求英语达人帮忙翻译一篇机械类英语文章，急！谢谢
Gear Materials (Reading Material)
Gears are manufactured from a wide variety of materials, both metallic as well as nonmetallic. As is the case with all materials used in design, the material chosen for a particular gear should be the cheapest available that will ensure satisfactory performance. Before a choice is made, the designer must decide which of several criteria is most important to the problem at hand. If high strength is the prime consideration, a steel should usually be chosen rather than cast iron. If wear resistance is the most important consideration, a can be made, for problems involving noise reduction, nonmetallic. Materials perform better than metallic ones. However, as is true in most design problems, the final choice of a material is usually a compromise. In other words, the material chosen will conform reasonably well to all the requirements mentioned previously, although it will not necessarily be the best in any one area. To conclude this discussion we will consider the characteristics of various metallic and nonmetallic gear materials according to their general classifications.
Cast Irons Cast iron is one of the most commonly used gear materials. Its low cost, ease of casting, good machinability, high wear resistance, and good noise abatement property make it a logical choice. The primary disadvantage of cast iron as a gear material is its low tensile strength, which makes the gear tooth weak in bending and necessitates rather large teeth.
Another type of cast iron is nodular iron, which is made of cast iron to which a material such as magnesium or cerium has been added. The result of this alloying is a material having a much higher tensile strength while retaining the good wear and machining characteristics of ordinary cast iron.
Very often the combination of cast iron gear and a steel pinion will give a well balanced design with regard to cost, strength, and wear.
Steel gear are usually made of pain carbon steels or alloy steels. They have the advantage, over cast iron, of higher strength without undue increase in cost. However, they usually require heat treatment to produce a surface hard enough to give satisfactory resistance to wear. Unfortunately, the heat treatment process usually produces distortion of the gear, with the result that gear load is not uniformly distributed across the gear tooth face. Since alloy steels are subject to less distortion due to heat treatment than carbon steels, they are often chosen in preference to the carbon steels.
Although it is not the purpose here to discuss the various heat treatment methods and their effect on the properties of materials so treated, the designer should be aware of possible problems arising from the use of heat treated materials.
齿轮材料（阅读材料）
Gears are manufactured from a wide variety of materials, both metallic as well as nonmetallic.
齿轮由多种种类的材料制造，包括金属材料和非金属材料。
As is the case with all materials used in design, the material chosen for a particular gear should be the cheapest available that will ensure satisfactory performance.
在设计中可以使用多种材料的情况下，对于特定齿轮，应当做到选用满足使用要求下的最便宜的材料。
Before a choice is made, the designer must decide which of several criteria is most important to the problem at hand.
在作出选择前，设计师必须决定在众多设计准则中哪个是当前最重要的。
If high strength is the prime consideration, a steel should usually be chosen rather than cast iron.
如果高强度是第一要考虑的因素，通常就选择钢材而不选择铸铁。
If wear resistance is the most important consideration, a can be made, for problems involving noise reduction, nonmetallic. Materials perform better than metallic ones.
如果耐磨性是最重要的因素，可以选用非金属材料要比金属材料更好，同时也可以解决降低噪声的问题。
However, as is true in most design problems, the final choice of a material is usually a compromise.
然而，在大部分实际设计问题中，对材料的最终决定往往是一个折衷的方案。
In other words, the material chosen will conform reasonably well to all the requirements mentioned previously, although it will not necessarily be the best in any one area.
换句话说，材料的选择要考虑到合理的达到所有的预定要求，尽管这样就不能在其中任何一方面达到最好。
To conclude this discussion we will consider the characteristics of various metallic and nonmetallic gear materials according to their general classifications.
为了总结这次讨论，我们将按照通常的分类来考虑多种金属和非金属齿轮材料所具有的特性。
Cast Irons
铸铁
Cast iron is one of the most commonly used gear materials.
铸铁是最常用的齿轮材料之一。
Its low cost, ease of casting, good machinability, high wear resistance, and good noise abatement property make it a logical choice.
它具有低成本，铸造性好，机械加工性能好，高耐磨性，以及高减噪性的特点，这些特点使铸铁成为一个合适的选择对象。
The primary disadvantage of cast iron as a gear material is its low tensile strength, which makes the gear tooth weak in bending and necessitates rather large teeth.
铸铁主要的缺点是，作为一种齿轮材料，铸铁的抗拉强度很低，这使得轮齿的抗弯强度很弱而且不能造出很大的轮齿。
Another type of cast iron is nodular iron, which is made of cast iron to which a material such as magnesium or cerium has been added.
另一种类型的铸铁是球墨铸铁，是在普通铸铁中加入了镁或者铈制成的。
The result of this alloying is a material having a much higher tensile strength while retaining the good wear and machining characteristics of ordinary cast iron.
这种合金的特点是既具有高的抗拉强度，又保持了普通铸铁的高耐磨性和优秀的机械加工性能。
Very often the combination of cast iron gear and a steel pinion will give a well balanced design with regard to cost, strength, and wear.
通常，铸铁大齿轮和钢制小齿轮的组合能够在成本、强度和耐磨性之间达到较好的平衡。
问题补充：Steel gear are usually made of pain carbon steels or alloy steels.
钢制齿轮通常由碳钢或者合金钢制造。
They have the advantage, over cast iron, of higher strength without undue increase in cost.
它们具有比铸铁更高的强度，同时又没有是成本过高的增加。
However, they usually require heat treatment to produce a surface hard enough to give satisfactory resistance to wear.
然而，它们通常需要经过热处理，以生成表面的硬化层来达到足够的耐磨性。
Unfortunately, the heat treatment process usually produces distortion of the gear, with the result that gear load is not uniformly distributed across the gear tooth face.
不幸的是，热处理过程通常会使齿轮发生扭曲和形变，这样齿轮上的载荷就不能均匀的分布到轮齿的表面。
Since alloy steels are subject to less distortion due to heat treatment than carbon steels, they are often chosen in preference to the carbon steels.
合金钢具有变形量小的特点，因此比碳钢更适合热处理，它们通常比碳钢使用的更多。
Although it is not the purpose here to discuss the various heat treatment methods and their effect on the properties of materials so treated, the designer should be aware of
possible problems arising from the use of heat treated materials.
尽管这里讨论的目的不是热处理的方法和这些方法在材料上产生的不同影响，设计师仍然应当认识到对不用热处理材料的选择可能带来的各种问题。
我们毕设都用雅信，指导老师看了说差不多就行~~
