Experimental studies of coastdown time

An Experimental Investigation on the Misalignment Effects in Journal Bearings

Abstract: In this paper an investigation is made to evaluate the experimental performance of misaligned cylindrical and three-lobe journal bearings. A three-bearing double-disc rotor system with a test bearing in the middle and driven by a variable speed DC motor through an electromagnetic coupling is used. Various parameters which have been studied are friction through coastdown analysis, unbalance response and film thickness. The system damping also has been evaluated. The film thickness decreases, friction increases and system damping increases as the bearing misalignment increases. While the first, third and fourth harmonics vibration response is found to be almost steady with a increasing degree of misalignment, the second harmonics vibration response tends to decrease slightly. Presented as a Society of Tribologists and Lubrication Engineers paper at the ASME/STLE Tribology Conference in San Francisco, California, October 13–17, 1996

Effects of journal misalignment on the performance characteristics of three-lobe bearings

Abstract: In this paper an investigation has been made to evaluate experimentally the performance characteristics of a misaligned 3-lobe journal bearing. Various parameters which have been studied are: friction through coast down time analysis, vibration responses, minimum film thickness, stiffness and damping coefficients of the fluid film, system natural frequency and damping factor. The film thickness decreases, friction increases and system damping increases as the bearing misalignment increases. © 1997 Elsevier Science S.A.

Thermoelastohydrodynamic Analysis of Tilting Pad Journal Bearing—Theory and Experiments

Abstract: Thermal and elastic effects play a very important role in lubrication of tilting pad journal bearings. This paper presents both theoretical and experimental analysis of tilting pad journal bearing. Theoretical analysis includes the simultaneous solution of Reynolds equation, energy equation and deformation equation. The computer code has been developed based on FEM which will work for large number of pads. Experimental study has been carried out on a four-pad tilting pad journal bearing, load between pad configuration and load on pad configurations with the rotational speed varied from 500-4000 rpm. Twelve thermocouples are used to measure pad temperatures. Coastdown time analysis results are presented in the form of Stribeck diagram of friction and compared with theoretical ones. Theoretical results are presented for steady-state and dynamic-state conditions of a four-pad tilting pad journal bearing. Presented as a Society of Tribologists and Lubrication Engineers paper at the World Tribology Congress in...

Experimental investigation on the performance characteristics of tilting pad journal bearings for small ratios

Abstract: In the present paper an experimental investigation has been carried out on the steady state and dynamic performance characteristics of a tilting pad journal bearing. Pad temperature and oil temperature measurements have been made using a thermocouple measuring system. Coast down time experiments were conducted on a rotor bearing test rig, and the coefficient of friction of tilting pad journal bearing has been found out experimentally. The deceleration vs. speed diagrams have been drawn for different length to diameter ( L D ) ratios and ror different loading configurations. Stiffness and damping coefficients have been identified using an identification algorithm and the identified coefficients were compared with the theoretically predicted coefficients.

Coast-Down Time Monitoring for Defect Detection in Rotating Equipment

Abstract: Rotating equipment under the action of dynamic forces, are prone to defects, such as misalignment, unbalance, change of rotor slope, skewed bearings, etc. These defects, if ignored for prolonged periods can cause sudden outages that may have serious consequences. Therefore, application of an appropriate condition monitoring technique is desirable to assess the health of the equipment and plan its maintenance. In this paper, monitoring of coast-down time (CDT) is undertaken to meet the objective. The CDT is the time elapsed between the instant the power is switched off to the rotor system till it comes to rest. The work demonstrates that, the CDT does detect the defects of the shaft assembly. Experiments were conducted on a specifically fabricated rig. The results revealed that the speed decay pattern followed a second order fitting of percentage speed reduction as a function of time. Defect identification parameter (DIP) is defined, which is a ratio of the polynomial coefficients of the first and the second order terms. The DIP values were found to correlate uniquely with the unbalance and the radial off-set defects in the shaft assembly.

Wear Characteristics of Plain Hydrodynamic Journal Bearings During Repeated Starting and Stopping

Abstract: The onset and development of wear in plain hydrodynamic journal bearings under repeated cycles of starting and stopping has been studied experimentally. The wear which occurred caused easily discernable but localized changes in diametral clearance, surface finish, and roundness of the bearing's bore and these changes were measured after various numbers of operating cycles had been completed. Study of the location, within the bearings of the wear which arose, showed that it was caused entirely by the sliding which occurred during starting and that no significant contribution to the wearing process was made during stopping. It was also observed that, once an initial rapid phase of wearing was completed, the surface finish of the hardened steel shaft was reproduced in the regions of the bearing's surface which continued to be worn.

The Behavior of Plain Hydrodynamic Journal Bearings During Starting and Stopping

Abstract: The work described is concerned with the behavior of plain, hydrodynamic journal bearings during starting and stopping under a steady load. The starting behavior indicated that a rapid buildup of hydrodynamic forces occurred in all cases. A hydrodynamic film was formed in a very short time, after which the shaft moved in a spiral shaped whirling locus to the steady state operating position. Prior to separation of the shaft and bearing surfaces, the contact was mainly a sliding situation with little or no initial rolling. At stopping, the shaft followed a typical hydrodynamic locus until rotation ceased and then a squeeze film trajectory to the final resting position.

Coastdown Time as a Mechanical Condition Indicator for Vertical Axis Motors with Grease-Lubricated Ball Bearings

Abstract: A technique is presented to assess the mechanical condition of vertical axis electric motors equipped with grease-lubricated ball bearings by comparing observed and predicted rotor coastdown times. A theoretical expression for calculating the coastdown time required, as input, a relationship between rotor torque and rotational speed. Torque values derived from existing theory in the literature proved unsatisfactory. Experiments were conducted on four electric motors with varying bearing size and preload, blade configuration and grease lubricant properties to refine the input criteria. Substitution of these empirically derived torque values into the expression then gave acceptable results. Deviation of actual coastdown times from those predicted indicates a probable mechanical problem and need for investigation. Presented at the 33rd Annual Meeting in Dearborn, Michigan, April 17–20, 1978