Extreme Pressure Additives and FunctionStratson
Extreme Pressure Additives and Function
You will find the word Extreme Pressure (EP) on labels for a variety of lubricants, especially on gear oils and greases. The function of these additives is to prevent metal to metal contact during times of high load, shock load, high temperature, and slow speeds during start up or shut down. There are several ways this can be accomplished.
When equipment is running normally, the lubricant should provide a fluid film between the metal surfaces to prevent contact. If the fluid film becomes too thin this is called boundary lubrication. When boundary lubrication occurs asperities on the metal surface may come into contact, weld together, then break off forming hard particles that will cause further damage and eventual failure. Boundary lubrication usually occurs when high loads, shock loads, and high temperature operation are applied to the equipment. It usually occurs during start up or shut down as the lubricant film has not formed yet or is reduced in thickness.
Additives such as Molybdenum Disulfide, Calcium Sulfonates, Graphite, Zinc and Antimony will form a protective coating on the metal surface and wear away when boundary lubrication occurs to prevent contact with metal surfaces. These additives have a natural attraction to the metal surfaces and will work at any temperature.
Sulfur, Phosphorous, Chlorides, Boron and other similar chemistries are temperature activated to react with the metal surface to form salts that provide the protective film during boundary lubrication. These functions happen in gear boxes, hydraulic pumps, bearings, bucket pins, and anywhere Extreme Pressure lubricants are needed. SWEPCO Products are designed to work over a wide range of temperatures, loads and speeds.
Contact your SWEPCO® Sales Agent if you have any questions or concerns regarding your equipment’s performance.