第二单元 铸造
第一节 铸造
一.What is casting(铸造)? 定义
Generally speaking, it means pouring molten metal into a refractory mould with a cavity of the shape to be made, and allowing it to solidify. When solidified, the desired metal object is taken from the refractory mould either by breaking the mould or taking the mould apart. This process is also called founding.
二.Advantage(铸造的优点)
A)Any intricate shapes either internalor external can be made.
B)It is possible to cast practically anymaterial be it ferrous or nonferrous.
C)It favors trial production or small or mass production.
D)Weight reduction in design canbe achieved.
E)Casting of any size and weightcan be made.
三.Limitation(铸造的缺点)
A)The products are usually with porosityand low toughness as well as ductility.
B)The dimensional accuracy andsurface finish achieved by normal sand casting are usually not ideal.
C)The sand casting process is labour intensive to some extent.
四. Applications(应用)
Machine tool beds,Cylinder blocks,Liners,Pistons,Crankshafts,Water supply pipes and valves,Mill rolls,Wheels,Housings,Statues
五.铸造过程
The casting process is basically simple. First, a cavity is formed into a mold. The shape of cavity determines the shape of the casting.
Liquid (or molten) metal is poured into the mold, then is allowed to cool and became solid. After the metal has solidified, the casting can be removed from the mold. The procedure can be repeated for production of duplicate parts.
六.Casting terms(铸造术语)
1)_Pouring basin(浇口杯): A small funnel shaped cavity at the top of
the mould into which the molten metal is poured.
2)Pattern（铸模）: Pattern is a replica of the final object to be made
with some modifications. The mold cavity is made with the
help of pattern.
3)Pattern(模型): Pattern is a replica of the final object to be made
with some modifications. The mold cavity is made with the
help of pattern.
4)Core(型芯): It is used for making hollow cavities in casting.
5)Sprue（直浇道）: The passage through which the molten metal from
the pouring basin reaches the mould cavity. In many cases
it controls the flow of metal into the mould.
6)Runner（横浇道）: The passageways in the parting plane through which
molten metal flow is regulated before they reach the mould
Cavity.
7)Gate（内浇道）: The actual entry point through which molten metal
enters mould cavity.
8)Riser（冒口）: It is a reservoir of molten metal provided in the
casting so that hot metal can flow back into the mould
cavity when there is a reduction in volume of metal due
to solidification.
9)Chill(冷铁): Chills are metallic objects which are placed in the
mould to increase the cooling rate of castings to provide
uniform or desired cooling rate.
Translate the last paragraph in P.23 into Chinese.
七.翻译(影响因素)：Regardless of the method of casting, there are certain,
fundamental aspects that must be well understood and controlled in order to produce parts successfully. The most important of these is mechanism of solidification of metals. Other important aspects are the preparation of molds, cores, melting and pouring of metals, and cleaning and inspection
不管是什么铸造方法，有一点是肯定的：就是为了成功的生产部件，必须很好的理解和控制铸造的基本方面。最重要的就是金属凝固的机制。其他重要的方面是铸型，型芯的准备；金属的熔化和浇注；铸件的清理和检查。
八.无缺陷铸件的要求：
To provide a defect free casting, the following requirements should be followed:
（1）：The mould should be completely filled in the smallest time possible without having to raise metal temperature nor use higher metal heads.
（2）：The metal should flow smoothly into the mould without any turbulence.
（3）：Unwanted material such as slag, dross and other mould material should not be allowed to enter the mould cavity.
（4）：The metal entry into the mould cavity should be properly controlled in such a way that aspiration of the atmospheric air is prevented.
（5）：A proper thermal gradient should be maintained so that the casting is cooled without any shrinkage cavities or distortions.
（6）：Metal flow should be maintained in such a way that no gating or mould erosion take place.
（7）：The gating system should ensure that enough molten metal reaches the mould cavity.
第二节 铸模和型砂
一.What is pattern?铸模的定义
A pattern is a replica of the object to be made by the casting process, with some modifications.
二.The main modifications are(主要修正):
(a) The addition of pattern allowance.
(b) The provision of core prints.
(c) Elimination of fine details which cannot be obtained by casting and hence are to be obtained by further processing.
