An experimented investigation of the coastdown characteristics of a two-rotor system consisting of a variable-speed d.c. motor driving a flexible rotor on two journal bearings is presented. The characteristics are plotted in terms of decelaration versus speed for various operating conditions (speed, lubricant type, misalignment and commutator carbon brushes). The coast-down curve resembles the classical Stribeck friction diagram and hence can be used to evaluate the transition speed of journal bearings of rotating systems. The results confirm that this simple technique provides a measure of the friction present and indicates the mechanical condition of the rotating assemblies. © 1983.

G. Santhanakrishnan

B. V.A. Rao

BEARINGS - RELIABILITY

MECHANICAL DRIVE - SPEED CONTROL

Machinery

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

An experimental investigation of tribological effects on coastdown phenomena in horizontal rotating machinery

Wear

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. © 2000 Taylor & Francis Group, LLC.

Tribology Transactions

Thermoelastohydrodynamic analysis of tilting pad journal bearing—theory and experiments

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.

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

The behavior of a rotating system after its power supply is cut off is called the coastdown phenomenon. An experimental investigation of the coastdown characteristics was carried out on a rotor rig, with different types of lubricants including a Newtonian oil, a.blend of ISOVG 32 and hydrogenated styrene isoprene, multigrade oils, and aqueous polymer solutions in a hydrodynamic journal bearing. The characteristics were plotted in terms of deceleration vs. speed, which resembled the Stribeck diagram of friction due to viscous drag. Thus, the apparent Stribeck diagrams of friction for the above oils were obtained by plotting the derived coefficient of friction against the reciprocal Sommerfeld number. Theoretical results were obtained through the solution of the governing Reynolds equation and energy equation, for Newtonian and cubic law fluid models. The experimental results are compared with the respective theoretical results for the case of friction in journal bearings lubricated with non-Newtonian fluids. © 1993 Taylor & Francis Group, LLC.

Non-newtonian effects on the coastdown phenomenon of hydrodynamic journal bearings

An experimental investigation carried out of the coastdown characteristics of a variable-speed d.c. motor and a motor-rotor system is detailed in this paper. The characteristics obtained through an XY recorder in terms of speed vs. time are replotted in terms of deceleration vs. speed for both unreleased and released conditions of the motor commutator carbon brushes during the coastdown experiments. The deceleration vs. speed curves (coastdown curves) for the motor-rotor system resemble the classical Stribeck diagram of friction. © 1987.

Commutator carbon brush effect on the coastdown times of a horizontal motor and a motor-rotor coupled system

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.

Fulltext

International Journal of Rotating Machinery

Condition Monitoring of Forward Curved Centrifugal Blower Using Coast Down Time Analysis

Coastdown time (CDT) monitoring of power driven rotating systems during every routine stoppage, using the coastdown phenomenon (CDP), is investigated for prediction of onset of failure. CDP plots were made for a variable speed motor with oil, multipurpose grease and Servogem grease lubrication, with released carbon brushes and with various misalignments, each at four cut-off speeds. Results facilitated determination of transition speed by sudden increases and decreases in deceleration on a deceleration versus speed curve of a CDT study. Decrease in CDT after reassembly of the rotating system indicates deviation from correct alignment. Dry friction arising from carbon brushes increases deceleration rate considerably. © 1988.

Journal	Wear
ISSN	00431648
Open Access	No