Gear oil: EP additive selectivity as a longevity factor
The EP mechanism — and what happens when it is activated unnecessarily
Extreme-pressure additives work by chemical reaction with metal surfaces. Sulfur, phosphorus and chlorine compounds react with steel when the local temperature at contact points exceeds 150–200 °C, forming sacrificial layers that prevent welding and seizure under severe loads.
The catch: this activation temperature is reached not only under extreme loads but in many normal operating conditions of precision gearboxes. When the EP additive reacts with surfaces that don't need its intervention, it is not protecting — it is corroding.
The three forms of damage from inadequate EP
Attack on non-ferrous components
Highly reactive sulfur compounds do not distinguish between steel and copper. In gearboxes that incorporate phosphor bronze bushings, synchroniser rings or copper-alloy bearings, conventional EP produces:
- Progressive dissolution of bronze surfaces — visible as pitting or material loss
- Embrittlement of synchroniser rings from continuous chemical attack
- Oil contamination with copper particles, accelerating abrasive wear throughout the circuit
Chemical degradation of seals
High EP concentrations interact destructively with elastomers. NBR, FKM and PTFE seals show alterations that compromise their sealing function:
- Hardening from chemical reaction, reducing elasticity
- Loss of accommodation under thermal swings
- Progressive leaks signalling imminent seal collapse
Sedimentation under normal operation
Poorly balanced EP formulations precipitate at moderate temperatures — not just at load peaks. The cascade effect: filters clog with solid particles, viscosity rises locally, and those very retained particles cause the abrasive wear the system was supposed to prevent.
Turan S: EP protection with selective activation
Turan S solves the problem in the formulation, not in the usage procedure. 100% synthetic PAO (Group IV) bases offer a uniform molecular structure that eliminates the unstable compounds present in conventional mineral oils.
What the synthetic base delivers:
- Minimal batch-to-batch variation — consistent specification over time
- Oxidation resistance five times higher than mineral bases under equivalent conditions
- Compatibility with elastomers without documented side effects
How selective activation works: The additive technology in Turan S calibrates the reactivity threshold. At normal operating temperatures, EP activity is low — protecting non-ferrous metals and seals from unnecessary attack. Under load that drives local temperature above the critical threshold, EP protection activates progressively, proportional to real demand. The result is the same protection in the moments that matter, with less aggression during the hours when it isn't needed.
Where this distinction defines performance
Wind turbine gearboxes: High gear ratios and load variations from wind gusts demand active EP during peaks but low aggressiveness during steady operation. The advanced seals used in this equipment do not tolerate continuous high-reactivity EP.
Plastic extruder gearboxes: Loaded starts and continuous long-duration operation combine with precision components that define product quality. Turan S delivers protection at startup without aggressing sensitive components during the following hours of stabilised operation.
Pulp and paper gearboxes: High humidity, acidic compounds and variable temperature create an environment that dissolves conventional formulations. Resistance to water contamination and compatibility with fine filtration systems are requirements mineral bases struggle to sustain consistently over time.
Validation by specifications that require broad compatibility
Turan S was formulated to simultaneously meet standards that historically were hard to reconcile:
- DIN 51517 Part 3 (CLP) — EP protection validated under load
- ISO 12925-1 CKC/CKD — compatibility with non-ferrous materials confirmed
- Flender — approval for wind turbine gearboxes
- Cincinnati Machine — qualification for high-precision machine tools
This combination confirms the chemical balance has been achieved: extreme protection when needed, neutrality when protection would mean damage.
Kelpen Oil: twenty-five years developing balanced formulations
The distinction between aggressive and selective EP is not a marketing difference — it is a difference in additive chemistry Kelpen Oil has been developing for 25 years. Turan S is the result: maximum protection where needed, no cost to the components that don't need it.
For gearboxes with sensitive components, variable operating conditions or the requirement of extended intervals with reliability, our team analyses equipment specs and service conditions to confirm the right viscosity and formulation. Consult our technical team.
