Page 256 - Subyek Teknik Mesin - Forsthoffers Best Practice Handbook for Rotating Machinery by William E Forsthoffer

Be st Practice 4 .1 Gear and Coupling Best Practices

Best
Best Practice 4.1Practice 4.1
Do not use planetary gears for critical applications; use same axial plane. The design for this requirement re-
parallel shaft gears for optimum reliability and lower MTTR. quires many additional gears and bearings which can
Planetary or epicyclic gears are maintenance-intensive and have result in lower reliability and MTTR that is at least twice
higher mean time to repair (MTTR) than parallel shaft gears. as long.
Planetary gears are more complex in design, having multiple gears
and bearings, and consequently are more difficult to monitor than Benchmarks
parallel shaft gears.
This best practice has been used since the early 1980s for all
Always require parallel shaft gears for critical (un-spared) applications.
applications, and has resulted in gear reliabilities higher than
99.5%.
Lessons Learned
Planetary gears are quoted to minimize baseplate size
since they enable the input and output shafts to be in the

B.P. 4.1. Supporting Material Parallel axes are the most common gear arrangement,
consisting of a meshing pinion and gear. Parallel arrangements
Figure 4.1.1 shows the type of parallel shaft gear preferred for can be simple, or compounded with other parallel gear sets to
ease of maintenance and minimum components. obtain high gear ratios. The conventional way to describe such
a gear is ‘double increaser’ or ‘reduction’ or ‘triple increaser’ or

Fig 4.1.1 Parallel shaft gear (Courtesy
of Allen-PGC)

230