Page 251 - Intro Predictive Maintenance

242 An Introduction to Predictive Maintenance

Table 10–11 Common Failure Modes of Mixers And Agitators

THE PROBLEM

Surface Vortex Visible Incomplete Mixing of Product Excessive Vibration Excessive Wear Motor Overheats Excessive Power Demand Excessive Bearing Failures

THE CAUSES

Abrasives in Product
Mixer/Agitator Setting Too Close to Side or Corner
Mixer/Agitator Setting Too High
Mixer/Agitator Setting Too Low
Mixer/Agitator Shaft Too Long
Product Temperature Too Low
Rotating Element Imbalanced or Damaged
Speed Too High
Speed Too Low
Viscosity/Specific Gravity Too High
Wrong Direction of Rotation
Source: Integrated Systems, Inc.

Installation problems are normally the result of misalignment where the roll is not
perpendicular to the travel path of the belt or transported product. If process rolls are
misaligned, either vertically or horizontally, the load imparted by the belt or carried
product is not uniformly spread across the roll face or to the support bearings. As a
result, both the roll face and bearings are subjected to abnormal wear and may
prematurely fail.

Operating methods may cause induced loads that are outside the acceptable design
limits of the roll or its support structure. Operating variables, such as belt or strip
tension or tracking, may be the source of chronic reliability problems. As with mis-
alignment, these variables apply an unequal load distribution across the roll face and
bearing-support structure. These abnormal loads accelerate wear and may result in
premature failure of the bearings or roll.

10.8 GEARBOXES/REDUCERS
This section identifies common gearbox (also called a reducer) problems and their
causes. Table 10–15 lists the more common gearbox failure modes. One of the primary
causes of failure is the fact that, with few exceptions, gear sets are designed for oper-