This paper will pertain mainly to the gear lubrication of heavy duty off-road equipment and industrial applications.
In the past, lubricants were purchased strictly on the basis of cost per pound and/or gallon. Labor, equipment and replacement parts were inexpensive. Lubricant disposal costs were nil.
The pound or gallon cost is not critical but how cost effective it is in use is critical.
In the past, gear lubricants for industrial use and for use in off-road equipment were not always highly refined. The chemistry was Pb, S, Cl and the cost relatively low.
The life of these lubricants was short and lubricant changes of three to six months were recommended. When subjected to temperatures over 120°F for long periods of time, lubricants would solidify into a greaselike mass, causing gear and bearing failure. The lead acted as a pro-oxidant, resulting in this solidification. The need for improved performance became very strong, resulting in the development of S-P gear oil and more complex chemistry to improve the life and performance of gear lubricants.
Now, even more improvements are required to extend the life of the lubricant and component parts being lubricated. Also, longer life of the gear lubricant is required because disposal costs are extremely high.