What Is Extrusion?
Extrusion, from the Latin past participle extrudere meaning “to thrust out,” refers both to the process in which material is forced through a die or series of dies in order to shape it as well as to the product of that operation. It also refers to the outpouring of lava from a volcano. The process is used in the home and in manufacturing. The shapes most often produced by extrusion include round objects like tubes, rods, and pipes, rectangular objects like solid and hollow bars, and plates.
In the home, the most familiar example of extrusion may be the pastry bag. Used to form cookies and to frost cakes, the pastry bag extrudes icing or dough through a tip that shapes the output. This kind of extrusion is done in short bursts to produce a set of identical items speedily. Kitchen equipment that makes pasta or sausage may also feature an extruder that shapes the finished product. A very popular toy extrusion machine is the accessory sold with Play-Doh, a modeling compound made by Hasbro. The user selects a die and slides it across the front of the machine, inserts the soft material, and presses the handle to produce either long or short extrusions in the shape desired.
In manufacturing, extrusion is used with a variety of materials, including metal, plastic, ceramics, and food. Different materials undergo extrusion to make different types of products. Copper is extruded to make pipes for plumbing, while aluminum is used to make frames, such as window frames, tracks, and railings. Steel is extruded into tracks or rods, and some titanium aircraft parts are produced through extrusion. Plastic extrusion results in an array of shapes, including cylindrical tubes, pipes, and rods, rails, and very thin rectangular surfaces which are characterized as sheets or films.
Food manufacturing uses extrusion in ways that go beyond what is possible in the standard home kitchen. Cheese curls and other snacks, pastas, cereals, and nutritional bars all are made using extrusion, as are a number of pet foods. In fact, extruded foods is a food science specialty, and scientists who have training and experience in this particular realm of food manufacturing oversee these processes. There is debate over whether extrusion, in at least some cases, reduces the nutritional quality of food.
Written by Mary Elizabeth
