Page 179 - Root Cause Failure Analysis

Process Rolls 167

Figure 13-3 Load zones determined by wrap.

PERFORMANCE
Process rolls are subjected to variable loads induced by tension, tracking, and other
process variables. Figure 13-3 illustrates the wrap of the strip as it passes over a series
of rolls in a continuous process line. The load zones are indicated by arrows. In a nor-
mal operation, the force or load induced by the strip is uniformly applied across the
roll’s entire face or body, as illustrated in Figure 13-4.

The width of the product or belt in contact with the roll has a direct effect on loading
and how the load is transmitted to the roll and its bearing-support structures.
Figure 13-5 illustrates a narrow strip that is tracking properly. Note that, with a narrow
strip, the load is concentrated more in the center of the roll and not uniformly trans-
ferred across the entire roll face. This tends to bend the roll, with the degree of deflec-
tion depending on three factors: roll diameter, roll construction, and strip tension.

Figure 13-4 Strip uniformly loads roll.