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Virtually all machines contain shafts. The most common shape for shafts is circular and the cross can be either solid or hollow (hollow shafts can result in weight savings). Rectangular shafts are sometimes used, as in screwdriver blades, socket wrenches and control knob stems. www.mapeng.net 马棚网机械资讯
A shaft must have adequate torsional strength to transmit torque and not be overstressed. It must also be torsionally stiff enough so that one mounted component does not deviate excessively from its original angular position relative to a second component mounted on the same shaft. Generally speaking, the angle of twist should not exceed one degree in a shaft length equal to 20 diameters.www.mapeng.net 马棚网机械资讯
Shafts are mounted on bearings and transmit power through such devices as gears, pulleys, cams and clutches. These devices introduce forces which attempt to bend the shaft; hence, the shaft must be rigid enough to prevent overloading of the supporting bearings. In general, the bending deflection of a shaft should not exceed 0.01 in. per ft of length between bearing supports.www.mapeng.net 马棚网机械资讯
In addition, the shaft must be able to sustain a combination of bending and torsional loads. Thus an equivalent load must be considered which takes into account both torsion and bending. Also, the allowable stress must contain a factor of safety which includes fatigue, since torsional and bending stress reversals occur.www.mapeng.net 马棚网机械资讯
For diameters less than 3 in., the usual shaft material is cold-rolled steel containing about 0.4 percent carbon. Shafts are either cold-rolled or forged in size from 3 in. to 5 in. For sizes above 5 in., shafts are forged and machined to size. Plastic shafts are widely used for light load applications. One advantage of using plastic is safety in electrical applications, since plastic is a poor conductor of electricity. www.mapeng.net 马棚网机械资讯
Components such as gears arid pulleys are mounted on shafts by means of key. The design of the key and the corresponding keyway in the shaft must be properly evaluated. For example, stress concentrations occur in shafts due to keyways, and the material removed to form the keyway further weakens the shaft. www.mapeng.net 马棚网机械资讯
If shafts are run at critical speeds, severe vibrations can occur which dart seriously damage a machine. It is important to know the magnitude of these critical speeds so that they can be avoided. As a general rule of thumb, the difference between the operating speed and the critical speed should be at least 20 percent. www.mapeng.net 马棚网机械资讯
Another important aspect of shaft design is the method of directly connecting one shaft to another. This is accomplished by devices such as rigid and flexible couplings. www.mapeng.net 马棚网机械资讯
A coupling is a device for connecting the ends of adjacent shafts. In machine construction, couplings are used to effect a semi-permanent connection betw
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