Fastener Follies : People Just Don't Understand.

One example is trying to establish critical location with a standard socket head cap screw instead of using dowel pins.

What about shoulder bolts?

Anyways, not knowing the full story, share it and enlighted us.

There are too many stories for me to list.

Yes, a shoulder bolt would have worked out in that particular situation.

The intent of starting this thread is to pull stories from the collective here on issues they have had with co-workers or customers not understanding the proper application of threaded fasteners.

"... customers not understanding the proper application of threaded fasteners."

What? Why can't I just ream it out and rivet it? What do you mean no warranty?

A handy janitor doing maintenance in a facility can create an absolute nightmare. As you say in your OP, not understanding fasteners, but acting anyway, creates several problems.

Hey, if I'm having trouble with a threaded fastener, I just get a bigger hammer.

Also there??...

I get a chuckle out of people who use tie wired bolts thinking that the tie wire will keep the fasteners from working loose.

What's the last thing you want to hear....There's a problem with those prop bolts giving way...

Incident report:

We have several reports on the Lazier of the bolts holding the prop on the hub shearing off. Laboratory testing showed that these bolts are the proper bolts but that they had failed from bending, following progressive fatigue. The bolts had been installed approximately 1 hour prior to failure, and had been torqued to the proper requirements.

In 1984 Ultraflight Sales Ltd. issued an alert warning of the possible vibration problems associated with using non standard propellers on their craft.

We also have reports of prop bolt failure on 64 inch props, when used on the Beaver, Maxair and Chinook aircraft.

Suggestions:

Sorry folks your on your own on this one, as far as the Lazair goes.

A solution that has worked for the other aircraft mentioned above is the use of the GSC systems ground adjustable propeller. This propeller uses an aluminum hub with 6 bolts, plus 6 dowel pins, which screw into the Rotax reduction drive, flange and fit into blind holes in the back of the propeller hub. These dowel pins relieve the bolts of any stress.

http://www.ultralightnews.com/safety_bulletins/lazair_propbolts.htm

This is a prime example of something I have seen over and over.

My business partner, whom is an experienced and talented MDE calls it:

The wisdom of shear pins.

The crux of this issue is that bolts themselves should never be put into a situation where they can be put into shear, the friction between two bolted components is what make this stuff work.

Let alone employing them is a fashion where vibration is clearly a major factor.

For those of you in the know, adding vibration to a failure analysis puts it into the realm of Phds who do nothing but that.

Hey I think wow, engineers really did that on those planes?

It's like that old commercial here in the US where the punchline is "People do."

GA

Thanks Solar Eagle!

Fatigue failure as noted in Solar Eagle's post is quite common. It's often caused by people "properly torquing" fasteners (with calibrated torque wrenches, even) and assuming that all is well. They expect that every bolt in the same flange will consistently apply the same clamp load to the joint. Hah! Ludicrous! Some of these "properly torqued" bolts may be too loose while others may be too tight

Too many put the reliability and integrity of bolted joints on hopes, guesses and prayers. Sadly, this continues to be advocated by not only "conventional wisdom" but also by manufacturer's often-useless torque specs and misleading assembly guidelines and regulations.

This is an excellent and important point raised by BoltIntegrity, and needs a thread of it's own...The science of consistent torque on critical bolts has been tweaked as of late, and the results are eye opening to say the least...

GA

You are so damn right on this point, well put. Belongs to the name?

I see almost every day where people are using torque wrenches, completely blind to the correct usage, car wheel bolts for the best example...I could go on and on.....but I am sure most people here know what I am talking about already.....

Indeed, good point, SolarEagle. However, your use of the phrase "consistent torque" is what is at the heart of this matter. Don't feel badly; Almost everybody else would have said the same thing.

It isn't consistent torque that one should be concerned about but rather consistent bolt stress. When seeking to acheive consistent bolt "tightness" on a flange containing the same type and size of bolts, it's often necessary to apply different levels of torque to each fastener. Alas, this is often sacrilege to those who've "been swinging wrenches for years"

Yes, the word torque has nothing to do with the actual amount of force applied to the joint by the fastener.

Yes maybe preloading is better terminology....Here's a video I saw on HP tv talking about ARP lube...

http://www.youtube.com/watch?v=6-XXVk_vwKw&list=UUMXg56yV409b62PCJFfWr7w&index=10&feature=plcp

I have since years professional contacts with machine manufacturers among others automotive and airplane producers. I dare say that in comparison with the risk level their knowledge is very very low and incomplete. I tried several times to explain the physics of bolting but speaking to a wall would have brought same results. How often I heard but we do so since many years and have no complains why should we change? In fact the complains were there but due to the segmentation of informations from the field it did not come to the right ears. How often having a discussion with top managers (technical or development) did I got the answer you exaggerate bolting is a simple technology you put in place put a spanner on and tighten strong enough and that's ALL!

Years ago incoming parts were quality check at the assembly plant, now this is shifted at the manufacturer place. results are some times funny but all times do cost a lot of money in repair which could have been saved.

