Vibration damping couplings: sometimes bigger is better
A customer sizing an elastomer insert coupling recently asked us if using a larger body size would provide better vibration damping. In a word, the answer was, yes. Vibrations in machine shafts come from a wide variety of sources. Machines that crush and shred materials can impart quite a bit of vibration into the drive line and prime mover. These types of machines can cause motors and mechanical driveline components to fail prematurely if proper damping measures are not in place. Conversely, driving components, especially internal combustion engines, can impart severe vibration down the driveline. While R+W specializes in vibration damping couplings for electric motor drives, the concept of increasing driving inertia for smooth continuous rotation is most easily explained and widely understood in terms of internal combustion engines.
One of the oldest methods mechanical designers have used to damp vibrations is employing a flywheel. This device is still widely in use, in many parts of industry. Using laws of basic classical mechanics, “a body in motion tends to stay in motion, while a body at rest tends to stay at rest,” designers know that it is difficult to change the rotating velocity of a massive, high inertia flywheel easily. This is why a flywheel is used on the output shaft of many combustion engines, since they tend to continue rotating smoothly rather than jerking severely every time a cylinder fires. A large drive coupling or belt pulley would have the same effect. Piston air compressors often have massive cast iron sheaves driving them for this reason.
In situations where inertia, space and power consumption are not of concern, it can be beneficial to use shaft couplings with larger and heavier hubs than are necessary to simply transmit the torque. At R+W we have machined flywheel features directly into steel coupling hubs on many occasions in order to assist customers with torsional vibration damping, especially in pump coupling applications. Another reason to consider upsizing for vibration damping is that in the case of elastomer insert couplings, the vibration is spread over a larger area which can also provide damping. In general, using the “bigger is better” concept is often a good policy when the priority is to make a robust and smooth running machine more so than a quick moving, light or compact machine. For many folks this concept is basic common sense, however in this day and age of making everything more compact, this principle can be overlooked when it might make a lot of sense.