The Stribeck memorial lecture

Abstract

Stribeck’s publications ‘Kugellager für beliebige Belastungen’ and ‘Die wesentlichen Eigenschaften der Gleit- und Rollenlager’ were remarkable for their time. Many of the findings were revolutionary and are still considered quite modern.

The method used by Stribeck to calculate load distribution between the balls within a ball bearing is still used today, otherwise, a full finite element analysis would be required.

His measurements and analysis of bearing friction is also astonishingly accurate. Most of the ball-bearing types studied by Stribeck are not in use any more, but the deep-groove ball bearings he investigated were similar enough to be compared with modern deep-groove ball bearings. Stribeck measured the friction coefficient 0.0015 and SKF gives the friction coefficient 0.0015 for deep-groove ball bearings in the catalogue from 1989. For the first time, in the SKF catalogue from 1989, the life calculation method took into account contamination also. Stribeck had stated already 100 years ago that cleanliness was very important for bearing life and function.

Stribeck’s investigation of journal bearing friction, as a function of load and speed, was also extremely important, as he showed the possibility of finding a point of minimum friction for lubricated applications. He also showed that the friction for sliding bearings started at high friction at low speeds, decreased to a minimum friction when metal to metal contact stopped, and then increased again at higher speeds, which is the well known ‘Stribeck curve’.

Introduction

It is now 101 and 100 years, respectively, since Richard Stribeck published his famous papers, ‘Kugellager für beliebige Belastungen’ (1901), and ‘Die wesentlichen Eigenshaften der Gleit- und Rollenlager’ (1902) in Zeitschrift des Vereines deutscher Ingenieure [[2], [3]]. The first paper treated the load-carrying capacity of ball bearings brilliantly and the second paper resolved the longstanding dispute over bearing friction characteristics as a function of load, speed and lubrication.

Stribeck [1] was born in Stuttgart in Germany on 7 July 1861. He received his basic education in his hometown where he finished his studies at the Technische Hochschule in Stuttgart. Later, he gained practical experience in various places, including Königsberg. At the age of 27, in 1888, he was back in his hometown, Stuttgart, and was appointed as Professor of Machine Construction at the Building School. Two years later, in 1890, he moved to the Technische Hochschule in Darmstadt. After three years, on 1 April 1893, he moved to the Technische Hochschule in Dresden. As Professor für Maschineningenieurswesen, he gave his inaugural address in Dresden on 6 May 1893 on the subject ‘Progress in the production of steam and in the exploitation of its energy in steam engines during the last 20 years’. Seven weeks later, on 1 July 1893, he went on a sabbatical leave to the United States of America.

Later, when he was back in Dresden, in the academic year 1896–1897, he was appointed to the governing body of the newly founded Machines Laboratory I (Strengths). He did not stay there long and moved to Berlin in March 1898. There, he became head of the metallurgical division of the Centralstelle für wissenschaftlich-technische Untersuchungen in Neubabelsberg, Berlin.

During the years 1889–1893, when Stribeck worked in Stuttgart and in Darmstadt, he published some 10 scientific papers. This large early output was mainly on giving solutions to the problems of boilers and steam turbines for marine applications. Only in the last paper in this group, Stribeck dealt with dynamic loading on the main and cross-head bearings of steam engines. That was thus the first time he became involved with tribology and tribological problems. When he was in Dresden, Stribeck studied gears, with particular emphasis on experimental studies of worm gear drives. He experimentally determined the limiting loading for correctly working worm gear drives as a function of load (F) and speed (n). He found that a hyperbola described the function well and that F·n=constant described the combination of load and speed, which could be allowed for any specific drive lubricated with a certain specific oil. In 1897, he published a paper on the consequences of wear of gears.

As mentioned above, Stribeck moved in 1898 to Berlin to work as one of the directors of the newly created Centralstelle für wissenschaftlich-technische Untersuchungen in Neubabelsberg, and to head the metallurgical division. There, he undertook and published the findings from his most basic tribological studies between 1898 and 1902. They were in two different areas: the load-carrying capacity of ball bearings and the friction characteristics of plain bearings and radial rolling element bearings. Stribeck applied sound physical principles to his experimental investigations, and used the theoretical background information available at that time.

In his very well known study on the load-carrying capacity of ball bearings Stribeck [2] gave scientific basis for the development of a large industry. He used the Hertzian contact theory, which by then had been known for 20 years, to connect the loads on the different balls to the external load. He then compared the loads on single ball contacts of different geometry, which were needed to give visible plastic deformations. He used three balls in contact, see Fig. 1, a steel plate sandwiched between two balls, and more conforming contacts of the type found in deep-groove ball bearings. Stribeck’s studies, which were commissioned by the Deutsche Waffen-und Munionsfabriken, Berlin, were epoch-making in their effect on the ball-bearing industry. Its major impact arose from the analysis of the carefully conducted experiments, see Fig. 2, and the sound appreciation of Hertzian contact theory, together with the presentation of practical formulae in a form suitable for the bearing designer. Stribeck’s approach to the question of load-carrying capacity of ball bearings was about seven years in advance of similar considerations in gear design.