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Friction and Lubrication
摩擦和润滑

In many of the problems thus far, the student has been asked to disregard or neglect friction.
到目前为止，在许多问题的处理中，学生都被告知不计入摩擦力或者忽略摩擦力。

Actually, friction is present to some degree whenever two parts are in contact and move on each other.
实际上，当两部分接触并且相对运动时，总要产生一定程度的摩擦。

The term friction refers to the resistance of two or more parts to movement.
边界摩擦力取决于两个或者多个部分相对运动时相互之间的阻碍程度。

Friction is harmful or valuable depending upon where it occurs.
根据产生时所处的位置不同，摩擦力可以是有害的也可以是有益的。

Friction is necessary for fastening devices such as screws and rivers which depend upon friction to hold the fastener and the parts together.
摩擦力在锁紧装置中是必须存在的，比如螺旋副和rivers，这些装置依靠摩擦力保持锁紧状态并且使各部分连接起来。

Belt drivers, brakes, and tires are additional applications where friction is necessary.
带传动、制动器、轮胎都是必需摩擦力的应用例子。

The friction of moving parts in a machine is harmful because it reduces the mechanical advantage of the device.
机器中运动部件产生的摩擦力是有害的，因为它会降低装置的机械效率。

The heat produced by friction is lost energy because no work takes place.
摩擦产生的热量又损失了能量，因为它没有做功。

Also, greater power is required to overcome the increased friction.
另外，需要大量的能量来克服增长的摩擦力。

Heat is destructive in that it causes expansion.
热量引起的膨胀变形是具有破坏性的。

Expansion may cause a bearing or sliding surface to fit tighter.
热膨胀可能使轴承或者滑动表面更紧。

If a great enough pressure builds up because of expansion, the bearings may seize or freeze.
当热膨胀引起的压力变的足够大时，轴承可能停止运动甚至是烧结。

In addition, as heat is developed, bearings made from low temperature materials may melt.
另外，随着热量的增加，由低温工作用材料制成的轴承可能会熔化。

There are three types of friction which must be overcome in moving parts:
运动的物体中存在三种类型的必须克服的摩擦力：

(1)starting, (2)sliding, and(3)rolling.
1、静摩擦力，2、滑动摩擦力，3、滚动摩擦力

Starting friction is the friction between two solids that tend to resist movement.
静摩擦力是在两个相互限制对方运动的物体之间产生的摩擦力。

When two parts are at a state of rest, the surface irregularities of both parts tend to interlock and form a wedging action.
当两部分在静止状态时，两表面的不规则形状使它们产生互相锁紧并且产生楔形作用。

To produce motion in these parts, the wedge-shaped peaks and valleys of the stationary surfaces must be made to slide out and over each other.
在两部分产生运动的过程中，静止表面的楔形的尖端和凹处必然与另以表面相互滑进滑出。

The rougher the two surfaces, the greater is the starting friction resulting from their movement.
两表面越粗糙，由它们引起的静摩擦力就越大。

Since there is usually no fixed pattern between the peaks and valleys of two parts, the irregularities do not interlock once the parts are in motion but slide over each other.
由于通常两配合面的尖端和凹处没有固定的形状，一旦发生相对的运动不规则表面将不再互锁。

The friction of the two moving parts is known as sliding friction.
两运动表面间的摩擦被称作滑动摩擦。

As shown in Fingure1,starting friction is always greater than sliding friction.
如图1中所示，静摩擦力总是比滑动摩擦力大。

Rolling friction occurs when roller devices are subjected to tremendous stresses which cause the parts to change shape or deform.
滚动摩擦力产生在受到引起部件形变的巨大压力的滚动装置上。

Under these conditions, the material in front of a roller tends to pile up and forces the object to roll slightly uphill.
在这种情况下，滚动件的前部的材料产生堆积并且产生使物体向相反方向滚动的力。

This changing of shape, known as deformation, causes a movement of molecules.
这种被看作弹性变形的形状的改变，引起了分子之间的相对运动。

As a result, heat is produced from the added energy required to keep the parts turning and overcome friction.
结果，需要额外的能量来保持部件的转动并且克服摩擦力，并由此产生的热量。

The friction caused by the wedging action of surface irregularities can be overcome partly by the precision machining of the surfaces.
由不规则表面的楔形作用引起的摩擦力，能够部分的通过机器的表面精度被克服。

However, even these smooth surfaces may require the use of a substance between them to reduce the friction still more.
然而，即使这种光滑的表面也仍然需要在表面之间填充一些一些物质来降低摩擦。

This substance is usually a lubricant which provides a fine, thin oil film.
这种物质通常是能产生一层精细而且薄的油膜的润滑剂。

The film keeps the surfaces apart and prevents the cohesive forces of the surfaces from coming in close contact and producing heat.
这层薄膜保持两表面分离并且通过紧密的接触和产生的热量提供黏着力。

问题补充：Another way to reduce friction is to use different materials for the bearing surfaces and rotating parts.
另一种降低摩擦的方式是使用不同的材料来制作轴承的表面和滚动部件。

This explains why bronze bearings, soft alloys, and copper and in oilite bearings are used with both soft and hardened steel shafts.
这便解释了为何青铜、软合金和紫铜用在与软表面或者硬表面钢轴配合的自润滑轴承中。

The oilite bearing is porous. Thus, when the bearing is dipped in oil, capillary action carries the oil through the spaces of the bearing.
自润滑轴承是多孔状的。应此，当轴承浸入油中时，油会通过毛细作用充满轴承中的小孔。

This type of bearing carries its own lubricant to the points where the pressures are the greatest.
这种类型的轴承能把它自身存储的润滑油释放在压力最大的位置。

Moving parts are lubricated to reduce friction, wear, and heat.
对运动部件的润滑能够降低摩擦、磨损和生成的热量。

The most commonly used lubricants are oils, greases, and graphite compounds.
最常用的润滑剂是油、脂、以及石墨复合物。

Each lubricant serves a different purpose.
不同的润滑剂使用在不同的条件下。

The conditions under which two moving surfaces are to work determine the type of lubricant to be used and the system selected for distributing the lubricant.
两运动表面的工作情况决定系统的润滑方式和布油方式。

On slow moving parts with a minimum of pressure, an oil groove is usually sufficient to distribute the required quantity of lubricant to the surfaces moving on each other.
低速轻载运动的部件，一个润滑油槽通常就能够为相对运动表面提供足够的润滑。

这是一篇关于摩擦和润滑的专业英语，这篇文章算难吗？？？？

太长太麻烦了。。。又很简单。。。您自己来吧。

三十分翻译这个我决定有点浪费时间了，要是一百分我可以浪费这个时间。