Thread Inserts û Inspection of installed inserts and their life 2

[roberto1brazil]

Please, I would like to have some information about the procedures of inspecting thread inserts installed in parts. Note – The tapped holes are blind holes.
At our shop floor we have a part with 32 holes at the flange face. These holes have inserts of nominal thread size diameter 5mm. According to our Technical Data it is required a locking torque between 0,25 and 2,0 N.m ( 2,21-17,7 lb.in). The torque to be set related to the nominal diameter of 5mm is 4,8 N.m (42,48 lb.in) with a tolerance of +/- 7%.
Questions
1- When inspecting the insert installation applying a final torque (torque to be set) in the bolts, just to test and not executing the final assembly, were we contributing for a reduction of insert life and perhaps affecting the properties of the inserts (working pressure) ?
2- Could you say us if the best way of inspecting the condition of inserts already installed in the part can be done applying the locking torque on them associated with a visual inspection? The use of a common bolt placed and threaded manually into the thread without the use of a torquimeter would be enough?
3- Why some inserts lose totally their capability of gripping the bolts when are being inspected during the disassembly of the parts? Some are able to be removed by hand.
Thanks and regards.

 

[MikeHalloran]

1. Yes.
2. I'm not sure I understand the question.
3. I would >guess< that the inserts are cracked or broken or corroded or annealed. . and should be removed for inspection.




Mike Halloran
Pembroke Pines, FL, USA

 

[roberto1brazil]

Hello Mike.
First of all I would like to thank you. Regarding my second question, my doubt is about the possibility of inspecting inserts installed just using a bolt and feeling by hand if the self-locking system of the insert is still acting. The minimum locking torque of 0,25 N.m required in the Technical Instruction is not so high, and so I would like to know if that procedure described above would be enough to inspect the insert condition.
Thanks again
Roberto Azevedo

 

[drawoh]

roberto1brazil,

What kind of inserts are these?

Helical thread inserts are removable if you have the tool. I am not familiar with Keenserts.

JHG

 

[roberto1brazil]

Drawoh and Mike.
The inserts are from Heli-coil and we have the tool to remove them. My main problem is not to remove them but another issue that is taking place. I will try to explain the problems that I am dealing. We have a combustion chamber that has 32 holes with inserts in its flange face. The engine comes to overhaul and all components are disassembled including the Combustion Chamber. All components are inspected. All inspectors say that they check all thread holes with a bolt in order to identify which holes need those inserts be replaced. Those ones are identified and marked. We are able to repair (replace) them. But when the part is going to be assembled again (after inspection and repair) and after some weeks, the mechanists stop the line with an argument that there is a part that has some inserts loose and the self-locking system does not actuate any more. In fact, when verified again in the assembly shop, those parts had confirmed that nonconformance claimed. I am trying to discover the cause of this problem.
- Inspectors say that the parts are being inspected and they do not allow parts with inserts loose. For that reason I was asking about the correct way to check them. Perhaps the way that they were applying (just using a common bolt to check insert condition) was not reliable.
- Mechanists show us (to Engineering area) that the part has loose inserts. My suspicion is that the part when assembled, it is not assembled at its final condition. Perhaps they assemble it and for some reason disassembly it again and all these tasks can affect the inserts in the definitive assembly. But I am not sure of nothing.
NOTE: The holes repaired (the ones that were identified and had the inserts replaced), do not display problems during assembly, but just some ones that were not considered with problems.
Please, any comments will be welcome.
Regards
Roberto

 

[MikeHalloran]

Surely the insert manufacturer publishes technical guidance, or will answer the phone.

Mike Halloran
Pembroke Pines, FL, USA

 

[WKTaylor]

roberto1brazil,

Everything You need to know should be in these docs...

ASME B18.29.2M Helical Coil Screw Thread Inserts: Free Running and Screw Locking (Metric Series)

and/or

SAE MA1567 Insert, Screw Thread, Helical Coil Metric Series, Standard Assembly Dimensions For



Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[roberto1brazil]

Thanks Wil. I will try to get those documents. Unfortunately it is not so easy to me. The library of my company has not so much information available to research, but I will ask for helping from our Quality dept in order to purchase the norms called out.
I thank everybody for the support in this issue.
Best regards
Roberto

 

[MikeHalloran]

So, some of the inserts that appear to be okay, and pass some kind of inspection at initial teardown, are found to be loose and/or non-locking at final assembly.

That smells like some process step after teardown, e.g. chemical cleaning with something aggressive, is affecting the inserts left in place.

If you can't figure out what process step is affecting the inserts and do something about it, you might be better off removing all of the inserts at teardown and installing new ones in every hole.


Mike Halloran
Pembroke Pines, FL, USA

 

[WKTaylor]

Roberto...

Mike has a strong-point. Any chemical processing done to a part with installed helical coils MUST be done (1) of (2) ways.

Chemicals have a nasty habit of reacting [dissimilar] with the base metals and the helical coil CRES wire.

A. Strip-out [remove] the helical coils.

B. Completely mask-off the helical coils and their holes from exposure to any chemicals. This can be done with tooling, special mask "patches" or (simply) with a fully threaded b installed in the helical coils with a thick washer and chemical resistant gasket-rings or sealant applied to both sides of the washer... and the bolt is torqued tightly into position.


Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[roberto1brazil]

Hi Wil and Mike.

I have appreciated so much your tips. Now I am seeing a light in the end of the tunnel. I believe that you have reason when do a mention of chemical cleaning, and perhaps you have hit the target. In fact we have some steps of cleaning before inspection and after inspection and the part sometimes wait weeks to be assembled. The cleaning process can use alkaline scouring or hydrocarbon solvents and according to the combustion chamber condition, the part can be cleaned more than once. Besides it, if the part requires a repair which asks for sheet metal work (frequently it is required), a FPI inspection is performed and I can say that it is more common to do it than not to do. Perhaps we will have to simulate some situation and so follow up all the process step by step inspecting the inserts. I am so glad for your attention and if you have more comments, please, do it.
Best regards.
Roberto