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 .

2.1.2 发动机组
发动机缸体(如图2-4)充当着发动机所有零部件的刚性装配基体,缸体包括汽缸,支撑曲轴和凸轮轴.在老式的发动机中,气门座,推杆和套管都包括在缸体里.必要的附件和离合器壳也和是缸体相连接的.注意曲轴箱是由缸体组成的.
图2-4 典型的缸体结构为四缸引擎顶置阀.缸体是由铸铁或者铝制成的.在一些小的单汽缸引擎中.制作材料则是合金压铸的金属.合金压铸的金属相对较轻较软.尤其适合压铸过程.
制造汽缸通常有两种方法.第一种方法是往一个由砂子做成的模具中浇铸溶化的铸铁或者铝.这种方法的一个关键是将溶化的金属放置于模具中来形成缸体的空腔和通路.待其冷却后再从模具中取出.并将砂芯溶解和冲刷掉.
第二种方法是在压力的作用下,促使溶化的铝或者合金压铸的金属进入一个用金属制成的模具.这种压铸法有很多优势.它能够让汽缸在制作过程中不形成气泡(或称之为孔隙).形成尖锐的棱角并且可以维持一个很高的空气精度.这就能最大程度的降低机械加工的操作难度.另外制作缸体的模具可以被重复的使用.
这么晚还在一个字一个字的码..自己都被感动了...-0-.