Dynamic lead effects on journal bearings

Patrick, James K (1967) Dynamic lead effects on journal bearings. PhD thesis, University of Glasgow.

Abstract

This thesis presents the findings of an Experimental Investigation of the behaviour of the oil film in a journal bearing supporting Dynamic Loads. The instrumentation developed for an existing loading frame is described and includes a balance piston capable of detecting tensile stresses in the oil film, and a lever system which measures journal centre displacement with commercially available displacement transducers. The conversion of a crankshaft test rig into a Second Testing Machine is described. A feature of this second machine is the use of an Externally Pressurised Bearing as a 'frictionless support' for the test bearing housing. This construction enabled extremely sensitive bearing friction measurements to be recorded simultaneously with the co-ordinates of the journal centre within the clearance circle, and of the applied load. The loading mechanism in both testing machines consisted of a Hydraulic Load Capsule pressurised from an eccentric driven ram pump. The diaphragm was bonded to the capsule body in the First Testing Machine and was sealed by a series of piston rings to form a free piston arrangement in the Second Testing Machine. Oil film pressures in bearings of 3 inches diameter and 3 inches long with diamentral clearance of .0015 and .003 inches were surveyed in the First Testing; Machine for a range of Static and Dynamic Loads. The Dynamic Loads were of sinusoidal form with unit bearing loads up to 1650 lb f./in.2 and the ratio of the Load Frequency to the Journal Speed set at unity. Integration of the oil film pressures acting on the bearing surface, indicated pressure loads which were in good agreement with the applied loads. The pressure surveys indicated that, under conditions of Static or Dynamic Loads, the load bearing film pressures were retained within an arc bounded by the axial supply grooves, and that the clearance space on the unloaded arc of the bearing was not full of oil but contained a large quantity of air released by the cavitation of the oil film. The oil film over the unloaded arc of a Dynamically Loaded bearing consists of a trough of very low pressures prior to the area of constant sub-atmospheric pressures previously reported for dynamic loads. The oil film sustains tensile stresses in this trough during the period OF increasing load, and on eventual rupture air is released from solution and forms cavities in the oil. As the oil film does not rotate within the clearance space under Dynamic Loads, it cavitates and reforms within the same bearing arc. This process forms depressions in the profile of the developing film pressures as the entrapped air is dissolved. Journal displacement measurements made in the First Testing Machine indicated that a certain degree of restraint was imposed on the test bearing housing by the loading mechanism. It was also noted that the bulk of the balance piston cylinder gave the test shaft a stiffness which varied with the plane of bending. These factors combined to make interpretation of the Dynamic Load Displacement measurements difficult without recourse to correction factors. To avoid these problems in the Second Testing Machine no pressure transducer was included in the test shaft and the bearing was mounted so that the Journal was simply supported in the plane of loading. Static Load measurements were compared with published experimental results to evaluate l3ie measuring techniques before their application to Dynamic Load Conditions. Journal centre co-ordinates were measured in .003 inch diameter clearance bearings with a length to diameter ratio of 1% and The journal paths under Dynamic Loads of sinusoidal form had the simple elliptical shape predicted from theoretical considerations. The presence of two axial grooves in bearings subjected to this form of loading, holds the major axis of the elliptical path in a position close to the line of applied load, irrespective of the magnitude or speed ratio of that load. The experimental techniques used, failed to detect a load frequency to journal speed ratio at which the oil film had zero load capacity.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: A ST Thomson
• Keywords: Mechanical engineering, Fluid mechanics
• Date of Award: 1967
• Depositing User: Enlighten Team
• Unique ID: glathesis:1967-73324
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 14 Jun 2019 08:56
• Last Modified: 14 Jun 2019 08:56
• URI: https://theses.gla.ac.uk/id/eprint/73324