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Friktionsbeteende i tågbromsar under inverkan av snö
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
2010 (Swedish)Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesisAlternative title
Friction behavior in train brakes under the influence of snow (English)
Abstract [sv]

Institutionen för Maskinkonstruktion KTH har fått i uppdrag av Stockholms Lokaltrafik att studera friktion, nötning och temperatur mellan blockbromsmaterial och tåghjulmaterial. Detta sedan ett antal tåg med kompositblock mist bromsförmågan på Roslagsbanan under vintertid. Kompositblock används i största möjliga mån då de, till skillnad från gjutjärnsblock, inte gnisslar högt vid inbromsning samt har bättre slitageegenskaper. Nackdelen med kompositblockens goda slitageegenskaper är dock att de har en mycket begränsad uppruggande effekt på hjulets löpbana. En slät löpbana ger sämre adhesion mot tågrälen och kan, vid inbromsning, orsaka vattenplaning mellan bromsblocket och löpbanan. För att förstå detta fenomen bättre undersöks möjligheterna att ställa upp en beräkningsmodell där konventionella teorier för hydrodynamiska lager används. Vattenplaningen betraktas som fullfilmssmörjning i ett hydrodynamiskt lager, där lagret består av blockbroms och tåghjul. Beräkningsmodellen som tagits fram har verifierats mot uppmätt data hos Futuris Dynamometer Facility i Australien, 1996. Det relativa felet för gjutjärnsbromsen är ca 4 % medan det för kompositbromsen är ca 10 %. Vidare har studien visat att gjutjärnsbromsar effektivt förhindrar fullfilmssmörjning då ytorna är grova i förhållande till den beräknade vattenfilmstjockleken på 3,66 μm. Trots vattenfilmen blir alltså den reella kontaktarean hög.

Abstract [en]

Since a number of trains with composite brake blocks lost their braking ability at the Roslagsbanan during the winter, The Department of Machine Design at the Royal Institute of Technology has been commissioned by the Stockholm Public Transport to study friction, wear and temperature between the brake block materials and the train wheel material. Composite brake blocks are preferred over cast iron brakes as they have better wear characteristics and do not tend to squeal when braking. However there is a drawback of having good wear characteristics, the composite blocks have a very limited roughening effect on the wheel tread, giving the wheel tread an almost polished finish. This smooth surface provides less adhesion to the train reel and an increased risk of aquaplaning between the brake block and the wheel tread during braking. To better understand this phenomenon the possibilities to set up a calculation model based on the use of conventional hydrodynamic bearing theory is explored, in which aquaplaning is considered to be a thin full-film condition of a hydrodynamic bearing, where the bearing consists of the brakes and train wheel. The calculation model developed is verified against measured data in the Futuris Dynamometer Facility in Australia, 1996. The relative error for the cast iron brake is about 4%, while the error for the composite brakes is about 10%. Further study has shown that cast iron brakes effectively prevent full film condition due to the fact that the surfaces are rough compared to the calculated water film thickness of 3.66 microns. Despite the water film the train brake and the wheel still has a large contact area.

Place, publisher, year, edition, pages
2010.
Series
MMKB 2010:26 MKNB 034
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-171995OAI: oai:DiVA.org:kth-171995DiVA: diva2:845154
Available from: 2015-10-19 Created: 2015-08-11 Last updated: 2015-10-19Bibliographically approved

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