TAILIEUCHUNG - Vibration Fundamentals Episode 6

Tham khảo tài liệu 'vibration fundamentals episode 6', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 144 Vibration Fundamentals Figure Vertical mechanical looseness has a unique vibration profile. In most cases the half-harmonic components are about one-half of the amplitude of the harmonic components. They result from the machine-train lifting until stopped by the bolts. The impact as the machine reaches the upper limit of travel generates a frequency component at one-half multiples . orders of running speed. As the machine returns to the bottom of its movement its original position a larger impact occurs that generates the full harmonics of running speed. The difference in amplitude between the full harmonics and half-harmonics is caused by the effects of gravity. As the machine lifts to its limit of travel gravity resists the lifting force. Therefore the impact force that is generated as the machine foot contacts the mounting bolt is the difference between the lifting force and gravity. As the machine drops the force of gravity combines with the force generated by imbalance. The impact force as the machine foot contacts the foundation is the sum of the force of gravity and the force resulting from imbalance. Horizontal Looseness Figure illustrates horizontal mechanical looseness which is also common to machine-trains. In this example the machine s support legs flex in the horizontal plane. Unlike the vertical looseness illustrated in Figure gravity is uniform at each leg and there is no increased impact energy as the leg s direction is reversed. Failure-Mode Analysis 145 Figure Horizontal looseness creates first and second harmonics. Horizontal mechanical looseness generates a combination of first 1x and second 2x harmonic vibrations. Since the energy source is the machine s rotating shaft the timing of the flex is equal to one complete revolution of the shaft or 1x. During this single rotation the mounting legs flex to their maximum deflection on both sides of neutral. The double change in direction as the leg first deflects to one side

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