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Coefficient of Friction of a Brake Disc-Brake Pad Friction Couple

Orłowicz A. W., Mróz M., Wnuk G., Markowska O., Homik W., Kolbusz B

Archives of Foundry Engineering

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2016

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Vol. 16, iss. 4

196--200

EN

The paper concerns evaluation of the coefficient of friction characterising a friction couple comprising a commercial brake disc cast of flake graphite grey iron and a typical brake pad for passenger motor car. For the applied interaction conditions, the brake pressure of 0.53 MPa and the linear velocity measured on the pad-disc trace axis equalling 15 km/h, evolution of the friction coefficient μ values were observed. It turned out that after a period of 50 minutes, temperature reached the value 270°C and got stabilised. After this time interval, the friction coefficient value also got stabilised on the level of μ = 0.38. In case of a block in its original state, stabilisation of the friction coefficient value occurred after a stage in the course of which a continuous growth of its value was observed up to the level μ = 0.41 and then a decrease to the value μ = 0.38. It can be assumed that occurrence of this stage was an effect of an initial running-in of the friction couple. In consecutive abrasion tests on the same friction couple, the friction coefficient value stabilisation occurred after the stage of a steady increase of its value. It can be stated that the stage corresponded to a secondary running-in of the friction couple. The observed stages lasted for similar periods of time and ended with reaching the stabile level of temperature of the disc-pad contact surface.

2

Rola morfologii wydzieleń grafitu w kształtowaniu odporności na zmęczenie cieplne żeliwa

Zych J. S.

Inżynieria Materiałowa

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2015

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Vol. 36, nr 5

343--347

PL

W pracy przedstawiono wyniki badań odporności na zmęczenie cieplne wybranej grupy gatunków żeliwa, w których postać wydzieleń grafitu obejmowała grafit kulkowy (sferoidalny), grafit wermikularny oraz płatkowy. Badania zmęczenia cieplnego były realizowane metodą L. F. Coffina — oporowego nagrzewania próbek z wykorzystaniem autorskiego stanowiska. Badania prowadzono dla cykli cieplnych w zakresie: Tmin = 200°C, Tmax = 650÷700°C. Kryterium odporności na zmęczenie cieplne była liczba cykli cieplnych do momentu pęknięcia próbki. We wszystkich badaniach stwierdzono, iż zwiększanie maksymalnej temperatury cyklu cieplnego prowadzi do szybkiego zmniejszenia liczby cykli do zmęczenia cieplnego. Stwierdzono również, iż odporność na zmęczenie cieplne w pierwszej kolejności zależy od wytrzymałości Rm żeliwa, a sam wpływ jest silniejszy niż wynikałoby z liniowej zależności. Stwierdzono ponadto, iż w przypadku żeliwa, w którym w mikrostrukturze zmianie ulega jedynie postać grafitu, odporność na zmęczenie cieplne jest tym większa im bardziej zwarta jest postać grafitu.

EN

The work presents the results of research on thermal fatigue resistance of selected group of casting alloys including spheroidal, vermicular and grey. Thermal fatigue tests were performed on an original test bench using the L. F. Coffin method — resistance heated samples. The thermal fatigue of cast iron was analyzed using the temperature cycle: Tmin = 200°C, Tmax = 650÷700°C. The carried out research confirms that with the maximum heating temperature increase the thermal fatigue resistance decreases. Wider examination has shown that the relation between tensile strength (Rm) and resistance to thermal fatigue is more than linear, i.e. exponential, in character. The shape of graphite has significant and decisive influence on the resistance to thermal fatigue of cast iron. The denser the form of graphite, the greater the cast iron's thermal fatigue resitance.

3

The Reliability of the Results of the Modified Low-cycle Fatigue Test for Cast Iron Evaluated by Metallographic Studies

Maj M., Pietrzak K.

Archives of Foundry Engineering

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2015

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Vol. 15, iss. 1

41--46

EN

This study discloses the characteristic features of the modified low-cycle fatigue test used for the determination of the mechanical properties of two types of cast iron, i.e. EN-GJL-250 and EN-GJS-600-3. For selected materials, metallographic studies were also conducted in the range of light microscopy and scanning microscopy.

