By Zak Khan
Resonant frequency, or natural frequency, is a concern when selecting bellows couplings. If not taken into account, an otherwise sound choice for a bellows coupling may perform poorly. Resonant frequency can be quite a destructive force. If left unchecked or unconsidered in the design of a system, it may cause significant faults or outright failure.
Resonant or natural frequency is the innate oscillation frequency of a system. It varies based on the geometry, arrangement, inertia and other factors in an assembly. Bellows couplings are meant to be torsionally stiff. That is, they are flexible in movements that are perpendicular or transverse to the shafts of the two coupled devices. As such, the natural rotational frequency of the coupling is the main concern. The coupling is designed to flex in those other directions, but it should transmit torque with as little vibrations or oscillations as possible.
This means selecting a bellows coupling that has a natural frequency that is far higher or lower than the motor’s oscillation frequency. This is because it is the bellows coupling that becomes a critical component that determines the natural frequency of the whole system. It is, after all, the bellows coupling that is transmitting the rotational motion. Its torsional stiffness is also an important factor to consider.
When selecting a bellows coupling, make sure to consider its resonant frequency. Compare this to the speeds at which the system operates. Make sure that the speed of the system and the resonant frequency rating of the bellows coupling are sufficiently far apart from each other. Manufacturers often provide equations and recommendations for bellows couplings and their resonant frequency.
Filed Under: Bellows, Coupling Tips