The Research Of Wear Resistance And Thermal Fatigue Resistance On Brake Drum Of Large Vehicles

This article is from the start of the gray cast iron brake drum scrapped partsfailure analysis. Then draw that brake drum failure is the main cause of wear andthermal fatigue crack. So in order to improve the service life of the brake drum mustimprove its material wear resistance and thermal fatigue resistance. For some of thecommonly used cast iron brake drum materials (HT250, Ru380, QT500) after theproperty analysis and comparison. According to the different conditions of road brakesimulation, firstly, develop two groups of friction and wear test, then combined withthe wearing amount, morphology and friction coefficient analysis the wear resistanceof the advantages. Finally, make20~300℃and20~600℃thermal fatigue test.Combined a-N curve, crack morphology analysis thermal fatigue resistance which isgood or bad.In normal temperature, QT500comprehensive mechanical is optimization, HT250is worst. When the temperature is higher then400℃,all of them tensile strength isdecreased sharply. Along with the increase of the temperature, the specific heatcapacity and coefficient of linear expansion will increase, the thermal conductivitydecreases gradually. In the same quantity of heat, the temperature of QT500risesmaximum, the temperature of HT250rises minimum, Ru380is between them.In10m/s-100N-120s wear condition, the wear resistance of QT500is the best, itis two times of HT250, Ru380is similar to QT500.But with wear time and loadincrease, Ru380’s wear resistance is superior to QT500. In low temperature, the wearstyle is mainly abrasion wear, in the high temperature, the wear style is mainlyoxidation wear. The friction coefficient is0.18~0.20, and is stable. Consideringnodular cast iron easy deformation in the high temperature of situation, so lowtemperature of brake should be made of QT500, high temperature should be used forRu380.The20~600℃cycletemperature is more easily lead to fatigue crack initiation then20~300℃cycle. Ru380crack initiation cycles is1.5~2.0times of HT250, QT500initiation cycles is2~4times of HT250. In20~600℃cycles thermal, crack growth ofHT250is the fastest, QT500is slowest. To achieve the same crack length, QT500’s lifeis about2.6times of HT250, Ru380’life is about2times of HT250. HT250crackgrowth is directly instability expansion, Ru380and QT500has a slow growth stage,finally begin to unstably expand. The crack source of HT250and Ru380is in tip ofgraphite, crack source of QT500mainly concentrated in the graphite ball spacing shortrange. Through the transition and convergence, micro crack grow up. Crack initiationand growth are accompanied by severe oxidation phenomenon.