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Tribological characteristics of some multi-layered Pb-free engine bearing materials
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Lead (Pb) containing alloys such as white metals and Cu-Pb-Sn (lining) with Pb-based overlay plating have been extensively used as materials for internal combustion engine bearings during the last several decades. However, owing to environmental and health concerns, the use of Pb containing materials in automotive engine components is being restricted. In view of this, attempts are under way to develop and replace Pb-containing materials with Pb–free bearing materials.

The tribological characteristics of these recently developed Pb-free bearing materials have, however, not been fully investigated and only a limited results about their tribological performance are available in open literature. This thesis therefore focuses on investigating the tribological performance of some recently developed Pb-free engine bearing materials. Although engine bearings are designed to operate in full film lubrication conditions yet they also operate in mixed and boundary lubrication regimes where the material properties do affect their tribological performance. There is thus a need to study the tribological behaviour of these new Pb-free bearing materials in mixed and boundary lubrication conditions vis a vis that of conventional Pb-containing bearing linings and overlays. This work has therefore aimed at investigating the tribological characteristics such as friction and wear, seizure behaviour, interaction with different oil formulations and embeddability behaviour of some selected Pb-free engine bearing materials.

Friction and wear properties of Pb-free bearing materials Al-Sn based lining without overlay, bronze lining coated with Polyamide-Imide (PAI) based overlay containing MoS2 and graphite, bronze lining coated with Al-Sn based and PAI based overlay containing MoS2 and graphite, bronze lining coated with Sn-based overlay, and bismuth (Bi) containing bronze lining coated with Sn-based overlay have been studied using a block-on-ring test configuration under unidirectional sliding conditions in mixed and boundary lubrication regimes. The conventional Pb-containing bearing material was also studied as a reference material. Al-Sn based material showed considerably higher friction compared to the other bearing materials. The bearing material with PAI based overlay containing MoS2 and graphite showed superior friction and wear properties compared to all other materials. Sn-based overlay coated materials resulted in comparable friction and wear properties to that of Pbbased overlay. Wear mechanism in Al-Sn based material is mainly adhesive and abrasive in case of Sn based overlay.

Seizure behaviour of the bearing materials were also studied using the block-on-ring test configuration in dry as well as lubricated conditions using pure base oil and a fully formulated engine oil. The PAI based overlay containing MoS2 and graphite showed no sign of seizure even at the highest test load in dry as well as lubricated conditions. Al-Sn based lining without overlay seizes at relatively lower load in dry condition compared to the other bearing materials. Adhesion or wear debris smearing onto the counter surface is the main causes of seizure in dry condition. In lubricated condition, seizure occurred at relatively higher load and the conventional Pb-containing material was found to have better seizure performance compared to the Al-Sn based and Sn-based overlay plated materials.

Tribological compatibility of Pb-free bearing materials with different oil formulations was studied using a ball-on-bearing specimen test configuration in boundary lubrication under reciprocating sliding conditions. Four different bearing materials were investigated using different lubricants with and without oil additives. In general, the bearing materials lubricated with pure PAO base oil showed higher friction compared to those lubricated with oils containing additives. Lubricants containing additives improved wear properties of the bearing materials except in the case of Al-Sn based lining without overlay. It was also observed that the anti-wear additive level did not significantly influence the wear performance of bearing overlays.

The embeddability behaviour of Pb-free bearing materials was studied using a fully formulated engine oil contaminated with SiC particles. Pb-free bearing materials with Snbased overlay, Bi-based overlay, PAI-based overlay containing MoS2 and composite overlay containing PAI, Al, PTFE were investigated. Tests at different rotational speeds (i.e. different oil film thickness) and a constant load were carried out using a journal bearing test rig. It was found that material removal from bearing and shaft surfaces due to abrasive wear is influenced by the lubricant film thickness. The steel counter surface showed lower wear in tests using Sn based overlay and a PAI, Al and PTFE containing composite overlay compared to Bi-based overlay and PAI-based overlay containing MoS2. 

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2017.
Series
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
National Category
Tribology
Research subject
Machine Elements
Identifiers
URN: urn:nbn:se:ltu:diva-62495ISBN: 978-91-7583-847-2 (print)ISBN: 978-91-7583-848-9 (electronic)OAI: oai:DiVA.org:ltu-62495DiVA: diva2:1081615
Public defence
2017-05-11, E231, Luleå, 09:00 (English)
Opponent
Available from: 2017-03-20 Created: 2017-03-14 Last updated: 2017-05-08Bibliographically approved
List of papers
1. Tribological performance of tin-based overlay plated engine bearing materials
Open this publication in new window or tab >>Tribological performance of tin-based overlay plated engine bearing materials
2015 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 92, 281-289 p.Article in journal (Refereed) Published
Abstract [en]

A block-on-ring test setup is employed to investigate tribological performance of Sn-based overlay plated bearing materials under mixed and boundary lubrication condition. Pb-containing bearing material is also studied as a reference. Sn-based and Pb-based overlays have shown similar transition in friction when rotational speed is varied. Under relatively longer test duration, Sn-based overlays exhibit comparable friction and wear properties with that of Pb-based overlay. It takes longer time to obtain steady-state friction for Sn-based overlay than Pb-based overlay. Wear behaviour of tested samples are also similar except for tests in the mixed lubrication regime where Sn-based overlays show better wear resistance. In the Sn-based overlays main wear mechanisms are adhesive and abrasive wear leading to exposure of the Ni interlayer.

