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[Medieval Latin extrūsiō, extrūsiōn-, from Latin extrūsus, past participle of extrūdere, to thrust out. See extrude.]
The forcing of solid metal through a suitably shaped orifice under compressive forces. Extrusion is somewhat analogous to squeezing toothpaste through a tube, although some cold extrusion processes more nearly resemble forging, which also deforms metals by application of compressive forces. Most metals can be extruded, although the process may not be economically feasible for high-strength alloys.
The most widely used method for producing extruded shapes is the direct, hot extrusion process. In this process, a heated billet of metal is placed in a cylindrical chamber and then compressed by a hydraulically operated ram (see illustration). The opposite end of the cylinder contains a die having an orifice of the desired shape; as this die opening is the path of least resistance for the billet under pressure, the metal, in effect, squirts out of the opening as a continuous bar having the same cross-sectional shape as the die opening. By using two sets of dies, stepped extrusions can be made.
The extrusion of cold metal is variously termed cold pressing, cold forging, cold extrusion forging, extrusion pressing, and impact extrusion. The term cold extrusion has become popular in the steel fabrication industry, while impact extrusion is more widely used in the nonferrous field.
Schematic of the direct, hot extrusion process.
The original process (identified as impact extrusion) consists of a punch (generally moving at high velocity) striking a blank (or slug) of the metal to be extruded, which has been placed in the cavity of a die. Clearance is left between the punch and die walls; as the punch comes in contact with the blank, the metal has nowhere to go except through the annular opening between punch and die. The punch moves a distance that is controlled by a press setting. This distance determines the base thickness of the finished part. The process is particularly adaptable to the production of thin-walled, tubular-shaped parts having thick bottoms, such as toothpaste tubes.
Advantages of cold extrusion are higher strength because of severe strain-hardening, good finish and dimensional accuracy, and economy due to fewer operations and minimum of machining required. See also
The movement of teeth beyond the natural occlusal plane that may be accompanied by a similar movement of investing tissues.
A formation of rock made of magma which has erupted onto the earth's surface as lava and has then solidified. The crystals in extrusive rocks are small, since the lava solidifies rapidly, giving little time for crystal growth. Extrusions emerge from fissure eruptions and volcanoes.
For more information on extrusion, visit Britannica.com.
1. The process of producing metal shapes of a constant cross section by forcing the hot metal through an orifice in a die by means of a pressure ram.
2. Any item made by this process.
A pushing out; e.g. an orthodontic procedure which makes a tooth emerge further from its alveolus.
Extrusion is a manufacturing process used to create long objects of a fixed cross-sectional profile. A material, often in the form of a billet, is pushed and/or drawn through a die of the desired profile shape. Hollow sections are usually extruded by placing a pin or piercing mandrel inside of the die, and in some cases positive pressure is applied to the internal cavities through the pin. Extrusion may be continuous (producing indefinitely long material) or semi-continuous (producing many short pieces). Some materials are hot drawn while others may be cold drawn.
The feedstock may be forced through the die by various methods. A single or twin screw auger, powered by an electric motor, or a ram, driven by hydraulic pressure (for steel alloys and titanium alloys for example), oil pressure (for aluminum), or in other specialized processes such as rollers inside a perforated drum for the production of many simultaneous streams of material.
Extrusion simulation tools help to understand the extrusion process and to optimize development of tools and products.
Extrusion is also the first step in the process of extrusion and spheronization, a commonly used process in the pharmaceutical industry.
Commonly extruded materials include metals, polymers, ceramics, and foodstuffs.
Metal extrusion is used by industry for various purposes such as:
Steel and titanium extrusions use glass powder as a lubricant. Invented in France in 1935 by Mr. Séjournet, this process was patented throughout the world and helped launch industrial steel extrusion, and was later applied to titanium where it was more effective[citation needed]
Plastic extrusion commonly uses plastic chips or pellets, which are usually dried in a hopper before going to the feed screw. The polymer resin is heated to molten state by a combination of heating elements and shear heating from the extrusion screw. The screw forces the resin through a die, forming the resin into the desired shape. The extrudate is cooled and solidified as it is pulled through the die or water tank. In some cases (such as fibre-reinforced tubes) the extrudate is pulled through a very long die, in a process called pultrusion.
A multitude of polymers are used in the production of plastic tubing,[1] pipes, rods, rails, seals, and sheets or films.[2]
Ceramic can also be formed into shapes via extrusion. Terracotta extrusion is used to produce pipes. Many modern bricks are also manufactured using a brick extrusion process.[3] Some Play-Doh toy products also make use of extrusion. Play-Doh is a modeling compound with similar physical properties to clay, but it is not actually ceramic.
Extrusion has found great application in food processing. Products such as pastas, breakfast cereals, Fig Newtons, prefab cookie dough, Sevai, Idiappam, and ready-to-eat snacks are now manufactured by extrusion. 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.
Extrusion is also a very important unit operation in shaping a catalyst. The shape of a catalyst is directly related to its working conditions. A high specific surface can be obtained by extrusion.
"Painted" road markings are often done with extruded two- or three-component compounds. Thermoplastics are also common. This is a low-pressure, high-flow process with very good contour and thickness control. Extrusion has more or less completely replaced the older "sliding mold" method. Benefits are much better economy, higher speed, and general appearance.
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 | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved. Read more |
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| Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved. Read more |
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| Dental Dictionary. Mosby's Dental Dictionary. Copyright © 2004 by Elsevier, Inc. All rights reserved. Read more |
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| Geography Dictionary. A Dictionary of Geography. Copyright © Susan Mayhew 1992, 1997, 2004. All rights reserved. Read more |
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| Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved. Read more |
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| Architecture. McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc. All rights reserved. Read more |
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| Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved. Read more |
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| Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Extrusion". Read more |
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