Using Nord Locks correctly takes planning

[wawrzynskivp]

Hello All,

In another forum the discussion of swapping out safety wires with Nord Lock washers was covered. If acceptable it seemed a seamless swap, but there is a difference.

We know that the choice of using a friction nut (example: nyloc) will increase the required torque to achieve the design bolt tension for any particular fastener compared to a standard nut. (Friction nuts have their own friction to overcome)

Nord Locks have their own friction too.

Using our standard torque values on a Nord Lock will result in up to 20% less fastener preload. Nord Loc offers this may be acceptable, but it's up to us to decide if that is the kind of work we want to do. If you want design preload or bolt tension you need another torque value when adding Nord Locks.

Consider Nord Locks to be friction washers (yes, yes, Nord calls them tension lockers). Just like friction nuts, friction washers require additional torque to achieve design bolt tension:

https://www.nord-lock.com/insights/...i-change-my-tightening-torque-with-nord-lock/

 

[tom_AZ]

Planning?

Hello All,

In another forum the discussion of swapping out safety wires with Nord Lock washers was covered. If acceptable it seemed a seamless swap, but there is a difference.

We know that the choice of using a friction nut (example: nyloc) will increase the required torque to achieve the design bolt tension for any particular fastener compared to a standard nut. (Friction nuts have their own friction to overcome)

Nord Locks have their own friction.

Using our standard torque values on a Nord Lock will result in up to 20% less fastener preload. Nord Loc offers this may be acceptable, it's up to us to decide if that is the kind of work we want to do. If you want design preload or bolt tension you need another torque value when adding Nord Locks.

Consider Nord Locks to be friction washers (yes, yes, Nord calls them tension lockers). They too require additional torque to achieve design bolt tension:

https://www.nord-lock.com/insights/...i-change-my-tightening-torque-with-nord-lock/

Interesting, thanks for posting. However, I'm not quite sure how to apply this. In the link, I see only metrics, and there's also a need to choose bolt grade. Difficult to extrapolate those to Cad-plated SAE AN bolts without more info. It would be good to know, and perhaps someone does, if there are curves for torgue v pre-load, e.g. if we increase torque by 10% on a certain size bolt, what is the percent increase in pre-load. I gather there are some guidelines about pre-load (stretch) v degrees of turn, but that those are used more in automotive/racing applications v. aircraft.

Rule of thumb? Tighten to the top of the indicated torque range? Add "x" percent? I wonder how many of us actually measure the frictional torque of each nylock, including new v. previously used, rather than apply an estimate to our (just calibrated of course) wrench settings.

 

[wawrzynskivp]

Interesting, thanks for posting. However, I'm not quite sure how to apply this. In the link, I see only metrics, and there's also a need to choose bolt grade. Difficult to extrapolate those to Cad-plated SAE AN bolts without more info. It would be good to know, and perhaps someone does, if there are curves for torgue v pre-load, e.g. if we increase torque by 10% on a certain size bolt, what is the percent increase in pre-load. I gather there are some guidelines about pre-load (stretch) v degrees of turn, but that those are used more in automotive/racing applications v. aircraft.

Rule of thumb? Tighten to the top of the indicated torque range? Add "x" percent? I wonder how many of us actually measure the frictional torque of each nylock, including new v. previously used, rather than apply an estimate to our (just calibrated of course) wrench settings.

That's the rub, the unknown right?

I wrote to Nord Lock to see if they would provide AN/NAS numbers. It's a sliding scale based on wear, probably why they post 10-20% reduction in tension.

To know on our own we can measure the stretch of the intended fastener under like conditions. This is after all the most accurate way to tension a bolt.

Unless we find the designed clamping psi at that particular fastener and do the math we can't know whether that 20% less number is meaningful. Our general rule unless prescribed elsewhere is to provide normal design bolt tension.

The Safety take away is to know that Nord Locks can not be expected to perform like plain washers. Nord Lock website will help with UNC Grade 5, 8, 9, and various metric sizes. Without good AN/NAS numbers do we know how to properly use them?