Extrusion
From Wikipedia, the free encyclopedia
- For the process that creates volcanic rock, see extrusive (geology).
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 (repeatedly producing many shorter pieces). Some materials are hot drawn whilst others may be cold drawn.
The feedstock may be forced through the die by various methods: by an auger, which can be single or twin screw, powered by an electric motor; by 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.
Commonly extruded materials include; Metals, Polymers, Ceramics, and Foodstuffs.
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[edit] Metal extrusion
Metal extrusion is used by industry for various purposes such as;
Steel and titanium extrusions use glass powder as a lubricant. This process was invented in France, in 1935 by Mr Séjournet. This solution was patented throughout the world and helped launch industrial steel extrusion. The process was later applied to titanium.
[edit] Plastic extrusion
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 as it is fed to the extrusion tooling. The die molds the heated mass 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]
Plastic Extrusion is also involved in the process of injection molding.
[edit] Ceramic extrusion
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.
[edit] Food extrusion
Extrusion has found a great application in food processing. Various products like pastas, breakfast cereals, Fig Newtons, prefab cookie dough, 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.
[edit] Extruded roadmarking compound
"Painted" roadmarkings 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 mould" method. Benefits are much better economy, higher speed, and general appearance.
