Method and apparatus for manufacturing dimpled structures from elastic cloth

DETAILED DESCRIPTION An object of this invention is, therefore, to provide a method of forming complex shapes with foamable polyimide precursor materials.
Another object is to provide a method of producing complex polyimide foam shapes having improved density uniformity.
A further object is to provide a method of distributing particulate materials through a polyimide foam structure in a selected distribution pattern.
The above objects, and others, are accomplished in accordance with this invention by a method of producing polyimide foam products having complex shapes and compositions which comprises the steps of providing a low density, open cell, reticulated foam body having a desired complex shape, impregnating the reticulated foam shape with a polyimide foam precursor and heating the assembly in a closed mold to the foaming and curing temperature of the polyimide precursor.
As the polyimide precursor foams, it fills the interstices of the reticulated foam, producing a polyimide foam product conforming to the mold shape, which is ordinarily the reticulated foam shape.
In some cases, it is desirable to remove the reticulated foam material from the final product.
Where the reticulated foam material has a sufficiently low melting and vaporization point, it will evaporate away during the high temperature cure of the polyimide foam.
For a number of ultimate purposes, it is desirable to substantially uniformly distribute a particulate material throughout the polyimide foam product.
Merely mixing the particulate material with the polyimide precursor is ordinarily not effective, particularly where the density of the particulate material is high, since the particulate material will tend to settle or otherwise not remain evenly distributed as the foam expands.
Those materials can be incorporated into, or coated on, the reticulated foam material.
That material will remain in place as the foam expands, assuring the desired distribution.
Depending on how the particulate material is applied onto the reticulated foam material, the distribution can be uniform or graded in any desired manner