Recertifying structural adhesives and bond primers?

[KirbyWan]

Howdy all,

I would like to create a process to recertify adhesives and bond primers that are nearing the end of their shelf life. I have done some web searches and have only found passing references in two documents. One in DOT/FAA/AR-02/110 where it states: "Procedures for the disposition of out of date material also need to be defined. This could include shelf life extension based on the performance of reinspection tests" and also in DOT/FAA/AR-05/13 titled 'Assesment of industry practices for aircraft bonded joints and structures' in which during a conference on bonded structures "Recertification of materials (extended life) should be addressed" was discussed.

Does anyone have a process spec that deals with recertifying shelf life controlled adhesives? Could you point me to useful links? Please feel free to share your thoughts on this. We run a process control sample with every bonded repair, but we often are required to use a special adhesive for a particular repair that we don't perform but every few months and would like to minimize scrap losses if we can use a recertification test to prove the continued acceptability of the adhesive or primer.

Thanks,

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[SWComposites]

Well, many spec's allow one to perform some retests on composite and adhesive materials and extend the shelf life by X months. However, IMO this is all based on wishful thinking. Just because the tests pass today does not mean they will pass tomorrow or X months from now; to say "the tests passed today so miraculously the material can be stored for another 6 months" does not have much technical basis.

The proper way to "extend" shelf life is to test material that has been stored for the desired time and, if the tests pass, set the max shelf life to that time; the "problem" is that it requires the foresight (which is typically lacking in management) to buy and store materials for the desired time BEFORE running into the situation where the in-stock materials reach their shelf life. Otherwise, one has to test the materials at the time of use once they are past the previously validated shelf life.

SW

 

[KirbyWan]

This issue is moot for me since we perform a process control test with each bond run. So say we perfrom an adhesive recert run and it passes. We add 1/2 the original shelf life to the material. Then when we use the extended adheisve we run another test which would end up being identical to the recert test anyway. If it fails throw out the old adhesive, rip it apart and rebond it with fresh adhesive.

I think Boeings specs are focused on a production environment where they get in adhesives and run acceptance tests and if it passes they never do another test on that adhesive. of course they also would rarely end up with adhesive beyond it's shelf life either, since even if the got close they could just make extra parts to use it up on the assumption they will be needed eventually.

Thanks for the resposne,

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[berkshire]

Kirby,
This is an item that used to drive me nuts when I ran a repair station. My spec sheet said, when it is at the end of its shelf life discard it.

I started only buying the material when I had a job for it and chucking it as soon as the job was done.

Prior to that I had been written up by the FAA for having expired material, even though it was only a month out of date.
Keeping adhesives and sealants because you might be able to use them later turned out to be not worth the hassle.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[KirbyWan]

berkshire,

I tend to agree if we could keep to small quantities. But we sometimes run into the problem that we need to buy a whole roll of adhesive when all we want or need is couple of feet. Alternately we have on occasion ordered too much of a material.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[MiketheEngineer]

If it's out of date - it's out of date... Period.

Take it home and use it on your model airplane or the junker you are rebuilding...