1、外文资料 Manufactre of Portland Cement Portland cement is made from some of the Earths most abundant materials.About two - thirds of it is derived from calcium oxide, whose source is usually some form of lime - stone (calcium carbonate),marls,chalk, or shells(for exam-ple oyster).The other ingredients -
2、 silica SiO2,about 20% ； alumina,Al2O3,about 5%； and iron oxide, Fe2O3 about 3%-are derived from sand shales, clays, coal ash, and iron ore metal slags. Because the individual ingredients must be fused and sintered to produce new compounds, they must be ground to pass a 200- mesh screen in order to
3、react within a reasonable time in the kiln. In addition, the composition of the raw materials must be held within narrow lim-its of the above oxides to produce a useful product. Other elemental oxides which can be detrimental to the cement must be limited, these include magne-siumMgO ； potassium oxi
4、de K2O ； sodium oxide, and phosphorus oxide, P2O5.After blending to the proper composition, the raw materials are interground in bail mills, rod mills,or roller mills. Depending on the raw material characteris-tics, they are ground either dry (dry process) or in water(wet process). The re-sultant ra
5、w feed is introduced into the kiln system usually a rotary kiln, where the material is heated to about 2700F(1482 ). The material progressively loses first the water then the carbon dioxide CO2 , at about 1750F(954 ), and at about 2300F(1260 ), a small amount at liquid phase forms. This liquid is th
6、e medium through which the higher - melting phases are formed. The resultant product, called clinker because the whole never truly melts, is cooled and again ground,in ball mills to such a fineness that about 90% will pass a screen having 325 openings per linear inch. The final product has a texture
7、 much like face pow-der. During grinding, about 5% of calcium sulfate (gypsum or anhydride) is added to control setting time,strength development, and other properties. The major trend in manufacture of Portland cement has shifted to a greater emphasis on the reduction of the energy consumed for its
8、 production and an in-creasing use of coal to replace gas and oil； which were the major fuels for burn-ing the clinker. Energy consumption is generally greater for the wet process； therefore most new plants use the dry process. The characteristics of the final product are not any different for eithe
9、r process. The worlds largest kiln ( as of 1957)produced about 7500 tons (6750 metric tons) per day of clinker. An aver-age kiln produces about 1800 tons (1620 metric tons) per day. The latest kilns utilize some form of preheating system which fully utilizes the hot exit gases to warm the incoming r
10、aw materials ； in addition decarbonation of the limestone can be done on the raw feed prior to its entrance to the rotary kiln by use of aux-iliary burners. These techniques enable much shorter rotary kilns for equal production and save much energy. Because of these developments, the worlds longest
11、kiln (760 ft or 228 m long, 25 ft or 7. 5 m in diameter) will probably re-main the longest. Another trend is toward a newer type of grinding mill, called a roller mill. This mill can use waste heat for drying, lends itself readily to auto-matic control, and uses less energy. These mills can grind up
12、 to 400 tons(360 metric tons) per hour. Several employees in a control room can operate a whole plant except for the quarry. Control is exercised by means of television monitors, sensors 9 computers 9 and automatic continuous chemical analysis. Other types of kilns which have been used or are in the
13、 process of being developed are vertical or shaft kilns, fluid-bed furnaces, and swirl calciners. Storage of Cement. Portland cement is a moisture-sensitive material； if kept dry, it will retain its quality indefinitely. When stored in contact with damp air or moisture, portland cement will set more
14、 slowly and has less strength than portland cement that is kept dry. When storing bagged cement, a shaded area or warehouse is preferred. Cracks and openings in storehouses should be closed. When storing bagged cement outdoors, it should be stacked on pallets and covered with a waterproof covering.
15、波特兰水泥的制造 波特兰水泥是由一些地球上最丰富的原料组成。原料约 /取自于氧化钙，它的来源通常是一些以石灰石、泥灰岩、白垩或贝壳形式，其它成分 SiO2 的约含 20%、 Al2O3约含 5%， Fe2O3约含 3%，取自于砂页岩，粘土，煤灰和铁矿石金属矿渣，因为各种组 分必须熔融和烧结以产生新的化合物，他们必须磨碎通过 200目筛子，以便于在合理的时间在窑中反应，此外，必须在以上氧化物很有限度内，进行原材料组合来制造有用的产品。对水泥有害的其它元素的氧化物必须限制：这些包括 MgO、 K2O、 Na2O 和 P2O5，适当的组分混合后原材料在球磨机、棒磨机或辊磨机内互相研磨 ,依据原材料特
16、性被干法或湿法粉磨，结果喂入的生料被传入窑系统，通常是回转窑，原料被加热到约华氏 27000F,原料逐渐地首先失去水，然后是约 17500F 失去 CO2, 约华氏 27000F，少量的液相形成，这个液相是通过较多的熔融相形成的中间相，因为不可能真正全部熔化而称作熟料的中间产品经冷却，在球磨机中磨到一定的细度，以便 90%能通过每条线上每英寸 325 个开孔的筛子，最终的产品有一个更象香粉的结构，在粉磨期间，加入约 5%的硫酸钙（石膏或天然硬石膏）来控制凝结时间，强度发展和其它性能。 波特兰水泥的制造主要趋于转向更强调降低生产能耗，并越来越多地用煤来代替煤气和油，煤气和油过去是煅烧熟料的主要燃
17、料，能源消耗对湿法生产来说普遍较高，因此大多数新厂用干法生产，就这两种方法最终产品的特性没有什么不同，世界上最大的窑（到 1957 年止）每天生产熟料约 7500 吨，平均窑产量每天生产约 1800 吨，最新式的窑采用某种形式的预热系统，这一系统充分利用热废气来给要入窑的原材料加热，另外，在原料进入回转窑之前通过使用辅助燃烧器来在原料上进行石灰石的脱碳，这些技术能使回转窑更短来应付（满足）生产并节省更多的能源，由于这些进展，世界上最长的窑将仍是最长，另一个趋势是转向较新型的磨机，称为辊磨机（立磨机），这种磨机能够利用余热来干燥，容易借助于自身来实现自动控制，并使用较少的能量，这些磨机能每小时粉磨达400，除了采 石场外，几个员工在控制室内能操纵整个工厂，通过电视监视器、传感器、计算机和自动连续的化学分析进行控制。 已经投入使用或还处于开发之中的其它类型的窑还有垂直或立窑，流化床炉，涡流分解炉，所有这些都是固定型式的窑炉。 水泥存贮。波特兰水泥是湿气敏感材料 ； 如果保持干燥，它将无限地保留它的质量。当存放与潮湿的空气或湿气联系，波特兰水泥比保持干燥的波特兰水泥慢慢地将设置并且有较少力量。当存放请求的水泥时，一个被遮蔽的区域或仓库
