Categories: Machinery Maintenance,Other Topics,Shaft Alignment

When Should You Replace the Coupling Insert?

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By on March 30, 2017

In industry, many couplings utilize an elastomeric insert or element.  This type of coupling has many advantages, among them:

  • Ease of replacement
  • Ability to absorb torsional loading
  • No need for lubrication
  • Tolerant of slight amounts of misalignment
  • Inexpensive

It is important to remember that even though these elastomer couplings can be tolerant of misalignment, the bearings and seals are not, and as such, precision alignment (normally closer than the coupling manufacturer recommends) is necessary.  Even with excellent alignment, the coupling element will eventually need replacement.

So, when should the elastomer be replaced?  While each manufacturer has good recommendations (read that little piece of paper they put in the box!), here are some good indications that is time to replace the element.

OBVIOUS SIGNS OF WEAR

Remember the most common reason for wear is misalignment.  If wear is excessive, then the ability of the insert to transmit power is reduced.

   

TORSIONAL DAMAGE

On two piece coupling inserts (or one piece inserts in which the two halves are vulcanized together), you may notice a twist in the seam between the two halves.  When this twist becomes excessive, the width of the coupling is decreased, which could result in a loss of tooth contact on the hubs.

 

ELASTOMER FAILURE

When some elastomer couplings have run beyond there capacity to transmit power, you may see some of the “legs” of the insert gone, or see the metal jaws making direct contact.  In these cases, the entire coupling should be replaced.

In most of these photos, coupling damage is obvious, so one may be led to believe these are extreme examples.  But all damaged couplings in these photos were taken by VibrAlign trainers, while teaching training classes in the field.  So, these types of failure do occur on a regular basis.

To minimize such failures:

  1. Make sure the proper insert is being used.
  2. Perform precision alignment-every time.
  3. Ensure proper installation and spacing.
  4. Inspect couplings on a regular basis.
  5. Replace them as needed.

Save Time. Save Money. Save the Machine.

 

About the Author

Stan Riddle joined VibrAlign in 2008. He has over 35 years experience in aligning industrial machinery. Stan received his AAS Degree in Machinist Technology from Surry Community College in Dobson, NC, and also holds a diploma in Industrial Systems Technology from Forsyth Technical Community College in Winston-Salem, NC, where he was also an instructor in the program.

Stan began his maintenance career working as a machinist and millwright for companies such as Weyerhaeuser, R.J. Reynolds, and Tyco Electronics. He also has over 25 years experience in Predictive Technologies, such as vibration analysis, thermography, oil analysis, and ultrasonic inspection. He is a certified Level III Vibration Analyst with the Vibration Institute, and is a Past Chairman and Board Member of the Piedmont Chapter.

Stan and his wife live in Yadkinville, NC.

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