| Abstract: | Lubricants and functional fluids may be grouped into those based on natural oils and those having man-made (‘synthetic’) base stocks. This paper is concerned with the ‘dilute synthetic lubricant’ in which the man-made component is blended with a major proportion of water. The developments covered include hydraulic and metal-cutting fluids, with examples drawn from experience with solutions and dispersions. The performance required from these fluids in service is discussed with particular attention to improvements in corrosion protection, antiwear performance, extreme-pressure properties, foam inhibition, air release, rolling bearing fatigue and resistance to erosion pitting. Water quality can have a significant impact on the performance properties of the fluids already listed. The service properties of aqueous lubricants may be classified according to their response to chemical additives. Examples are given of properties which respond well to additives and of those which are governed largely by the bulk physical properties of water. Manufacturers of equipment are continuing to develop new machinery. Fluid formulators are seeking to extend the current operating limitations of aqueous fluids. Future development relies on close co-operation between users, equipment suppliers and lubricant formulators. |
