countersunk structural fasteners? 1

[HgTX]

[I tried searching and didn't find what I wanted, but if there's another thread I missed that answers this very question, then please by all means send me that way.]

Is there a countersunk equivalent of ASTM A 490 bolts? If there is something with equivalent mechanical properties, would the slip coefficient of the connection be expected to remain the same?

Hg



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[hokie66]

I think Unbrako flat head socket screws are what you want.

 

[Tmoose]

Flat head SH screws have much lower recommended torque values than SHCS due to the wimpified head geometry. The clamping force and resulting slip resistance would be lower too.

 

[unclesyd]

I haven't been exposed to flat head structural bolts but have seen bolts similar to these with a full taper and reduced head height, like a button head. I know that a couple of times these were used to emulate rivets in restorations.

http://www.masterbolt.com/post_bolts.html

The folks at Master Bolt have been very helpful in the past and have run some small and large lots. You might want to give them a call.

If the section is thick enough a full taper on these bolts will not degrade the bolt, strength wise. It is also not very hard to get this type bolt tight.

 

[hokie66]

We have used the flat head socket screws in structural applications where the architect wanted the connection to be "aesthetically pleasing". These were used in tapped holes, so the threads were in the shear plane. The ones we used were available in Grade 10.9, in sizes M12, M16, M20.

http://www.unbrako.in/unbrako_standard.htm

 

[Screwman]

Any type of a flush head fastener with a recessed drive in it will fail thru the head and recess at a tensile load lower than the ultimate strength of the threads. You have to reduce your allowables and use more/larger recessed head fasteners than you would the same hex head structural bolts.
In rough terms an A490 is about the same relative strength as a grade 8, but the specific requirements are different, so they are not interchangable.

I would not consider flush head recessed drive fasteners to be structural fasteners (there are exceptions in NAS aerospace parts).

 

[HgTX]

Am I correct in drawing the conclusion that if an analysis was already done for A 490, there's no bolt-for-bolt substitution that can be made and still have the same connection capacity?

Hg

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[CoryPad]

If the joint is preload dependent or has axial forces applied to the screw, then no. If it is just a shear pin style joint, then it is possible to use a screw with a countersunk head and high material strength (like the Unbrako parts).

 

[Tmoose]

With good intentions Our assembly group substituted some flat head SHCs for SHCS when clearance problems were encountered securing a structural cover to a machine tool frame. The main structure contained tapped holes. The tapered heads insisted on trying to center themselves. Tests with stripes of magic market on bolt heads and tapered hole sides showed clearly that irreconcileable Disagreements between threaded hole locations and tapered cover holes, and even head runout, emerged. It was not a great solution.

 

[HgTX]

As far as I know, this is a slip-critical joint.

Hg


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