CHAPTER ONE

1.1 INTRODUCTION

Hydrodynamic journal bearings are typical critical power transmission

components that carry high loads in different machines. In machine design

therefore it is essential to know the true or expected operating conditions of the

bearings. These operating conditions can be studied both by experimental and

mathematical means for example in test rig experiments in field or laboratory

tests with engines and by calculation or simulation.

Numerous studies of the operating conditions of hydrodynamic journal

bearings have been made during the last decades. Still the case is far from

closed. For example there are a limited number of studies that carry out an in-

depth examination of the true operating conditions of bearings in true-scale

experiments. There is also a need for experimental studies to verify the

theoretical ones.

Fluid friction i.e. viscosity which exists in the lubricant being used is

studied alongside the pressure effect which is being generated in the bearing

thus the effect of lubricants with different viscosities are considered.

A simple journal bearing consists of two rigid cylinders. The outer

cylinder (bearing) wraps the inner rotating journal (shaft). A lubricant fills the

small annular gap or clearance between the journal and the bearing. The amount

of eccentricity of the journal is related to the pressure that will be generated in

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the bearing to balance the radial load. The lubricant is supplied through a hole or

a groove and may or may not extend all around the journal. The pressure around

the journal is measured on various manometers by means of pressure pipe/tubes.

This is done at various speeds to get the relationship between speed and the

pressure.

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1.2 HISTORICAL BACKGROUND

In the late 1880s experiments were being conducted on the lubrication of

bearing surfaces. The idea of “floating” a load on a film of oil grew from the

experiments of Beauchamp Tower and the theoretical work of Osborne

Reynolds.

Prior to the development of the pivoted shoe thrust bearing marine

propulsion relied on a “horseshoe” bearing which consisted of several equally

spaced collars to share the load each on a sector of a thrust plate. The parallel

surfaces rubbed wore and produced considerable friction. Design unit loads

were on the order of 40 psi. Comparison tests against a pivoted shoe thrust

bearing of equal capacity showed that the pivoted shoe thrust bearing at only

1/4 the size had 1/7 the area but operated successfully with only 1/10 the

frictional drag of the horseshoe bearing.

In 1896 inspired by the work of Osborne Reynolds Albert Kingsbury

conceived and tested a pivoted shoe thrust bearing. According to Dr. Kingsbury

the test bearings ran well. Small loads were applied first on the order of 50 psi

(which was typical of ship propeller shaft unit loads at the time). The loads were

gradually increased finally reaching 4000 psi the speed being about 285 rpm.

In 1912 Albert Kingsbury was contracted by the Pennsylvania Water and

Power Company to apply his design in their hydroelectric plant at Holtwood

PA. The existing roller bearings were causing extensive down times (several

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outages a year) for inspections repair and replacement. The first hydrodynamic

pivoted shoe thrust bearing was installed in Unit 5 on June 22 1912. At start-up

of the 12000 kW units the bearing wiped. In resolving the reason for failure

much was learned about tolerances and finishes required for the hydrodynamic

bearings to operate. After properly finishing the runner and fitting the bearing

the unit ran with continued good operation. This bearing owing to its merit of

running 75 years with negligible wear under a load of 220 tons was designated

by ASME as the 23rd International Historic Mechanical Engineering Landmark

on June 27 1987.

Since then there has been series of progressive research carried out on

bearings bringing to the advent of journal bearings which are not so different

from the bearings designed by Osborne Reynolds and Albert Kingsbury which

work on the same hydrodynamic lubrication system.

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1.3 RESEARCH PROBLEM

The operating conditions of hydrodynamic journal bearings can be

described by a set of tribological variables called key operating parameters. For

example the load level of a hydrodynamic journal bearing is described by two

parameters: the specific load and the sliding speed. The key operating

parameters most directly related to the bearing lubricant-shaft contact are the oil

film temperature oil film thickness and oil film pressure. These three key

parameters can be determined by experimental or mathematical means with

varying levels of complexity.

Until now oil film pressure in hydrodynamic journal bearings has been

studied mainly by mathematical means because the experimental determination

of oil film pressure has been a demanding or even an unfeasible task. Under real

operating conditions there are typically many practicalities that complicate the

experimental determination of true oil film pressure in a certain point or at a

certain moment. The oil film may be extremely thin and therefore sensitive to

different disturbing factors for example defects in geometry. In addition the

level of the oil film pressure may be extremely high or have a high level of

dynamic variability.

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1.4 AIM AND OBJECTIVE OF THE PROJECT

The research into the construction and design of the journal bearing

apparatus has several reasons and purposes which need to be achieved and

justified.

The main aim of the study was to determine the oil film pressure in

hydrodynamic journal bearings carrying realistic loads. In addition the

relationship between the oil film pressure and other key operating parameters of

journal bearings such as eccentricity and shaft speed was studied.

The study also included the determination of the relationship between the

speed of rotation of the shaft the pressure around the journal bearing and the oil

thickness.

1.5 SCOPE OF THE PROJECT

The design and construction of journal bearing demonstration rig covers a

very broad area. This area encompasses the design design considerations

construction assembly working conditions and governing mathematical

equations and laws. The design gives in depth details of the construction and

fabrication of the apparatus. The working conditions consist of the loading

acting pressures and the variable operating speed which the journal bearing

apparatus undergoes. Relevant design calculations and equations to include the

Pressure head calculation Sommerfeld’s equation and number Petroff’s

equation and Reynold’s equation to mention a few are contained in this work.

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