High-temperature applications and high-temperature performance were hot topics at the European Lubricating Grease Institutes 2014 Annual General Meeting in Dubrovnik, Croatia, in late April. Over 270 delegates from 32 countries focused on the challenges that higher temperatures present.
The need for greases capable of withstanding higher temperatures is growing, said Lubrizols Gareth Fish. As equipment power density has increased, running temperatures of automotive components and industrial machinery have increased. In response, the volumes of higher temperature greases have grown, putting pressure on formulators and their additive suppliers to screen and develop the additives that will boost high-temperature grease performance.
Rene Westbroek of Axel Christiernsson International AB in Sweden highlighted the difference between grease performance at its upper temperature limit – a temperature at which grease can function only briefly – and at its upper operating temperature. At the latter level, lubrication should be maintained for much longer time periods. Westbroek noted large differences in how grease manufacturers determine upper operating temperatures. For example, he said, product data sheets for similar mineral oil-based lithium EP2 greases give upper operating temperatures in a huge range from 120 to 250 degrees C.
Westbroek argued that alternate test methods, in addition to standard industry tests, will give the best understanding of oil loss at higher temperatures, and thus the best method to determine upper operating temperatures.
Afton Chemical Corp.s U.S.-based Joseph Kaperick likewise looked at both existing and new techniques to improve the integrity of grease formulations at high temperature. In grease-lubricated bearings, changes in torque with changes in temperature have been related to the stability of greases, he said. And greases that remain stable as temperature increases, and that control friction as temperature increases, can control torque increases.
Kaperick said, The ability to look at structural and thermal stability of grease, the effect of wear and friction on high-temperature torque, or the oxidative stability of the oil are invaluable tools for grease formulators.