Analysis of Isostatic Pressing Force of No Rigid Support

The following figure is isostatic pressing force figure, which can be divided into two models: circular and rectangular.

1.Round model
The pressure of the isostatic pressing blank is equal in everywhere. At the beginning of pressing, the powder particle outer layer is pressed first, and the movement of the powder particle starts from the surface and points to the interior of the powder along the surface direction.
The filling of the powder particles begins with the outer layer and gradually push the interior. Especially at the beginning of densification, filling the plastic areas (in this case, is the rubber mold). The core density of the blank is smaller than the edge density, and the density difference decreases gradually as the compression continues.
In the general molding process, only along the direction of the displacement pressure of particles, which are compressed in this direction; but for the spherical (or cylindrical) products isostatic pressing process, in addition to radial displacement of particles also have circumferential displacement, both have radial compression and circumferential compression. Because of the circumferential compression, the densification process is more rapid when the radial displacement is the same.
Due to the above characteristics, for spherical (or cylindrical) products, the surface of the body is preferentially densified. A thin, closed, thin layer of surface that prevents pressure from passing through the center of the heart, forming what is known as a thin shell vault.

In view of this, spherical or cylindrical isostatic pressing products have a large difference in surface density and core density, which can not even be eliminated by sintering.

2. Rectangle model
Through the analysis of the spherical model, when the section of product is a rectangle, the edge angle will be compressed, forming front point, but does not produce products such as round as the "dome shell" structure, so the density is less than circular products, but due to the existence of friction, the density difference still exists.
 

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