Basic principles are not considered. For instance how should be designed a side force holding assembly ? What happens if one part has minute sliding? How does an assembly lose its pre-load and why ? What can be done to avoid it ? Which washer should be used ? But also how fast should a nutrunner turn ? Which is the best assembly technology considering the assembly itself, the assy conditions, the materials the working conditions and the economical aspects ?

I shall give only one example which says a lot. A plant manager who supervised the assembly of subassies for a car noticed that although he respected all engineering specs as value and tolerances he had a small number of broken bolts a week. The number was very small in comparison with the number he had to assembly but it did cost a lot of labor to take off the broken parts and verify the threads and assembly again. I was asked to give an solution. When I computed with the values engineering gave at the specified torque ALL bolts should have lost their heads! The reason only a few broke was that the bolt manufacturer delivered with the specified quality bolts with a lot higher mechanical properties so that only the tail of the tail was in the dangerous zone and broke. But why did it happen simply because the engineer did compute the bolt only as tension loaded and neglected totally the shear due to the torque. The engineer was not a low class one but a "specialist" of bolting! Is that an answer ? I could give ten.

GA

Thank you. That's the right stuff.

Nick clearly has great insight into the woes of production line bolting issues. My focus is somewhat different: Bolts of a significantly larger size in service in some of the nastiest most arduous conditions imaginable. I can assure everybody that this theme of " Fastener Follies : People Just Don't Understand" exists in Heavy Industry situations where often the integrity of a single bolted connection is all that prevents Refinery process units from exploding, Cranes from toppling over, Mills from shaking themselves apart, Turbines from tripping, Reactors from leaking, hydro head covers from lifting and on, and on, and on....

I can an example in your field. I was recently on a exhibition and had a discussion with the manufacturer of a special type of bolt. He told me that some wind turbines loose about 30% of pre-loading within a short period of time after start of use and that could be a high risk situation. When we went deeper I saw where this came. It was (and still is) a design error of the whole assembly which does not respect basic rules and shows that the designer does not have any understanding of how an assy works under load. He surely made excellent FEA simulations but this is not enough since a simulation does not tell you how to interpret results.

I have found bolts almost loose:

because someone messed up with unit conversion for the local spanner.

because the foreman considered that stepped/crosswise tightening procedure was too slow, and just round-the-clock way was perfectly suitable.

and also almost elongated:

because someone thought that every bolt must have "good grease", and this grease is better than the "anti-seize/assembly paste" indicated in the instructions.

because a mechanic (with good will, the best!) ensured that every bolt was tightened properly with the torque wrench. Did not stop tightening till the wrench "clicked" at least 8 times on each bolt!!.

In other side of the assembly world, structures, I have at hand an 80m height structure, where machines were assembled, levelled and aligned, only to find that the bolts are not tightened yet in many of the structure links.

Shown here...

It has taken one month to convince the customer that it is absolutely necessary to tighten all links properly and, once finished, re-check/align/level the machines, prior to commissioning.

It seems that no inspection of the work was carried out above say, 3rd floor, and the contractor flew.

GA

Oh the humanity!

Brilliant pictures! I'd like to see more if anybody has any like this!

A note about your comment "and also almost elongated:" Well, we had better hope that they were elongated. Otherwise they wouldn't have been applying any clamp load at all. Don't get hung-up about bolts being elongated The only time that there is a problem is when they've been stretched more than the point commensurate with the required preload.

Dear Boltintegrity,

When I see, with my own very eyes the elongation... I would say that "we pass the point of no returnnn".(here music from the Phanthom of the Opera)

When I need to loose some suspicious bolt, I use a torque spanner set just at 50% of the nominal preload, 75%, 100%, 125%...etc till it comes out.

Sometimes you find out that the tightening was not exactly as it should be...

Yes Abelmh, when you can visually see the relative elongation, that is indeed the point of no return

Did you run? Did you get off of the platform as quickly as possible? I certainly would have!

"I do not know what quality is this extraction stud, but seems strong enough to me, uh???"

"WTF??.. "

"OK smarta**, we will get the black one 8.8 you said, but no special design washer, uh?, this thick flange will do!! See? is atomic-proof!!"

"Uhh??..."

Dear all, I do not want to cope the thread with pics, but I would like to have the input of SolarEagle about this. It was noticed during the approach and landing, from the window.

After landing, I asked the captain to have a peek at it.

What do you think? Extruded by overtightening?... Ripped?... It still worries me.

1.Normal one. (I do not know the technical name of this part of the wing)

2. The one.

3.A closer view.

I have some pics more of this issue, just in case.

Yes looks bad, maybe hit a bird who knows....needs to be taken apart...definitely not flight worthy...

Using mild steel bolts to hold rolls into a piece of equipment which spends most of it's life in a steam chamber. Then cutting back on maintenance because it costs too much and leaving the equipment in the steam chamber for more then a year longer the its supposed to. When we finally got it back to the workshop the only thing holding the rolls on was rust and ignorance. At which point we had to spend a week welding all the bearing blocks onto the frames of the the other equipment so their rolls did not drop.

