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Most machinery maintenance issues are caused when the basics of component care and inspections aren’t followed.

The process of shaft alignment is relatively straightforward nowadays, particularly with the arrival of easy-to-use and highly accurate laser alignment tools.  But technology can’t replace common sense and there is one crucial factor that should always be included in the shaft alignment process — and that is thorough coupling inspection.

Shaft couplings are simple and relatively inexpensive devices which provide an extremely efficient method of transmitting power/torque from the driving machine to the driven machine, and if they are properly sized, assembled, aligned and lubricated, they should perform well over a long period of time. However, when there are problems, the fall-out can extend beyond the coupling itself to the bearings, seals, gears and other components and lead to costly stoppages and productivity losses.

Couplings generally don’t require much maintenance beyond installation, but yet they still fail. 

Frequent and thorough inspections — which go beyond an alignment check - are crucial to ensure that the inserts aren’t excessively worn or damaged. Alignment shouldn’t go ahead until that sub-standard component is either repaired or replaced.

Here are some general guidelines for thorough coupling inspections which will see your couplings increase their performance for longer.

  • Ensure the set screws have the proper torque
  • Look for signs of wear or looseness in the keys
  • Inspect for any cracks or wear in the shaft which could be a sign that the hub is loose
  • Ensure that any coupling components are properly bolted
  • Check the condition of the guard. If it has been rubbing against the coupling, it may need to be repaired, adjusted or replaced.
  • Appropriate lubrication is crucial. If your coupling requires lubrication  don’t do what many mechanics do and let it run dry. Check for leaks and if lubrication levels are low, you may need to replace the gaskets or sealing rings and add more lubricant.

Those are some general tips for coupling inspections  here are a few more which are specific to particular types of couplings.

Elastomeric Couplings

On ‘gear type’ couplings, inspect the teeth for signs of wear, cracking from dry rot and twisting.  Replace if necessary.  Scrape away any material that has built-up between the mating teeth of the hubs and look for any dust beneath the insert which is a tell-tale sign of coupling misalignment.

On ‘tyre’ type couplings, a visual inspection is necessary to check for excessive cracking and improper bolting tension on the hubs.

Check spider couplings for excessive backlash which is a sign of elastic failure of the insert as well as looseness.

Disc-Pack Couplings

Look for cracks, waves or other deformities on the disc packs (shims) and replace them if necessary. Worn hub bushings can often be replaced without needing to replace the coupling itself.

Grid-type Couplings

Look for signs of wear in the flat faces of the coupling, the turns and in the hub teeth themselves. If a pile of dust appears when you’re removing the shell, you will need to replace the whole coupling, including the hubs. That’s a clear sign that maintenance personnel haven’t done their job properly and checked on the lubrication. 

Gear Couplings

These types of couplings also require lubrication, so check that levels are appropriate for optimum performance. Also inspect for signs of wear on the teeth and that the bolting torque is correct.

Couplings should be given the same levels of attention and good maintenance practice that are afforded to other parts of the machinery such as the pump, gearbox or bearing assembly. They’re important to the continued operation, reliability and longevity of the machine  and regular and thorough visual inspection of a coupling or coupling insert is a crucial element of shaft alignment.

Of course, having the right technical equipment is a key factor in the speed, efficiency and quality of the inspection job  and for the best results, you should match the instruments to your particular needs. 

Jason De SIlveira, is the founder, director and company secretary of a specialist equipment rental and services company, Nexxis Pty Ltd.

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