B级要求
10pouringREVIEW QUESTIONS
10。1 Why is casting an important manufacturing process？
As with all other manufacturing processes, an understanding of the fundamentals is essential— both for the production of good quality and economical castings， and to establish proper techniques for mold design and casting practice。
10。2 What is the difference between the solidification of pure metals and metal alloys?
The flow of molten metals into the mold cavity is discussed in terms of mold design and fluid
flow characteristics.
10.3 What are dendrites？
Note the formation of dendrites in the mushy zone.
10.4 State the difference between short and long freezing ranges. How is range determined?
The shorter the range （as in pure metals and eutectics),the higher the fluidity。 Conversely, alloys with long freezing ranges （such assolid—solution alloys) have lower fluidity。 
1Mold design。 2Mold material and its surface characteristics. 3Degree of superheat。 R4ate of pouring,  5Heat transfer。
10.5 Describe the parameters on which solidification time depends.
This lack of convection affects solidification structure and distribution of impurities. Recent experiments involve the growth of crystals for production of cadmium-zinc telluride, mercury-zinc telluride， and selenium-doped gallium arsenide semiconductor samples.
10。6 Define shrinkage and porosity。 How can you tell whether cavities in a casting are due to porosity or to shrinkage?
Porosity caused by gases evolved during solidification can be a significant problem, particularly because of its adverse effect on the mechanical properties of the castings。 Various defects can develop in castings from lack of control of material and process variables。
10。7 What is the function of chills?
Internal chills are usually made of the same material as the casting and are left in the casting
10.8 How are dissolved gases removed from molten metal?
Dissolved gases may be removed from the molten metal by flushing or purging with an inert gas， or by melting and pouring the metal in a vacuum。 If the dissolved gas is oxygen, the molten metal can be deoxidized。
10.9 Describe the features of a gating system.
The metal may [low through a variety of passages （including pouring basins， sprues, runners， risers， and gating systems） before reaching the final mold cavity. Bernoulli's thcorcm， the continuity law， and the Reynolds number are the an alytical tools used in designing， with the goals of an appropriate flow rate and the elimination of defects associated with fluid flow.
QUALITATIVE PROBLEMS
10.18 Describe the stages involved in the contraction of metals during casting。
Although most metals shrink during solidification, gray cast iron and some aluminum alloys actually expand. Dimensional changes and cracking （hot tearing） are difficulties which can arise during solidification and cooling. Seven basic categories of casting defects have been identified。
QUANTITATIVE PROBLEMS
10.46 For rhe spw ＆~＆btxi in Problem 10.45, what diameter runner is needed to ens
ure a Reynolds number of 2000？ How long will a 25 in3 casting take to fill with such a runner?
Fiber materials can be graphite， aluminum oxide, silicon carbide， boron, molybdenum， and tungsten。 The elastic modulus of nonmetallic fibers ranges between 200 GPa and 400 GPa, with tensile strengths being in the range from 2000 MPa to 3000 MPa。
From the information given， we estimate the weld nugget volume to be 30 mn1' (0。0018 in3). Assume that the density for steel (Table 3。1) is 8000 kg/m3 （0。008 g/mm3）； then the weld nugget has a mass of 0.24 g.
11REVIEW QUESTIONS
11。1 Describe the differences between expendable and permanent molds。
Expendable—mold casting usually involves lower mold and equipment costs， but produces
less dimensional accuracy。  Permanent molds， which are made of metals that maintain their strength at high temperatures.As the name implies, they are used repeatedly and are designed in such a way that the casting can be easily removed and the mold used for the next casting
11.2 Name the important factors in selecting sand for molds。
As its name implies, the centrifugal-casting process utilizes the inertial forces caused by rotation

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