HW4 - Hfimubrk #4 REVIEW QUESTIONSL 11.1 Describe the...

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Unformatted text preview: Hfimubrk #4 REVIEW QUESTIONSL 11.1 Describe the differences between expendable and permanent molds. ame the important factors in selecting sand for s. 11.3 What are the major types of sand molds? What are their characteristics? 11.4 List important considerations when selecting pattern materials. 11:5 1 What is the function of a core? 11.6 What is the difference between sand- and shell- mold casting? 11.7 What are composite molds? Why are they used? 11.8 Describe the features of plaster-mold casting. QUALITATIVE PROBLEMS ; you need only a few units of a particular Mwbich process(es) would you use? Why? 319 Qualitative Problems @ Why is the investment-casting process capable . producing fine surface detail on castings? 11.10 Name the type of materials used for permanent- mold casting processes. 11.11 What are the advantages of pressure casting? 11.12 List the advantages and limitations of die casting. 11.13 ,4 What is the purpose of a riser? A vent? 11.14 Give reasons for using die inserts. 11.15 What is squeeze casting? What are its advan— tages? 11.16 What are the advantages of the lost—foam casting process? 11.24 How would you attach the individual wax pat— terns on a “tree” in investment casting? 11-18 What are the reasons for the large variety 0f 11.25 Describe the measures that you would take to casting processes that have been developed over the years? Explain with specific examples. 1 1.19 Why does die casting produce the smallest cast parts? 11.20 What differences, if any, would you expect in operties of castings made by permanent mold versus sand casting? 11.21 Would you recommend preheating the molds used in permanent—mold casting? Would you remove the casting soon after it has solidified? Explain your reasons. 11.22 Referring to Fig. 11.3, do you think it is neces- sary to weigh down or clamp the two halves of the mold? Explain your reasons. Do you think that the kind of metal cast, such as gray cast iron versus alu- minum, should make a difference in the clamping force? Explain. 11.23 Explain why squeeze casting produces parts with better mechanical properties, dimensional accuracy, and surface finish than do expendable-mold processes. reduce core shifting in sand casting. l{11.26 “lifYou have seen that, even though die casting prodfi'CES thin parts, there is a limit to how thin they can be. Why can’t even thinner parts be made by this process? 11.27 How are hollow parts with various cavities made by die casting? Are cores used? If so, how? Explain. 11.28 It was stated that the strength—to—weight ratio of die—cast parts increases with decreasing wall thick— ness. Explain why. 11.29 How are risers and sprues placed in sand molds? Explain with appropriate sketches. 11.30 In shell-mold casting, the curing process is critical to the quality of the finished mold. In this part of the process, the shell-mold assembly and cores are placed in an oven for a short period of time to complete the curing of the resin binder. List probable 320 Chapter 11 Metal-Casting Processes causes of unevenly cured cores or of uneven core thicknesses. Why does the die—casting machine shown in 1. . 7 have such a large mechanism to close the dies? Explain. 11.32 Chocolate is available in hollow shapes. What process is used to make these candies? 11.33 What are the benefits and drawbacks to heat- ing the mold in investment casting before pouring in the molten metal? QUANTITATIVE PROBLEMS l_ 11.37 Estimate the clamping force for a die—casting machine in which the casting is rectangular with project- ed dimensions of 125 mm X 175 mm (5 in. X 7in.). Would your answer depend on whether it is a hot- c amber or cold—chamber process? Explain. " 11.38 The blank for the spool shown in Figure P11.38 ‘ to sand cast out of A-319—an aluminum casting alloy. Make a sketch of the wooden pattern for this part and include all necessary allowances for shrinkage and machining. FIGURE P1 1.38 11.39 Repeat Problem 11.38 but assume that the alu- minum spool is to be cast using expendable-pattern 11.34 The slushy state of alloys refers to that state be- tween the solidus and liquidus temperatures, as de- scribed in Section 10.2. Pure metals do not have such a slushy state. Does this mean that pure metals cannot be slush cast? Explain. 11.35 Can a Chaplet also be a chill? Explain. 11.36 Rank the casting processes described in this chapter in terms of their solidification rate. (That is, which processes extract heat the fastest from a given volume of metal?) casting. Explain the important differences between the two patterns. In sand casting, it is important that the cope— m ; alf be weighted down with sufficient force to keep it from floating when the molten metal. is poured in. For the casting shown in Figure P11.40, calculate the minimum amount of weight necessary to keep the cope from floating up as the molten metal is poured in. (Hint: The buoyancy force exerted by the molten metal on the cope is dependent on the effective height of the metal head above the cope.) 11.41 If an acceleration of 100 g is necessary to pro— duce a part in true centrifugal casting and the part has an inner diameter of 10 in., a mean outer diameter of 14 in., and a length of 25 ft, what rotational speed is needed? 11.42 A jeweler wishes to produce twenty gold rings in one investment—casting operation. The wax parts are attached to a wax central sprue of a 0.5 in. diameter. The rings are located in four rows, each 0.5 in. from the other on the sprue. The rings require a 0.125—in. di— ameter, 0.5—in. long runner to the sprue. Estimate the weight of gold needed to completely fill the rings, run- ners, and sprues. The specific gravity of gold is 19.3. 11.43 Assume that you are an instructor covering the topics described in this chapter, and you are giving a quiz on the numerical aspects to test the understanding of the students. Prepare two quantitative problems and supply the answers. Section A-A FIGURE P1 1.40 Material: Low-carbon steei Density: 0.26 ib/in3 All dimensions in inches 321 Synthesis, Design, and Projects '6 2.00 —>11.00 1+— SYNTHESIS, DESIGN, AND PROJECTS 11.44 Make a list of the mold and die materials used in the casting processes described in this chapter. Under each type of material, list the casting processes that are employed and explain why these processes are suitable for that particular mold or die material. 11.45 The optimum shape of a riser is spherical to en- sure that it cools more slowly than the casting it feeds. However, spherically shaped risers are difficult to cast. a) Sketch the shape of a blind riser that is easy to mold but also has the smallest possible surface area~to-volume ratio. (b) Compare the solidification time of the riser in part (a) to that of a riser shaped like a right circular cylinder. Assume that the volume of each riser is the same and the height for each is equal to the diameter. See Example 10.1) 11.46 Sketch an automated casting line c0nsisting of machinery, conveyors, robots, sensors, etc., that auto— matically could perform the expendable-pattern casting process. 11.47 Which of the casting processes would be most suitable for making small toys? Why? 11.48 Describe the procedures that would be in— volved in making a large bronze statue. Which casting process(es) would be suitable? Why? 11.49 Write a brief report on the permeability of molds and the techniques that are used to determine permeability. 11.50 Light metals commonly are cast in vulcanized rubber molds. Conduct a literature search and describe the mechanics of this process. 11.51 It sometimes is desirable to cool metals more slowly than they would be if the molds were maintained at room temperature. List and explain the methods you would use to slow down the cooling process. 11.52 The part shown in Figure P1152 is a hemi- spherical shell used as an acetabular (mushroom shaped) Dimensions in mm FIGURE P1 1 .52 ...
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HW4 - Hfimubrk #4 REVIEW QUESTIONSL 11.1 Describe the...

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