Investigation of factors influencing wheel–rail adhesion using a mini-traction machine

Adhesion in the wheel–rail contact is a key factor determining stable running conditions and safety during train driving and braking. This paper presents an experiment performed in a mini-traction machine to simulate the problems of low adhesion in the wheel–rail contact. Tests were conducted under dry conditions and using water or oil as lubricants to study the influence of surface roughness on the adhesion coefficient. The results indicate that the adhesion coefficient can be reduced to as low as 0.02 for smooth surfaces lubricated with water. For rougher contact surfaces, the water-lubricated tests indicate a higher adhesion coefficient than do oil-lubricated ones, but also a clear dependence on water temperature. The oil-lubricated tests indicate a very slight dependence of the adhesion coefficient on variation in rolling speed, temperature, and surface roughness.