英语翻译2.1.2 Engine BlocksThe block (Figure 2-4) serves as a ri
英语翻译
2.1.2 Engine Blocks
The block (Figure 2-4) serves as a rigid metal foundation for all parts of an engine .It contains the cylinders and supports the crankshaft and camshaft .In older engines ,the valve seats ,ports ,and guides are built into the block .Accessory units and clutch housing are bolted to it .Note that the crankcase is formed with the block .
Figure 2-4 Typical block construction for a four cylinder valve-in-head engine
Blocks are made of either cast iron or aluminum .In some of the small ,one cylinder engines ,the material is die cast metal .Die cast metal is a relatively light ,soft metal especially suited to the die casting process .
Blocks are commonly formed in two ways .One method is to pour molten cast iron ,or aluminum ,into a mold made of sand .A core is placed within the mold to form the cavities and passageways within the block .After the casting has cooled ,it is removed from the mold ,and the sand core is dissolved and washed out .
The second method is to use a mold of metal and force molten aluminum ,or die-cast metal ,into the mold under pressure.The pressure casting process has several advantages .It produces a block free of air bubbles (called voids ),gives sharp corners ,and a high degree of air accuracy can be maintained .This reduces machining operations to a minimum .The same mold can be used over and over .