Dished Head Blank Diameters

[PEHasan]

I am trying to find out the formula for the calculation of Blank Diameters for 2:1 Semi-Ellipsoidal, Torispherical and Hemispherical dished heads.

Please reply with full reference to the text (book or code).

Hasan.

 

[JStephen]

I doubt that there is a single published formula- I'm sure the different head manufacturers have this worked out for their own particular forming processes.

For a start, you could assume the diameter of the blank was equal to the arc length up across the dome.

 

[chaulklate]

JStephen is more than likely right, each manufacturer will probably have their own way of doing it. But could you not just use surface area formulas to determine the blank? Then take the actual area and work the formula backwards to determine the starting diameter? Surface area formulas:
SE = 1.084D^2
Hemi = pi*D^2/2
F&D (using 100% and 6%) = 0.9286D^2
D (diameter) is measured in feet. I don't have any formulas for other F&D ratios. I got these formulas from an old text book, but I only have a copy of the page so I can't confirm the book name or author.

 

[unclesyd]

Here are some downloadable spreadsheets for different heads and that give the approximate blank diameters.
You have to remember that you have to have a different size blank depending on the head thickness and don't forget to allow for the forming allowance on the thickness.

http://www.pveng.com/Soft/Heads/Heads.htm

 

[chaulklate]

...and don't forget your straight flange.