Cylinder Block and Head Materials and Manufacturing
Before addressing cylinder block and head layout design it is important to understand the restrictions imposed by material and casting process selection. This chapter begins with a brief look at the aluminum and gray iron alloys typically used for cylinde
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Cylinder Block and Head Materials and Manufacturing
Before addressing cylinder block and head layout design it is important to understand the restrictions imposed by material and casting process selection. This chapter begins with a brief look at the aluminum and gray iron alloys typically used for cylinder blocks and heads. Magnesium alloys, and composite blocks with magnesium portions are receiving increased attention for weight reduction, and will also be briefly covered. Many of the design constraints are imposed by the capabilities of the chosen casting process, so the commonly used casting processes will next be introduced. The chapter concludes with an overview of the machining lines used for block and head production.
7.1 Cylinder Block and Head Materials For many years the vast majority of automobile, truck, and agricultural and construction engines used cylinder heads and blocks that were sand cast from gray iron. While sand cast gray iron components remain important, automobile applications are seeing increased use of aluminum, and a variety of casting processes. Most new automobile engines use aluminum cylinder heads, while at this writing new engine block designs are closely split between aluminum and cast iron. This section begins with a look at gray iron and related alloys. Aluminum alloys are then discussed.
7.1.1 Gray Cast Iron A variety of irons and steels including gray and ductile iron are alloyed from iron, carbon and silicon. Further alloying elements may be added to provide specific properties desired for a particular application. Some of these elements will be discussed later in this section. © Springer Vienna 2016 K. Hoag, B. Dondlinger, Vehicular Engine Design, Powertrain, DOI 10.1007/978-3-7091-1859-7_7
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7 Cylinder Block and Head Materials and Manufacturing
Both gray and ductile iron alloys have relatively high carbon and silicon content as compared to steel—between 2 and 4 % carbon is typical, whereas 1 % is considered “high carbon” in steel. Even with its much higher carbon content gray iron is relatively soft and easily machined. Its properties also differ considerably from those of ductile irons having very similar carbon content. These facts suggest that there is much more that distinguishes these materials than carbon and silicon content alone. The differences can be far better explained by examining the micro-structure of each. In both gray and ductile iron the carbon precipitates out of the molten metal as graphite (as opposed to carbide in the case of steel). The gray iron alloys of interest for cylinder blocks and heads consist of mixtures of ferritic and pearlitic iron phases from which the carbon has precipitated out as graphite flakes as shown in the left photograph of Fig. 7.1. The silicon in the alloy creates precipitation sites controlling the size and distribution of the graphite flakes—increased silicon results in a finer distribution of smaller graphite flakes, generally resulting in increased strength. The resulting gray iron alloy is a low cost materia
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