无损检测专业英语教学课件ppt作者晏荣明unit8ManufacturingProcessesandRelevantDiscontinuities课件.pptVIP

8.1 Casting and Relevant Discontinuities8.1.1 introduction Casting is usually done in the primary production of metals and in the initial production of alloys, and is the starting point for many discontinuities in engineering components. When metals and most alloys are solidified, the crystalline structures are denser than the liquids from which they came. Consequently, the casting volume is less than the melt volume after the liquid changes to a crystalline solid. 铸造通常用于金属与合金材料的初加工，工程部件的许多不连续性就是在这个过程中出现的。 金属与大部分合金固化后，晶体结构的密度要高于液态。因此，结晶后铸件的体积小于液态。 8.1 Casting and Relevant Discontinuities8.1.2 Casting process As one of the oldest manufacturing methods, casting involves pouring molten metal into a mold cavity that is configured to the shapes and dimensions of the finished form. 作为最古老的加工手段，铸造是将熔融的金属注入到铸模型腔中，该铸膜型腔的形状和尺寸与成品一致。 8.1 Casting and Relevant Discontinuities8.1.3 casting discontinuities Porosity occurs when gas is trapped in the metal during solidification. The pores vary in size and distribution. Gases are more soluble in liquid alloys than in their crystalline solids. During the crystallization process, the gas is released from the growing crystal into the remaining liquid. If the gas is released in the interior of the casting, it may be entrapped and exist in the form of gas voids or gas porosity. 在金属凝固过程中，气体在熔融金属中聚集时会产生气孔。这些气孔的尺寸不一、分布不定。比起在结晶体里，气体更容易溶入到液态合金中。在结晶过程中，随着结晶体的生成，气体会从晶体释放到液体中。如果气体释放到铸件内部，它将陷入在固体内形成气孔。 8.2 Forging and Relevant Discontinuities8.2.1 Introduction It primarily consists of working a piece of metal usually hot, to a predetermined shape by one of the available forging methods. 锻造是将加热过的金属，通过合适的锻造方法将工件加工成预先确定的形状。 8.2 Forging and Relevant Discontinuities8.2.1 Introduction Selection of a basic process of forging is determined by two chief requirements-first, production of an object of a specified shape, and second, improvement of the physical properties of the metal by forging. 锻造工艺的选择由两个主要要求决定：首先是规定形状产品的加工；其次是通过锻造提高金属的物理性能。 8.