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 (producing many short pieces). Some materials are hot drawn whilst 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.
Commonly extruded materials include metals, polymers, ceramics, and foodstuffs.
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[edit] Metal
Metal extrusion is used by industry for various purposes such as:
- Copper pipe for plumbing
- Aluminium extrusion profiles for tracks, frames, rails, and mullions
- Steel rods or track
- Titanium aircraft components including seat tracks, engine rings, and other structural parts
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.[citation needed]
[edit] Plastic (Injection moulding)
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]
[edit] Ceramic
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 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.
[edit] 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.
