A coupling connects two parts to transmit rotary motion with a middle part made of polyurethane, metal, or similar material to reduce torsional distortion.The middle parts in the couplings are produced from polyurethane blocks, metal sheet or metal spring and are used to provide flexibility.
Flexible couplings are used to connect two separate shafts on the machine axes. One of these shafts is the driving motor shaft and the other is the screw shaft to be rotated.In some cases, flexible couplings are used to join bar shafts to transfer rotational force over long distances.
It is very important to know the following information while determining the type of coupling to be used;
1- Torque value to be transferred
2-Shaft diameters
3-Connection Type (Clamping Ring/Only Clamping Hub/Clamping Hub with Key)
4-Maximum Rotational Speed (RPM)
5-Maximum allowable backlash and angular displacements
1- Torque Value
First, we must precisely calculate the maximum torque value we will transfer. Then, by looking at the manufacturer’s catalogue, we determine a coupling size that will not be below the torque value we have calculated.For example, if we are going to transfer a torque of 100 Nm, we should start with a coupling with a body strength of at least 120 Nm-130Nm.
2-Shaft Diameters
If the torque value we want to transfer is less than the capacity of the coupling, but our shaft diameters are large for that coupling, we should choose a one size bigger coupling that allows those shaft diameters.The torque value according to the coupling size may be suitable for the job, but if the shaft diameter is smaller than it should be, the shaft may slip inside the coupling because the holding torque will decrease.The transmission torque according to the coupling size and the slip torque limits according to the shaft diameters to be connected are specified separately in the manufacturer’s catalogues.
3- Connection Types
There are three most commonly used connection types.
- Clamping Ring Only
- Clamping Hub
- Clamping Hub with Key
Product selection is made according to ease of assembly, life time and torque value.The keyed hole type is most efficient if there is movement in one direction. Because the impact movement may cause the key to be crushed over time.However, if there is bidirectional movement, a clamping ring is recommended.On the other hand, the clamping ring can transmit less torque than the keyed type. In other words, it is necessary to pay attention to the torque value while making the selection.
4-Maksimum Rotational Speed
Manufacturers try to produce couplings with a homogeneous body structure while being manufactured. Because an inhomogeneous structure will create centrifugal force during high speed and may cause the combined shafts or bearings to break.Maximum speed limits are specified in the manufacturer’s catalogues. These limits vary depending on whether the couplings are balanced for high speed or not.
5-Maximum Allowable Backlash and Angular Displacements
Rotational backlash directly affects linear positioning.For this reason, it is not desirable to have a backlash caused by flexing in the coupling’s absorber middle part ( spring, metal sheet lamina) or polyurethane). In cases where precise positioning is not important, polyurethane couplings may be preferred, in other cases spring or laminated metal sheet couplings may be preferred. If angular misalignment is sought to remedy, spring type or laminated sheet metal couplings are best.
