Lubricants for Optimal Running-in of Hydraulic Motors
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Bosch Rexroth Hägglunds Drives AB manufactures hydraulic motors, a mechanical device that transforms energy from a liquid medium to kinetic energy. The piston assembly in the motor consists of both sliding and rolling interfaces. During start and when the speed is low, these surfaces will be in contact without any separating lubrication film. This is called boundary lubrication and causes high friction losses. When the motor obtains its lift-off speed a transition from a mixed lubrication regime where the surfaces in the piston assembly are partly separated to a full film lubrication where they are completely separated by a lubrication film takes place. Running-in of an assembly is made to assure good conformity of the surfaces. The wear rate of the surfaces is high during running-in, but when the asperities of the surface are worn down, the wear that occurs after the running-in period will be mild and controlled. In this thesis work investigations were performed to determine if a lubricant in conjunction with a diamond-like carbon (DLC) coating can be used to improve running-in of the roller-piston interface of the motor. This could thereby decrease the lift-off speed and boundary friction. The running-in lubricant is proposed to be used during the 30 minute delivery test that is performed at Bosch Rexroth Hägglunds Drives to ensure improved and reliable functioning of the motor. In the experiments, varying concentrations of anti-wear (AW) and extreme pressure (EP) additives were blended into mineral base oil and reciprocating conformal and counterformal tribological tests were performed. The wear and the surface roughness of the samples after the test were investigated with an optical profiler and scanning electron microscopy. It could be concluded that a high content of EP additive gave the highest amount of wear of the tested additive combinations, while the AW content did not seem to affect the results. Oil with high EP content could therefore work as a running-in oil, and should be further tested in a piston test rig.
Place, publisher, year, edition, pages
2011. , 47 p.
Teknik, hydraulic motor, running-in, tribology
IdentifiersURN: urn:nbn:se:ltu:diva-51373Local ID: 8938dad3-e4eb-419b-b2fe-42bd34516986OAI: oai:DiVA.org:ltu-51373DiVA: diva2:1024734
Subject / course
Student thesis, at least 30 credits
Materials Engineering, master's level
Validerat; 20110617 (anonymous)2016-10-042016-10-04Bibliographically approved