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On wear transitions in the wheel-rail contact
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wear transitions in the wheel–rail contact are of increasing interest since the general trend in railway traffic is toward increased velocities and axle loads. Curving increases the risk of flanging, causing the contact to change from an almost pure rolling wheel tread–rail head contact to more of a sliding wheel flange–rail gauge contact on the high rail in curves.

Under wheel flange–rail gauge contact conditions, wear transitions to severe or catastrophic wear will occur if the contact is improperly lubricated. Such a transition is the most undesirable transition in the wheel–rail contact, as it represents a very expensive operating condition for railway companies. The contact conditions responsible for this transition are very severe as regards sliding velocity and contact pressure, and thus place high demands on both the lubricant and the wheel and rail materials.

The focus of this thesis is on the transitions between different wear regimes in a wheel–rail contact. Wear is discussed both in traditional tribological terms and in terms of the categories used in the railway business, namely mild, severe and catastrophic wear. Most of the work was experimental and was performed at the Royal Institute of Technology (KTH), Department of Machine Design.

The effects of contact pressure, sliding velocity, and type of lubricant have been investigated, producing results that resemble those of other studies presented in the literature. The absence of research relating to the wheel flange–rail gauge contact is addressed, and it is concluded that a lubricant film must be present on rails in curves to prevent severe or catastrophic wear. The formulation of this lubricant can further increase its wear- and seizure-preventing properties. To obtain a deeper understanding of wear transitions, methods such as airborne particle measurement and electron microscopy have been used.

Paper A presents the test methodology used to detect seizure and discusses the wear-reducing influence of free carbon in highly loaded contacts.

Paper B presents the testing of seizure-initiating conditions for a range of environmentally adapted lubricants applied to wheel and rail materials; a transient pin-on-disc test methodology was used for the testing.

Paper C presents the use of pin-on-disc methodology to study the wear-reducing effects of a wide range of lubricants. The best performing lubricant was a mineral oil containing EP and AW additives.

Paper D relates wear rates and transitions to airborne particles generated by an experimentally simulated wheel–rail contact. The airborne particles generated varied in size distribution and amount with wear rate and mechanism.

Paper E relates additional analysis techniques, such as FIB sectioning, ESCA analysis, airborne particle measurements, and SEM imaging of airborne wear particles, to the contact temperature.

 

Place, publisher, year, edition, pages
Stockholm: KTH , 2009. , 31 p.
Series
Trita-MMK, ISSN 1400-1179 ; 2009:23
Keyword [en]
Wear transitions; Wheel; Rail; Wear regime; Wear mechanism
Identifiers
URN: urn:nbn:se:kth:diva-11563ISBN: 978-91-7415-511-2 (print)OAI: oai:DiVA.org:kth-11563DiVA: diva2:277737
Public defence
2009-12-11, M3, Brinellvägen 64, KTH, Stockholm, 10:15 (Swedish)
Opponent
Supervisors
Projects
Samba 6
Note
QC 20100721Available from: 2009-11-20 Created: 2009-11-20 Last updated: 2012-01-27Bibliographically approved
List of papers
1. Influence of surface topography and surface modifications on seizure initiation in lean lubricated sliding contacts
Open this publication in new window or tab >>Influence of surface topography and surface modifications on seizure initiation in lean lubricated sliding contacts
2007 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 262, 986-995 p.Article in journal (Refereed) Published
Abstract [en]

Seizure initiation in lean-lubricated contacts was experimentally studied using a transient test method of ball-on-disc type at two different sliding velocities, 2 and 3.8 m/s. Four different nodular cast iron surfaces were tested against a bearing ball of 100Cr6 steel: a fine-milled and roller-burnished surface, a ground and lapped surface, a ground and lapped laser-melted surface, and finally a ground surface. The results show that the ground surface, even though it is smoother than the fine-milled and roller-burn i shed surface, shows indications of seizure at a lower load. No graphite nodules from the nodular cast iron were visible in the surfaces on inspection with an optical light microscope. In contrast, the ground and lapped surface suffered no initial or total seizure in these tests. In this case, many graphite nodules were visible in the surface, and these nodules became detached in the contact zone, where they probably acted as a solid lubricant. Many graphite nodules were also visible in the ground and laser-melted surface, though in this case the graphite nodules did not become detached. This surface topography initiated seizure under a low normal load, and increased sliding velocity lowered the total seizure load significantly.

Keyword
seizure, surface topography, sliding velocity, lubrication, nodular cast iron
National Category
Reliability and Maintenance
Identifiers
urn:nbn:se:kth:diva-11577 (URN)10.1016/j.wear.2006.10.014 (DOI)000245063500026 ()2-s2.0-33847060484 (Scopus ID)
Note
QC 20100721Available from: 2009-11-20 Created: 2009-11-20 Last updated: 2017-12-12Bibliographically approved
2. Seizure mechanisms of wheel–rail contacts under lubricated conditions using a transient ball-on-disc test method
Open this publication in new window or tab >>Seizure mechanisms of wheel–rail contacts under lubricated conditions using a transient ball-on-disc test method
2008 (English)In: Tribology International, ISSN 0301-679X, E-ISSN 1879-2464, Vol. 41, 867-874 p.Article in journal (Refereed) Published
Abstract [en]

This study focuses on the transition from mild to severe wear in the wheel and rail contact. Such a transition has been observed at increased loading (normal load, sliding velocity, or bulk temperature) which can be compared to a change from a wheel thread-rail head contact to a wheel flange-rail gauge contact. This transition was experimentally studied using a transient test method of ball-on-disc type at different sliding velocities, contact pressures, and lubricants. It can be seen in the results that different seizure mechanisms are active for different sliding velocities. Also the amount of applied lubricant clearly affects the transition to seizure.

