When the Pressure’s On: How EP Additives Step Up to Protect Your Equipment
Welcome to part two of our blog series on friction-fighting additives in lubricants! Last time, we unpacked how anti-wear (AW) additives protect machinery under lighter loads. This time, we’re turning up the heat—literally—with a look at extreme-pressure (EP) additives, the heavy hitters of the lubrication world.
EP additives are built for high-load situations like gearboxes and sliding surfaces – places where AW additives simply can’t cope. They’re tougher, more chemically aggressive, and often made with compounds of sulphur, phosphorus, or chlorine, with sulphur-phosphorus (SP) blends being the most common in industrial gear oils and greases.
Here’s where it gets interesting: unlike AW additives that simply bond to metal surfaces, EP additives react with the metal. When metal parts rub together and heat up past 90˚C, these additives kick in, forming a tough, protective chemical layer exactly where it’s needed. It’s clever stuff—only activating at hot spots where metal meets metal.
But there’s a catch. EP additives don’t play nice with everything. For instance, they’re not always compatible with zinc-based AW additives, so don’t go mixing lubricants unless you’re sure they’re designed to work together. Also, because SP additives can be harsh on “yellow metals” (like those in transmission synchronizers), they’re used cautiously in transmission fluids.
There are other EP additives out there too—like chlorinated hydrocarbons and sulphurized fatty acids—but some of these can hang around in the environment and build up in living organisms. That’s why there’s a global push to find greener alternatives.
At the end of the day, both AW and EP additives are vital in the world of lubrication, especially during boundary and mixed lubrication conditions when full oil film protection can’t be maintained. They help keep metal parts from wearing out prematurely—saving you downtime and money.
Got questions about wear-reducing additives? Drop us a line at info@bcl.co.za—we’re happy to help!