4

Przemysłowe zastosowania grafitu

Łuczak J.

Stal, Metale & Nowe Technologie

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2014

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nr 9-10

98--101

PL

Grafit to alotropowa odmiana węgla o charakterystycznej heksagonalnej budowie kryształów, której konsekwencją są jedna z najwyższych znanych w przyrodzie wytrzymałości i unikalne właściwości fizyczne. Materiały grafitowe stosowane w przemyśle nigdy nie mają w pełni wykształconej struktury, raczej są formą przejściową pomiędzy węglem amorficznym a kryształem grafitu. Ich właściwości, a przez to jakość, są ściśle skorelowane ze stopniem grafityzacji, strukturą wewnętrzną i z zawartością zanieczyszczeń, która nie przekracza 10 ppm w najlepszych grafitach.

5

Characterization of coatings on grey cast iron fabricated by hot-dipping in AlSi11 alloy

Mola R., Depczyński W.

Archives of Materials Science and Engineering

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2014

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Vol. 68, nr 1

20--23

EN

Purpose: In this study, grey cast iron was aluminized by hot-dip coating with AlSi11 alloy. The microstructure and chemical composition of the coatings were analyzed to determine the effect of the bath temperature on the thickness of the coating. Design/methodology/approach: Flake graphite cast iron was aluminized by hot-dipping in AlSi11 alloy at 700°C or 750°C for 20 min. The microstructure and phase composition of the coatings were determined by means of an optical microscope and a scanning electron microscope with an EDS X-ray analyzer. Findings: It was found that the overall thickness of a coating was dependent on the temperature of the bath. The coatings consisted of an outer layer with the composition similar to the aluminizing bath and an inner intermetallic layer and dispersed graphite. The outer layer was much thicker for coatings fabricated at a temperature of 750°C. The thickness of the inner layer was similar for both bath temperatures. The inner layer was composed of two zones: the Al5Fe2 phase, adjacent to the cast iron substrate and the Al5FeSi phase, adjacent to the Al-Si outer layer. The interface between the layer of the Al5Fe2intermetallic phases and the substrate showed flat morphology. The Al5FeSi phase-outer layer interface was irregular. Practical limitations/implications: The results obtained through the investigations show that the temperature of the Al-Si bath has influence on the overall thickness of the coating. The thickness of the outer layer increases with an increase in the bath temperature. The thickness of the inner layer, however, is not affected by the bath temperature. Originality/value: Coatings produced by hot-dipping in pure aluminium are characterized by a microstructure with a relatively thick inner layer of intermetallic phases.

6

Characteristics of flake graphite in Ni-Mn-Cu cast iron. Part 2.

Janus A.

Archives of Foundry Engineering

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2010

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Vol. 10, iss. 1

75-78

EN

The paper continues the article published by Archives of Foundry Engineering, vol. 9, issue 1/2009, pp. 185-190, that presented influence of chemical composition of hypo- and hypereutectic nickel-manganese-copper alloyed cast iron on properties of the contained flake graphite. In this second part of the research, effect of chemical composition of hypereutectic cast iron containing 3.5 to 5.1% C, 1.7 to 2.8% Si, 3.5 to 10.5 % Ni, 2.0 to 8.0% Mn, 0.1 to 3.5% Cu, 0.14 to 0.17% P and 0.02 to 0.04% S on properties of flake graphite is determined. Evolution of graphite properties with changing eutecticity degree of the examined cast iron is presented. For selected castings, histograms of primary and eutectic graphite are presented, showing quantities of graphite precipitates in individual size ranges and their shape determined by the coefficient [zeta] defined as ratio of a precipitate area to square of its circumference. Moreover, presented are equations obtained by discriminant analysis to determine chemical composition of Ni-Mn-Cu cast iron which guarantee the most favourable distribution of A-type graphite from the point of view of castings properties.

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Modeling the kinetics of solidification of cast iron with lamellar graphite

Kapturkiewicz W., Fraś E., Burbelko A. A.

