Extrusion
From Free net encyclopedia
- For the process that creates volcanic rock, see extrusive (geology).
Extrusion is a manufacturing process where a material, often in the form of a billet, is pushed and/or drawn through a die to create long objects of a fixed cross-section. Hollow sections are usually extruded by placing a pin or mandrel in the die. 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 specialised processes such as rollers inside a perforated drum for the production of many simultaneous streams of material.
Commonly extruded materials are copper (pipe for plumbing), aluminium (various extrusion profiles for tracks, frames, rails, mullions), steel (rod, track), titanium (aircraft components, including seat tracks, engine rings, structural parts), rubber (tire tread and sidewalls), a multitude of plastics (pipes, rods, rails, seals), and grains such as wheat, corn, and rice for food products.
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.
Plastic extrusion commonly uses plastic chip, which is heated and extruded in the liquid state, then cooled and solidified as it passes through the die. In some cases (such as fibre reinforced tubes) the extrudate is pulled through a very long die, in a process called pultrusion.
Extrusion simulation tools help to understand extrusion process and to optimize development of tools and products.
Food extrusion
Extrusion has found a great application in food processing. Various products like pastas, breakfast cereals, and ready to eat snacks are now manufactured by extrusion. Softer foods such as meringue have long been piped using pastry bags.