Hi
I have been following Karl Stanleys subs for some time and this was posted on another forum which is a yahoo group at http://tech.groups.yahoo.com/group/international_psubs_minisubs_rovs/ by Karl who is a member. It is about the construction of Idabel. I thought it might be of interest to some people here.
John
Idabel is made of three spheres. Three foot
diameter, 4 foot and 4.5 foot. The Largest is recycled from an old Perry lock
out sub; it was the sphere that held the gas for the divers. It is made of
HY-100 and a uniform 1/2 inch wall thickness. When sandblasted, you can see the
welding seems, it appears that plates were pressed into dished sections, trimed
to pentagons and welded together, then the welds x-rayed and ground almost
flat. While very labor intensive, this method has the advantage of uniform wall
thickness. In this case it was also the only way to produce that sphere, as to
try to press such a thin, strong material would have caused tearing.
The other two spheres are 516-grade 70- your most common pressure vessel steel.
If you order steel for a pressure vessel, or obtain end caps designed for
tanks, this is most likely what you are getting. The 3 and 4 foot spheres were
made by a company called Uniform components outside Houston. 8 or 9 yrs ago the
two spheres (4 hemis really) cost $2364-
The 3 foot one started as 5/8 plate that was heated to 1600 degrees f (red hot)
and pressed in a die. after this it was rolled between large solid metal
spheres that smoothed out any waves in the metal from the pressing. Then it was
checked with sound and also a template to make sure it was very close to round.
It does matter a lot for the strength of a sphere how close to spherical it is.
IN the case of my two spheres the came out with in 1/8th of an inch of perfect,
I think the tolerance is 1.5 times the wall thickness. The company had
guarentted the 3 foot diamter hemis would not thin to less than 3/8th from a
starting thickness of 5/8- and the 4 foot diameter .75 plate would not thin
below .5-
an easier way to think of it is they said the material would not loose more
than 1/3rd of it's thickness at any given spot, but in reality it worked out to
about half that- as made the 3 foot diameter hemis had a min thickness of .52
and the 4 foot had a min thickness of .634
An interesting part of this equation concerns payload. My design is only made
possible due to the buoyancy provided by the front, strong thin shelled sphere.
The HY-100 sphere gives me 1900 lbs of buoyancy, but the two spheres in the
back, only provide 1400 pounds combined. This is due to a great deal of weight
being carried around on the rear spheres as x-tra material due to the way they
were formed.