什么是铸铁
铁的合金,含碳2~4%,还含有数量不等的矽、锰、硫、磷。铸铁是在高炉内还原铁矿石生产的,放出铁水浇注冷却成锭,称为生铁。铸铁与熟铁不同,不能锻造,只能铸造成型,性脆、抗拉强度低,但产品价廉。铸铁有较高的抗压强度,以致成为首要的结构金属。18~19世纪时,铸铁是比熟铁较为便宜的工程材料。20世纪建筑业以钢取代铸铁,但在工业中仍有许多用途,如汽车发动机缸体、农业机械和机器零件、管道、凹形器皿、火炉、熔炉等。按照断面颜色,铸铁有灰口或白口之分。灰口铁含矽较高,硬度较低,比白口铁加工性能好。白口铁和灰口铁均较脆。18世纪,在法国发展了白口铸铁经长时间加热处理生产可锻铸铁。1948年在美国和英国发明了在铸造状态下就有延伸性的铸铁。这类韧性铸铁,现已形成重要的金属体系,广泛用於齿轮、模具、汽车曲轴和许多其他机械零件。
cast iron
Alloy of iron that contains 2-4% carbon, along with silicon, manganese, and impurities. It is made by reducing iron ore in a blast furnace (cast iron is chemically the same as blast-furnace iron) and casting the liquid iron into ingots called pigs. Pig iron is remelted, along with scrap and alloying elements, in cupola furnaces and recast into molds for a variety of products. In the 18th-19th century, cast iron was a cheaper engineering material than wrought iron (not requiring intensive refining and hammering). It is more brittle and lacks tensile strength. Its compressive (load-bearing) strength made it the first important structural metal. In the 20th century, steel replaced it as a construction material, but cast iron still has industrial applications in automobile engine blocks, agricultural and machine parts, pipes, hollowware, stoves, and furnaces. Most cast iron is either so-called gray iron or white iron, the colors shown by fracture; gray iron contains more silicon and is less hard and more machinable than white iron. Both are brittle, but malleable cast iron (produced by prolonged heat treating), first made in 18th-century France, was developed into an industrial product in the U.S. (see Seth Boyden). Cast iron that is ductile as cast was invented in 1948. The latter now constitutes a major family of metals, widely used for gears, dies, automobile crankshafts, and many other machine parts.
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什么是编组站
专门办理货物列车编组、解体作业的铁路车站。一般设置在有大量车流集散、铁路和铁路交汇的地点或铁路和港口、工矿企业衔接的地点。编组站主要设备有到发线(场)、调车线(场)、驼峰、牵出线以及机务段和车辆段等。编组站按其在铁路网上所起的作用可分为路网性、区...
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什么是矿井通风
向井下连续输送新鲜空气,稀释并排出有毒、有害气体和粉尘,调节矿内小气候,创造良好的工作环境,保证矿工安全与健康,提高劳动生产率。中国矿山安全条例与安全规程规定:向井下供给新鲜风量一般每人不得少于4m3/min,在采掘工作面进风风流中,按体积计算,O2不得低于20%,CO2不得...
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什么是砝码
具有给定质量和规定形状的实物量具。供检定衡器和在衡器上进行衡量时使用。砝码必须与天平或秤相结合(用于秤上的砝码常称为砣),才能用于测定其他物体的质量,故它是一种从属的实物量具。中国在夏代即出现相当于砝码的“权”。此后的4000多年间,不同朝代有不同形状和...
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什么是沥青喷洒机
将液态沥青均匀地喷洒在碎石铺层上,以修建沥青路面的机械。由沥青罐、沥青泵、加热系统和喷洒系统组成。分自行式和拖式两种。前者的全部装置装在一辆汽车底盘上,称为沥青喷洒车;后者的全部装置装在一辆挂车上,大多为小型。沥青罐是椭圆形金属筒,用以盛储液态沥青,周...