Another one for the accountants, they made us buy high tensile bolts from a local supplier instead of the recommended supplier over seas, but the drawing that was supplied by the original supplier did not specify the heat treatment of the bolts (I wander why ). So when we recieved these non-heatreated bolts, anyone want to guess what happend when we tried to torque these bolts up?

1.Quick calls.

2.Swearing.

3.Panda eyes from the accountant.

4.Double price (at least) for express delivery of the right bolts.

5.Overtime to compensate the delay due to the failing bolts.

A few pictures from a vast library:

Wrong material following a cost reduction!

Wrong material delivered but correct quality marking.

Modification of surface treatment without modification of tightening procedure. Friction coefficient from 0.12...0.14 went down to 0.08...0.1. Material is high strength steel thus the type of fracture. The magnified view shows where the crack started= at the root of the first free thread as expected since it is the highest stress region!

In fact as a comment to the structural problem this problem is allover the world present which lead to the development of a technology dedicated to this kind of assembly.

A special tool closes the tightening torque loop between nut and bolt without involving the structure. The end (left in the picture) shears at the groove level and so the bolt is tightened to a torque only function of material shear limit and groove tolerances. Although - Boltintegrity will say- friction dispersion is not compensated at least it can not be applied 7 times a torque with may be blocked limits. It is for metallic structures a very well accepted procedure. For instance the hall where AIRBUS are assembled are build with this technology.

As for vibrations the situation is not as bad as many think. A good designed assembly with the RIGHT washer can keep for ever! Technique evolutes but many are not well informed or even worse do not inform themselves since bolting is simple and every body knows a lot more than required!

Yes, I do have something to say about this ...

Consider a "sprung" joint like the ones in Abelmh's post. Granted, these likely sprung after poor assembly but if you had one where a gap existed at assembly due to deflection or surface irregularities, a significant amount of the pre-set torque would be needed to close this gap. Torque then continues to be increased until the spline shears off as designed. Unfortunately, in such a situation, it will happen before the required bolt stress has been reached. Hence, the fastener will be too loose. Yet, everybody assumes that it is tight enough

One cannot put blind faith into design alone. Nor can one assume that out in the real world, most of the critical but oft-ovelooked variables will be as controlled as they 'usually' are on a production line. Without fully understanding and appreciating the "down and dirty" practical aspects of joint assembly, the picture can never be complete.

I totally agree ! In bolting it is really the problem to imagine before it happens what could have been distorting the ideal conditions assumed many times for design. But this is valid for all concepts where reliability is a must.

One example is Fukushima nobody imagined that a wave higher than 6 m could occur!

What I noticed in structural assembly is that very often there is a first step with normal bolts to put the parts in contact and correct relative position and after it the TC bolts are used, the "normal bolts are taken off and replaced by TC bolts.

It is the same way used in the Taperlock assembly although the applications are so far one from the other the basics are the same.

I read once more your remark. In fact if the spline sheared this means that the force has been reached but here is the BUT. Since plates are not in contact the assembly has a lower stiffness which leads to an increase of load variation in the blot and reduces its life expectancy since load variations are more important. Here is the real danger as you know an assembly works properly ONLY if the stiffness ration Bolt/Parts is low enough under a threshold. If this increases (due to the fact that clamped parts are more compliant) asymmetry of cycle for bolt changes in the direction of higher fatigue sensitivity.

Indeed! I think (I apologize but I find it difficult to follow your prose. I'm sure that if this were a French-language forum if would facing the same comment from you).

The "bottom line" is that many bolting processes place the safety and reliability of a critical joint on guesses and assumptions made before the joint is even assembled . To my rather simple mind, it seems much more logical to verifying the effect of the tightening process afterwards.

But then again, perhaps those who disagree are, in fact, absolutely correct and what I've said is a steaming load of kack! In that case, they should apply the same "logic" and consult their Oracles, read their tea leaves, throw their chicken bones, read their Tarot cards (or do whatever else they usually do to predict the future) and then run out to reserve the winning numbers for next week's lottery.

When I read again my explanation I can only share your comment. I was in a hurry and did not make the effort to read it again and make sure it is clear enough!

As for the "others" I believe we share same opinion!

This is one of the best blogs I have seen on CR4 for a long time!

Thanks to all concerned.

No bad manners either!! Probably because the professionals are here only......few amateurs.

PBS has a video on the in-outerspace repair of the Hubble space telescope's electronics.

If I recall properly, the ground training took about two years and involved numerous specialized jigs/tools to get the job done.

The technical people blast off, rendezvous with the telescope craft, exit their craft, start the repairs and part way through one of the bolts breaks!

I've had my fill of broken bolts on automobiles and farm machinery. But those incidents were always subject to corrosive environments.

Here's a NASA design in an outer space environment with NO corrosion (no moisture, no oxygen) and a bolt breaks as its removal is attempted.

Wonder what was really wrong.

The reason are many and none to due with corrosion, poor or improper assembly on earth, temperature variations...