National Category
Tribology
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-12915 (URN)10.1016/j.triboint.2015.06.014 (DOI)c10166dd-deed-4d4a-8263-f3eae3b36406 (Local ID)c10166dd-deed-4d4a-8263-f3eae3b36406 (Archive number)c10166dd-deed-4d4a-8263-f3eae3b36406 (OAI)
Note
Validerad; 2015; Nivå 2; 20150624 (andbra)Available from: 2016-09-29 Created: 2016-09-29 Last updated: 2017-04-25Bibliographically approved
2. Friction and wear characteristics of different Pb-free bearing materials in mixed and boundary lubrication regimes
Open this publication in new window or tab >>Friction and wear characteristics of different Pb-free bearing materials in mixed and boundary lubrication regimes
2015 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 340-341, 63-72 p.Article in journal (Refereed) Published
Abstract [en]

Traditional bearing materials contain different amounts of lead (Pb) because of its friction reducing properties. However, in view of the negative health and environmental impact of Pb, there is growing emphasis on restricting the usage of Pb in engine bearings. Owing to this, new bearing materials that provide at least comparable tribological performance to that of Pb containing alloys are being developed and some new Pb-free materials are being already used in engine bearing applications. It is, however, still unclear how these new engine bearing materials would perform in mixed and boundary lubricated conditions. In this study, a block-on-ring test setup was employed to investigate the tribological performance of several bimetal and multi-layer Pb-free bearing materials with different compositions of bearing lining and overlay plating. Pb-containing bearing material was also studied as a reference material. Friction and wear properties of these bearing materials were investigated and their wear mechanisms under lubricated conditions have been analysed. Bearing material with Polyamide-Imide based overlay containing graphite and MoS2 exhibited better friction and wear properties than Pb-based and Al-Sn based materials. Pb-containing bearing material shows higher wear of material and Al-Sn based material has shown higher friction compared with the other test materials.

National Category
Tribology
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-38459 (URN)10.1016/j.wear.2015.06.002 (DOI)cddfd036-3cb8-4082-a8fb-5f18d912f803 (Local ID)cddfd036-3cb8-4082-a8fb-5f18d912f803 (Archive number)cddfd036-3cb8-4082-a8fb-5f18d912f803 (OAI)
Conference
Nordic Symposium on Tribology : 10/06/2014 - 13/06/2014
Note
Validerad; 2015; Nivå 1; 20150611 (andbra); Konferensartikel i tidskriftAvailable from: 2016-10-03 Created: 2016-10-03 Last updated: 2017-04-25Bibliographically approved
3. Seizure behaviour of some selected Pb-free engine bearing materials under lubricated condition
Open this publication in new window or tab >>Seizure behaviour of some selected Pb-free engine bearing materials under lubricated condition
2017 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 111, 265-275 p.Article in journal (Refereed) Published
Abstract [en]

Under severe operating conditions seizure can occur in engine bearings. Therefore it is important to study seizure behaviour of selected Pb-free bearing materials that may replace the conventional Pb-based materials. Seizure tests were carried out using a block-on-ring test configuration by stepwise increasing applied load at a constant rotational speed using base oil and also fully formulated engine oil respectively. The bearing materials are ranked in terms of friction and seizure load. Al-Sn based lining without overlay shows higher friction and lower seizure load in both oils. Polyamide-imide based overlay containing MoS2 and graphite and Pb-based material show no sign of seizure. For Sn-based overlay plated materials seizure load is higher in fully formulated engine oil than in base oil.

National Category
Tribology
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-62562 (URN)10.1016/j.triboint.2017.03.021 (DOI)000400039100029 ()2-s2.0-85015752363 (Scopus ID)
Note

Validerad; 2017; Nivå 2; 2017-03-27 (andbra)

Available from: 2017-03-20 Created: 2017-03-20 Last updated: 2017-06-08Bibliographically approved
4. Embeddability behaviour of some Pb-free engine bearing materials
Open this publication in new window or tab >>Embeddability behaviour of some Pb-free engine bearing materials
2016 (English)Conference paper, Presentation (Other academic)
Abstract [en]

An important requirement on engine bearing materials is its ability to embed dirt/abrasive particles onto the bearing surface and minimize damage to the expensive crankshaft. This property is achieved by applying an overlay onto the lining. In this work, a journal bearing test rig that operates under steady loading condition has been employed to investigate the embeddability behaviour of selected multi-layered Pb-free engine bearing materials in the presence of contaminant/abrasive particles in engine oil. Test materials include Pb-free bearing materials with overlay compositions of Sn, Bi, PAI containing MoS2 and graphite. Pb-based overlay has also been studied as a reference. Embeddability behaviour in terms of wear and changes in surface topography has been investigated. The damage on the shaft and the bearing surfaces were studied in order to elucidate the mechanisms involved. It has been possible to distinguish between the embeddability characteristics of different materials.

National Category
Tribology
Research subject
Machine Elements
Identifiers
urn:nbn:se:ltu:diva-28440 (URN)23d64d51-dd27-4755-9e4f-fd0f54f0f2a2 (Local ID)23d64d51-dd27-4755-9e4f-fd0f54f0f2a2 (Archive number)23d64d51-dd27-4755-9e4f-fd0f54f0f2a2 (OAI)
Conference
STLE Annual Meeting & Exhibition : 15/05/2016 - 19/05/2016
Available from: 2016-09-30 Created: 2016-09-30 Last updated: 2017-04-25Bibliographically approved

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