Masters Theses

Stephen Jesse

Date of Award

8-2001

Degree Type

Thesis

Degree Name

Master of Science

Major

Mechanical Engineering

Major Professor

J. W. Hines

Abstract

This thesis examines the characteristics of misalignment of rotating machinery. The first phase of this research determined the effects of motor shaft misalignment on power consumption, and the second phase determined the relationships between motor shaft alignment, roller bearing load, and predicted life. U.S. industry invests significant resources performing precision alignment of rotating machinery. The basis for this expenditure is two assumptions: misalignment causes a decrease in motor efficiency, and misaligned machinery is more prone to failure due to increased loads on bearings, seals, and couplings.

To determine the effects of rotating machinery misalignment on power consumption, controlled experiments were performed at The University of Tennessee and at the Oak Ridge Center for Electrical Machinery System Testing. The testing was performed using a 50 HP and a 60 HP AC induction motor with four different types of flexible couplings. Approximately 15 different alignment conditions were examined for each coupling.

To determine the effects of misalignment on bearing load, sensors were designed, fabricated, and installed into a working motor. These sensors could measure transverse bearing loads in both the vertical and horizontal directions at both the inboard and outboard bearings. The testing was performed using a 60 HP induction motor and four different types of flexible couplings. Testing was performed while the motor was static and while the motor was in operation at full speed and maximum torque.

The results of alignment versus efficiency tests show no significant correlation between misalignment and efficiency when the couplings were operated within the manufacturer's recommended range. Power consumption and power output remained constant regardless of the alignment condition.

The results of bearing load tests show that relatively small amounts of shaft misalignments can have a significant impact on the operational life of a bearing. The magnitude of the bearing life reduction varies with the coupling type, bearing load capacity, and dimensions of the motor. The results from this research show that, in some cases, up to 50% percent of the expected bearing life can be lost with as small as a 5 mil offset misalignment.

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