换挡拨头表面异常分析

Analysis of Abnormal Surface of Shifting Head

采用熔模铸造,铸造了一批换挡拨头,经正火、氧化酸洗处理后发现部分换挡拨头表面出现麻坑现象。采用宏观观察,显微观察,耐腐蚀试验,化学成分分析,并结合铸造工艺进行了综合分析,结果表明,换挡拨头在浇注时,熔模壳内壁存在硅酸盐夹杂瘤附着在零件的表面,酸洗氧化过程中零件表层的硅酸盐夹杂脱落造成表面麻坑现象。

A batch of shifting heads were easted by using investment casting in a facory, the pockmarks were observed on the surface of some shifting heads after normalizing and oxidation of acid pickling. Combined with the foundry technology,the comprehensive analysis was proceeded by means of macroscopic observation, microexamination, corrosion resistance test, and chemical composition analysis. The results showed that the silicate mixed tumor which existed in investment casting shell attached to the surface of parts when the shifting heads were casting,the silicate on the surface of parts tailed off in the process of oxidation of acid pickling,and then the surface pockmark was formed.