Archives of Metallurgy and Materials

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2009

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Vol. 54, iss. 2

369-380

EN

The most important results of own studies on modeling the solidification kinetics in lamellar (flake) graphite cast iron were reviewed. A set of basic equations used for modeling the solidification process in macro- and micro-scales was given. A numerical solution of these model equations enables the determination of thermodynamic equilibrium temperature and actual temperature of cast iron solidification, the cooling rate, the heat flux generated during solidification, the fractions of the solidified structural constituents, the size of graphite eutectic grains and austenite dendrites, thickness of graphite lamellar, as well as the segregation of cast iron alloying constituents in liquid phase and in the forming grains. It has also been proved and confirmed by experiments that the grains of graphite eutectic are formed in a two-step process, that is, at the beginning and end of the solidification process. Some important differences in the size of graphite precipitates were observed to exist between the cast plate and cylinder.

PL

Zaprezentowano najistotniejsze rezultaty własnych prac, dotyczących modelowania komputerowego krystalizacji żeliwa z grafitem płatkowym. Przedstawiono zestaw podstawowych równań procesu, odnoszących się do mikro i makro skali. Rozwiązanie numeryczne zestawu równań w postaci programu symulacyjnego pozwoliło na wyznaczenie przebiegu temperatury w czasie stygnięcia odlewu wraz z rozkładem temperatury równowagowej, ciepła generowanego podczas krystalizacji, ilości frakcji zakrzepłej poszczególnych składników strukturalnych żeliwa, wymiaru ziaren austenitu i eutektyki grafitowej, wymiary płatków grafitu jak również mikrosegregacji składników stopu w ziarnach. Potwierdzono eksperymentalnie, że ziarna eutektyki grafitowej mogą zarodkować w dwóch etapach: na początku i pod koniec procesu krystalizacji. Istotne różnice zauważono w wymiarach grafitu w zależnosci od kształtu odlewu.

8

Characteristics of flake graphite in Ni-Mn-Cu cast iron. Part 1

Janus A.

Archives of Foundry Engineering

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2009

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Vol. 9, iss. 1

185-190

EN

Relationship between chemical composition of cast iron and properties of flake graphite occurring in hypoeutectic and eutectic nickelmanganese-copper cast iron was determined. The research covered over 60 alloys of cast iron containing 1.6 to 4.1 % C, 1.3 to 2.8 % Si, 2.4 to 10.5 % Ni, 0.2 to 8.2 % Mn, 0.1 to 3.5 % Cu, 0.14 to 0.17 % P and 0.02 to 0.04 % S. Evolution of graphite properties with changing eutecticity degree of the examined cast iron is presented. For selected castings, histograms of eutectic graphite colonies are presented, showing numbers of graphite precipitates in individual size ranges and their shape described by the coefficient [...], defined as the ratio of a graphite precipitate area to square of its circumference. Statistical evaluation of individual elements influence on graphite properties will be presented in part 2 of the work.

9

Wear characteristic of exfoliated graphite nano sheets/copper metal matrix composite

Ashraf A.A.

Zeszyty Naukowe Politechniki Rzeszowskiej. Mechanika

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2008

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z. 73 [253]

19-26

EN

Powder Metallurgy technique has been used to prepare composite samples made of exfoliated graphite nano sheets (EGNS)and graphite flakes (GF) of 1, 3 and 5 weight % with copper chips. Effect of both graphite and its size on morphological, mechanical, and tribological behavior of copper matrix camposite has been investigated. Same unexpected characteristics have been identified due to the addition of graphite flakes and its exfoliated nano sizes with copper metal matrix. Nano-like grain boundary (NLGB) phenomenon has been reported. A decrease in hardness has been measured within the used weight fractions. Surprisingly, there was an increase in wear rates with an increase in wt % GF added to the copper matrix. In the case of EGNS, an increase in wear rate is reported for a weight fraction of 1%, which then decreases as more EGNS is added until it reaches approximately the same wear rate of pure Cu matrix at 5% EGNS. It is believed that the increase in wear at 1% EGNS is due to delamination domination theory. Measuring the counter part wear characteristics more deeply, evaluating the dispersion quantitatively, and explaining the delaminating theory of the EGNS/Cu metal matrix composites is recommended for future work.