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Lesson11 Designs of Machine Components-Bearings A bearing is a support system for rotating, oscillating, or translating machine elements, in which friction has been greatly reduced. Since it has been estimated in various studies that on the average about 30% of all mechanically transmitted energy are lost to friction, an understanding of friction phenomena in bearings is essential to the machine designer.

轴承是一个用于旋转，摆动，或移动机构中大大降低摩擦的支持系统。据各项研究中估计，摩擦所造成的能量损失平均大约占全部机械传递能量的30%，机械设计者对轴承中摩擦现象的了解是必不可少的。

Plain bearings provide sliding support, and friction is usually reduced by a liquid, solid, or gaseous lubricant. The following types of plain bearings are in use:

滑动轴承提供滑动支承，摩擦通常由液体、固体或气体的润滑剂减少。滑动轴承有以下类型的使用：

1 Journal bearings or sleeve bearings support a rotating or oscillating shaft. The bearing usually has a cylindrical shape, while the journal is most often physically a portion of the shaft. When the bearing completely surrounds the journal, we speak of a full bearing; when the bearing only partly surrounds the journal, it is called a partial bearing.

轴颈轴承或套筒轴承支撑旋转或摆动轴。轴承通常具有圆柱形状，而轴颈是物理轴最多的一部分。当轴承完全包围轴颈时，我们称之为一个完整的轴承;当轴承仅部分地围绕轴颈时，它被称为一个局部轴承。

2 Thrust bearings support an axial load on a rotating or oscillating shaft.

旋转或摆动轴上的推力轴承支撑轴向负荷。

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3 Line or guide bearings guide and support translating motion.

线或导轨轴承引导和支持平移运动。

The lubricant in journal bearings is most often oil, in special cases water, and sometimes grease or gas such as air. Some bearing materials provide self-lubrication. Idealy, a film of lubricant separates the surfaces in relative motion. If the lubricant is a fluid, the layer touching the journal moves along with it, while the layer adjacent to the bearing remains stationary. The closer intermediate layers are to the journal, the motion is that of the shear forces between adjacent lubricant layers. To avoid metal-to-metal contact, the minimum film thickness must exceed the combined height of the surface irregularities in journal and bearing. To provide space for the bearing diameter.

轴颈轴承的润滑剂，最常用的是油，在特殊情况下可用水，有时是润滑脂或空气等气体。一些轴承材料提供自润滑。理想的情况下，润滑油膜分离在相对运动的表面。如果润滑剂是一种流体，接触轴颈层与它一起移动，而邻近于轴承的层保持静止。越靠近中间层的轴颈，相邻的润滑层之间的剪切力使其运动。为了避免金属与金属接触，最小膜厚必须超过在轴颈和轴承的表面凹凸的组合高度。为轴承内径提供空间。 Bearing Materials 轴承材料

Journal bearing materials should preferably have the following characteristics:

滑动轴承材料最好应具有以下特征： 1 Good compressive and fatigue strength. 良好的压缩性能和疲劳强度。

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2 Good heat conductivity. 良好的导热性。

3 Chemical inertness to shaft and housing materials, as well as lubricants.

轴，外壳材料以及润滑剂的化学惰性。

4 Ductility, to conform to the shape of housing and journal, and to permit the embedment of foreign particles which would otherwise scour the shaft.

延展性，以符合壳体和轴颈的形状，并允许外部颗粒的嵌入否则将会冲刷轴。

5 Reasonable price. 合理的价格。

The most commonly used, general-purpose bearing materials are bronze alloys, such as copper-tin-lead, copper-tin, and copper-aluminum bronze, which meet these requirements well.

最常用的，一般用途的轴承的材料是铜的合金，如铜 - 锡 - 铅，铜 - 锡，铜和铝青铜，能较好地满足这些要求。

Babbits (alloys consisting mainly of either tin or lead), which have mostly poor fatigue characteristics, and silver, are often used in thin layers with cast iron or steel backing. Silver is used for heavy-duty applications, such as reciprocating aircraft engines.

轴承合金（以锡或铅为主的合金），它具有很差的疲劳特性，银，通常以薄层镀在铸铁或钢表面。银是用于高强度应用，如往复式飞机发动机。

Cast iron bearings are low in cost and are sometimes made integrally with a frame or structure. They operate well with

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hardened steel journals; however, they have low embeddability and poor heat conductivity.

铸铁轴承成本低，有时用整体框架或结构。它们因具有淬硬钢的轴颈而运作良好;然而，它们可嵌入性低、导热性差。 Rubber bearings are used for underwater applications, such as hydraulic turbines, pumps, and propeller shafts. The water serves as both lubricant and coolant. Shaft must of course be made from non-corroding materials such as monel, stainless steel or bronze.

橡胶轴承用于水下应用，如液压涡轮机，泵，和螺旋桨轴。水充当润滑剂和冷却剂。当然轴必须由非腐蚀材料制成，如蒙乃尔合金，不锈钢或青铜。

Phenolic compounds are often used for structures with integral bearings, such as docks, instruments, and switch gear, or for bearings used in locations similar to those in which rubber bearings are used. The material has low heat conductivity, and some swelling and warping may occur in larger sizes, requiring greater than average clearance values.

酚类化合物通常用于整体结构轴承，如码头，仪器，和开关装置，或用于那些使用橡胶轴承的结构和位置。该材料具有低的导热性，一些胀大和变形可能会发生在较大尺寸的地方，需要大于平均间隙值。

Sintered bearings are made by compressing mainly metallic powder mixtures in a die and subsequently sintering the compacts in an oven. The powders used are mostly copper and tin mixtures, sometimes iron, with the possible admixture of other powdered materials imparting some desirable property. A small amount of graphite is sometimes added to the powder mixture for bearings used in oscillating and reciprocating motion applications to provide a certain amount of lubricity. Such bearings are more or less porous, depending upon the

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