文档库

最新最全的文档下载
当前位置:文档库 > 6.轴的设计

6.轴的设计

A shaft is a rotating or stationary member, usually of circular cross section, having mounted upon it such elements as gears, pulleys, flywheels, and other power-transmission elements.

轴是一个固定或转动部件,通常是圆形截面,在它上面安装了诸如齿轮,皮带轮,飞轮,和其他动力传动元件。

If a shaft carries several gears or pulleys, different sections of the shaft will be subjected to different torques, because the total power delivered to the shaft is taken off piecemeal at various points. Hence one must note the amount of torque on each part of the shaft. Then study the distribution of the bending moment, preferably sketching( freehand is all right) the shear force and bending moment diagrams.

如果一个轴进行几个齿轮或滑轮,轴的不同部分将经受不同的扭矩,因为传递到轴的总功率被取下零散各个点。因此必须注意在轴的每一部分的转矩的量。然后研究弯矩的分布,最好草图(手绘是所有权利)的剪切力和弯矩图。

From this preliminary examination, which is a problem in mechanics, we note the section where the bending moment is a maximum and the section where the torque is a maximum. If these maximums occur at the same section, the diameter needed for that section is determined- and and also for the section of maximum bending moment, and use the larger value.

从这个初步的检查,这是力学中的一个问题,我们注意到,弯矩最大,扭矩最大的节段。如果这些最大值出现在同一段,这段的直径的确定,同时也为最大弯矩截面,并使用较大的值。

The diameter of shaft is often varied from point to point, sometimes for structure reasons. In this case, check the stress or determine the size needed for each section. The designer makes certain that all sections of the shaft are subjected to safe stresses, taking due note of holes, keyways, and other stress raisers(应力集中).

轴的直径通常从点到点变化,有时因为结构的原因。在这种情况下,检查应力或确定所需的每个部分的大小。设计者就可以确保轴的所有部分都受到应力的安全,适当注意到孔,键槽,和其他应力集中(应力集中)的。

Hollow round shafts sometimes serve a useful purpose, usually in large sizes, though they are more expensive than solid ones. They have the advantage of being stronger and stiffer, weight for weight, because the outer fibers(纤维)are more effective in resisting the applied moments(作用力矩), and they respond better to heat treatment because quenching (淬火)can proceed outward as well as inward.

空心圆轴有时会提供有用的功能,通常是在大尺寸,虽然他们比固体更贵。它们具有作为更为坚固耐用,重量为重量的优势,因为外纤维(纤维)更有效地抵抗所施加的力矩(作用力矩),和他们的反应更好的热处理,因为淬火(淬火)可以向外进行如下还有向内。

Deflection(扰度)is a significant consideration in the design of shafts. Criteria for the limiting torsional deflection vary from 0.25 degree per meter of length for machinery shafts to 1 degree per meter or 1 degree in a length of 20 diameters for transmission shafting(轴系). Even short shafts become special problems in rigidity when the load is applied in impulses, as on an automobile crankshaft. The impulses produce a torsional vibration, usually compensated(补偿)by torsional-vibration dampers in an automotive engine.

挠度(扰度)是一个重要的考虑轴的设计。为限制扭转变形标准从每米长度0.25度机械轴每米或长度为传动轴系20直径1度1度的变化(轴系)。即使短轴成为特殊问题刚度作用的冲动,如汽车曲轴。冲动产生扭转振动,通常补偿(补偿)的扭转振动阻尼器在汽车发动机。

Data on permissible values of deflections are rare, probable because the range of values would be large and each situation has its own peculiarities. An old rule of thumb(经验法则)for transmission shafting is that the deflection should not exceed 0.0005L, where L is the shaft length between supports; although greater stiffness may be desired.

对挠度的允许值的数据是罕见的,可能是因为值的范围将是大和每一种情况都有其自己的特点。拇指(经验法则),用于传输轴系的旧规则是,偏转不应超过0.0005L,其中L是支持件之间的轴的长度;尽管更大的刚性可能期望。Preferably, on transmission shafts, the pulleys and gears should be located close to bearings in order to minimize moments. If journal bearings with “thick film” lubrication are used, the deflection across the bearing width should be only a small fraction of the oil-film thickness;

优选为在传输轴,滑轮和齿轮应位于靠近轴承,以便最小化的时刻。如果轴颈轴承用“厚膜”润滑时,在整个轴承宽度偏转应油膜厚度的一小部分;

if the slope is excessive here, there will be “binding” in the journal. A self-aligning bearing may eliminate this trouble if the deflection is otherwise acceptable.

如果斜率是过度这里,将有“绑定”在杂志。自动调心轴承可以消除这种麻烦,如果偏转,否则是可以接受的。

On machine tools, rigidity is a special concern because of its relation to accuracy. If a shaft supports a gear, deflection is more of a consideration than if it carries a V-belt pulley.

机床的刚度是一个特殊的关注,因为对精度的关系。如果一个轴支撑齿轮,它是否带有三角皮带轮的变形比更多的考虑。

The center of mass of a symmetric, rotating body does not coincide with its center of rotation. This is because (a) it is impossible from a practical viewpoint to get the mass uniformly distributed about the geometric center of the body and (b) the shaft on which the body rotates deflects under load, thus moving the center of mass away from the true axis, which passes through the center line of the bearings. Rotation may begin about the geometric axis,

对称的质量中心,旋转体不会与它的旋转中心相重合。这是因为(a)它是从实

际观点来看不可能得到均匀分布在主体和(b)该轴在其上的主体旋转载荷下挠曲的几何中心的质量,从而移动质量中心距真轴,其穿过轴承的中心线。旋转可以开始关于几何轴线,

but at some speed, the centrifugal force of the displaced center of mass will equal the deflecting forces on the shaft; the shaft with its attached bodies will then vibrate violently, since the centrifugal force changes its direction as the turns.

但在某些速度,质量的位移中心的离心力将等于在轴的偏转力;与其连接的机构轴之后就会剧烈震动,因为离心力改变其作为转弯方向。

This speed is termed the critical speed(临界速度). Above the critical speed, a smooth-running(平稳转动) state of equilibrium is again reached when the body is then rotating virtually about its mass center (centrifugal forces balance).

这个速度被称为临界速度(临界速度)。高于临界速度,平衡的平稳运行(平稳转动)状态再次达到当人体然后旋转几乎绕其质心(离心力平衡)。

High-speed turbines often operate above the critical speed. Additional critical speeds, higher than the first, are successively attained, but the amplitudes of the corresponding vibrations progressively decrease.

高速涡轮机操作往往高于临界速度。依次获得额外临界速度,高于第一,,但相应的振动的振幅逐渐减小。

Many shafts supported by three or more bearings, which means that the problem is statically indeterminate. Texts on strength of materials give methods of solving such problems. The design effort(设计工作)should be in keeping with the economics of a given situation. For example, if one line shaft supported by three or more bearings is needed, it probably would be cheaper to make conservative assumptions as to moments and design it as though it were determinate. The extra cost of an oversize shaft may be less than the extra cost of an elaborate(精心)design analysis.

许多轴支持三个或多个轴承,这意味着,这个问题是静态不确定的。关于材料强度文本给解决这些问题的方法。设计工作(设计工作)应符合的特定情况下的经济性。例如,如果需要三个或更多的轴承支撑一行轴,它可能会更便宜,使保守的假设为时刻,设计它,仿佛它是确定的。一个特大型轴的额外成本可能不到一个精心制作的(精心)设计分析的额外费用。