Hydrodynamic Lubrication

Bearings and Thrust Bearings

J. Frene, D. Nicolas, B. Degueurce, D. Berthe, M. Godet

• Publisher: Elsevier Science
• Year: 1997
• Print ISBN:
  9780444823663
• eBook ISBN:
  9780080534312
• Topic: Technology & Engineering
• Subtopic: Physics
• Index: Physics

Hydrodynamic Lubrication is the culmination of over 20 years close, collaborative work by the five authors and discusses the practical use of the formalization of low pressure lubrication. The work concentrates on the developments to journal and thrust bearings and includes subjects such as: • the dynamic behaviour of plain and tilting-pads • the thermal aspects • the positive and negative effects of non-cyclindricity and shape defects resulting from manufacturing or operation • the effects of inertia • the appearance of Taylor's vortices and of turbulence and their repercussions. The book contains an abundance of test results objectively compared with theoretical conclusions and a chapter on "technical considerations" to ensure that draft mechanisms will work satisfactorily under the imposed conditions. Hydrodynamic Lubrication is an essential reference book for future and practising engineers who want to put hydrodynamic and hydrostatic journal bearings and thrust bearings into operation under conditions of total safety.

Chapter 1

Tribology from Antiquity to Our times^*

The name Tribology was created in 1967 and comes from the Greek word τριβειν Tribein: to rub, and λó γoςLogos: speech, study or science. It includes the study of lubrication, friction and wear of machine elements.

Friction has not only negative aspects: the road holding of a car depends directly on the friction between tires and road. Similarly, man would not be able to walk without friction. Finally it was by rubbing a piece of hard wood in the interior of a hollow part of softer wood that man learnt out to master fire, more than 100,000 years ago.

However, since he produced the first mechanisms, man has tried to suppress wear and diminish friction to limit efforts. Let us again quote the example of a car in which more than one quarter of the power is lost by friction in the engine and the transmission system.

1.1 The Prehistoric Period

The first bearings produced by man were the door sockets, i.e., the thrust bearings composed by a wooden shaft rotating in the interior of a hollow part of a piece of wood or stone. Elements made of stone, dated 2500 B.C., were found in Mesopotamia (Fig. 1.1).

Fig. 1.1 Lower pivot of door, Mesopotamia, 2500 years J.C.[13]

Pottery production also led, very early, about 4000 years B.C., to the turning wheel, which included a pivot; this pivot was made of wood, stone or even pottery. A stone pivot, dated 2000 years B.C., and lubricated with either bitumen or animal fat, was found in Jericho.

Wheels and carts were invented towards 4000 B.C. The wood wheels were solid and very often consisted of several assembled pieces. Later on, their surfaces were nailed to diminish wear. Finally, the spokes appeared around 2000 B.C.: 4, then 6 to 8 spokes considerably increased the wheel strength. The wheel carts could not carry heavy loads; for this purpose wood cylindrical pieces, interposed on a track between a wood path formed by large cut stems and the object to be moved were used.

The demonstration of this technique was made in 1979 on the plateau of Exoudun, close to Saint-Maixent, Deux-Sèvres (France), under the direction of J.P. Mohen, curator of the museum of Saint-Germain-en-Laye (France).

Fig. 1.2 shows one photograph of this demonstration, during which 170 people moved a replica, made of concrete, of a dolmen table weighing 32 tonnes. Elsewhere, an Assyrian bas-relief at Kouyunjik, dated 700 B.C., clearly shows the use of wood rollers to move a statue (Fig. 1.3). Such a technique, known for over 5000 years, allows friction to be diminished by replacing sliding friction by rolling friction.

Fig. 1.2 Reconstitution of the transportation of a dolmen, Tableland of Bougon, Exoudun, Deux-Sèvres, 1979. (From LA NOUVELLE REPUBLIQUE)

Fig. 1.3 Restored bas-relief at Kouyunjik, Assyria, 700 B.C.[14]

To carry heavy loads, Egyptians slid them on roads made most probably out of wood and well lubricated. Several bas-reliefs show this technique. The oldest was found in the tomb of Saqqara, dated 2400 years B.C. and shows the removal of the statue of Ti. One can notice a man, in front of the statue, pouring a liquid, water or oil, to ease the sliding motion. This is the first known example of lubrication. Another bas-relief, dated 1800 years B.C. and coming from the tomb of Tchuti Hetep at El Berrheh shows the same system of transport (Fig; 1.4). The man pouring water is now on the pedestal of the statue and no longer in front of it, where he could be crushed. The importance of lubrication was recognized.

