1、中文 4200 字 毕业设计 (论文 )外文翻译 学生姓名： 系 别： 机 械 工 程 系 专 业： 机械设计制造及其自动化 班 级： 学 号 : 译文出处 ： Science and Technology Engl- ish for Mechanical Engineering 毕 业 设 计 (论 文 )参 考 文 献 译 文 Casting、 Forging and Welding 1. Casting Metal casting is one of the oldest of all industries, both ancient and medieval history offer
2、ing examples of the manufacture and use of casting. From simple axeheads poured from copper in open moulds some 5000 years age, casting in the pre-Christian world developed to a point at which elaborate bronze statuary could be produced in two-piece and cored moulds. By the end of the medieval perio
3、d, decorated bronze and pewter casting had begun to be used in European church and domestic life. The widespread adoption of cast iron as engineering material awaited the success of Abraham Darby in 1790 in smelting in the coke blast furnace； this paved the way for the massive use of cast iron in co
4、nstruction during the years following the industrial revolution. Many foundries sprang up after the industrial revolution, the vast majority being for the manufacture of the cast iron then being used as a structural material. The quantity production of iron castings in the nineteenth century was not
5、 matched by a universal advance in quality and the engineering use of the products encountered more serious risks in a non-ductile material. Despite the skill of the molder in producing complex forms, there was little change in the metallurgical and engineering situation until the modern era brought
6、 a better understanding of the factors determining quality. With modern techniques of process control the rudimentary judgment of the operator could give way to objective measurements of metal temperature, molding material properties and other production variables. These improvements have been appli
7、ed not only to cast iron but to a wide range of cast alloys. There are four basic casting methods: sand-casting, die-casting, investment-casting, and centrifugal casting. Sand-casting is the most widely used method employed in foundry. In this process, sand moulds are contained in metal molding boxe
8、s that have four sides but no top or bottom. During the molding operation the boxes are located together by pins so that they can be separated to remove the pattern, and replaced in the correct position before the metal is poured in. The boxes are clamped together, or the cope (top section) weighted
9、 down when pouring to prevent the cope from “floating away” from the drag (lower section) when the mould is full of molten metal. The sequence when molding the simple 毕 业 设 计 (论 文 )参 考 文 献 译 文 two-part mould to cast a bracket is illustrated as follows. At the first stage the pattern is seated on the
10、 moulding board. The pattern is covered with facing sand, which is a specially prepared sand of good quality, which can take a clean and smooth impression, and can resist the heat from the molten metal that will be in contact with it. The facing sand is backed up with molding sand, which is old faci
11、ng sand from previous moulds. The molding sand is carefully rammed up so that it is fairly tight around the pattern to produce a good solid mould, yet permeable enough to allow the gases produced during casting to escape. The sand is finally leveled off. At the second stage the mould with the patter
12、n still in position is inverted； the exposed sand lightly covered with parting sand, and the exposed pattern with facing sand.(The parting sand has no cohesion, and is introduced to permit a clean separation when the mould is opened up to remove the pattern .) The second molding box is located in po
13、sition on the first box and filled with molding sand. Two or more plugs are introduced when the second box is being filled (these are removed later, leaving channels in the sand). One of these plugs is positioned to one side of the pattern. The sand is rammed up and leveled off. Now, at stage 3, to
14、allow the pattern to be removed. This is done by screwing a bar with a threaded end into a suitable insert in the pattern, damping the sand around the pattern, and gently rapping the bar in all directions so that the pattern can be carefully withdrawn. To facilitate the removal of the pattern withou
15、t scuffing the sides of the impression, all surfaces that lie in the direction of pattern removal are inclined slightly by a small amount (the draw angle). A groove called a gate is cut in the sand face to allow the channel produced by the plug that is outside the pattern to connect with the impress
16、ion .The metal is poured through this channel (called the runner), and the gate prevents it from dropping straight into the impression and damaging it .The cross-section of the gate is slightly smaller than that of channel so that a full runner will always supply metal to the gate at a slight pressu
17、re. Finally, the mould is reassembled, carefully locating and securing the two sections. The top section is known as the cope, and the lower section is known as the drag. The sand in the cope is vented. These vents allow the sand to be rammed up more tightly at the earlier stages without the risk of gases being trapped in the molten metal and forming blowholes in the solid metal. A sand-feeding
