Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Applicability of LFC-EAL combinations

Results of a tribological screening of different biodegradable oils (sunfloweroil, saturated and unsaturated ester) in combination with different DLC- coating types (different dopants). Biodegradable oil based lubricants are prone to thermal degradation, hence frictional heating during accidental contacts of the moving parts or start-up, shut-down contacts limit the lifetime of such environmentally adapted lubricants (EAL). The tests evaluate the potential of DLC types to solve this degradation problem and mainly investigates the difference of oil additive interaction with pure steel or DLC-coatings. The results of this screening can be used to make a first material choices (oil/additive/coating-combination) for the development of sustainable tribological systems in hydraulics (automotive) and centers and rests in grinding machines and others.

Several tests have been performed to simulated different contact conditions:
Disc on disc tests simulate the contact present in the center/workpiece of grinding machines and ball on disc tests the contact in a guide/workpiece and in a piston/liner system. In both tests it was found that the studied coatings reduce the friction in a combined coating/EAL system, with the best results by an undoped DLC coating. Additives in the lubricant did not show any effect in these test conditions. The wear of the coatings is evidently reduced by applying a lubricant. Early failure of the doped coatings was due to delamination. The steel counter body however is protected by the coating on the ball. Additives in the oil can improve the wear resistance, but the most beneficial type of additive depends on the dopants used in the coating.

Block-on-ring tests simulated the rest system in grinding machines. The tests showed a reduction by factor 10 of the wear.

The combination of a fully formulated EAL lubricant with an optimised DLC show even lower coefficient of friction and better wear resistance than the coatings and oils used in the screening tests.

FZG tests were performed to study the effect of using a coating on oxidation stability of the EAL.DLC/DLC systems showed lower friction coefficient than steel/steel or Steel/DLC combinations, hence there is lower frictional heat generation.

A test on a piston pump, which is one of conventional and very frequent types of pumps used in hydraulic applications, has been performed. The results of oil analyses are all favourable for the DLC system, including viscosity (more stable, and not showing the oxidation trend) and TAN is strongly better for DLC than steel system. Contamination of the oil was reduced and the combination EAL/DLC showed very little running in effect.

Doimak and Volvo will use this result for exploitation on grinding machines and in hydraulic components.

Reported by

Boeretang 200
2400 Mol
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