1. Chapter 5: Metal-Casting Processes and Equipment; Heat Treatment

2. Solidification of Pure Metals
FIGURE (a) Temperature as a function of time for the solidification of pure metals. Note that freezing takes place at a constant temperature. (b) Density as a function of time.

3. Grains of a Two-Phase System
FIGURE (a) Schematic illustration of grains, grain boundaries, and particles dispersed throughout the structure of a two-phase system, such as lead-copper alloy. The grains represent lead in a solid solution of copper, and the particles are lead as a second phase. (b) Schematic illustration of a two-phase system consisting of two sets of grains: dark and light. Dark and light grains have their own compositions and properties, respectively.

4. Iron-Iron-Carbide Phase Diagram
FIGURE The iron-iron-carbide phase diagram. Because of the importance of steel as an engineering material, this diagram is one of the most important phase diagrams.

5. Open and Closed Molds

6. Sand Casting Sequence

7. Features of a Sand Mold
FIGURE Schematic illustration of a sand mold, showing various features.

8. Types of Patterns Used in Sand Casting

9. Temperature Distribution at Mold Wall in Casting
FIGURE Temperature distribution at the mold wall and liquid-metal interface during solidification of metals in casting.

10. Solidified Skin on Steel Casting
FIGURE Solidified skin on a steel casting. The remaining molten metal is poured out at the times indicated in the figure. Hollow ornamental and decorative objects are made by a process called slush casting, which is based on this principle. Source: H. F. Taylor, J. Wulff, and M. C. Flemings.

11. Volumetric Solidification Contraction
TABLE 5.1 Volumetric solidification contraction or expansion percentages for various cast metals.

12. Shrinkages in the Casting

13. Shrinkage in Casting Liquid Solid Contraction of molten metal.
Melting point
Solid
Room temperature
Contraction of molten metal.
Contraction of the metal during phase change.
Contraction of the solidified metal to room temperature.

14. Various Types of Chills Used in Castings to Eliminate Porosity
FIGURE Various types of (a) internal and (b) external chills (dark areas at corners), used in castings to eliminate porosity caused by shrinkage. Chills are placed in regions where there is a large volume of metal, as shown in (c).

16. FIGURE 5. 21 (a) The continuous-casting process for steel
FIGURE (a) The continuous-casting process for steel. Typically, the solidified metal descends at a speed of 25mm/s (1 in/s).Note that the platform is about 20 m (65 ft) above ground level. Source: Metalcaster’s Reference and Guide, American Foundryman’s Society. (b) Continuous strip casting of nonferrous metal strip. Source: Hazelett Strip Casting Corp.
Continuous Casting

17. A Semipermanent Composite Mold
Operation Sequence of Making a Ceramic Mold
FIGURE Schematic illustration of a semipermanent composite mold. Source: Steel Castings Handbook, 5th ed., Steel Founders’ Society of America, 1980.
FIGURE Sequence of operations in making a ceramic mold. Source: Metals Handbook, 8th ed., Vol. 5: Forging and Casting, Materials Park, OH: ASM International, 1970.

18. Vacuum-Casting Process
FIGURE Schematic illustration of the vacuum-casting process. Note that the mold has a bottom gate. (a) Before and (b) after immersion of the mod into the molten metal. Source: After R. Blackburn.

19. Investment Casting
FIGURE Schematic illustration of investment casting (lost-wax process). Castings by this method can be made with very fine detail and from a variety of metals. Source: Steel Founders’ Society of America.

20. Pressure-Casting Process
FIGURE The pressure-casting process uses graphite molds for the production of steel railroad wheels. Source: Griffin Wheel Division of Amsted Industries Incorporated.

21. Die Casting in Hot-Chamber Process
FIGURE Sequence of steps in die casting of a part in the hot-chamber process. Source: Courtesy of Foundry Management and Technology.

22. Die Casting in Cold-Chamber Process
FIGURE Sequence of operations in die casting of a part in the cold-chamber process. Source: Courtesy of Foundry Management and Technology.

23. Centrifugal Casting Process
FIGURE Schematic illustration of the centrifugal casting process. Pipes, cylinder liners, and similarly shaped parts can be cast by this process.

24. Semicentrifugal Casting Process
FIGURE (a) Schematic illustration of the semicentrifugal casting process. (b) Schematic illustration of casting by centrifuging. The molds are placed at the periphery of the machine, and the molten metal is forced into the molds by centrifugal forces.

25. Squeeze-Casting Process
FIGURE Sequence of operations in the squeeze-casting process. This process combines the advantages of casting and forging.

26. Melt-Spinning Process
FIGURE Schematic illustration of the melt-spinning process to produce thin strips of amorphous metal.

27. Casting Processes
TABLE 5.8 Casting processes, and their advantages and limitations.

28. Guidelines for Casting Design
Risers: Major concern is the size and placement of risers. Based on experience and considerations of fluid flow and heat transfer.
Corners, angles and section thickness: Sharp cornes, angles and fillets should be avoided, because they may cause cracking and tearing durinf solidfication of the metal.
Flat Areas: Large flat areas should be avoided, they cause warp, poor surface finish.
Shinkage: Allowance for shrinkage should be provided to avoid cracking. Pattern makers shrinkage allowance: 10 to 20 mm/m.
Parting Lines: Should be along a flat plane, rather than contoured, should be at the corners or edges, rather than on flat surface in the middle of the casting.
Drafter (taper): is provided in sand-mold pattern to enable remove of the pattern. Draft angle: 0.50 ~ 20.
Machining Allowance: increasing with the size and section thickness as usually from 2 ~ 5 mm for small to more than 25 mm for large castings.

29. Design Modifications to Avoid Defects in Castings
FIGURE (a) Suggested design modifications to avoid defects in castings. Note that sharp corners are avoided to reduce stress concentrations. (b)-(d) Examples of designs that show the importance of maintaining uniform cross-sections in castings to avoid hot spots and shrinkage cavities.

30. Casting Design Modifications
FIGURE Examples of casting design modifications. Source: Steel Castings Handbook, 5th ed., Steel Founders’ Society of America, Used with permission.

31. Design Practices for Die-cast Parts
FIGURE Examples of undesirable and desirable design practices for die-cast parts. Note that section-thickness uniformity is maintained throughout the part. Source: Courtesy of The North American Die Casting Association.

32. Costs Comparison for Different Casting Processes
FIGURE Economic comparison of making a part by different casting processes. Note that because of the high cost of equipment, die casting is economical for large production runs. Source: The North American Die Casting Association.