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The Effects of Shaft Rub on Bearing Housing Vibration Signatures

Lin Liu & Suri Ganeriwala
SpectraQuest Inc., 8227 Hermitage Road, Richmond, VA 23228
Published: July, 01 2006


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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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