The use of cast iron blocks in Table 2.1 has been widespread due to low cost as well as formability. Figure 2.2 shows a V6 block used for a car engine.
The block is normally the integral type where the cylinders and upper crankcase are all one part. The cylinders are large holes that are machined into the
block. The iron for the block is usually gray cast iron having a pearlitemicrostructure, typically being JIS-FC200 (Table 2.2). The microstructure is shown in Fig. 2.7. Gray cast iron is so called because its fracture has a gray appearance. Ferrite in the microstructure of the bore wall should be avoided because too much soft ferrite tends to cause scratching, thus increasing blow-by.
Cast iron blocks are produced by sand casting. For cast iron, the die casting process using a steel die is fairly rare. The lifetime of the steel die is not adequate for repeated heat cycles caused by melting iron. As its name
suggests, sand casting uses a mold that consists of sand. The preparation of sand and the bonding are a critical and very often rate-controlling step.
Permanent patterns are used to make sand molds. Generally, an automated molding machine installs the patterns and prepares many molds in the same shape. Molten metal is poured immediately into the mold, giving this process very high productivity. After solidification, the mold is destroyed and the inner sand is shaken out of the block. The sand is then reusable. Two main methods are used for bonding sand. A green sand mold consists of mixtures of sand, clay and moisture. A dry sand mold consists of sand and synthetic
binders cured thermally or chemically.
Figure 2.8 shows a schematic view of a sand mold used to shape a tube. This mold includes a sand core to make the tube hollow. The casting obtained from using this mold is shown in Fig. 2.9. Normally, molten iron in a ladle is gently poured into the cavity under the force of gravity using a filling system. The sand core forming an inside hollow shape is made from a dry sand component. The bore as well as the coolant passages in the cylinder block are shaped as cored holes.
The science and technology of materials in automotive engines
Hiroshi Yamagata
Woodhead Publishing and Maney Publishing
on behalf of
The Institute of Materials, Minerals & Mining
CRC Press
Boca Raton Boston New York Washington, DC
WOODHEAD PUBLISHING LIMITED
Cambridge England
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