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September, 2014
MAINTENANCE MINUTE
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Welcome to the Centrifugal Blower Maintenance Minute,  
the 60 second newsletter designed specifically for centrifugal air & gas blower operators.  Each month we will feature a different aspect of service and maintenance to centrifugal blowers. We will review operation, troubleshooting, actual case histories, and answer reader questions.  

Locknuts & Lockwashers 

 

Locknuts are used to locate bearings and other components onto the shaft. Lockwashers are "the simple, stable, reliable, fastening element" to hold the locknut in position. Both are used in centrifugal blowers, motors, and some pumps. If not installed correctly, premature bearing wear and catastrophic blower failure can occur. Such a simple device is so very important to the health of your equipment.

The bearing is press fitted to the shaft(interference fit), and fit tight against the shaft shoulder. The lockwasher has a "tang" that fits into the shaft keyway to keep it from moving on the shaft. It also has "tabs" all around the washer of which one is selected to be bent into the locknut grooves thereby holding the locknut from moving, or loosening, from the shaft. The locknut has 45O relief angle machined on one side that fits into the concave shape of the lockwasher. This allows the nut to be firmly seated against the lockwasher, which is firmly against the bearing inner race. So many times I've found the locknut and/or washer installed backwards jeopardizing the required tight fit.

If the concave of the washer is facing the bearing, a tight fit to the bearing cannot be achieved. If the locknut relief is facing out, the tabs cannot lock the nut in place effectively. Simply not locking the tab will allow the nut to become loosened. I've found all of these situations when called to replace bearings on blowers and motors. An expensive solution to a mechanics' error.

Lockwashers are stamped with a letter and number designation, such as W10, W12, or W14, which corresponds to the shaft diameter and bearing size/number. A 6310 bearing uses a W10 lockwasher. Similarly, the locknuts have a N10 designation for the 6310 or 6410 bearing, and so on. Metric nuts use the KM designation. Metric and inch lockwashers are used interchangeably. Metric and inch locknuts are not.

When shafts are manufactured, the threads are created and verified correct by fitting the standard locknut to the shaft. Many manufacturers include the locknuts with each shaft. An off the shelf locknut is supposed to fit the shaft, but, in my experience, it is not always true. The standard thread for locknuts N6 thru N14 is 18 threads per inch. After that, the designation for locknuts can change to AN, using 12 threads per inch, and a different pitch. Some impeller locknuts can be N or AN. They are not interchangeable. An N24 locknut cannot be used with a AN24 thread.

Locknuts are designed to be tightened with a spanner wrench. If you can't get a spanner on, the old hammer and blunt chisel works. The nut is tightened 'firmly'. If you have a special locknut socket tool, you could measure the torque, but I have no idea where you could find a torque setting value.

It is best to replace locknuts whenever you change a bearing. It is called preventative maintenance. Invest in PM, it will save you money!


 


 

 


© Copyright 2014 Snyder Technical Services, LLC. All Rights Reserved

                                                 --- Bill Snyder

Maintenance Minute is published each month by Snyder Technical Services, LLC and is based on the work of former Lamson National Service Manager, Bill Snyder.  Should you have any questions, or problems to discuss, please contact me. 
 
Sincerely,
 
Bill Snyder
Founder - Snyder Technical  Services, LLC 

Next Month: 


 

  

Blower Expansion Joints & Sleeves 

 
Thought for Today:

                                  

  

  

   A banker is a fellow who lends you his umbrella when the sun is shining and wants it back the minute it begins to rain. -- Mark Twain


 

             


 


 

 

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