The fundamentals of flexible shaft couplings
Understanding the basic requirements for shaft couplings
The requirements to connect shafts on different types of machines have led to a diverse market for flexible couplings. At one extreme are simple, low cost couplings perhaps connecting shafts of 4 or 5mm diameter. At the other are large, expensive multi-
For the design engineer, backlash in a drive train is unwanted. However shaft couplings with backlash can be lower in cost and easier to fit. So the question is whether backlash can be tolerated? Couplings that have a one-
Torsionally soft or rigid?
Torsionally soft couplings usually incorporate a rubber or plastic element, and their use leads to reduced shock transmission, higher misalignment capacity and lower costs. They will exhibit an amount of wind-
Note that no couplings are absolutely rigid. The torsional stiffness values will be given in units of Nm/° or Nm/radian. Typically for a shaft diameter of 25mm a coupling with high rigidity will have a stiffness of 200 to 500Nm/°. The wind-
The three types of shaft misalignment can be defined as angular, radial and axial. Sometimes designers believe they can align shafts so accurately that no flexible coupling is needed. In reality tiny amounts of misalignment will remain and if a rigid shaft connection is used problems such as high bearing loads can result.
This is the angle between the centrelines of the two shafts. Torsionally soft couplings can accept up to 3° of angular misalignment, torsionally rigid couplings are generally capable of about 1°. It is good practice to align shafts as accurately as possible and an accurate assembly will have less than 1° misalignment. In some cases more angular misalignment is needed and couplings capable of 6° exist. However above 3° it is often better to go for a universal joint.
Radial misalignment is also known as parallel misalignment and is the radial distance between the centrelines of two shafts. A well aligned installation would have a radial misalignment value below 0.2mm. However torsionally soft couplings can accept values up to 0.6mm.
Also known as end-
When searching for the right coupling, it is best to talk to a supplier who can offer alternatives, not just the best combination of price and performance but also to consider other requirements such as high/low temperatures, corrosion protection, blind assembly and electrical insulation. Techdrives in Bedford have an extensive range and have been supplying shaft couplings to the UK market for 40 years.
Jaw Couplings -
Bolted rubber disc coupling -