bearing retaining nut torque specifications 1

[Fugeguy]

Does anyone know if there are standard recommendations for these types of lock nuts?

http://www.whittet-higgins.com/part.php?series_id=43

If we are using the nut to preload the bearing we can calculate that, however if it is just retaining the bearing what is the recommended torque to keep the nut tight?

As an example- here is a good reference for typical bolts:

http://www.efunda.com/DesignStandards/screws/calc_bolt_torque.cfm

Thank you.

 

[JJPellin]

In this application, the ideal torque is defined for the bearing not for the nut. The bearing catalog should include the torque recommendations for these nuts. We use nuts that are in inch sizes and we torque them based on the table from the SKF catalog. The torque ranges we use are these:

Nut Size Washer Size Torque Value Acceptable Torque Range
N-06 W-06 45 Ft-Lbs 32 - 60 Ft-Lbs
N-07 W-07 55 Ft-Lbs 39 - 70 Ft-Lbs
N-08 W-08 65 Ft-Lbs 50 - 80 Ft-Lbs
N-09 W-09 75 Ft-Lbs 64 - 90 Ft-Lbs
N-10 W-10 85 Ft-Lbs 67 - 100 Ft-Lbs
N-11 W-11 105 Ft-Lbs 82 - 125 Ft-Lbs
N-12 W-12 125 Ft-Lbs 99 - 150 Ft-Lbs
N-13 W-13 155 Ft-Lbs 131 - 175 Ft-Lbs
N-14 W-14 175 Ft-Lbs 152 - 200 Ft-Lbs
N-15 W-15 210 Ft-Lbs 173 - 250 Ft-Lbs
N-16 W-16 235 Ft-Lbs 197 - 275 Ft-Lbs
N-17 W-17 275 Ft-Lbs 222 - 325 Ft-Lbs
N-18 W-18 310 Ft-Lbs 248 - 375 Ft-Lbs
N-19 W-19 350 Ft-Lbs 277 - 425 Ft-Lbs
N-20 W-20 410 Ft-Lbs 345 - 475 Ft-Lbs


For metric nuts, the bearing manufacturer should also supply appropriate torque ranges. We have been torquing these nuts with a particular procedure for 6 months or so and are pleased with the results.



Johnny Pellin

 

[Fugeguy]

Thank you.

I found a similiar table on-line here:

http://www.uiitraining.com/b51a/300/eer524t.htm

Probably does not matter whether it is a metric or inch locknut? There are thread pitch differences but these are just to be used as "rules of thumb" to be used when the application does not warrent more extensive study.

 

[caoimhin1]

It shouldn't really be an issue. If you are using the tab (star) washer along with the locknut, as in your link, then the tab on the star washer which slots in the shaft combined with the tab which slots on the nut should keep everything in place and prevent the nut from loosening. So long as there is no slack, with a KM lock nut and washer the torque you apply doesn't matter.

 

[caoimhin1]

I should add, the main reason for using the lock nut and tab washer combination is so that you don't have to worry about torque...makes bearing assembly much easier. You do however have to machine that slot in the shaft.

 

[JJPellin]

My experience is a bit different. We started torquing this nut on all pumps that use a back-to-back pair of angular contact thrust bearings. We did not do this to resolve a problem with the nuts coming loose. We did it to address a problem with the nuts being over-tightened which can affect bearing pre-load, distortion of the bearings or shaft. I think torquing this nut is a good practice that promotes a culture of quality.

Johnny Pellin

 

[caoimhin1]

Yes I agree on that ... universal angular contacts are a different case. You need a minimum tightenening level to ensure the preload gap is closed.

 

[lowdrag]

The clamping force of a locknut can vary widely based on the shaft and locknut thread condition and lubrication applied. Back in the mid 80s the railways brought a problem
of fretting wear on the radius from the bearing seat diameter up to the wheel seat diameter to the bearing manufacturers. At the back of the bearing there is a fillet ring with a radius equal to the axle radius. The double row taper roller bearing has a spacer between the cones that provides a set clearance in the bearing. The testing program found some curious variations in clamping force when the three blots in the end of the axle were torqued to the specs with new wrenchs and regular verification during the program.

