The extrusion process uses heat, pressure, and cooling to create complex cross-sectional patterns in materials such as plastic, aluminum, ceramics, metals, and even food. It produces strong and durable fittings and parts that are difficult to shape using other methods. The process involves feeding raw material into a heated barrel, forcing it through a shaped die, and cooling it to harden. The temperature, pressure, and extrusion ratio are crucial factors in determining the best extrusion method.
Often, manufactured parts are designed to have a certain complex cross-sectional pattern, with fillets, flanges, protrusions and flat edges that need to be built into a particular shape with specific tolerances in the finished product. The production of these special shapes or cross sections is usually done using an extrusion process. This process uses heat, pressure and cooling to produce a semi-liquid, or paste, to be forced through a mold and, after exiting the mold, hardened to a designated temper.
The extrusion process is most frequently used to form plastic and aluminum parts or products. However, ceramics, heavier metals or alloys, and foods such as pasta are also shaped and produced through the extrusion process. Basically, as long as a material can be easily liquefied, it can be extruded.
The extrusion process differs from stamping or molding, for example, in that the extruded material will form intricate, strong, and durable fittings, parts, and pieces from a brittle material that is difficult to shape by stamping, bending, or hammering. Complex cross-sections such as hollow tubes or solid pieces or bars with flanges or fins are much easier to produce through the extrusion process. Additionally, the finished surface of extruded products is consistently of higher quality than molded or stamped products.
Basically, the extrusion process involves loading small pieces of raw material or stock into a hopper at one end of the extruder. In the case of the plastic extrusion process, this raw material is called pellets and in the aluminum extrusion process, billets. The crude is fed from the hopper into the extruder, essentially a heated barrel, where it is softened. A ram, usually a worm gear, forces the slurry feedstock through a smaller chamber, then through a shaped die. From the mold, the shaped football extrusion, rope, tube or rod, is cooled with water or air, along the discharge table to harden. At the end of the depletion table, the cured product is cut, wrapped, shipped, or sent on for further refining.
Both heated and cold raw materials are changeable for extrusion process. Naturally, the colder feedstock, pellets or billets, for example, require much higher pressure to force the less malleable material through the smaller chamber and die. The temperature and pressure factors in the extrusion process are crucial to the tempering, strength and finish of the final product. The extrusion ratio, the division of the cross-sectional area of the entire die by the cross-sectional area of the extruded product, is also critical in determining the best extrusion method, cold or hot, high or low pressure.
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