Loctite Inspection?

[mdcondro]

Is there a way or a device to inspect for anaerobic loctite application on a screw threads after installation?

The assemblies I'm involved in building require loctite on every screw, followed by thorough cleaning which removes any traces of excess loctite. The method I have set up to assure that loctite has been applied is making the assembly operators record loctite cure start time on each part's mandatory history log. This is merely a "warm-fuzzy" rather than a mistake-proof method.

 

[CoryPad]

The only methods that come to my mind would involve applying torque to the fastener, which is a terrible idea in general.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[MikeHalloran]

Let a little dribble out for visual verification. Catalyze it before cleaning, so it can't be washed away. A spritz of accelerator after assembly, or pretreatment with an accelerator should do it. Ask your Loctite rep for help in selecting which products to use.



Mike Halloran
Pembroke Pines, FL, USA

 

[MadMango]

If you need to remove the excess, then inspect for application prior to cleaning.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of these Forums?

 

[mdcondro]

Thanks for the suggestions so far. Inspecting prior to cleaning makes complete sense. Unfortunately that would induce additional work, material handling, lead time increase, plus a complete revision of product line work instructions. If possible I would like to be able to inspect at the current in-process and final inspections steps.

It would be nice to have something that can measure the difference between an installed screw with and without loctite.

 

[MikeHalloran]

Or, you could just buy all your screws with microencapsulated threadlocker preapplied. It costs a little extra, but not nearly as much as inspecting for the presence of threadlocker does.



Mike Halloran
Pembroke Pines, FL, USA

 

[MadMango]

You could weigh the items before and after, but I fear that there's not enough volume of loctite to account for the other weight variables that you would encounter (length of fasteners, thickness of paints, etc). Mike above has a good option.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of these Forums?

 

[btrueblood]

Mike has given two good options (catalyse spill-off to leave an uncleanable residue, or use preapplied coating). A third possibility is to use the pentrating type of loctite (green), that you apply after running down the fastener. It leaves a nice fillet behind, acting as a tamper-evident seal. Whether it acts as an adequate thread lock in your service depends, but is easily tested. A fourth possibility is to have "peer witness" sign-off, i.e. a fellow employee must witness loctite application.

 

[unclesyd]

You might try a UV light as some of the thread lockers will glow profusely under UV light. I observed this on some parts we were doing MT. Even though the parts been wiped clean there was still enough material around the head to fluoresce. There was not problem seeing the back side of the screw.
yOu might do this immediately afer assembly before the parts are cleaned.

 

[mdcondro]

Thanks again for all of your suggestions.

Mike - your idea of buying preapplied thread locker is practical and I will investigate further.

btrue- I am limited to using the materials approved by the customer. Right now, using the green penetrating loctite is out of my control. The witness idea is good but I feel that the loctite cure start time recording we have in place now is just as effective

unclesyd- I have investigated using our UV lights. However, our cleaning process is so thorough that it completely removes all trace of such fluorescent material. I am trying to avoid adding an inspection step after installation and before cleaning because of the sheer amount of non-value added work.


Does anyone know if ultrasonic technology can be useful for this application?

thanks again for the help

 

[KENAT]

If your cleaning process is that thorough, are you sure it's not degrading the loctite in the threads?

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at

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[CoryPad]

Is the idea that the chemical bond would alter the ultrasonic path length?

Actually, what might change is the resonance of the assembly. Quasar/Magnaflux/ITW provides equipment to do this, but I believe it would be prohibitively expensive for this application.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[unclesyd]

I am at a loss.
You say you need to have Loctite on every connection yet an inspection step to insure this is true is of is of no value.
A question would be why inspect at all?

It seems to me that a simple automated inspection step after the fabrication but before the wash would be better than using the Ford principle of inspection, only count the rejects that get back to factory.

If you can't inspect for all the reasons you hae stated I would certainly go with MikeHollran's suggestion of using a pre applied Loctite. Not only would this insure that all screws had Loctite, it would take away one step in your process where someone has to apply the Loctite to each fastener.

 

[mdcondro]

unclesyd - I am right there with you at a loss. This all came about because of an escape where and operator built an entire batch without loctite. Our customer discovered it somehow and is requesting proper corrective action.

I agree that it is best to build the quality into the assembly rather than inspect for poor quality. That's why I like the pre-applied loctite idea.

Thanks

 

[btrueblood]

One guy messed up?

Start by holding a stand-up all-hands meeting, where the purpose of the time recording is emphasised (QC check that it gets applied). Then single out your maverick employee, make an example out of him. Severely reprimand him, make him sweep floors and clean toilets (at least figuratively) for a week, in full view of the remaining crew.

More effective when the 2nd-pair of eyes technique is used, and the signatures are actually controlled stamps with employee numbers on them (harder to fake times, fake signatures).

But, all of that nasty cr$p goes away if you use pre-applied loctite. The problem with that approach is convincing the purchasing dept. not to skimp and buy off-brand stuff that doesn't work, or is surplused because it passed its pull date. Or, it sat past its pull date on YOUR shelf.

 

[unclesyd]

btrueblood,
Your first approach is now equilibrated to taking one out to the woodshed for an attitude adjustment. The HR people would be on you like the proverbial "Duck on a June Bug".
You would have to spend a couple of weeks in all kinds of management classes and take all manner of tests.

 

[KENAT]

Yeah, far better to use these 'tough economoic times' as an excuse to remove the problem.

The message to other employees is clear and you get to miss the management training;-)

Does it have to be pre-applied loctite or equivalent? This never seems to work out every time I look at it however the nylon patches on screws I have seen work.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at

http://eng-tips.com/market.cfm?

 

[unclesyd]

A little different approach to the Nyloc fasteners mentioned above.

http://www.apmselfsealingfasteners.com/threadlockers.asp

 

[KENAT]

That's the type of thing I was talking about unclesyd, used the MIL-DTL-18240F on aircraft related stuff at a previous employer.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at

http://eng-tips.com/market.cfm?

 

[CoryPad]

KENAT,

Are you saying preapplied thread adhesives have not worked for you, but preapplied thermoplastic inserts/patches do work? There is no reason for that to be true.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.