1、附录 1：英文资料 Metal-Casting Processes Abstract-Following a description of the fundamentals of solidification of metals in the preceding chapter and the roles of fluid flow and heat transfer in molds, we now describe in detail: Characteristics of expendable-mold and permanent-mold processes. Applications
2、 advantages, and limitations of common casting processes. Casting of single crystals. Inspection techniques for castings. Brief review of foundries and their automation. Typical products made by casting: engine blocks, crankshafts, hubcaps, power tools, turbine blades, plumbing, zipper teeth, dies a
3、nd molds, gears, railroad wheels, propellers, office equipment, statues, and housings. Alternative processes: forging, powder metallurgy, machining, and fabrication. 11.1 Introduction The first metal castings were made during the period from 4000 to 3000 B.C., using stone and metal molds for casting
4、 copper. Various casting processes have been developed over time, each with its own characteristics and applications (see also Fig. 1.7a), to meet specific engineering and service requirements (Table 11.1). A large variety of parts and components are made by casting, such as engine blocks, crankshaf
5、ts, automotive components and powertrains (Fig. 11.1), agricultural and railroad equipment, pipes and plumbing fixtures, power tools, gun barrels, frying pans, office equipment, and very large components for hydraulic turbines. Two trends have had a major impact on the casting industry .The first is
6、 the mechanization and automation of the casting process, which has led to significant changes in the use of equipment and labor. Advanced machinery and automated process-control systems have replaced traditional methods of casting. The second major trend has been the increasing demand for high-qual
7、ity castings with close dimensional tolerances. This chapter is organized around the major classifications of casting practices (see Fig. .2 in the Introduction to Part ). These classifications are related to mold materials, molding processes, and methods of feeding the mold with molten metal. The m
8、ajor categories are as follows: 1. Expendable molds, which typically are made of sand, plaster, ceramics, and similar materials and generally are mixed with various binders (bonding agents) for improved properties. A typical sand mold consists of 90% sand, 7% clay, and 3% water. As described in Chap
9、ter 8, these materials are refractories (that is, they are capable of withstanding the high temperatures of molten metals). After the casting has solidified, the mold is broken up to remove the casting. 2. Permanent molds, which are made of metals that maintain their strength at high temperatures. A
10、s the name implies, they are used repeatedly and are designed in such a way that the casting can be removed easily and the mold used for the next casting. Metal molds are better heat conductors than expendable nonmetallic molds (see Table 3.1)； hence, the solidifying casting is subjected to a higher
11、 rate of cooling, which in turn affects the microstructure and grain size within the casting. 3. Composite molds, which are made of two or more different materials (such as sand, graphite, and metal) combining the advantages of each material. These molds have a permanent and an expendable portion an
12、d ate used in various casting processes to improve mold strength, control the cooling rates, and optimize the overall economics of the casting process. The general characteristics of sand casting and other casting processes are given in Table 11.2. Almost all commercially used metals can be cast. Th
13、e surface finish obtained is largely a function of the mold material； although, as expected, sand castings generally have rough, grainy surfaces. Dimensional tolerances generally are not as good as those in machining and other net-shape processes. However, intricate shapes can be made by casting, su
14、ch as cast-iron engine blocks and very large propellers for ocean liners. Because of their unique characteristics and applications, particularly in manufacturing microelectronic devices (Part ), basic crystal-growing techniques also are described in this chapter, which concludes with a brief overvie
15、w of modern foundries. 11.2 Expendable-Mold Casting Processes The major categories of expendable-mold casting are sand, shell mold, plaster mold, ceramic mold, evaporative pattern, and investment casting. 11.2.1Sand casting The traditional method of casting metals is in sand molds and has been used
16、for millennia. Sand casting is still the most prevalent form of casting； in the United States alone, about 15 million tons of metal are cast by this method each year. Typical applications of sand casting include machine bases, large turbine impellers, propellers, plumbing fixtures, and numerous comp
17、onents for agricultural and railroad equipment. The capabilities of sand casting are given in Table 11.2. Basically, sand casting consists of (a) placing a pattern (having the shape of the desired casting) in sand to make an imprint, (b) incorporating a gating system, (c) removing the pattern and fi
18、lling the mold cavity with molten metal, (d) allowing the metal to cool until it solidifies, (e) breaking away the sand mold, and (f) removing the casting(Fig.11.2). Sands.Most sand-casting operations use silica sand (SiO2) as mold material. Sand is inexpensive and is suitable as mold material becau
19、se of its high-temperature characteristics and high melting point. There are two general types of sand: naturally bonded (bank sand) and synthetic (lake sand). Because its composition can be controlled more accurately, synthetic sand is preferred by most foundries. For proper functioning, mold sand
20、must be clean and preferably new. Several factors are important in the selection of sand for molds, and it involves certain tradeoffs with respect to properties. Sand having fine, round grains can be packed closely and, thus, forms a smooth mold surface. Although fine-grained sand through pores. Goo
21、d permeability of molds and cores allows gases and steam evolved during the casting to escape easily. The mold also should have good collapsibility to allow for the casting to shrink while cooling and, thus, to avoid defects in the casting, such as hot tearing and cracking(see Fig.10.12). Types of s
22、and molds. Sand molds (Fig.11.3) are characterized by the types of sand that comprise them and by the methods used to produce them. There are three basic types of sand molds: green-sand, cold-box, and no-bake molds. The most common mold material is green molding sand, which is a mixture of sand, cla
23、y, and water. The term “green” refers to the fact that the sand in the mold is moist or damp while the metal is being poured into it. Green-sand molding is the least expensive method of making molds, and the sand is recycled easily for subsequent use. In the skin-dried method, the mold surfaces are dried, either by storing the mold in air or by drying it with torches, Because of their higher strength, these molds generally are used for large castings. In the cold-box mold process, various organic and inorganic binders are blended
