LOW TEMPERATURE PROPERTIES OF HYDRAULIC FLUIDS - DESIGN TOOLS AVAILABLE FOR THE LUBRICANT FORMULATOR
Hydraulic fluids are utilized under varying ambient conditions during the long winter season on the Northern Hemisphere, and in aviation, space and off-shore applications. High performance lubricants are required in hydraulic systems; and can deliver reliable service even under harsh conditions. The challenge for the Lubricant Formulator is how to create a lubricant solution with an attractive price/ performance ratio, and with favourable rheological properties, e.g. startability and low temperature fluidity. This paper is based on an experimental study of low temperature fluid behaviour, where results from low temperature base oil rheology and tribology are compared. Also, a new specialty fluid that Nynas has developed is compared to other base oils, and a model hydraulic fluid with improved low temperature performance is described. The selection of wax-free base oils is an important design tool for the fluid formulator. Some comments on base oil availability are also given.