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Re: [PSUBS-MAILIST] Nuytco sub observations
The issue is really the extraneous weight that you would end up carrying
if you used, for example, two formed hemispheres versus the segmented
construction. To achieve the minimum required shell thickness at all
points, the deviation from this with a smaller pressed segment is much
less than that with a fully formed hemisphere. The extra weight would
otherwise reduce your payload capacity significantly, and this is
significant enough to justify doing three times the welding that would
otherwise be required with a pair of full hemispheres. I recently
emailed a sales representative at Edmonton Exchanger for some background
information on this, as I was curious how much deformation is actually
expected during head forming. His reply is below.
-Sean
Bear in mind that they tend to work with SA 516-70 N steel
plate, and also typically make much larger heads than the submarine hulls
we're discussing here. Here's what he had to say :
*****
Forming SE2:1 heads.
There is no advantage to forming SE2:1 heads in Segments if it can be hot
forming using a press in one piece. We can form up to 4" SE2:1 head with
only
1/8" thinning and up to 8" with 1/4" thinning ( based on ID being 48" ID or
more). The thinning on a hot formed head occurs at the top of the head (
middle of head). During the forming process the material moves toward the
Straight Flange so the SF thickness of head after forming is usually 1/8" to
1/4" thicker depending on the thickness and size of head. It is true that
forming a SE2:1 head is segments would give you a more uniform
thickness..........but the disadvantage is the additional welding and the
shape of the head. When you hot form a SE2:1 head the inside shape of the
head is a perfect SE2:1 shape. When making the head in segments and putting
it together the head will deviate from its true shape which is not
desirable.
If SE2:1 head is too big to form in press we would have to cold dish and hot
spin head manually with different equipment. During this process the
head can
thin up to 20% and the shape can deviate slightly. I Segmented head may be a
option in this case because of the material savings and the extra labor
involved in dishing and spinning.
Forming Hemi Heads.
Because Hemi heads are very deep they tend to thin more than SE2:1 head. The
loose rule for hot forming a Hemi head is that it will thin 1/8" for every
inch of thickness. Based on this if you form a 5" x 96" ID
Hemi............it
could thin as much as 5/8". Again, the head would thin on the top and
material would move into the SF of Hemi making it approx 5% thicker. The
advantage of hot forming is the ID shape of Hemi is perfect. Also, in both
the SE2:1 heads and Hemi heads - the labor involved in hot forming is
minimal
compare to segmented construction. Even with the extensive thinning on hemi
heads it is usually more cost effective to hot form a Hemi head rather than
form in pieces and weld together.
Sorry, I only have a few minutes to put the info together so it is not
presented as well as I'd like............but it is the best I can do
with the
time I have.
Alex wrote:
It looks like that spehrical section is both pressed and welded. That's the
best of both worlds. The spherical end is not too big to where metal thinning
is a a problem. And the welded sections look like they were made on the same
press to match the same sphere. That way everything fits together perfectly,
and only a few sections are needed!
Alex
On 11-Oct-2009 Jon Wallace wrote:
2) I noticed that the back head on Phils newest sub ( click this link
http://www.psubs.org/convention/2009/photos/jonw/800/DSCN0773.JPG ) is
segmented rather than pressed from a single blank of steel. I remember
Phil talking about this but don't recall the benefit of using segments.
I've been looking at Prescor in Tulsa Oklahoma who heat steel blanks and
then press them into the correct shape with a die. Is there any reason
this is not as viable as a segmented head?
Jon
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