Gear couplings are mechanical devices used to join shafts of two different machines. Commercial gear couplings are best for more torque transferring due to their size. Gear couplings are widely used in high speed applications for their high load transmitting capacity in applications that require high torque capacity.
Gear couplings have two shaft hubs with external teeth that are connected with sleeve of two pieces containing internal teeth. A gear coupling works like flexible spline that has sleeves and hubs moving together. Proper lubrication of the right type is required to help the gear couplings work properly.
Since, gear couplings are mechanical devices; they are subjected to failures as well. So, here we will discuss the different causes of failures of gear couplings:
Failures due to lubrication
Adequate maintenance of lubrication is extremely important for the proper working of gear couplings. It has been found that the lack of lubrication is the primary cause of failure of gear couplings.
When there is loss of lubrication between the external and internal teeth, the surface rubbing against each other leads to breakage of small metal particles. In some rare cases, you can also find fretting corrosion. As the gear continues to operate without proper lubrication, it leads to a worn out surface where 70% of teeth are worn out. If the wear is stopped immediately, the teeth will suffer severe damage. Lack of lubrication is often the result of a damaged gasket or seal, a lost lube plug and insufficient lube filing.
Gear couplings can also fail due to failure of hubs due to a blend of hoop stress produced by interference fit and high tension stress. To prevent hub fractures, you need to select couplings with the service factor in mind according to the motor capacity. You should also consider the brake involved and make it a point to select a coupling based on brake capacity.
Gear couplings operating under severe misalignment will result in wearing of teeth. Couplings are designed in such a way that it can accommodate alignment limits without metal to metal contact in seal area. Very often, lube leakage at the seal results in misalignment.
Sleeve seal end ring failures
This type of failure results from heavy loads imposed on sleeve seal cage. This kind of failure may be a result of radial flexing from increased misalignment or axial contact because of improper gap setting or hub axial float.
Flange fastener failures
This is another cause of failure that needs to be taken care of. Flange fastener failure can be a result of insufficient fastener tightening torque, some reverse load that have exceeded the flange joint capacity and system torsional vibration.
These are some of the main types of failures that will ultimately affect the working of your machine. So, to make the couplings work properly, you need to maintain the device properly.