GTA
All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Engineering- Research & Development => Topic started by: moorepower on August 18, 2014, 10:43:56 AM
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What thickness of 4130 tube would be needed for 1" tube running 3kspi. ?
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It calcs to 0.075" at a stress of 20,000psi
Available 1" tube will be 0.083" so good to go.
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Thanks for the info.
Pat
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4130 CrMoly normalized has a yield strength of 63K and a tensile of 97K.... For a 1" OD tube with a 0.065" wall (ID of 0.870"), that works out to a yield pressure of 9,414 psi and a burst pressure of 14,494 psi.... With a 3K fill, that gives a safety margin of 3.1:1 to yield and 4.8:1 to burst.... I use that exact tubing on my Hayabusa at 3000 psi all the time, but of course you can use thicker if you want a higher safety margin....
Bob
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Thanks Bob for the info. I use Aircraftsprue.com for my 4130 tubing. They say it has a 90K tensile so I use that even though I know 4130 normally has 97k. I plug my numbers into this calculator to find what I'm looking for.
http://www.engineersedge.com/calculators/pipe_bust_calc.htm (http://www.engineersedge.com/calculators/pipe_bust_calc.htm)
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Bob, what is your plug design and dimensions?
Oring inboard or outboard ?
Threaded or pinned fastening
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The question was about the tubing, Walter, please stay on topic.... You are well aware that it is quite possible to design and construct a proper plug for that tubing at 3K with safety margins of over 3:1.... If you really care, please PM me with your concerns....
Bob
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The question was about the tubing, Walter, please stay on topic.... You are well aware that it is quite possible to design and construct a proper plug for that tubing at 3K with safety margins of over 3:1.... If you really care, please PM me with your concerns....
Bob
To be fair to the OP you must consider the complete assembly. Especially when you advocate for thinner tubing than any other builder would select. IMO it is on topic if the fixing method is to be by threading then the removal of material changest the suggested wall thickness.
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I didn't say anything about threading the tube.... Perhaps you can glean some knowledge about attaching a valve from this thread.... http://www.gatewaytoairguns.org/GTA/index.php?topic=72672.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=72672.0)
7,500 lbs. force to the tubing wall yielding on a 1" OD x 0.065" wall tube is a 4.2:1 safety margin at 3000 psi using three low profile high tensile SHCSs.... and the screws didn't fail in shear at that load.... My calculations don't put the safety margin that high, but the proof is in the pudding, as they say....
Bob
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That is a very cool testing of the fasteners.
Would like to see edge tearout failure tested. IMO some builds put the holes too close to the tube end ie QB79 style.
Center of hole 2x diameter is the spec IIRC? and I use 2.5x diameter to give 2x hole diameter of tubing to support the compression load.
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Thanks for the info.
Pat
You are most welcome. What fastening method are you wanting to use?
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When I do the math on the tearout I find that 1.5 x D to the center of the hole yields a tearout strength safety margin similar to what Lloyd finds in his tests (~4:1), and from what I have read 2 x D is the standard, but I think that is on a screw shank size, where you are dealing with a smaller diameter supporting the shank before it shears (ie more likely to tear out at the same load).... With the way we use larger holes for the head of the screw to increase the bearing area, 1.5D is the minimum, and 2D gives a larger safety margin.... The thickness of the material comes into play as well, of course....
Yes, the QB 79 is a classic example of screws too close to the end of a tube, particularly with the thin wall.... They will bulge on a hot day with CO2....
Bob