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Friction and wear characteristics of different Pb-free bearing materials in mixed and boundary lubrication regimes
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.ORCID-id: 0000-0003-2705-9195
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.ORCID-id: 0000-0003-1162-4671
Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Maskinelement.ORCID-id: 0000-0003-1454-1118
2015 (Engelska)Ingår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 340-341, s. 63-72Artikel i tidskrift (Refereegranskat) 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.

Ort, förlag, år, upplaga, sidor
2015. Vol. 340-341, s. 63-72
Nationell ämneskategori
Tribologi (ytteknik omfattande friktion, nötning och smörjning)
Forskningsämne
Maskinelement
Identifikatorer
URN: urn:nbn:se:ltu:diva-38459DOI: 10.1016/j.wear.2015.06.002ISI: 000362926400010Scopus ID: 2-s2.0-84947862997Lokalt ID: cddfd036-3cb8-4082-a8fb-5f18d912f803OAI: oai:DiVA.org:ltu-38459DiVA, id: diva2:1011960
Konferens
Nordic Symposium on Tribology : 10/06/2014 - 13/06/2014
Anmärkning
Validerad; 2015; Nivå 1; 20150611 (andbra); Konferensartikel i tidskriftTillgänglig från: 2016-10-03 Skapad: 2016-10-03 Senast uppdaterad: 2018-07-10Bibliografiskt granskad
Ingår i avhandling
1. Tribological characteristics of some multi-layered Pb-free engine bearing materials
Öppna denna publikation i ny flik eller fönster >>Tribological characteristics of some multi-layered Pb-free engine bearing materials
2017 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
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. 

Ort, förlag, år, upplaga, sidor
Luleå: Luleå University of Technology, 2017
Serie
Doctoral thesis / Luleå University of Technology 1 jan 1997 → …, ISSN 1402-1544
Nationell ämneskategori
Tribologi (ytteknik omfattande friktion, nötning och smörjning)
Forskningsämne
Maskinelement
Identifikatorer
urn:nbn:se:ltu:diva-62495 (URN)978-91-7583-847-2 (ISBN)978-91-7583-848-9 (ISBN)
Disputation
2017-05-11, E231, Luleå, 09:00 (Engelska)
Opponent
Tillgänglig från: 2017-03-20 Skapad: 2017-03-14 Senast uppdaterad: 2018-03-13Bibliografiskt granskad

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