Looking for specialty pliers or wrench

If production quantities warrant, a collapsing mandrel could be the answer. There are several ways of doing this... One is to make the mandrel in several pieces lengthwise, with the key piece slightly tapered. Removing this key piece allows the mandrel to collapse radially inward, facilitating removal.

Another method would be to make an elastomeric inflatable mandrel... Inflate for casting... deflate for removal.

Wolfgang

You can buy plastic / rubber ones from the dollar store. Or make one out of a dollar store luggage strap.

If mild heating would work, hot water or steam through the mandrel?

Or hot water through the mandrel, allow heat to soak into the material, then run cold water through tha mandrel?

Seems like a lot of effort, but then again, it *is* rocket science. ;)

Dave

Drill a hole lengthwise in through mandrel and use a rubber-tipped compressed air blowgun to "inflate" the casting and pop it off the mandrel. (Plug the hole with a small piece of tape or foil if you don't want urethane to flow into the hole.)

A couple of ideas for consideration. Since it for rocket propellant, does the mandrel have to be absolutely straight? A slight taper would help a lot in sliding the cast part off the mandrel after release.

Second, could you use an arbor press to push the mandrel out of the casting? You might want to make a plate with a hole that is just bigger than the mandrel diameter for the casting to rest on instead of using the bit with various slots that comes with the arbor press. A slight ridge next to the hole would concentrate the force at the casting mandrel interface.

Fishing rods are made by curing graphite expoxy around a mandrel. They remove the mandrel by pulling as the mandrel is very long and slender. They use a mandrel with a couple of flats cut near the end pulled to make a simple way to pull. And they may use hydraulics to do the pulling. But I would think you could push.

Third, if you use a strap wrench the pressure is pushing inward around the entire outside of the casting making the casting grip the mandrel even more. If you applied pressure on two sides, the casting would distort and the sides orthogonal to the sides with pressure would release. Then apply pressure on both sides 90 degrees away from the sides where the pressure was originally applied to release the rest of the mandrel.

If you want to build something, how about taking a tube with the same id as the casting and as long as the casting or a little longer. Cutting it lengthwise into two pieces and welding them crosswise to some vise grips. Of course you would need to make three sizes.

=20 Dan

I'd add a presure regulator to your very excellent suggestion for additional control.

Wes

The mold release isn't working, have you considered a paper layer over the mandrel? If the paper sticks to the casting, would that really be a problem?

The idea of clamping around a torus to REMOVE it from a mandrel is flawed; that will just add to the friction. Your best bet would be to press the mandrel through a close-sized aperture, I suspect.

Split the mandrel and use a thin section of the same material to fill the split. Then cast the part and remove the center. The sides will collapse and free the casting.

In a previous job, I made a fixture that used compressed air to separate rubber rolls from their cores. It worked much better than the previous brute force method.