What is the difference between rigid and flexible coupling?

In the world of mechanics and power transmission, an often underestimated but critically important role is played by mechanical couplings. Also called couplings, they consist of devices whose essential task is to connect two rotating shafts, typically the drive shaft (the one that generates the force) and the driven shaft (the one that receives the force and transmits it to another machine), transferring motion and torque from one shaft to the other and ensuring that the generated power is effectively transmitted to where it is required.

There are two types of couplings: rigid and flexible.

Rigid couplings are designed to connect two shafts to form one solid entity and prevent any kind of movement. They are used exclusively when the shafts are perfectly aligned; not surprisingly, their main (and limiting) characteristic is their absolute intolerance of misalignment. In essence, rigid couplings are the ideal choice for absolute precision and power transmission without any margin for flexibility.

Flexible couplings, on the other hand, are specially designed to compensate for some degree of misalignment between connected shafts. The difference between rigid and flexible couplings lies in their ability to tolerate and absorb misalignment of various types: angular (axes intersecting at a small angle), parallel (axes parallel but not coincident) and axial (movement of shafts along their own axis). Another significant advantage is the ability to absorb vibrations and shocks: many flexible joints, especially those with rubber or polyurethane elastic elements, effectively dampen torsional vibrations and absorb sudden shocks, helping to reduce noise, protect components and improve operational stability.

Flexible couplings are therefore the ideal solution in systems that have or could develop misalignment, offering protection and increased tolerance to operational imperfections.