CLOSED MOLD TRAPPED RUBBER MOLDING 3

[bigINNER]

WONDERING WHAT TYPE OF PRESSURES CAN BE DEVELOPPED IN TRAPPED RUBBER MOLDING. IF I KNOW THE CTE OF THE RUBBER AND THE MAX COMPRESSIVE STRESS OF IT, IT FEELS LIKE I WOULD STILL BE MISSING SOMETHING IN THE EQUATION TO CALCULATE THE EQUIVALENT PRESSURE (CONSIDERING THAT I WOULD BE FILLING-IN RUBBER/SILICONE BEADS).

I AM HOPING TO MY REPLACE BLADDER MOLDING PROCEDURE OF 140 PSI.

THANKS

 

[Dentarthurdent]

Huge pressures can be developed in trapped rubber moulding, depending on the stiffness of the mould. The difficult bit is getting a low enough pressure not to distort things too much. You will need CTE and Bulk Modulus values for the rubber, a bit of internet searching should bring up the required formulas.

If, as I think you're suggesting, you want to use rubber beads, then you will have to compress the air between the beads before you will start to generate any pressure. As a guide, random packing of spheres will give you approximately 36% air content by volume.

Sounds like an interesting application, be interested to hear how you get on.

 

[G1DESIGN]

cna anyone explain a bit more about this procedure

we use closed mould bladders but would like to know more about how this works

 

[Compositepro]

Trapped rubber molding is a process where the high coefficient of thermal expansion (CTE) of rubber is used to generate high pressures while curing thermoset composites in closed molds.

For example prepreg can be wrapped around a 1" diameter rubber cylinder and placed in a closely fitting steel tube at room temperature. When heated to 250F the rubber expands much more than the steel. The pressure generated depends on the CTE of rubber versus steel, the temperature rise, the volume of rubber, the initial void volume, the bulk modulus of the rubber, and resin bleed, if any.

The rubber can also be placed around the part and because it is restrained from expanding outward it will expand inward.

The process is very effective but isn't used much because of it complexity in application to each individual part. Also there are often problems with longevity of the rubber in contact with uncured epoxy resins.