Fig. 1.4 Transport of a statue, tomb of Tchuti Hetep, El-Bersheh, Egypt, 1800 B.C. [14].

Wheels obviously existed in Egypt at that time, but carts were used only to carry light loads or for war. Towards 1400 B.C. lamb or beef fat was used for lubricating the bearings of cart wheels.

The spoke wheel appeared in India towards 2500 B.C. and in China at about 1500 B.C. The copy of a Chinese cart with iron rimmed wheels is shown in Fig. 1.5.

Fig. 1.5 Chinese South pointing Cart, 255 B.C. [1].

This peculiar cart has a statue with orientation linked to the differential rotation of the wheels, with two sets of gears and a differential gear. The distance between the two wheels is equal to the wheels’ diameter and the transmission ratio of the two sets of gears is equal to 1. Therefore, irrespective of the path of the cart on a flat area, the hand of the statue remains constantly pointed in the same direction (South), if rolling without sliding takes place between wheels and soil. This cart was used by the Chinese for orientation when crossing, the desert of Gobi.

1.2 The Greek and Roman Period

Greeks and Romans developed the use of the wheel; they knew the use of vegetable and animal oils as lubricants as well as that of bitumen and petroleum oils.

The Greeks invented gears; the screw could be attributed to Archytas, while Aristotle, Archimedes and others less known described the principle of various gear systems. Heron of Alexandria used a shaft with cams on it. In fact, the Greeks had at their disposal all the necessary elements for technical progress, except for the connecting-rod-crankshaft system (invented in the 14th century). Nevertheless, the development of mechanism did not actually take place, due to a lack of wood and of hydraulic energy, transport problems due to an insufficient network of roads, and the existence of slavery. And above all, a way of thinking based only on pure reasoning and rigorous demonstration, not leaving room for experimental thinking.

Romans used and developed the technology worked out by Greeks. Important progress was achieved in producing olive oil and in grinding corn. Water mills were used, towards 120 B.C.

An interesting example is the TRAPETUM; several samples were found at the excavation of Olyntha (5th century B.C.). Olive kernels were crushed and taken off with the Trapetum (Fig. 6). They were composed by two hemispherical grind stones (Orbis) placed vertically and sustained by a wooden horizontal shaft (Cupa), turning around a central pivot (Columnella). The circular mill-trough (Mortarium) had a shape similar to modern grind stones.

Fig. 1.6 A trapetum for olive crushing [15].

The presence of a ring (Cunica), most probably made of metal, prevented a rapid wear of the wood shaft; it is the first example of such a bearing.

In a similar way, to reduce the wear of their shoe soles, the Romans used iron nails; this habit has been abandoned only recently.

The Romans knew ball thrust bearings as well as conical roller thrust bearings and cylindrical roller sliders. Parts of such thrust bearings were found in a Roman galley laying at the bottom of lake Nemi in Italy. This galley which sunk around the year 40 was found in 1895 and the search lasted until 1933 when Mussolini dried the...

Table of contents

• Cover image
• Title page
• Table of Contents
• Inside Front Cover
• Copyright page
• Preface
• Foreword
• Acknowledgements
• Main used Notations
• Chapter 1: Tribology from Antiquity to Our times*
• Chapter 2: Lubricating Oils
• Chapter 3: General Equations in Hydrodynamic Lubrication with a Newtonian Fluid
• Chapter 4: Plane Sliders and Thrust Bearing Pads*
• Chapter 5: Static Characteristics of Journal Bearings*
• Chapter 6: Dynamic Characteristics of Journal Bearings
• Chapter 7: Non Circular Journal Bearings with Fixed Geometry and with Tilting Pads
• Chapter 8: Journal Bearings Subjected to Dynamic Loading
• Chapter 9: Influence of Shape Defects and of Surface Deformations
• Chapter 10: Thermal Effects in Hydrodynamic Journal Bearings
• Chapter 11: Superlaminar Flow Regimes
• Chapter 12: Hydrostatic and Hybrid Journal and Thrust Bearings
• Chapter 13: Technological Aspects