TAPPED BOLT HOLES IN ALUMINUM 4

[wynn]

We need to connect the skirtings for 30" bus ducts to the wall of the isophase box. Details as follows:

Wall is 1/2" thick in 6061 aluminum. Bolt groups are 24 - 3/8" dia on 18" radius. Design load achieved 20 times in life. At other times, nominal loading only but box continually vibrating. Open to weather in medium industrial setting (30 yrs design life).

Can you advise:
Is it safe to tap the aluminum wall, or must we use through bolts?
What material for the bolt (inc nut, washers, gaskets if used)?

 

[MadMango]

I would consider inserts into the aluminum panel. Hardware should be at least grade 5. "Happy the Hare at morning for she is ignorant to the Hunter's waking thoughts."

 

[nashjp]

To prevent thread strip in aluminum, you should usually try for two diameters of thread engagement for grade 8 hardware. Your 1/2" / 3/8" is at the very bottom edge of what I would use but might be ok for grade 5. If you do not have to use a high torque to handle your loading, threading the box might be ok.

Through holes allow for more bolt stretch which would be more forgiving to relaxation. USE WASHERS, to spread out the bolt clamp load and not yield the aluminum box badly. Note if you are near yield tighten your bolt pattern twice, the first pass will work harden the aluminum so that it can suppport more clamp load the second time.

For coating info you need someone elses advice.

 

[diamondjim]

You might want to consider using stainless steel
bolts for this application. The heli-coil inserts
might have to be painted per their instructions.
You might want to consider stainless steel inserts too.

 

[evelrod]

wynn---From the standpoint of shop application, HeliCoil and SS inserts are fine. In the field, however, their use is expensive, time consuming and, difficult to maintain quality control with installations in high quantity. Through bolts using SS hardware would seem to be cost effective and efficient in this appllication.


Rod

 

[boo1]

Tap the threads in the aluminum, and you use a galvanic isolator (proseal) to seperate the steel and aluminum or paint the structure to seal water out.