Keyword
rail, wheel, seizure, lubrication
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:kth:diva-11580 (URN)10.1016/j.triboint.2007.12.011 (DOI)000257736800008 ()2-s2.0-44749093034 (Scopus ID)
Note
QC 20100721Available from: 2009-11-20 Created: 2009-11-20 Last updated: 2017-12-12Bibliographically approved
3. Seizure and wear rate testing of wheel–rail contacts under lubricated conditions using pin-on-disc methodology
Open this publication in new window or tab >>Seizure and wear rate testing of wheel–rail contacts under lubricated conditions using pin-on-disc methodology
2008 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, 1425-1430 p.Article in journal (Refereed) Published
Abstract [en]

An increased wear rate and a shift of wear mechanism in the wheel-rail contact has been observed in tight curves, mainly due to the change from an almost pure rolling contact to more of a sliding contact. The wheel flange-rail gauge contact is commonly known to experience the toughest conditions of the overall wheel-rail contact in terms of contact pressure and sliding velocity. The wheel flange-rail gauge contact is preferably lubricated to reduce the wear rate and to minimise the risk of transition to severe wear or seizure. The amount and type of lubrication are therefore important parameters if one is to control the wear rate. In this study, a flange contact is experimentally simulated using pin-on-disc testing, to determine the difference in wear rate among a selection of lubricants under different contact conditions. The selection of lubricants consisted of environmentally adapted oils, mineral oils, and greases containing different amounts of EP and AW additives.The results of the pin-on-disc testing indicate that both the amount and type of lubrication applied is decisive for the wear rate and active wear mechanism. Tests have also been performed to simulate either on-board or wayside lubrication, by applying the lubricant at different intervals. A general observation is that under starved lubrication conditions a transition to severe wear is initiated and the wear rate increases rapidly, i.e., all tests indicate that the contact between wheel and rail must be lubricated to avoid high wear rates.

Keyword
rail; wheel; wear rate; environmentally adapted; lubrication
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:kth:diva-11581 (URN)10.1016/j.wear.2008.03.025 (DOI)000258891700035 ()2-s2.0-48049117761 (Scopus ID)
Note
QC 20100721Available from: 2009-11-20 Created: 2009-11-20 Last updated: 2017-12-12Bibliographically approved
4. Wear rate testing in relation to airborne particles generated in a wheel-rail contact
Open this publication in new window or tab >>Wear rate testing in relation to airborne particles generated in a wheel-rail contact
2009 (English)In: Lubrication science, ISSN 0954-0075, Vol. 21, no 4, 135-150 p.Article in journal (Refereed) Published
Abstract [en]

This study examines the relationship between generated airborne particles and wear rate in the wheel-rail contact. The wheel-rail contact is experimentally simulated by using pin-on-disc testing to determine the difference in wear rate between selected contact conditions.

Wear is discussed both in tribological terms and by using the wear categories prevalent in the railway industry, namely, mild, severe and catastrophic wear. The discussion is based on wear depth, the coefficient of friction, topographical measurements and measurements of airborne particles generated in the contact.

The tests were performed under selected loading conditions representative of different contact conditions in a real wheel-rail contact. The results indicate that wear rates vary with the contact conditions arising from different types of triggered wear transitions. This is emphasised by the number and size of the airborne particles generated.

Keyword
seizure; wear; airborne; wheel; rail
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:kth:diva-11582 (URN)10.1002/ls.80 (DOI)000268398500002 ()2-s2.0-66849101930 (Scopus ID)
Note
QC 20100721Available from: 2009-11-20 Created: 2009-11-20 Last updated: 2011-12-15Bibliographically approved
5. Relating contact temperature and wear transitions in a wheel-rail contact
Open this publication in new window or tab >>Relating contact temperature and wear transitions in a wheel-rail contact
2011 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 271, no 1-2, 78-85 p.Article in journal (Refereed) Published
Abstract [en]

Earlier in an ongoing research project, we identified wear transitions, mechanisms, and regimes by experimentally testing the sliding part of a wheel-rail contact. Going further, the present study investigates the effects of elevated contact temperature and severe contact conditions corresponding to those of a wheel flange-gauge corner contact.

Prior studies discussed wear in terms of contact pressure, amount and type of lubricant, sliding velocity, generated airborne particles, wear depth, coefficient of friction, and topographical measurements. This study shifts the focus to contact temperature, elemental and morphological analysis of the airborne particles, and surface-layer microstructure of test specimens by using several analytical techniques (i.e., SEM, FIB, ESCA, and energy mapping).

As contact severity increased, the bulk temperature of the contacting bodies increased rapidly; this can be related to elevated contact temperature by judging the size and shape of the ultrafine particles generated. After test runs, the contacting bodies were analysed, revealing microstructural surface layer changes and differences in the amount of oxide formed in the immediate surface.

When the sliding part of the wheel-rail contact under severe contact conditions is experimentally simulated using pin-on-disc methodology, the discussion shifts from analyzing steady-state measurements, such as average wear rate, to more transient behaviours during running-in. Wear transitions occurring during running-in are decisive for the outcome of the rest of the test run, according to the present results.

Keyword
Wheel, Rail, Wear transition, Temperature, FIB, ESCA, SEM
National Category
Reliability and Maintenance
Identifiers
urn:nbn:se:kth:diva-14164 (URN)10.1016/j.wear.2010.10.046 (DOI)000291777600011 ()2-s2.0-79955765504 (Scopus ID)
Note
QC 20100721 8th Conference on Contact Mechanics and Wear of Rail/Wheel Systems (CM2009), Florence, ITALY, SEP, 2009Available from: 2010-07-21 Created: 2010-07-21 Last updated: 2017-12-12Bibliographically approved

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