Chapter 5: MetalCasting Processes and Equipment Heat Treatment

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Chapter 5 Metal-Casting Processes and
Equipment Heat Treatment
2
Solidification of Pure Metals

• FIGURE 5.1 (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.

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Grains of a Two-Phase System

• FIGURE 5.2 (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.

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Iron-Iron-Carbide Phase Diagram

• FIGURE 5.4 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.

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Open and Closed Molds
6
Sand Casting Sequence
7
Features of a Sand Mold

• FIGURE 5.14 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 5.15 Temperature distribution at the
  mold wall and liquid-metal interface during
  solidification of metals in casting.

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Solidified Skin on Steel Casting

• FIGURE 5.16 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.

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Volumetric Solidification Contraction

• TABLE 5.1 Volumetric solidification contraction
  or expansion percentages for various cast metals.

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Shrinkages in the Casting
13
Shrinkage in Casting
14
Various Types of Chills Used in Castings to
Eliminate Porosity

• FIGURE 5.17 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).

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Continuous Casting

• FIGURE 5.21 (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 Metalcasters Reference and Guide,
  American Foundrymans Society. (b) Continuous
  strip casting of nonferrous metal strip. Source
  Hazelett Strip Casting Corp.

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A Semipermanent Composite Mold
Operation Sequence of Making a Ceramic Mold

• FIGURE 5.22 Schematic illustration of a
  semipermanent composite mold. Source Steel
  Castings Handbook, 5th ed., Steel Founders
  Society of America, 1980.

FIGURE 5.23 Sequence of operations in making a
ceramic mold. Source Metals Handbook, 8th ed.,
Vol. 5 Forging and Casting, Materials Park, OH
ASM International, 1970.
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Vacuum-Casting Process

• FIGURE 5.24 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.

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Investment Casting

• FIGURE 5.25 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.

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Pressure-Casting Process

• FIGURE 5.27 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 5.28 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 5.29 Sequence of operations in die
  casting of a part in the cold-chamber process.
  Source Courtesy of Foundry Management and
  Technology.

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Centrifugal Casting Process

• FIGURE 5.30 Schematic illustration of the
  centrifugal casting process. Pipes, cylinder
  liners, and similarly shaped parts can be cast by
  this process.

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Semicentrifugal Casting Process

• FIGURE 5.31 (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.

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Squeeze-Casting Process

• FIGURE 5.32 Sequence of operations in the
  squeeze-casting process. This process combines
  the advantages of casting and forging.

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Melt-Spinning Process

• FIGURE 5.35 Schematic illustration of the
  melt-spinning process to produce thin strips of
  amorphous metal.

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

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Design Modifications to Avoid Defects in Castings

• FIGURE 5.39 (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.

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Casting Design Modifications

• FIGURE 5.40 Examples of casting design
  modifications. Source Steel Castings Handbook,
  5th ed., Steel Founders Society of America,
  1980. Used with permission.

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Design Practices for Die-cast Parts

• FIGURE 5.41 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.

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Costs Comparison for Different Casting Processes

• FIGURE 5.42 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.