鏡面磨き時のピンホール発生に及ぼす非金属介在物および炭化物の影響

概要

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Mirror polishability is one of the most important properties of the plastic injection mold for making transparent or mirror surface products. Mirror surfaces are to be free from pinholes and undulation. Pinhole is a kind of small pit which appears during polishing process. Although the effects of metallurgical factors such as microstructure, hardness, cleanliness on pinhole susceptibility have been studied, the actual forming mechanism of pinholes has not been fully clarified. To make it clear this mechanism current injection mold steels have been studied by observing actually polished surfaces with gradually refining polishing media. The results obtained are as follows. (1) Soft non-metaric inclusions such as sulfides cause pinholes by beeing ground preferentially. Hard particles:nitrides, oxides and carbides, on the other hand, form pinholes by dropping themselves off. (2) Pinhole shape depends on the type of particles. Shallow and wide for soft inclusions and deep and narrow for hard patricles. (3) In case of large polishing grits, pinholes hardly appear whether they are in the manner of preferential grinding or peeling off. Small grits, however, increases the number of pinholes. (4) When grit size is close to those of particles, hard inclusions and carbides tend to drop off easily. (5) When hard inclusions are distributed together with soft ones, they drop off easier than solely distributed.
電気製鋼研究会の論文