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Friction and lubrication in machinery has great economic and environmental impact

16 March 2022
Article by Pedro Marques, researcher specialist in mechanical gear transmissions

There is currently a need for a drastic change in the energy paradigm, both in terms of storage and of energy transformation processes, to reduce the emission of greenhouse gases, namely CO2.

As far as industry and transport are concerned, this transformation or paradigm shift may involve fundamental innovations in the processes and methods used, as well as in the type of energy sources used. However, one of the aspects that is often seen as secondary or even forgotten is the mechanical efficiency of the machinery that is part of every machine or means of transport.

Taking into account the amount of machinery that exists in industrial environments, as well as in transport and even in electricity generation, it is necessary to optimize this equipment to achieve maximum efficiency and reliability.

Direct gains from increased machinery efficiency are enormous

In the wind energy industry, for example, the end product is the electrical energy produced, so every kWh of energy that is produced counts. Many of the wind turbines use mechanical transmissions by gears with multiple stages between the turbine and the generator, so that, in this way, part of the energy that the turbine receives directly from the wind is dissipated as heat in the mechanical transmission. Due to the very high driving powers, a small gain in efficiency (0.5 to 1%) translates into an increase in the power that reaches the generator in the order of tens, reaching hundreds of kW. Considering a 5 MW wind turbine operating at rated power, a gain of 0.5% in the efficiency of the mechanical transmission corresponds to an increase of 25 kW in the useful power that reaches the generator.

This example proves the direct gains of increasing the efficiency of the machinery, in this particular case of the mechanical transmission. It is therefore easy to imagine that any machine or machinery which is driven by a system whose motion has to be mechanically converted into another, will almost inevitably be subject to energy losses through friction.

Indeed, recent studies show that approximately 23% of all energy produced worldwide is spent on friction and wear in machinery [1]. Of this share, 20% is needed to overcome the friction inherent in the operation of mechanical systems and 3% is used for the repair, manufacture and replacement of worn/damaged components [1]. Thus, the need to optimize machines and machinery, with a view to reliability and efficiency, becomes evident.

Optimizing lubrication and geometry in an integrated way translates into efficiency gains

Designing any equipment considering mechanical efficiency as a fundamental design variable, considering lubrication concepts and optimized geometry in an integrated way, can easily allow mechanical efficiency gains of more than 1%. This, in turn, can represent a 40% decrease in dissipated energy, if we are talking about mechanical transmissions by gears [2], although as mentioned earlier, these concepts can be applied transversally to any machinery.

Furthermore, efficiency and reliability often go hand in hand, as greater mechanical efficiency means less energy dissipated in machinery. This, in turn, translates into a reduction in temperatures on the contact surfaces of the mechanical parts and, therefore, a decrease in the probability of damage to those surfaces.

In lubricated systems, greater efficiency further lowers the lubricant's operating temperatures and can decrease its oxidation rate over time, allowing for potentially longer maintenance intervals.

The accumulation of these efficiency gains means that the development and implementation of efficient and reliable machines and machinery has, and will play in the coming years, a leading role in terms of reducing CO2 emissions. In concrete terms, it is estimated that the impact of measures in this direction can translate, in the long term (about 15 years), into a potential decrease in CO2 emissions of around 3140 Mt per year [1]. In this way, the gains associated with efficient mechanical systems go far beyond a reduction in the energy bill.


[1] - K. Holmberg, A. Erdemir, Influence of tribology on global energy consumption, costs and emissions. Friction 5, 263–284 (2017).

[2] - Carlos M.C.G. Fernandes, Pedro M.T. Marques, Ramiro C. Martins, Jorge H.O. Seabra, Gearbox power loss. Part II: Friction losses in gears, Tribology International, Volume 88, 2015, Pages 309-316, ISSN 0301-679X.

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