My company has made quite a few polyurethane press blocks, to replace rubber pads. I don't know that much about it myself, but please feel free to contact
"jon@kaylan.co.uk" who is my brother, and who may be able to either help you directly, or put you in touch with some people who can.

"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams

Hi, I know this was an old post but wondering how you are making out with this endevour, we have extensive knowledge on this subject and provide machinery for high pressure sheet metal forming, please let me know if you are still interested in learning more....reply to me direct at jp@fluidforming.com thanx-JP Cheneski

Also check Personal Press in Wichita, Kansas.

They make a line of small rubber head presses
for the aircraft industry.

Sizes range from a 16 inch diameter forming
area to a 1,100 ton press with a 30 inch by
70 inch forming area.

A sister company to Personal Press, Automated
Aircraft Tooling can make the tooling and
provide flat pattern development.

Does anyone know the spec of the rubber used in the press ?
I already use a small shop press but am having trouble getting rubber pads of the right grade.

Another Karl.

For a bladderpress "Verson Wheeler" or "Hydro form" the most commonly used rubber is a white natural rubber of 60 to 70 Durometer rating.
  When I used to work at General Dynamics we used to buy it in sheets 4x3x1/2 then trim it to the sizes we needed.
Brian Evans.

Urethane works well and can be purchased
in sheet or cast form.  Gallagher Corp
can provide either and have molds for
the Verson bladders.  

Check www.gallaghercorp.com.

Oops,
 I did not make myself clear in my reply. The rubber I was refering to was the rubber placed over the parts for the forming action to protect the bladder from the sharp metal edges.we would apply several sheets up to a total of 3" depending on the height of the forming die.
   The bladders themselves were formed from cast urethane elastomer.

 We had tried urethane sheets and found that they worked well for a short time, then started disintegrating, splitting apart where they were formed over sharp corners.
B.E.

If you go to a shop that does a lot of
rubber head forming, the operators will
often have a variety of sacrificial pads.

They will use both rubber and urethane that
varies in both thickness and durometer.

Pad selection comes from experience and
what works best for a particular family of
parts.  

In my opinion, a 90 durometer quarter-inch
thick pad works best, but then I do not do
this sort of thing for a living.

You might have fewer problems if you would
first remove the sharp edges from your tooling.
A .200 or larger radius should eliminate
shredding of the sacrificial pads.

And if you are building a tool for lets say
a trailing edge rib, go past the part a bit
then add an inch diameter boss to eliminate
the knife edge.

URETHANE is the answer for forming, try different grades or hardnesses or vendors or sizes.  Some people have been inserting block shapes into the dies, but it depends on the application.  Oh, try to reduce the sharpness.

http://www.sdplastics.com/polyuret.html
http://web.me.unr.edu/me353/pdf/smf.pdf

Something to keep an eye on.
http://www.vm.lr.tudelft.nl/research/projects.php?id=9
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For a bladder I would call Firestone, same guys that make the tire, thier industrial division.

_______________________________________
Feeling frisky.........
www.tailofthedragon.com

After seeing the maintainence performed on a Verson bladder press it is most likely easier to buy a press than to engineer your own. What size of parts are you forming?