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Critical Speeds of Rotating Shafts or Mass Review
Critical Speeds of Rotating Shafts with Distributed Loads - First Critical Speed : When calculating critical speeds, the weight or mass of the rotating cylinder or shaft is assumed to be zero or add 1/2 to 2/3 of the rotating shaft to the load mass. These formulas assume steel shafts having a modulus of elasticity E = 29,000,000. Keep in mind that a shaft with more than one load or distributed loads may have an infinite number of critical speeds. Typically, the first critical speed is most important for your design.
Load Configuration |
Equation |
Bearings |
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Bearings Supported |
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Bearings Fixed |
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One bearing fixed, one free end |
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| N |
= critical speed, RPM |
| N1 |
= critical speed of shaft alone |
| d |
= diameter of shaft, in inches |
| W |
= load applied to shaft, in pounds |
| l |
= distance between centers of bearings, in inches |
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