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Loose Hub Flange Factors Fl and Vl
- Thread starter cros826
- Start date
gr2vessels
Mechanical
cros826, are you asking about formulas in Table 2-7.1?
If you use the ASME VIII div 1 equations and plot the lines you will find that within the 'normal' sector defined by ASME limits they are quite simple curves. But once you get significantly outside of the limits some, not all the curves go towards asymmtotic. Checking a typical flange geometry, this does occur both with 'F' and 'f' results, when h/ho is around 8... Thus it would give wildly incorrect answers. I would advise, stick closer to the ASME limits.
- Thread starter
- #4
Yes gr2vessels, I am asking about that table. Would Both of you suggest shortening the hub length in order to get back within the ASME range? I would prefer not to do this and keep the flange as all one piece. Surely a lower number for Fl and Vl can be estimated with such a long hub. Is there a safe estimation for these factors?
- Thread starter
- #5
cros826, yes you can compute values for Fl and Vl, using the equations in Table 2-7.1, as per gr2vessels reply above.
Your particular flange detail is not defined. I infer that you are considering the hub in the flange stress calculations, otherwise Fl and Vl are not used. I infer you have an unusually long hub. I see no limits on hub length stated in Appendix 2. I see no practical benefit of an unusually long hub, if you are machining from a forging you are just throwing away material unecessarily.
Care to provide more detail?
Regards,
Mike
Your particular flange detail is not defined. I infer that you are considering the hub in the flange stress calculations, otherwise Fl and Vl are not used. I infer you have an unusually long hub. I see no limits on hub length stated in Appendix 2. I see no practical benefit of an unusually long hub, if you are machining from a forging you are just throwing away material unecessarily.
Care to provide more detail?
Regards,
Mike
- Thread starter
- #7
SnTMan,
Thank you for the reply!
the hub length is 3.89 [inches] with B = 0.9 [inches] h0 = sqrt(B*g0) where g0=g1=0.23 [inches]. h/h0 yields a value close to eight which is off the Vl and Fl charts, given such a high ratio. I understand it is a waste of material, but the machining time for a separte short piece wouldn't be worth it. I have also used MS Excel to automate the calculations for Fl and Vl, it took forever. I get reasonable, correct, answers for these factors as long as I'm between an h/h0 ratio given in the table. As soon as I exceed the ratio (greater than 2) my numbers seem to error out.
Thank you for the reply!
the hub length is 3.89 [inches] with B = 0.9 [inches] h0 = sqrt(B*g0) where g0=g1=0.23 [inches]. h/h0 yields a value close to eight which is off the Vl and Fl charts, given such a high ratio. I understand it is a waste of material, but the machining time for a separte short piece wouldn't be worth it. I have also used MS Excel to automate the calculations for Fl and Vl, it took forever. I get reasonable, correct, answers for these factors as long as I'm between an h/h0 ratio given in the table. As soon as I exceed the ratio (greater than 2) my numbers seem to error out.
Which numbers? Error out how? It appears your hub length is much greater than flange ID? I expect the theory behind the numbers does not really account for such relative proportions.
I think I would place an imaginary butt-weld at, say, h=3/4 in. and go on down the road.
Regards,
Mike
I think I would place an imaginary butt-weld at, say, h=3/4 in. and go on down the road.
Regards,
Mike
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