Extrusion

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 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.

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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 where it was more effective^{[citation needed]}

Plastic

  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

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.

Food

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. 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.

Catalysis

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.

Road marking compound

"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.

See also

• Plastics extrusion
• Injection moulding
• Hydrostatic Extrusion
• Equal Channel Angular Extrusion
• Impact Extrusion