LITERATURE AND CURRENT EVENTS 375

Thus, the removal of dust and oil from the rails will be one of the major means of increas- ing adhesion. The spark method of cleaning is proposed for the removal of the oily film. At low winter temperatures the main reason for the sharp decrease of adhesion is due to the rails being colder than the air, which favours the formation of ice.

Adhesion as a Statistical Problem. S. Johnsson, ASEA, Vasteras, Sweden. In studying experimentally the coefficient of sliding friction for a driven locomotive axle, consistent results are rarely obtained in a series of tests performed under seemingly identical conditions. In earlier publications the author has intro- duced a statistical theory to take account of this fact. The coefficient of friction between wheel and rail should not be considered as a discrete value in the mathematical sense, but as a random variable. With the aid of this theory, the author compares the adhesion of different locomotives, (e.g., bogie locomotives with all axles free or mechanically coupled to each other, fixed-frame locomotives, and those with electric axle load compensation). He also discusses the influence of weather on the random variable of friction.

Control of Tractive Effort on Electric Tractors. H. W. Lucas and A. S. Robertson, English Electric Co. Ltd, London. Adhesion between wheel and rail can often be improved by the use of sand or other means, but wheel slip will occur when tractive effort exceeds the available adhesion. Methods of detecting and correcting slip with both electric and diesel-electric transmissions are examined and it is shown that the use which can be made of the available adhesion is affected by traction motor connections, control of tractive effort peaks, the load con- trol system in the case of a diesel-electric transmission, and other considerations. Equip- ment should be designed so as to prevent damage when wheel slip does occur and trac- tive effort should be controlled near the limit of adhesion. Ways and means of doing this will be discussed. Under favourable rail conditions, high adhe- sion can be assumed. Maximum train loads have to be matched to an adhesion level for both starting and running which will give an acceptable level of wheel slip most of the time.

Weight Transfer in a Two-bogie Loco- motive and its Compensation. G. Borgeaud, Swiss Locomotive and Machine Works, Winterthur. The tractive effort on the draw hook provides a torque on the locomotive, shifting the resul-

tant of the axle loads backwards. In the case of bogie locomotives the torque is taken up by the bogies themselves and by the body. Ideally there should be no weight transfer between axles of the same bogie, the whole torque being compensated, via the body, by suitable load distribution between the bogies. Normally axle load compensating equipment has to provide such conditions. In order to examine the conditions occuring it is necessary to investigate separately the forces involved at the body, bogie, wheel set and axle drive, taking into consideration the load compensating device. It is thus possible to determine what arrangement of the trac- tion motors, in combination with the axle suspension, leads to favourable solutions and to a considerable improvement of the distri- bution of axle load.

The NEL Contribution to Adhesion Studies. F. T. Barwell, British Transport Commission, London, and R. G. Woolacott, National Engineering Laboratory. Adhesion ,was studied by observations of actual phenomena on a railway; simulation of conditions in the laboratory; and by basic experiments aimed to elucidate laws of fric- tion in various atmospheric environments. Accounts have appeared elsewhere but the work as a whole is reviewed. The incidence of slipping on a stretch of track was recorded, together with meteorological data, and samples of contaminant on the rail head were subjected to inorganic analysis. A wheel and tyre machine was modified for adhesion research and test results show that the relative sliding-torque curve changes with relative humidity and surface contamination. To synthesize the situation, tests were made with clean steel in a vacuum, the effect of various additions being determined. Sanding is a most effective but undesirable remedy for slip. The marked effect of surface- active chemicals and the large area of the rail surface on which colloidal debris is deposited pointed to a physico-chemical solution. If the effect of the surface-active ions could be neutralized, the whole complex of the surface, including its reaction to high humidities, could be changed. Detergents of the sodium metasilicate type appear to offer the greatest promise. Their action may be too slow for application from a locomotive in difficulties, but their continual application will raise the level of adhesion.

Stresses in the Contact Zone. E. Ollerton, Department of Mechanical En- gineering, Nottingham University. This paper was intended to outline the develop- ment of contact stress theory from the time of Hertz’s original paper to the present time, with particular reference to the adhesion problem.

Wear, 7 (1964) 373-333