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Reduction of the fluid lubricant use in heavy loaded motion transmission systems through the application of self-lubricant coatings

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Self-lubricant coating materials

Motion transmission systems, like gearboxes and ballscrews, used considerably in the aerospace industry and in industrial manufacture, need to run at high speeds. Hydraulic fluids are used to prevent contact failure of metal surfaces in relative motion. Self lubricant coatings have been developed to reduce the hydraulic fluids used, minimising waste generation and disposal costs.

Industrial Technologies

To prevent wear and damage of heavy loaded motion transmission systems hydraulic fluids are used as lubricants. Engines need most lubrication when motion is starting or stopping, for it is then that the elastohydrodynamic lubrication regime is unstable, requiring excessive quantities of hydraulic fluid. Although during the remaining time of normal operation, there is no need for such excessive quantities, however, there is no way to dispense with them. Excess of fluids naturally results in increased frictional resistance and puts an upper limit in the maximum effective working speed of the mechanical system. Hydraulic fluids become, after use, a major source of waste, difficult and expensive to dispose of. Low friction high resistant coatings may reduce substantially the quantities of hydraulic fluids used. The current project has developed two coatings, a carbon based and a MoS2 based, which can be applied to mechanical components, but can also be used for cutting and forming tools. The coatings are magnetron sputtered and can be deposited to coat complicated geometries. Their properties, compared to traditional hard coatings, such as TiN or TiC, are superior. They show low friction and low wear rate at extremely high loads and have very good tribological properties in ordinary mineral oil and in dry environments. They can be used with less lubricant, or even without any lubricant fluid. The immediate consequences are increased lifetime of the components, reduction in consumed energy since friction is reduced and decrease of environmental risks for the quantities of lubrication fluids are minimised. The project has also available for demonstration and testing a new generation of ballscrews made of parts coated with a self-lubricant material based on MoS2. These ballscrew systems after reaching a D-N factor of 120,000mm/rpm exhibited a temperature increase inside the nut of about 35 degrees Celsius. If, due to the need of extreme positioning precision, the temperature is limited to 25 degrees Celsius, the corresponding D-N factor can go up to 90,000.

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