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A new device has been developed and used to study metallic contact and friction between sliding, lubricated surfaces. The system consists basically of a fixed metal ball loaded against a rotating cylinder. The extent of metallic contact is determined by measuring both the instantaneous and average electrical resistance between the two surfaces. Friction between the ball and cylinder is recorded simultaneously with contact.In general, the electrical resistance was found to oscillate rapidly between an extremely low value and infinity, suggesting that metallic contact is discontinuous. The average resistance of an oil film is therefore a time-average, that is, a measure of the per cent of the time that metallic contact occurs. The results indicate that metallic contact is much more prevalent than would have been expected from other published studies in which electrical resistance or discharge methods were employed.Using this apparatus, the entire region from hydrodynamic (no metallic contact) to pure "b oundary" lubrication (continuous metallic contact) can be readily investigated. Load, speed, mineral oil viscosity, the presence of additiv es, and operating time were found to be important variables influencing metallic contact.The apparatus is particularly useful in studying the action of antiwear and "extreme pressure" additives. It allows one to measure not only the effectiveness of these compounds in reducing metallic contact, but also the rate at which they act and the durability of protective films which may form. Introduction IN spite of the fact that preventing metallic contact isprobably the most important function of a lubricant, there is still much to be learned about the transition from a condition of " no-contact" to one of continuous contact. Thi s is the region where lubrication goes from the desirable " hydrodynamic" condition to the lessacceptable " bounda ry" condition, where increased metallic contact usually leads to higher friction and wear. Consequently, it is important to learn as much as possible about the factors which determine or influence the extent of metallic contact in a lubricated system.The present paper describe s the results of st udies which have been made of metallic contact, friction and surface dama ge between sliding, lubricated surfaces. The object of this invest igation was fourfold: (a) to develop a simple device for measuring both metalli c contact and friction ; (b) to determine to what extent metallic contact actually occurs under these conditions ; (c) to find out what are the important factors influencin g the degree of contact (e.g., load , speed , time , lubri cant composition); and (d) to relate metallic contact, if possible , to friction and /or surface damage . Future papers will deal with the importance of lubricant variables-including

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