三.Pattern allowances（模型余量）
1. Shrinkage: Liquid shrinkage and solid shrinkage.
2. Draft
3. Finish or machining allowance
4. Shake allowance
5. Distortion allowance
四.Pattern Materials(模型材料)
The usual pattern materials are wood, metal and plastics. The most commonly used pattern material is wood, the main reasons being the easy availability and the low weight. Also, it can be easily shaped and is relatively cheap. But the main disadvantage of wood is its absorption of moisture as a result of which distortions and dimensional change occur.
Choice of the pattern materials depends essentially on the size of the casting, the number of castings to be made from the pattern, and the dimensional accuracy required.
Wood may be the only practical pattern material for very large castings, and metals are good and extensively used pattern material for large scale casting production and for closer dimensional tolerances.
五.The important properties required for moulding materials(型砂的重要特性):
1)Refractorine
ss(耐火性)
2)Fineness(精细度或粒度)
3)Strength (green, dry, hot)(强度) or bond(结合性)
4)Permeability(透气性)
5)Durability(耐用性)
6)Plasticity(塑性)
六.The main ingredients of any moulding sand are:（型砂的主要成分）
1)The silica grains (SiO2)
2)The clay as binder
3)Moisture to activate the clay and provide plasticity.
七.The properties of moulding sand are dependent to a great extent on a number of variables. （影响型砂性能的因素）The important ones are:
1)Sand grain shape and size
2)Clay type and amount
3)Moisture content
4)Method of preparing sand mould
第三节 砂型
一.名词解释：
1)分型面：The plane separating the cope and drag is called the parting plane，when viewed as a line, it is called a parting line.
2)上箱，下箱：Medium-sized green sand molds are enclosed in flasks that consist of two part, the upper half or cope, and the lower half or drag.
Molding sands have three principal ingredients: silica sand of specified grain size, shade, and uniformity; green bond of desired plasticity; and moisture.
3)直浇道：The vertical passageway through which molten metal flows down to the parting plane is called the sprue.
4)横浇道：The horizontal connection in the parting plane between the mold cavity and the sprue is the gate.
5)原砂：The sand is called green because it depends on moisture for bond.
6)Draft(拔模斜度):sufficient taper ,called draft,is placed on sides of the pattern to facilitate withdrawal ofthe pattern without damage to the mold cavity.
二.Dry sand molds(干砂造型)
1.定义：Dry sand molds:dry sand molds zre oven-dride to a depth of 1/2in. or more,the molds are baked at 300 to 700 F for 8 to 48 hr.depending on the binders used in the sand mixture and amount of sand surface to be dried and on the requirements of production cycles,dry sand molds generally are used in preference to green sand molds for making medium sizze to large castings,such as large rolls,housings,gears and machinery components.
2.干砂造型优点：1:they are stronger than green sand molds,and thus are less susceptible to damage in handing.2:over all dimensional accuracy of the mold is better than for green sand molds.3:surface finish of castings isbetter,mainly because dry sand molds are coated with wash.
干砂造型缺点：1：castings are more susceptible t hottears.2:distortion is greater than for green sand molds,because3 of the baking.3:more dlaks equipment is needed to produce the same number of finished pieces,because processingcycles are longer than for green sand molds.4:production is slower than for green sand molds.
三.Green sand molds(原砂造型)
Green sand molds:the green sand molds can made by hand or machinery.the sand is called green because it depends on molding sands have three principal ingredients;sillca sand of specified grain size,shade,and uniformity ;green hond of desired plasticity ;and moisture.
第四节 浇注系统
Gating
1)浇注系统:The term gating, or gating system, refers to all the passageways through which the metal enters a mold.
2)What are various elements that comprise the gating system?(浇注系统的组成部分)
Gating may include a pouring basin(浇口杯), sprue(直浇道), runner(横浇道), strainer core(浇口滤片), risers(冒口), gates(浇道), and many other devices(设备) to help fulfill its purposes.
3)Explain why the sprue should be tapered?(为什么直浇道有锥度)
If the sprue were to be straight cylindrical,the metal flow would not be full at the bottom, but some low pressure air would be breathed into this area which would then be carried to the mould cavity. A tapered sprue is to eliminate this problem.
