An eco-friendly alternative gear oil

All vessels of a certain size today are manoeuvred by propeller units and thrusters of different designs. Depending on the size of the vessel, these propulsion units may be filled with up to 8,000 litres of oil. During normal operation, oil may leak into the sea through the propeller seals even when they are well-maintained. Oil leakage can also occur due to wear and tear, accidents or faulty handling. While the effect of an individual leakage may be small, the total oil contamination in the seas worldwide amounts to several million litres per year. As shipping traffic is increasing, this constitutes a growing potential problem for the environment.

For this reason, many ship-owners call for eco-compatible alternatives to today’s mineral oil-based lubricants. A solution that would satisfy all requirements has not been available for gears in thrusters and rudder propellers so far. In terms of technical performance, any alternative must be at least equal to mineral oils, while at the same time being compatible with the propeller shaft seals – a considerable challenge for lubricant development engineers.

CHALLENGES FOR ECO-FRIENDLY ALTERNATIVES

Using readily biodegradable gear oils instead of mineral oils is a sizable contribution to preventing pollution of the seas and their inhabitants, as microorganisms can quickly decompose them into carbon dioxide, water and biomass. The biodegradability of mineral oils shown in the OECD 301 F test is about 20 %. The new gear oil from Klüber Lubrication, by comparison, shows a biodegradability of 80 %. However, readily biodegradable gear oils must comply with certain requirements in order to be considered an alternative to mineral oils, particularly in terms of performance. They must ensure excellent lubrication and fulfil all requirements of bearing, tooth flank and sealing lip lubrication. Moreover, the oil must be compatible with the elastomer seals used.

When looking for readily biodegradable oils, ester oils or low-viscous polyethylene glycols may be considered, however these oils must be chosen with great care as they might affect the characteristics of the elastomer seal used.

PASSED AND APPROVED

To meet the special requirements of thrusters and rudder propellers, Klüber Lubrication developed a gear oil and launched it under the name Klübersynth EG 2-150.

The additive-treated special oil is based on a synthetic, biodegradable and non-toxic ester oil. Its rapid biodegradability in the presence of bacteria has been proven according to the OECD 301 F test: > 60% within 10 days, and acute toxicity according to OECD 201 (EC₅₀): > 1000mg/l, 202(EC₅₀): > 1000mg/l and 203(LC₅₀): > 1000mg/l.. It complies with all tribological requirements of high-performance gear oils and the requirements of leading manufacturers of thrusters and rudder propellers.

STRONG PARTNERSHIP

In the development of the new gear oil, Klüber worked in close cooperation with its affiliated companies SIMRIT and Merkel Freudenberg Fluidtechnik, both leading suppliers of shaft seals and profiled seals to the maritime industry. The result of their cooperation is a tailor-made, environmental-friendly combination of radial shaft seal and lubricant for increased reliability and lifetime to reduce costs for downtime and repair. As Klübersynth EG 2-150 is a synthetic oil, its lifetime is three to four times longer than that of mineral oil under comparable operating conditions. Klübersynth EG 2-150 is miscible with mineral oil, trouble-free changeover to the new oil is possible and existing sealing systems can continue to be used; Klüber recommends checking with the manufacturer of the thrusters or rudder propellers about compatibility of oil and radial shaft seal.