Can you re-use a Keensert?

[dag113]

I don't mean "re-use" as in install the Keensert, then remove it, then reinstall it.

I mean "re-use" as in install the Keensert, then install a bolt into it, then remove the bolt, then install a different bolt into it. (Did that make sense?) What does this do to the Keensert? Are there any structural implications to doing this?

Any help anyone on these boards could provide would be greatly appreciated!

 

[btrueblood]

In the sense you described it, yes, you can reuse the installed insert indefinitely.

Eventually, the keensert will wear out, and the thread pitch will gradually enlarge. This effect, if of concern, could be monitored by standard thread plug gages. We saw this behavior in vibration fixtures used in production of aerospace hardware, which had threaded fasteners installed hundreds of times, using air tools. I would say the rate of wear would be no worse than any other threaded nut made of similar materials as the insert.

 

[Ron]

Yes, as BTB notes, they are "re-usable" in the way you describe.

Agree with BTB's limitations as well.

 

[jimkinney]

If they are locking inserts, there is even less re-usable life. The deformable thread type are usually good for 6-12 uses then they won't lock anymore. The threads are ok, but they won't stay locked. Locking life is even less if they are over-torqued.

Jim Kinney
Kennedy Space Center, FL

 

[dag113]

Thank you all very much for the information.

These are locking inserts, so Mr. Kinney's point is taken. My scenario should not have the inserts being used for more than just a couple of uses, though, so I think I'm still in good shape.

Regarding the bolts going in to the Keensert: does anyone have any good (and accessible!) references that talk about re-using bolts, particularly in a locking insert? Other than the fact that it's "not a great idea" and a lot of generalities regarding torque and subsequent preload, I'm having difficulty finding a source with more specifics (and especially regarding locking inserts). I'm not happy with the idea of re-using the bolts, even if it's just on a temporary basis, but I need a reference that can back this up a little better.

Again, thank you very much for the help you've already provided and anything else you might feel inclined to add!

 

[btrueblood]

Depends on the use and loading the bolts see in service. For the vib. fixtures I mentioned, we would routinely discard fasteners after one use, as the value of the fasteners was negligible compared to the hardware and test time involved.

If you are using the fastners in, for instance, a piping hydrotest to 1.5x or 3x the system pressure, it might be a good idea to discard the fasteners.

If these are in any critical location, esp. one involving life safety, I'd be inclined to discard after one use.

A simple female set of thread gages (or in a pinch, a fresh nut) works to determine if bolts have worn or stretched, and if not they can also be re-used indefinitely.

 

[dag113]

Thanks, btrueblood. Your experience and comments on safety, etc., back up my own experience and what I was thinking. My issue is going to end up being a matter of assessing risk, as the bolt cost is high in this particular application. Thanks again.