湖南镇水电站4~#机组蜗壳焊缝质量检查采用超声波探伤工艺。为了确定判断焊缝缺陷的灵敏度,须在厚度为16毫米的一批试块中钻φ0.5毫米的深孔。孔径小,深度大,钻削时没有力的感觉,经常出现钻头折断,以致无法加工。我们分析了小孔难钻的原因,归纳为三点:一是转速欠高,钻头不能达到 Hunan Province Hydropower Station Unit 4 ~ # volute weld quality inspection using ultrasonic testing process. In order to determine the sensitivity of weld defects, a depth of φ0.5 mm was drilled in a series of test blocks with a thickness of 16 mm. Small aperture, large depth, no sense of force when drilling, often broken drill, which can not be processed. We analyzed the reasons for difficult holes, summarized in three points: First, the speed is low, the drill can not be achieved