We then tested with bolts provided by the Railway shops as they would have cleaned them and applied them to the rebuilt axles. The clamping force values varied enough to cause concern. We then removed the bearings from the test axles, and reassemble and tested the same bearings but the bolts had been immersed in oil prior to installation the clamping force averaged 65% greater with the same torque measurement. The shops now oil all bolts.

Angular contact bearings are supplied as "Universaly ground spec" which means they can be paired face to face, back to back or in tandem. However, these paired bearings are supplied with axial clearance, zero clearance, light preload, medium preload and heavy preload which is stated in the suffix marked on the bearing.

If you mount a pair with medium preload in back to back arrangement, when positioned on the shaft by normal heating and shrink fit assembly, there will be clearance between the inner side faces of the bearings. When the lubricated locknut is tightened with a torque wrench, there should be a rise in the reading and then a sharp drop as outboard ring shifts and the two rings come together. The nut is now tightened till the torque value is reached.

 

[rmw]

JJPellin,

Is this with or without the use of a tabbed lock washer? And if with, how do you correlate the correct torque with getting a tab positioned for locking? Do you have a method or procedure?

rmw

 

[lowdrag]

lowdrag
JJPelin
The table shown earlier in this thread is typical of torque range values that you would use with a tab washer application. In cases where a specific torque is used, locknut designs such as the SKF "KMTA" or Whittet-Higgins locknuts are used. These are common in high speed precision machine tool spindles. The design of these locknuts have their own locking mechanism built into the thread area, and the abbutment face of these nuts is more accurate relative to the thread.

 

[Tmoose]

"it is just retaining the bearing"

What is the loading, and what is the guaranteed ID and OD fit?

 

[lowdrag]

lowdrag-(Mechanical)
The application of this type of locknut is used in angular contact bearing arrangements that are back to back. When the nut is correctly secured, the preload is set. For the rebuilders of spindles, they usually apply the specification of clamping force from the machine manual. If the machine is older and no manual is available, they depend on the experience of known application information and record the values on the work order for future refference.

The loading can vary depending on the application.
For O.D. or I. D. tooling grinder spindles, the loads are relativly light, but rigidity of the spindle shaft is critical to prevent chatter on the work surface
Milling spindles vary from light end mill cutting to heavy cuts with Face Milling cutters that are used for hogging of material. Also motorized lathe spindles can have light or heavy loads.
Generaly for milling and and grinding spindles, the shaft fits are js4 and housing fits are JS5 or JS6.
Lathe spindle fits are dependent on the actual usage of the machine and would be specified by the the machine builder in conjunction with a bearing company Engineering department. The use of these special locknuts is for the accuracy of the squareness of the nut face to the shaft thread so there is a positive uniform contact against the inner ring side face.

 

[Tmoose]

I did not see what Fugeguy's application is.

Lock nuts can't be trusted to "retain" a bearing inner ring under many loading/operating conditions. The shaft and housing fits (clearance, interference, how much ) need to be carefully considered. The nut also has to provide clamping in excess of the thrust involved.

With info like which race rotates and direction of loading (If belts or gears are involved, gravity, etc) the ID and OD fits will initially be be determined from rules like this -

http://www.maintenanceresources.com/referencelibrary/bearings/rbshf.htm

If a machine tool spindle's speeds are real high some extra interference will be required, and specified to ensure the inner ring centrifugal growth won't result in clearance. The "tight" inner ring fit required by high speed will increase preload, requiring an adjustment to bearing face offset or spacer offset to decrease nominal preload and arrive at the desired installed preload.

 

[JJPellin]

The torque values I included above were for a standard lock nut with a tab lock washer. There is a range for the torque to allow for the possibility that you might need to go a little bit further to get a tab to line up with a groove in the nut. We have a procedure for this task, but I don't have access to that just now.

Johnny Pellin

 

[Fugeguy]

I was just looking for a good "general" reference and did not have a specific application in mind.