Overcoming Torsional Vibration In The Drive Train
Vibration can be present in any drive train, whether it is the low level naturally occurring type produced from combustion engines or electric motors, as a result of their speed and number of cylinders or stator poles, or being induced as a result of other factors. Either way, vibration if left unchecked, can be the root cause of pre-mature wear or even catastrophic failure within a drive train.
In this article, David Proud General Manager of Reich Drive Systems UK explains how to overcome the potentially damaging effects of vibration using drive couplings with a high torsional flexibility.
Many drive train problems encountered with rotating or reciprocating equipment can usually be traced back to some form of vibration being generated by whilst in operation. There are many factors that can influence the type and severity of the vibrations being produced. Some may relate to equipment moving slightly over time, out of balance items, poor alignment between the different drive train elements during installation, or instances where the vibrations occur as a result of the natural characteristics of the engine or motor.
For example, within a diesel engine, the number of cylinders, their firing order and speed of operation induces torque pulses, adding to the normal torque being transmitted through the drive train. These torque pulses pass through the drive train in the form of torsional vibrations, which are often much more difficult to identify, as they do not exhibit the same visible characteristics as vibrations caused for example, as a result of a misalignment issue.
Torque pulses also add a twisting effect on the drive train and the various elements react in the same manner as a spring might, by releasing the energy generated by the initial twisting motion – but in the opposite direction. The rate at which this happens is determined by the stiffness of the different elements in the drive train, which in turn determines the frequency of the system. To avoid these issues, a detailed torsional vibration review should be undertaken, and calculations made, which will allow the selection of a drive coupling suitable for the specific application.
Drive couplings are much more than just a physical connection between drive elements. They protect the drive train through their ability to accommodate mechanical discrepancies, such as axial, angular or radial misalignment and also mitigate other factors such as shock loads, starting frequencies, temperature variation, environmental conditions, and of course vibration. Selecting a drive coupling which has the correct torsional stiffness characteristics is the first step to ensuring that vibration does not become the prime cause of failure.
The process of coupling selection for any application should always be given detailed consideration, to take into account all of the factors which the coupling is likely to encounter in service. Discussing the application with a reputable coupling manufacturer, and providing them with the information needed to undertake a torsional analysis, will ensure that the recommended coupling will be capable of accommodating the natural frequencies, whilst at the same time reducing any effects from torsional vibration. Engineers who have experienced pre-mature failure of existing coupling types should also consider whether excessive torsional vibration has played a part in that failure, and take steps to ensure that any new coupling has been selected following a torsional analysis of the application.
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