the gear set has torque reversals. Large amounts of backlash
should never be used as criteria for determining whether a gear is
acceptable for use. On nonreversing drives, backlash is only im-
portant when it becomes so excessive that the tooth strength is re-
duced.
12. Too Little Backlash-A gear set without sufficient backlash to ac-
count for manufacturing errors and thermal growth is a disaster.
These gears will be noisy and will fail in a very short time.
13. Noise Transmitted From Driving or Driven Machine-A gear
housing is a large drum-like container and can amplify the noises
emitted through the structure from the motors, compressors,
pumps , generators, etc .

14. Load Zntensity-As a rough rule of thumb, the higher the load in-
tensity, the higher the noise level. As just pointed out, gear teeth
require tooth form modifications to account for deflections under
load. As a result, the higher the load intensity, the harder it is to
make these corrections properly.
15. Rolling Element Bearings-This type of bearing tends to be more
noisy than others due to the loose pieces in the bearing such as
cages and rollers. Also, the roller passing frequency is quite high
and will produce noise.
16. Clutches and Couplings-Couplings are some of the primary
noise producers of rotating machinery. Windage noise is produced
by the bolts and other openings in the coupling flanges. Clutches
have all of the problems of couplings but in addition have a ten-
dency to rattle.
17. Fixe Overlap Ratio-This is the number of teeth in contact at any
time across the face of a gear. With more teeth in contact, gear
errors tend to average out producing quieter gear operation. The
best way to increase face overlap ratio is to use a higher helix an-
gle during manufacture.
18. Transverse Contact Ratio-This is the number of teeth in contact
in a transverse plane. Low pressure angle gears have higher con-
tact ratios and are quieter but do not have adequate tooth strength.
Generally, a compromised pressure angle is selected to give an op-
timum balance between contact ratio and bending strength.
19. Lube Oil Pump and Piping-Lube oil pumps can be extremely
noisy if the piping is not properly designed. The most common