Cause Of Wear Research Articles

Some Aspects of Engine Wear

OF all modern engineering constructions, it is difficult to imagine a unit the components of which are more liable to general wear than the present‐day internal combustion and compression ignition engines. The performances demanded of aero‐engines in particular, have instigated the enormous amount of research and investigation that has been made on the problem of reducing metallic wear under various conditions of temperature, load, atmosphere, etc. The importance of this problem is manifest when one reflects that the great majority of the components of the aero‐engine (with the exception of details, nuts, bolts, pins, etc.) are subject to continual wear in one form or another. In other words, the serviceable life of any engine is largely a function of the degree to which particular forms of wear have been minimized. While the question of adequate lubrication is undoubtedly of vital importance in reducing friction, the primary causes of wear are dependent upon the properties and surface conditions of the materials at their respective working temperatures. For the majority of components, the selection of material must necessarily be mainly decided by such considerations as yield point, compression strength, fatigue range, specific tenacity, maximum stress, resistance to scaling, thermal expansion, etc., and the question of wear is reckoned rather as a problem for which the metallurgist will find a treatment which can be suitably applied to the material. Thus we have seen evolved the many processes for surface‐hardening, and numerous anti‐friction materials, etc. It is interesting to review the present position of the practical applications of the science of reducing metallic friction, and to note tendencies of future developments.

Experience with, and problems relating to, bottom bearings of electricity meters

The paper first outlines the results obtained over a period of 10 years with oiled sapphire-steel bearings on a single type of meter used by a large supply undertaking, and describes tests carried out on new and worn pivots and jewels with various lubricants and abrasives. The results indicate that oil greately increases the life of a bearing, but that, even when oiled or greasy jewels are used, the presence of rust or debris is the major cause of wear and consequent errors in the reading of the meter.A series of wear tests on various pivot materials, both oiled and dry, is next described. The results show that materials of all hardnesses give comparatively good results when oiled. No conclusive evidence is obtained of the validity of Stott's theory that oxygen is set free from sapphire under the influence of the large cohesive forces which operate in meter bearings.The cause of surface cracking in sapphire jewels is then investigated, by means of a device which initiates impacts at the rate of 18 per minute between the pivot and the jewel of a meter bearing.Finally, an account is given of apparatus designed for the rotational testing of meter bearings in air and inert atmospheres, providing special facilities for the microscopical examination of jewels. The results of tests in nitrogen, argon, neon, hydrogen, and a vacuum, are discussed, and it is concluded that further experimental work is necessary in order to confirm or disprove the sapphire-oxygen theory.

The rotor bearings of electricity meters

In this paper an accumulation of experimental and statistical data which have been obtained by the author has been brought under review for the purpose of discussing the leading problem in the sphere of meter maintenance, namely that of worn bearings.Attention is drawn to the necessity for improving the reliability of meters in service in consequence of the vast number to be dealt with under modern conditions. The period of sustained accuracy needs to be extended in order to reduce the work of periodically exchanging meters, which is becoming increasingly difficult to contend with.It is submitted that the solution lies in increasing the durability of the bearings and particularly the combination of bottom jewel and pivot which constitutes the footstep bearing.The subject is dealt with in five main sections, which are outlined in the following:In Section (1) typical bearings to be found in electricity meters are illustrated and described and the principal features of design are pointed out. Reference is also made to methods of examining the condition of bearing jewels.Section (2) is directed to a study of the movements of the pivots of meters under load which contribute to the wearing of the bearings. Included in this section is an explanation of the method devised by the author for compensating for fluid friction in mercury motor meters, in which the upward movement is put to practical advantage. The vibratory movements of the rotors of a.c. meters produced by the action of the voltage and current fluxes are dealt with, and the differences observed in the amount of vibration exhibited by different designs are commented upon.In Section (3) the condition in which bearings are found after the meters have been removed from service is discussed. The frequency of the occurrence of defects in the bottom jewel is pointed out and the variety of forms which they take, as revealed by the microscope, is described. Examples of long-life jewels are given and the difficulty of drawing any conclusion as to the cause of wear from the contradictory evidence of life statistics of jewels is pointed out. The extreme obscurity of the problem is recognized, but the author suggests some possible explanations and certain lines along which laboratory research might prove fruitful.Section (4) deals with a special application of the diamond cupped bearing in connection with h.t. polyphase meters working under low-load conditions in exceptional circumstances. Extensive experiments with agate pivots working in sapphire cups are described.In Section (5) the author endeavours to formulate some opinions on various aspects of the bearing question, based on the experience and investigations set out in the paper.