The Effects of Shaft Rub on Bearing Housing
Vibration Signatures
Lin Liu,
Suri
Ganeriwala
SpectraQuest Inc., 8201 Hermitage Road, Richmond, VA 23228
Published: July 2006
Abstract
In this study the vibration signature on
bearing housing caused by shaft rub was studied by applying a rotor
rub device on a machinery fault simulator TM. Full annular rub was
simulated with three types of rub head materials: aluminum, brass,
and plastic. Experiments were carried out at three rotatory speeds,
i.e., 1000, 2000 and 3000 RPM. Acceleration signals on bearing
housing were collected and analyzed. Several observations on the
effects of rub on bearing housing vibration were presented.
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Introduction
For rotating machinery, rub is an undesired
contact between the rotating and stationary parts. It causes direct
damage to the contacting parts. The damage can range from mild, for
light rub, to complete destruction of the machine.
Generally, rub is caused by some malfunction that
produces a shaft/rotor and stator contact. Some examples of the
malfunction which can cause rub include: excessive radial loads,
looseness, misalignment, etc. The rub can be categorized into
partial radial rub and full annular rub. If the actual rub contact
occurs over a fraction of the vibration cycle, it is called partial
rub. If it occurs over the entire vibration cycle, maintaining
continuous contact, it is called full annular rub.
How to identify the vibration signature caused by
rub on bearing housing is very critical in preventing rub related
machinery failure. Also, the effects of rub material and speed on
vibration signature associated with rub are two other key issues. In
this work, efforts have been made to answer the above questions by
simulating rub in a controlled way.
Shaft rub was simulated on a Machinery Fault
Simulator (MFS) TM with a rub kit. The rub kit is illustrated in
Fig. 1 (a). This kit permits the simulation and evaluation of
typical rub phenomena associated with a variety of materials in
different angle, loading, and lubricant conditions. The kit consists
of an adjustable tool holder for the rub material, a vertical post,
a horizontal bar, and clamping mechanism.
(a) rub kit installed on MFS TM
(b) rub head pressing against shaft
Figure 1. Rub Kit
Diagram
Fig 2:
Rub Vibration Spectra for 2000RPM Tests
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