Page 324 - Intro Predictive Maintenance

Failure-Mode Analysis 315

Figure 14–27 Typical vibration profile with uneven loading.

Figure 14–28 Vertically misaligned roll.

Single Rolls. With the exception of steering rolls, all single rolls in a continuous-
process line must be perpendicular to the pass line and have the same elevation on
both the operator and drive sides. Any horizontal or vertical misalignment influences
the tracking of the strip and the vibration profile of the roll.

Figure 14–28 illustrates a roll that does not have the same elevation on both sides (i.e.,
vertical misalignment). With this type of misalignment, the strip has greater tension
on the side of the roll with the higher elevation, which forces it to move toward the
lower end. In effect, the roll becomes a steering roll, forcing the strip to one side of
the centerline.

The vibration profile of a vertically misaligned roll is not uniform. Because the strip
tension is greater on the high side of the roll, the vibration profile on the high-side
bearing has lower broadband energy. This is the result of damping caused by the strip
tension. Dominant frequencies in this vibration profile are roll speed (1¥) and outer-