Torque specifications for fasteners in Aluminum castings

[Guest0527211403]

Hello,

I'm reviewing my company's existing standards for our fastener torque specifications, particularly as they apply to our metric SHCS' in aluminum castings (AA356-T6 material).

I understand that under specific loading conditions, we need to review the bolt torques in detail based on the strength of the materials and the applied loads.

However, in some applications we use brackets that are used to mount sensors and other items to the casting (i.e. there is no special loading, only machine vibration.) In such applications, I'd like to start working with a "general purpose" torque table based on fastener size.

Is anyone aware of a standard or document (I've been looking at Aluminum Association and various other organizations' standards with no luck) that has some recommended torques into aluminum castings? My plan is to use this as a starting point, take a scrapped casting, tap some holes in it and make sure our more experienced assemblers are ok with the torque specs.

Thanks in advance,

 

[gadkinsj]

If you are tapping into aluminum, you can put the screw in one time to a sufficient torque to prevent the bolt from vibrating loose. But If you remove that bolt then try to tighten it again you will find that the threads will most likely be damaged beyond use.

If you want to do it well, then all tapped holes in the casting have a threaded insert.

If you want to prevent damage then you don't tighten the bolts to their optimum torque in the aluminum and you rely on secondary means of retention.

Obviously I recommend the former solution.

 

[MiketheEngineer]

Maybe a bit of Loctite??

 

[KENAT]

Patched fasteners...

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[KENAT]

Sorry, as a more direct answer to your explicit question.

It seems that while 'standard torque tables' are fairly common and well accepted for typical structural fasteners/materials etc. they are hard to come by for less common/typical applications.

Folks here have spent time looking for information for 'non standard' applications and not had much luck.

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[Guest0527211403]

Thanks for the replies.

As gadkinsj pointed out, in areas where frequent disassembly/reassembly is required, we use helicoils and have a set of torque requirements for those.

Loctite is also specified where needed, but we cannot spec this in lieu of torque requirements.

Agreed that this is a non-standard application, however our company has heavily adopted the use of aluminum castings, so this will warrant further study with the guys on the floor so that we can start to work towards an "internal" standard.

 

[SnTMan]

justkeepgiviner, Machinery's Handbook has calculations on thread strengths for differing materials, might be a good starting point for you.

Regards,

Mike

 

[Guest0527211403]

Thx Mike, I'm starting to build a table from those equations and our material data. I think combining this with some trials on a junked casting would be a good starting point,

 

[KENAT]

You could be really nice and when you come up with something post it here as a FAQ if it's not considered IP.

Just saying;-)

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