Common coupling selection errors happen all the time. Some more than others. Here, Robert Watkins, VP of Sales for Ruland Manufacturing, tells us about a few he’s seen and should be avoided at all costs.
In one dampening application, we saw a food processing OEM who had a hard start, hard stop, aggressive move profile. They used a spider that was too stiff and would prematurely lose elasticity. They tested a softer spider which eliminated the premature failure and had no negative impact on system performance. Ruland’s curve jaw couplings, in most sizes, have 3 choices of spider hardness. Taking into consideration how much dampening you need will help point the right direction as to what spider to use. Use the 85 durometer blue, the 92 durometer yellow or the 98 durometer red.
Other times, we’ve seen rigid couplings in a system design that had to accommodate misalignment between the shafts. That’s a bad choice for a rigid coupling because they will not accommodate any misalignment. If you do use a rigid coupling in an application where misalignment is present, you’re going to have premature bearing failure. More specifically, premature bearing failure on both your motor and your actuator. Again it’s an example of choosing the right coupling right out of the gate.
In another example of using the wrong type of coupling, we saw a mixer OEM using a bellows coupling to connect a motor and a paddle. They experienced failings within a few hours of running. Bellows couplings require close bearing supports on both sides to properly function, the solution was to use a rigid coupling which is suitable front supported applications.
And we do run into applications where customers will make a design and only have a bearing on one side and you cannot use a flexible coupling in a design that has a bearing on one side only. The only coupling that has a possibility of working with bearing support on one side only is a rigid coupling, even at that you should review the application just to be sure. These are all just a few examples of common errors we see frequently.