Bolts into Aluminium - Lost! Question
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Posted by: Eamon
Huckleberry
04/04/2006, 09:40:20

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I am lost, with so many different formulas and guides on yield strength, torque, etc, with the problem below.
I need stainless steel bolts that will clamp a cover onto an aluminium housing and 'be safe' under a force of 30,000 Newtons (6750 pound Force), spring force.
I have no idea of how to calculate the bolt quantity, thread size, thread engagement or torque range to account for desired bolt stress and whatever, especially as it is threading into aluminium rather than a nut-bolt configuration.
The sizing of the cap/housing is such that the ideal sizing would be around M8 thread size SHCS and I could fit up to 10 bolts in the cap/housing on a PCD of diameter 8''.
Any advice on how to select the correct bolts and torquing to verify a safe design, preferably that doesn't involve long formulas! It doesn't matter if it's over-speced so long as it is safe and I am confident the assembly will not burst apart.







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Re: Bolts into Aluminium - Lost!
Re: Bolts into Aluminium - Lost! -- Eamon Post Reply Top of thread Forum
Posted by: devitg
Bart
04/04/2006, 13:29:43

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Forget about direct contact between Alum and bolt , get a shop to insert HELICOIL INSERTS , This will solve your problem , but if you want not to USE, I STROGNLY RECOMEND USE IT, do the whole threaded lenght part in aluminiun at least 2 times the bolt diameter.







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Re: Bolts into Aluminium - Lost!
Re: Re: Bolts into Aluminium - Lost! -- devitg Post Reply Top of thread Forum
Posted by: Kelly_Bramble

04/04/2006, 13:53:39

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I agree with devitg, go ahead and design in threaded inserts of some type.

Look at the following webpages.

Minimum Length of Thread Engagement
/thread_strength/thread_minimum_length_engagement_fed-std-h28.htm

Minimum Length of Thread Engagement ISO
/thread_strength/thread_minimum_length_engagement.htm

Thread shear area
/thread_strength/thread_bolt_stress_area_iso.htm

Thread tensile area external thread
/thread_strength/thread_tensile_stress_area.htm








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Re: Bolts into Aluminium - Lost!
Re: Re: Bolts into Aluminium - Lost! -- Kelly_Bramble Post Reply Top of thread Forum
Posted by: Eamon
Huckleberry
04/06/2006, 08:08:12

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Thanks for the advice, guys, although while the helicoil option is stronger, it still doesn't tell me the design info on what safety magin is built in.
I'm trying another (lazy) way.
Hopefully, a bolt manufacturer will supply the information for standard classification of M8, M10, etc that will say what they should be torqued to, and what loading/force they will take for 1x or 1.5x diameter thread. I can then build in a safety margin based on Al having 50% strength of SS.
Another option I have is to screw the cap on instead of small bolts. e.g. M25 on a diameter of 200mm. It still doesn't give a design figure but I assume would have a huge safety margin due to the huge shear area.







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