The casting structures of the solid and ventilated brake discs were introduced.Black spots defect was found at root place of the braking surface after casting being machined,its outer morphology was similar to the occurring location,it's very hard to distinguish only according the macroscopic appearance.The micro morphology of the defects were compared by using EVO18 tungsten wire lamp SEM,OXFORD and ZEISS metallographic scopes,it was found there were obviously difference between two sorts defects.Combining with formation mechanism,it was considered that two sorts defects were shrinkage porosities and large graphite respectively.Finally,by increasing modulus of riser neck to enlarge feeding channel of the riser,the shrinkage porosities problem was solved,by cast-making concave grooves at root location of mounting surface and friction surface to reduce local hot spots,the large graphite problem was solved.
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