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

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

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

Abstract: 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.