4)What are the advantage and disadvantage of the top gate?(顶注式浇注系统的优缺点)
advantage：The advantage of top gatings is that all the metal enters the casting at the top so that the hottest metal comes to rest at the top of the casting. Hence, the proper temperature gradients are formed. By using this type of gating, directional, solidification in the casting toward risers located on top the casting is attained. The gates themselves may be made to serve as the risers.
disadvantage ：The disadvantage of top gating is the erosion of the mold by the dropping metal, which should be prevented if possible.
5)Explain the reasons which make a riser a necessity in some castings?(冒口的作用)
Most of the casting alloys shrink during solidification. As a result, voids are likely to form unless additional molten metal is fed into. This is why a riser is used.
第五节 制型机械
Molding Machines
翻译：If no consideration were taken of the large increase in production possible by their use, the improvement in the quality of castings alone would oftentimes warrant their installation, as the decrease in cost of machining casting produced by this method pays good dividends on the investment .The use of unskilled workmen on these machines is no small item in their favor.
即使不考虑用铸模机可能导致的产品的大量增长，仅仅（由于使用铸模机带来的）铸件质量的改进就足以确保他们经常会被采用，同时通过使用这种方法带来的机器铸造成本的降低，也会给投资方带来很好的回报。对于投资方而言，在这种机器上可以使用不熟练的工人（来降低成本），这也是一个不小的数目。
二.
Molding machines操作 :the chief operations performed by molding machins consist of ramming the sand into the mold ,rolling the mold over ,and drawing the pattern .
Molding machines优点：1,molding machines are more easily applied where mass production of duplicate parts is the problem.2,molding machines eliminate or reduce the slow hand operations and heavy backbreaking labor 3,molding machines reduce training time by reducing the need for skilled artisans.4,molding machines promote g
reater uniformity of molds and castings,which leads to faster production and fewer defects.
Molding machines缺点：1,molding machines are limited somewhat ,owing to size and complexity of jobs.2,high preater capitl outlay involved with molding machines. 3,the degree of flexibility required in jobbing foundry is lacking in molding machines operations.
第六节 型芯
core
1)What is Core?定义
Core is the material used for making cavities and hollow projections which cannot normally be produced by the pattern alone.
介绍：if casting is to be hollow or have a hole thrpugh it,a core must be used .the core will be placed in the mold ,positioned by core prints ,and the molten metal allowed to solidify around it.the external shape of the core thus becomes the internal shape of the casting.
2)The normal characteristics desired of a core:特性
Green strength(原砂强度)
Dry strength(干砂强度)
Refractoriness(耐火性)
Permeability(透气性)
Collapsibility(退让性)
Smoothness(平滑度)
Low gas emission(低含气量)
3) 成分：Most cores are made of core-sandI(芯砂) mixture consisting of sand grains and organic binders(有机粘结剂)
Dry-sand core:most cores contain special binders and are baked ,becoming strong enough to be handled and to resist the metal being poured into mold,these are called dry sand cores.
Green-sand cores :a smaller number of cores ,called green sand cores,are made of ordinary molding sand.
4)翻译：Today, cores are used in many different ways and for many purposes so that it is indeed difficult to give a satisfactory definition of the term core. Originally, cores were probably used only for making hollow castings, and the name was suggested by the fact that they shaped the inside, or core, of the castings. Cores are made by coremakers in the coremaking department.
Most cores contain special binders and baked, becoming strong enough to be handled and to resist the forces caused by the metal being poured into the mold. These are called dry-sand cores. A smaller number of cores, called green-sand cores, are made of ordinary molding sand.
现在，为了各种不同的目的，型芯被用在各种不同的场合，因此，给术语“型芯”作出一个令人满意的定义实在是很困难。最初，型芯极有可能仅仅用来成型空心铸件，它是用来成型铸件的内表面，或者说铸件的芯，因此得名型芯。型芯是在制芯厂由制芯工人来制造的。
大多数的型芯都含有某种粘结剂，并且被烘烤过，以使他们能够足够的结实。从而可以被夹持和抵抗金属浇注进铸型时的冲击力。这些型芯叫做干沙芯。还有一小部分型芯，叫做原沙芯，他们是用普通的造型沙制作的。
第七节 金属的凝固
Solidification of Meals
一.纯金属与合金凝固过程区别
1)Pure metals :Pure metals have a clearly defined melting (or freezing) point, so solidification takes place
at a constant temperature. When the temperature of the liquid metal is reduced to the freezing point .it remains constant while the latent heat(潜热) of solidification is given off. At the end of this cycle, complete solidification takes place and the solid metal begins to cool off.
