Torque of austenitic 304 bolts in aluminum beams of geodesic dome
Torque of austenitic 304 bolts in aluminum beams of geodesic dome
(OP)
Greetings, I hope somebody can help me with this one, I am in a project involving the erection of a geodesic aluminum roof, is necesary to aply torque to the stainless steel fastners of the estructure of the dome, this is the node and the beam, both of aluminum, AA 5454 H34 and AA 6061 T6, the bolts are A2-70 1/2".
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
Regards,
Mike
The problem with sloppy work is that the supply FAR EXCEEDS the demand
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
Maybe 38
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
These had better thread in very smoothly.
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P.E. Metallurgy, Plymouth Tube
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
Again thank you all
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
This sounds like a critical joint that contains mixed materials; for the manufacturer or designer to not tell you what the assembly torque should be is nearly criminal.
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
Sometimes the cheapest and most empirical thing that you can do is to make up a few of these joints and break them !
I suggest a formal letter to the dome vendor asking the torque question. Someone is paying for his product and he has a responsibility to answer it !!!
MJCronin
Sr. Process Engineer
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
For a critical application I would sacrifice one bolt per lot to determine actual mechanicals. I would base my torqueing procedure on that, and I would have the connection validated by a 3rd party.
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
Remember - you read this on the World Wild Web !!
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
If you tell us the size of your screws, we can work out a clamping torque on solid aluminium. If you are clamping to a hollow tube, all bets are off. Some bolts in building are methodically not clamped down, so that joints can expand and contract when the temperature changes.
How catastrophic will it be if this roof collapses? There must be a professional engineer somewhere whose license is on the line if you are not given proper installation instructions.
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JHG
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
Hunh? We torque/prestress ss bolts and cap screws all the time, just like we do with more typical steel fasteners. It all depends on the spec. the bolts were made to.
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
If I am a mechanical designer I would try very hard to avoid austenitic SS fasteners for any critical application.
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
You cab torque them...but you cannot relay on the prestress because SS material will creep away
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
Using anti-seize only facilitates yielding of SS bolts.
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
Am I missing something from a material science perspective? Any competent engineer designing bolted joints should understand and be able to quantify the effect of lubricants and adhesives on the joint in question.
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
Have you observed how torquing (an indirect and at best crude measure of pre-stress) is often done on the ground? The detailed science underlying the tightening of a bolt group (e.g., pipe flange) is extremely complex.
There are good reasons I do not permit tire installers to use their pneumatic or other weapons on the lug nuts of my vehicle.
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
I've never used stainless fasteners that exhibited any creep, unless they were operating at relatively high temperatures (where they shouldn't be operated). I have seen fasteners that exhibited creep, but they were used on rocket engines at very high operating temperatures, and they were not stainless, but a super-alloy. Over-torqued or overloaded and stretched stainless fasteners are pretty common, as they typically have a lot more ductility than a high strength alloy fastener...but that is not creep per se, that is just idiot installers using the "grunt" method for estimating torque.
"Using anti-seize only facilitates yielding of SS bolts. "
No, come off it. Stainless and other alloys are used daily in piping systems, we use them for our products by the thousands and rarely yield them, and they have never been the cause of a product failure - but the torques we used, and the rated proof load of the fasteners, are substantially lower than what you see for a grade 5 or grade 8 or similar alloy steel fastener. You need to do a proper bolt joint calculation (see Shigley), prescribe a bolt torque based on best guess for the friction coeff. (lubricate them and the error due to friction becomes manageable), and then run some tests. Oh, and find a fastener supplier who will sell you bolts that are made to a spec., like ASTM F837 for ss and alloy cap screws, or A193 or F593, or similar Euro standards that specify the min. proof strength or yield strength of the fasteners.
Again, what facilitates yielding of any bolt is an un-trained installer and poor QC.
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
I handled field support for a construction machinery OEM in the third-world for several years. Much as I like to jokingly compare my current environment working in various UAW plants, I don't believe maintenance nor repair gets any more crude than in developing nations.
As to fasteners, in the realm of mechanical design a bolted joint analysis is commonly a junior engineer's task and often special fastener design is as well. Many companies today have in-house fastener testing capability and outsourcing is very common as well. This isn't a black art, the impact of common adhesives and lubricants on torque and bolt stretch is well understood.
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
The problem with sloppy work is that the supply FAR EXCEEDS the demand
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
So we are pretty much in agreement.
CWB1,
I don't disagree with anything you are saying, I'm saying I don't see nearly enough of those practices in my neighbourhood. I watched an international bridge being fastened with not a lot more than torque wrenches.
Nevertheless, I stand by my statement that austenitic SS bolts are inherently more problematic.
"Everyone is entitled to their own opinions, but they are not entitled to their own facts."
RE: Torque of austenitic 304 bolts in aluminum beams of geodesic dome
Hello If your making something for a ocean boat stainless bolts and screws are a standard. I have a Max torque chart, but would need to scan it.
We have made quite a few cranes with stainless bolts on the main bearings. If loads are high we will spend the $ on 17-4 bolts.