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Indirect extrusion

Extrusion process in which a hollow die is pushed through a pressure chamber toward an ingot which is pushed back through the center of the die into a solid rod.

Illustration of Indirect extrusion

The process

The working material consists of a preheated ingot [1] placed in a pressure chamber [2]. A hollow plunger [3] with a hollow die [4] mounted on the end is pressed against the ingot with an applied pressing force which forces the ingot through the center of the die in the opposite direction to the pressing force. The ingot then assumes the same shape as the die cross section and is pushed out as a solid axially symmetric rod [5].

The friction force between the ingot and the pressure chamber is small when the ingot is pushed into and back through the die.

Advantages and disadvantages
In comparison with alternative methods
Less force than direct extrusion, less friction than direct extrusion
Large production runs
less tendency to fracture
Many kinds of raw materials
container last longer due to less wear
The cross sectional area is limited by the maximum size of the stem
Impurities and defects on the surface of the ingot affect extrusion surface