Page 255 - Intro Predictive Maintenance

246 An Introduction to Predictive Maintenance

Table 10–15 Common Failure Modes of Gearboxes and Gear Sets

THE PROBLEM

Variations in Torsional Power Insufficient Power Output

Gear Failures Overheated Bearings Short Bearing Life Overload on Driver High Vibration High Noise Levels Motor Trips

THE CAUSES
Bent Shaft
Broken or Loose Bolts or Setscrews
Damaged Motor
Eliptical Gears
Exceeds Motor’s Brake Horsepower Rating
Excessive or Too Little Backlash
Excessive Torsional Loading
Foreign Object in Gearbox
Gear Set Not Suitable for Application
Gears Mounted Backward on Shafts
Incorrect Center-to-Center Distance Between Shafts
Incorrect Direction of Rotation
Lack of or Improper Lubrication
Misalignment of Gears or Gearbox
Overload
Process Induced Misalignment
Unstable Foundation
Water or Chemicals in Gearbox
Worn Bearings
Worn Coupling
Source: Integrated Systems, Inc.

10.8.1 Normal Wear
Figure 10–2 illustrates a gear that has a normal wear pattern. Note that the entire
surface of each tooth is uniformly smooth above and below the pitch line.

10.8.2 Abnormal Wear
Figures 10–3 through 10–5 illustrate common abnormal wear patterns found in gear
sets. Each of these wear patterns suggests one or more potential failure modes for the
gearbox.