Coastdown Time as a Mechanical Condition Indicator for Vertical Axis Motors with Grease-Lubricated Ball Bearings
TL;DR: In this article, a technique was 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.
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
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TL;DR: In this paper, the experimental performance of misaligned cylindrical and three-lobe journal bearings was evaluated using a double-disc rotor system with a test bearing in the middle and driven by a variable speed DC motor through an electromagnetic coupling.
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
29 citations
TL;DR: In this article, the authors investigated the coastdown characteristics of a two-rotor system consisting of a variable-speed d.c. motor driving a flexible rotor on two journal bearings.
9 citations
TL;DR: In this article, the coastdown time (CDT) monitoring of power driven rotating systems during every routine stoppage was investigated for prediction of onset of failure, and the CDP plots were made for a variable speed motor with oil, multipurpose grease and Servogem grease lubrication.
7 citations
Journal Article•
TL;DR: In this article, the authors used the coast-down time (CDT) to detect the defects of the shaft assembly and found that the speed decay pattern followed a second order fitting of percentage speed reduction as a function of time.
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.
4 citations
TL;DR: In this article, the Coast Down Time (CDT) is used to assess the condition of the rotating machine as a condition monitoring parameter, which is the total time taken by the system to dissipate the momentum acquired during sustained operation.
Abstract: Mechanical malfunctions such as, rotor unbalance and shaft misalignment are the most common causes of vibration in rotating machineries. Vibration is the most widely used parameter to monitor and asses the machine health condition. In this work, the Coast Down Time (CDT), which is an indicator of faults, is used to assess the condition of the rotating machine as a condition monitoring parameter. CDT is the total time taken by the system to dissipate the momentum acquired during sustained operation. Extensive experiments were conducted on Forward Curved Centrifugal Blower Test Rig at selected cutoff speeds for several combinations of combined horizontal and vertical parallel misalignment, combined parallel and angular misalignment, as well as for various unbalance conditions. As mechanical faults increase, a drastic decrease in CDT is found and this is represented as CDT reduction percentage. A specific correlation between the CDT reduction percentage, level of mechanical faults, and rotational cutoff speeds is observed. The results are analyzed and compared with vibration analysis for potential use of CDT as one of the condition monitoring parameter.
3 citations
Cites background from "Coastdown Time as a Mechanical Cond..."
...Hindawi Publishing Corporation International Journal of Rotating Machinery Volume 2010, Article ID 962804, 12 pages doi:10.1155/2010/962804 Research Article Condition Monitoring of Forward Curved Centrifugal Blower Using Coast Down Time Analysis G. R. Rameshkumar,1 B. V. A. Rao,2 and K. P. Ramachandran3 1 Department of Mechanical & Industrial Engineering, Caledonian College of Engineering, P.O. Box 2322, CPO 111 Seeb, Oman 2 Advisor to Chancellor, VIT University, Vellore, Tamil Nadu 632 014, India 3 Associate Dean (PGS and R), Caledonian College of Engineering, P.O. Box 2322, CPO 111 Seeb, Oman Correspondence should be addressed to G. R. Rameshkumar, ramesh@caledonian.edu.om Received 19 April 2010; Accepted 17 August 2010 Academic Editor: R. Amano Copyright © 2010 G. R. Rameshkumar et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited....
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...In this work, the Coast Down Time (CDT), which is an indicator of faults, is used to assess the condition of the rotating machine as a condition monitoring parameter....
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...The exact time period between the power cutoff time and the time at which the rotor stops is called Coast Down Time [5, 6]....
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46,339 citations
01 Oct 1968
TL;DR: In this paper, the authors determine the fraction of the total capacity of bearing voids and available housing space that can be filled with grease (pack optimization) before leakage or excessive temperature rise occurs.
Abstract: : The specific objectives of the present study are to: (1) determine the fraction of the total capacity of bearing voids and available housing space that can be filled with grease (pack optimization) before leakage or excessive temperature rise occurs; (2) to determine, for the cases of a few bearing sizes, the effect of bearing size and housing geometry on the optimum grease pack; (3) to determine the effect of shaft attitude (axis horizontal or vertical) on the optimum grease pack; (4) to seek a relation between bearing operation and modification to the physical and chemical characteristics of various greases; and (5) to establish rules for packing grease in bearings and housings.
1 citations