Extrusion facts for kids
Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed through a die of the desired cross-section. The two main advantages of this process over other manufacturing processes are its ability to create very complex cross-sections, and to work materials that are brittle, because the material only encounters compressive and shear stresses. It also forms parts with an excellent surface finish.
Drawing is a similar process, which uses the tensile strength of the material to pull it through the die. This limits the amount of change which can be performed in one step, so it is limited to simpler shapes, and multiple stages are usually needed. Drawing is the main way to produce wire. Metal bars and tubes are also often drawn.
Extrusion may be continuous (theoretically producing indefinitely long material) or semi-continuous (producing many pieces). The extrusion process can be done with the material hot or cold. Commonly extruded materials include metals, polymers, ceramics, concrete, modelling clay, and foodstuffs. The products of extrusion are generally called "extrudates".
Also referred to as "hole flanging", hollow cavities within extruded material cannot be produced using a simple flat extrusion die, because there would be no way to support the centre barrier of the die. Instead, the die assumes the shape of a block with depth, beginning first with a shape profile that supports the center section. The die shape then internally changes along its length into the final shape, with the suspended center pieces supported from the back of the die. The material flows around the supports and fuses together to create the desired closed shape.
The extrusion process in metals may also increase the strength of the material.
Images for kids
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HDPE pipe during extrusion. The HDPE material is coming from the heater, into the die, then into the cooling tank. This Acu-Power conduit pipe is co-extruded - black inside with a thin orange jacket, to designate power cables.
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Extrusion of a round metal through a die.
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A horizontal hydraulic press for hot aluminum extrusion (loose dies and scrap visible in foreground)
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Two-piece aluminum extrusion die set (parts shown separated.) The male part (at right) is for forming the internal cavity in the resulting round tube extrusion.
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Plot of forces required by various extrusion processes.
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Sectional view of a plastic extruder showing the components
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Sectional view of how a caterpillar haul-off provides line tension
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Elbow macaroni is an extruded hollow pasta.
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Front side of a four family die. For reference, the die is 228 mm (9.0 in) in diameter.
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Close up of the shape cut into the die. Notice that the walls are drafted and that the back wall thickness varies.
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Back side of die. The wall thickness of the extrusion is 3 mm (0.12 in).
See also
In Spanish: Extrusión para niños
