Spiralock fasteners? 4

[Grunchy]

I am interested if anyone has had experience with spiralock fasteners. I am considering changing out a bunch of my stuff like taps, nuts, PEM-type fasteners and so forth. My principal activity is automation equipment, on my last project I used Nordlock 2-part lockwashers but they're kind of confusing to use, and if someone misplaces them then what? The nordlocks worked fine otherwise. Much better than the split-type washers (which I refuse to call lockwashers).<br>
<br>
Oyster

 

[evmundo]

Like your self I would never call a split or spring washer a locking device, most of these devices, perhaps with the exception of the Nordlock are really shake proof devices. The only way to add a degree of locking (as no device can be certified 100%) is to either employ a nyloc or allmetal locking nut, like philidas mkV or employ an adhesive or plastic patch on the male threaded fastener, also consider a screw with serrations under the head such as a durlok bolt (SPS) although these are in the same vain as your washers.

 

[CoryPad]

I have some experience with Spiralok internal threads, as well as all the other locking/prevailing torque designs mentioned. Spiralok can improve vibration loosening resistance, although it does not completely remove the problem. The only way to remove this problem is to insure enough joint preload to resist applied service forces. If this is not possible, then thread adhesives are the best option. Anything that damages the bearing surfaces (serrated fastener faces, etc.) can result in significant problems with long-term durability.

 

[hrehman7]

Spiralock results into increased minor dia of nut threads. This might be a problem in a highly loaded application.

 

[tday]

There is always a trade-off between the potential backout torque you may gain when using some kind of locking feature located on the tapping threads and the clampload you may never realize when the screw is put into tension, because the of the quality of the mating thread that is formed after tapping.

I would like to direct you to

http://www.shakeproof.com

and in particular the round-bodied Tap/R product.

Let me know if you have any questions.

timday2002@yahoo.com

 

[wdiv]

Spiralock's threadform causes unreliable preload of the bolted joint for a given torque. May be risky for a critical application.

 

[strokersix]

How about considering old-school methods of retention. Specifically safety wire or cotters through castellated nuts?

Mike

 

[CoryPad]

Grunchy asked the original question almost 3 years ago, and hasn't logged in to Eng-Tips for over a month, so this thread has been about sharing general fastener information rather than solving Grunchy's problem. Bearing that in mind, safety wire and cotter pins are poor substitutes for adequate joint preload. They don't actually help hold joints together, they just extend the time between joint loosening and part separation. The idea is that during this time, the joint failure is noticeable and can be fixed before catastrophe occurs. Additionally, they require weakened fasteners (machined holes & slots), which is not a good solution.

 

[strokersix]

Corypad,

I agree with you 100% that proper joint design and fastener preload to begin with is the best approach.

Mike

 

[unclesyd]

I have used the Spiralok thread form in many application involving exteremly high stresses with no problems. The beauty of this thread form is the ability to reuse it in a high stress condition. I have used it on a bolt with 120k/psi stress with no problems. Care should be taken on unloading any configuration with high stress and multiple fasteners. This is true for any thread form.

 

[Grunchy]

Hiya, yeah it has been a long time since I posted that first request (more than 4 years)! Believe it or not, my internet account was not able to connect to eng-tips.com for a long long time, although a notice of each of your replies was e-mailed to me.

I got interested in spiralocks because I had heard that was one of the fundamental technologies needed to make space shuttles feasible. Everybody remembers the development of the heat-shield tiles (who can forget, now), but not a lot remember that the original rocket motors would self-destruct on the test stand due to fastener loosening, and that it was the spiralock threadform that made it work. That was way back in the 80's, I would imagine the original patents must have expired now so I wonder, why aren't more companies manufacturing Spiralock-type fasteners?

Incidentally, I would recommend Carroll Smith's &quot;Nuts Bolts Fasteners and Plumbing&quot; for anyone who has to deal with this type of stuff on a practical day-to-day basis.

In the end, we wound up using Nordlocks on the project from 1999 and to date no failure. The machine was running through 30 cycles per minute for minimum 8 hr shifts, naturally it has had regular service since then. I imagine each time it is serviced though, more and more nordlocks get mixed up.

About the comment of split-type lockwashers: they do work but only for small sizes, i.e. 3/8&quot; and smaller, and I think it is because the small screws can only withstand so much stress anyway. With bigger screws they withstand bigger stresses, at which point the split lockwashers fatigue and spread, and all the preload is instantly and catastrophically lost. I remember from the oilfield days how much failure was attributable just to failure of split lockwashers, it was substantial.

 

[subshock]

Hello,

I'm an engineer looking to use spiralock fasteners in military applications, I've studied this technology for several months and it is good to see that others are interested as well. I'm looking for someone with experience in design, installation, and performing shock testing of these fasteners in accordance with MIL-S-901D requirements. Several questions:

1) The manufacture claims that fasteners can be torqued to 75% of yield without damaging the female thread. But what about the male thread. At what ratio of female to male thread modulus of elasticity will the system become susceptible to this type of failure.

2) Can design, installation, maintanence and life-cycle costs offset the initial investments to convert over.

3) Will significant shock loadings be sufficient to permanently damage the threads thereby causing a release of prelead which then leads to the fastener coming adrift from the connection?

4) Does anyone have Junkers vibration test experience of a standard NYLON locking nut with an SPL nut? If so how does the response compare to the advertized response of an all metal prevailing torque nut?

 

[unclesyd]

A little late reading this post.
I think one thing that has been missed is that Spiralock thread form distributes the load across the threads instead of severly loading the 1 & 2 thread. With Spiralock thread form nuts we were able to eliminate fatigue and loss of integrity in several high speed applications and also were able to reuse the nuts. You can find a ream of information on testing the Spiralock thread form in the NASA archives. I also received copies of some the work from Spiralock. At one time NASA allowed the reuse of a Spiralock nut in some applications up to 50 times.

 

[unclesyd]

Still comming by. A vry interesting website.

http://www.surebolt.com/

 

[jcrowell]

We make off-road vibrators for seismic exploration and have been using Spiralock for over 25 years on most all female threads.

I agree with unclesyd that the load distribution on the bolt is probably the most overlooked advantage. I convinced myself with a 3/8 NC hole and a 3/8 Spiralock hole in SAE 660 brass. I tightened a SHCS to failure in each, with the NC female threads stripping out while the bolt in the Spiralock hole broke under the head.

One thing to caution you, most guys in the field have never heard of it and will sometimes try to clean out tapped holes with a conventional tap, thereby &quot;erasing&quot; the Spiralock.

 

[EngJW]

Hello,

Does anyone know of a website for Spiralok, or what company makes it? I have a thread form on an old drawing and it looks like a Spiralok, but there is not enough information on the drawing to make it or specify it.

Is the mating thread standard or special?

I have also heard that a Spiralok nut has a lot more slop when loosening it. Don't know if that is true.

Thanks,
John Woodward

 

[jcrowell]

http://www.spiralock.com/