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Comparison of anodised aluminium surfaces from four fabrication methods
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Tribomaterial)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Tribomaterial)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Tribomaterial)
2012 (English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774, Vol. 212, no 11, 2272-2281 p.Article in journal (Refereed) Published
Abstract [en]

This study presents a comparative analysis of surface characteristics and properties of anodised aluminium cylinders produced by sand casting, permanent mould casting, extrusion, and high pressure die casting. Differences in micro structure and distribution of silicon particles in the aluminium, due to the fabrication method and the silicon content in the alloy, resulted in varying thickness of the oxide layers (mean thicknesses between 7 and 19 m) and surface topography. The oxide layer was unevenly thick for the permanent mould cast and the sand cast cylinders, resulting in a surface with higher plateaus and lower areas. This was more prominent for the sand cast surface. The oxide of the extruded cylinder was thick and even and its surface was smooth. The high pressure die cast surface had an oxide that was very thin and uneven. The surfaces displayed different results in the scratch test due to the variations in the surface structure. For the permanent mould cast and the sand cast surfaces the silicon particles present in the oxide deflected the cracks that were formed during the scratching. This resulted in smaller wear debris. The nanohardness values of the oxides had a large scattering due to the inhomogeneous nature of the oxide layers, with pores and particles. However, the highest nanohardness values were between 5000 and 6000 MPa for the four surfaces, which is significantly lower than that of sintered alumina. In the micro abrasion test the wear mechanism for all four surfaces was microcutting resulting in chippings.

Place, publisher, year, edition, pages
Elsevier, 2012. Vol. 212, no 11, 2272-2281 p.
Keyword [en]
Aluminium, Anodising, Surface structure, Oxide thickness, Abrasive wear resistance
National Category
Materials Engineering
Research subject
Engineering Science with specialization in Materials Science
Identifiers
URN: urn:nbn:se:uu:diva-183184DOI: 10.1016/j.jmatprotec.2012.06.007ISI: 000309569400013OAI: oai:DiVA.org:uu-183184DiVA: diva2:562063
Available from: 2012-10-23 Created: 2012-10-23 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Tribological Aspects of Pneumatic Clutch Actuators
Open this publication in new window or tab >>Tribological Aspects of Pneumatic Clutch Actuators
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A clutch actuator is used in a vehicle to transmit movement and force from the clutch pedal to the release bearing of the clutch. A pneumatic clutch actuator consists of an anodised aluminium cylinder, inside of which a piston, with a rubber lip seal and a PTFE guiding ring, slides. The system is lubricated with silicone grease before assembly. A commercial clutch actuator of this type, has a service life of 3 million actuations and must function in a wide temperature range, from -40 ºC to 140 ºC.

In this thesis, the complex tribological system of pneumatic clutch actuators has been studied. Field worn actuators have been disassembled and investigated. A laboratory test method has been developed to understand the tribomechanisms present in pneumatic clutch actuators. The test method's capability of simulating the real contact has been verified, by the comparison with studied actuators from the field. The influence of contact parameters: temperature, load, lubrication and particle contamination, has been investigated. In addition, different anodised aluminium surfaces have been studied.

The manufacturing method of the aluminium cylinder influences surface topography and structure of the oxide, resulting in different mechanical and frictional properties.

The wear during tests with only silicone grease is reminiscent, but on a lower scale, to the wear during tests with a mixture of silicone grease and standard dust.

The initially applied amount of silicone grease is not important, the friction seems to depend on the amount of silicone grease that is dragged into or pushed out from the contact area during testing. Silicone grease lubrication reduces wear of the lip seal. However, during some tests, an adhesive layer, composed of  grease residuals and some PTFE, was formed on the lip.

A triple PTFE transfer, from guiding ring to aluminium surface, to lip seal, to aluminium surface, occurred. Such transfer of material from the PTFE guiding ring was detected from the unlubricated tests, and also from the silicone grease lubricated tests, i.e. silicone grease lubrication does not prevent PTFE material transfer.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 67 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1021
Keyword
Wear, friction, PTFE transfer, anodised aluminium, NBR rubber lip seal, silicone grease, casting, extrusion
National Category
Materials Engineering
Research subject
Engineering Science with specialization in Tribo Materials
Identifiers
urn:nbn:se:uu:diva-195330 (URN)978-91-554-8601-3 (ISBN)
Public defence
2013-04-12, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (Swedish)
Opponent
Supervisors
Available from: 2013-03-20 Created: 2013-02-24 Last updated: 2013-04-17Bibliographically approved

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Riddar, FridaHogmark, StureKassman Rudolphi, Åsa

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