AskDefine | Define extrusion

Dictionary Definition



1 something that bulges out or is protuberant or projects from a form [syn: bulge, bump, hump, gibbosity, gibbousness, jut, prominence, protuberance, protrusion, excrescence]
2 squeezing out by applying pressure; "an unexpected extrusion of toothpaste from the bottom of the tube"; "the expulsion of pus from the pimple" [syn: expulsion]

User Contributed Dictionary



  1. A manufacturing process where a billet of material is pushed and/or drawn through a die to create a shaped rod, rail or pipe.
  2. An item formed by the process of extrusion.

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Extensive Definition

Extrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed or drawn through a die of the desired cross-section. The two main advantages of this process over other manufacturing processes is its ability to create very complex cross-sections and work materials that are brittle, because the material only encounters compressive and shear stresses. It also forms finished parts with an excellent surface finish.
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, and foodstuffs.


In 1797, Joseph Bramah patented the first extrusion process for making lead pipe. It involved preheating the metal and then forcing it through a die via a hand driven plunger. The process wasn't developed until 1820 when Thomas Burr constructed the first hydraulic powered press. At this time the process was called squirting. In 1894, Alexander Dick expanded the extrusion process to copper and brass alloys.


The process begins by heating the stock material. It is then loaded into the container in the press. A dummy block is placed behind it where the ram then presses on the material to push it out of the die. Afterwards the extrusion is stretched in order to straighten it. If better properties are required then it may be heat treated or cold worked.
Another breakthrough in lubrication is the use of phosphate coatings. With this process, in conjunction with glass lubrication, steel can be cold extruded. The phosphate coat absorbs the liquid glass to offer even better lubricating properties. Some Play-Doh toy products also make use of extrusion.


Extrusion has found great application in food processing. Products such as pastas, breakfast cereals, Fig Newtons, prefab cookie dough, Sevai, Idiappam, jalebi and ready-to-eat snacks are now manufactured by extrusion. Krispy Kreme doughnuts are also manufactured by extrusion to keep the doughnuts uniform in shape and size. Softer foods such as meringue have long been "piped" using pastry bags. Extrusion is also used with grains such as wheat, corn, and rice. In feed industry it is used for process with floating and slow sinking feed.


The following guidelines should be followed to produce a quality extrusion. The maximum size for an extrusion is determined by finding the smallest circle that will fit around the cross-section (called the circumscribing circle). This diameter, in turn, controls the size of the die required, which ultimately determines if the part will fit in a given press. For example, a larger press can handle 25 inch diameter circumscribing circles for aluminium and 22 in. diameter circles for steel and titanium.
Thicker sections generally need an increased section size. In order for the material to flow properly legs should not be ten times longer then their length. If the cross-section is asymmetrical, adjacent sections should be as close to the same size as possible. Sharp corners should be avoided; for aluminium and magnesium the minimum radius should be 1/64 in. and for steel corners should be 0.030 in. and fillets should be 0.125 in. The following table lists the minimum cross-section and thickness for various materials.


  • Schmid, Serope Kalpakjian and Steven R. Manufacturing Engineering and Technology, Fifth Edition. Pearson Prentice Hall, 2006.
extrusion in German: Extrusion (Verfahrenstechnik)
extrusion in Spanish: Extrusión
extrusion in French: Extrusion
extrusion in Italian: Estrusione
extrusion in Dutch: Extruderen
extrusion in Norwegian: Ekstrudering
extrusion in Portuguese: Extrusão
extrusion in Russian: Экструзия (технологический процесс)
extrusion in Finnish: Ekstruusio
extrusion in Swedish: Extruder
extrusion in Ukrainian: Екструзія

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