Torque Question

You don't give bolt size or number, or what is being bolted, or the accuracy required.

My experience is in structural steel where we used twist-off bolts or tension indicator washers. We looked for an open hole to decide if a bolt is missing.

Sorry I should have been a little more specific....

This will be used in the repair and overhaul of aircraft engine accessories. The values could possibly be anywhere from 10 to 300 inch pounds.

To count? By weight

No, not by weight....by number of completed rundowns.

I think this may be too cost prohibitive and have too many variables involved to be productive and accurate. What I am dealing with is trying to reduce the amount of human error....ie forgetting to completely torque a fastener...

Any best practices to share from anyone?

Good old fashioned torque pattern. Mark the first bolt and keep going around the pattern until you reach the first bolt again. I watched my Dad do this (A&E) when I was a boy. The trick seems to be that you don't interrupt the process once started.

Okay, was only a partial answer and a fishing expedition I suppose.

The method used to apply torque; the specific tool, may be helpful in advising a solution. But regardless any tool would be expected to use a reasonably consistent amount of energy during the course of torquing each part. If the amount were outside specific limits either a fastener were missed or is operator error.

Am I making sense?

NO!

Look at what Bolt Integrity wrote, energy is NOT directly related to pre-loading. If friction changes then you can have same energy consumption and still ALL bolts loose.

In the torque range mentioned above I indicated the best OBJECTIVE approach all others are subjective since the operator is involved and which ever procedure you use the operator can make an error and the quality is not guaranteed. In such operation the quality is conformity to reload spec and safety that ALL fasteners have been tightened the right way.

That is true....you have to allow for the dummy that cross threads the bolt, or lubes it when it calls for a dry value...ect....

Low tones, low tones...

Precisely the reason parameters should be set to warn of these factors.

Use pre-lubed bolts.

If a fastener were cross threaded the energy variable would be exceeded and an alert issued.

Any assembler will have a fairly consistent pattern of movements involved in repetitive evolutions. So parameter adjustment maybe needed and saved for each assembler.

Hello Bwire,

You wrote:

"If a fastener were cross threaded the energy variable would be exceeded and an alert issued"

Not really...

The energy variable would never be exceeded because, as soon as one reaches the desired level, "tightening" would stop . Alas, in spite of the correct torque being applied, the fastener would still be loose!

You will find tightening a cross threaded fastener requires greater energy sustained for a longer time than when correctly threaded.

More effort is required, try it yourself.

Mr Bwire,

You wrote,

"You will find tightening a cross threaded fastener requires greater energy sustained for a longer time than when correctly threaded"

You're absolutely correct: Of course it does!!

But, the point is that you would stop the clock when you've reached the desired torque. You wouldn't spend any more time trying to tighten the fastener than usual! Exceeding your expected time would only happen if you apply more than the specified torque in order to generate the correct preload. However, anybody who is too stuck on simply "achieving the proper torque" and thus can't understand what's actually happening to a bolt when it's being tightened, won't even get to that point: The fastener would remain loose.

It should be noted that the opposite can also occur: If the threads are too loose or, if somebody has applied too much lubricant or applied a lube which results in less coefficient of friction, the fastener would be over-tightened beyond the desired preload!

I have tried it. Properly. Many, many times

Thank you for the discussion.

Let's backup a bit, we are thinking of using both time and energy? Correct?

A fastening event when observed using a set standard could be qualified to use a certain degree of energy initially with a gradual increase of energy within a reduced time frame as the fastener is properly preloaded. When improperly threaded there is the need for more than usual effort initially and if detection were possible stopping the tool is too.

I am sorry to have to insist, you try to apply theories where practice already solved the problems. I do not know which your experience with bolt technology but I doubt that you have large experience in series production as for instance automotive. The discussion is very interesting since it shows that you do not accept to be wrong.

Bolt integrity due to his activity has a lot of experience in big bolts (especially) but much of it -with exception of tools- can be used for the torque domain mentioned as required for the original message.

For your information there are -for pneumatic driven tools- devices which accept a "teaching" and analyse the torque curve, the time and last but not least if a bolt was tighten for instance twice. Of course they also count the number of successive tightenings as the request was. The only inconvenient is that the precision of the result is less the one expected for aeronautics. As far as I know such devices (boxes) are offered by IR. Those devices (as also the suggested electrically driven and piloted nutrunners) analyse the torque versus time derivative for recognition of problems during the operation.

Thank you, I am not familiar with current methods of series production as you've stated.

I'm an old school machinist with experience in aeronautic, automotive, gas and steam turbine propulsion applications and bolts yes.

Hello Mr Bastard,

A couple of things:

As in a previous answer, a cheap'n'nasty way of ensuring that each fastener has been "torqued" is to mark it after the fact. However, if you want to be sure that the landing gear or whatever else you're bolting together won't fall apart, this won't tell you much. Please read on...

It is important to understand that "Torque does" not indicate how tight a bolt is! In fact, of two bolts tightened to the same torque value (with a calibrated torque wrench even!), one may be too loose and the other may be too tight. Without getting into a long diatribe about the common-sense facts surrounding this, here's a link for those who need further details: Torque Danger

The only way to ensure that a fastener is preloaded to the desired stress level is to verify this after tightening. "Torquing" and it's variants requires you to verify this before tightening - silly, isn't it?

There are a number of options available to make sure that a fastener has been tightened properly ranging from "instrumented" bolts, to indicating washers to ultrasonic bolt elongation measurement. In fact, NASA uses the latter UT process on many critical fasteners - they understand that doing anything less may result in another space craft falling out of the sky.

Interestingly, there is also another option: Load indicating bolts. These are bolts which are calibrated to change colour upon reaching a certain load and revert to the original colour when they're loose again. They're somewhat subjective for precise load indication (how "geen" is "green"?) but, they're perfect as "go, no-go" indicators of bolt load. Thus, with a quick glance, one can see if the bolt is tight or not.

How about 'Hydraulic Bolt Torquing' all bolts simultaneously?

There are many manufacturers and suppliers. Furmanite is one such pioneers.

Hello yesyen,

I do believe that you mean to say "Hydraulic Bolt Tensioning". As you're likely aware, Bolt Tensioning and Bolt Torquing are two vastly different bolting processes. Both have their pros and cons. It's important to understand when to use one and not the other.

As you can see in the adjacent photo, standard industrial bolt tensioners would be much too large for Mr bastard's application.

Currently we are marking with a gelpen the fasteners that are torqued to show that the next person that is working on it has a visual indication that all screws.bolts have been torqued to spec, however the whole shop does not follow this protocol as it is a trial method, hence the reason I am throwing it out there for suggestions...

Good info to share with some of the technicians from your webpage...Thanks

JH