2)alloys:Unlike pure metals, alloys solidify over a range of temperatures .Solidification begins when the temperature drops below the liquidus; it is completed when it reaches the solidus. Within this temperature range the alloy is in a mushy or pasty state. Its composition and state are given by phase diagram of the particular alloy.
二.哪些因素影响金属凝固
The significant factors are the type of metal (whether it is a pure metal or an alloy), thermal properties (thermal conductivity(导热性) and specific heat(比热)), the geometric relation(几何关系) between volume and surface area of the liquid metal, and the shape of the mold, and the mold material.
三.翻译
A typical cast structure of a solid solution alloy is of an inner equiaxed granular zone. This zone can be extended throughout the casting by the addition of a catalyst .This induces heterogeneous nucleation of grains, instead of the usual grain formation from the mold walls and progression toward the center. Another method to obtain heterogeneous nucleation is to reduce or eliminate thermal gradients within the mold.
固溶体合金的一个典型的铸造组织就是内部等轴粒状区域。通过增加催化剂可以使这个区域扩大到贯穿整个铸件。这包括晶粒的异质形核，代替了通常的从型壁处成型并向中心进行的结晶。另一种达到异质形核的方法是减少或消除铸型内部的热温度梯度。
第八节 铸件的宏观结构
Macrostructure of Castings
一.铸件的三个区域：
(1) The chill zone(激冷区)--a boundary layer, adjacent to the mould wall, of small equiaxed crystals with random orientations;
(2) The columnar zone(柱状晶区)--a band of elongated crystals aligned parallel to the directions of heat flow;
(3) The equiaxed zone(等轴晶区)--a central, region of uniform crystal. The properties of this central region are comparatively isotropic provided the size is small. The grain size in the equiaxed zone is, however, normally larger than that of the chill zone.
二.翻译
1)If the object of the control of grain structure is to obtain isotropy, a fine-grained equiaxed structure is required. This is brought about by encouraging those conditions that lead to the breakdown of columnar growth and the formation of the equiaxed zone. On the other hand, if anisotropic properties are required, the columnar zone will need to predominate. The relative proportions of the different zones can be controlled by altering the casting variables, e.g., the alloy composition, the rate of cooling, etc., and an ingot can vary from being fully columnar to being fully equiaxed.
如果控制晶粒结构的目的是达到各
向同性，就需要有精细等轴晶组织。这可以通过鼓励柱状晶生长破坏和等轴晶区的形成达到。另一方面，如果需要各向异性，就需要控制柱状晶，通过改变铸件的变量可以控制各不同晶区的相关比例。比如，合金的成分，冷却速度等等。并且铸件可以从全部是柱状晶到全部是等轴晶变化。
2)The grain boundaries are formed by the impingement of the growing grains and the effects of the boundaries derive both from crystallographic sources and particularly from the accumulation of soluble and insoluble impurities that can occur. Thus the effects of these grain boundaries depend both on the change in orientation at the boundary and on the special properties of the boundaries themselves. So far as fracture is concerned they can form easy paths for crack propagation, especially in the presence of solute segregation. If the equiaxed zone is absent, accumulation of soluble and insoluble impurities in the regions where the columnar structures impinge can have disastrous results。
晶界是通过晶粒生长的碰撞形成的，晶界的（对铸件性质）影响作用一方面是由于晶体学的原因造成的，另一方面，特别是由于可溶和不可溶杂质的积累而得来的。因此这些晶界的影响一方面取决于晶界处晶向的改变，另一方面还取决于晶界本身的特性。考虑断裂的情况下，他们会给裂纹扩展提供容易进行的路径，尤其是在有溶质偏析存在的情况下（更是如此）。如果没有等轴晶区的话，可溶的或者不可溶的杂质，在柱状晶组织相遇的区域的积累可以造成灾难性的后果。