Extrusion is a process used to create objects of a fixed cross-sectional profile by pushing material through a die of the desired cross-section. Its two main advantages over other manufacturing processes are its ability to create very complex cross-sections; and to work materials that are brittle, because the material encounters only compressive and shear stresses. It also creates excellent surface finish and gives considerable freedom of form in the design process.
Extruded aluminium with several hollow cavities; T slots allow bars to be joined with special connectors.
Clay body being extruded from a de-airing pug
HDPE pipe during extrusion. The HDPE material is coming from the heater, into the die, then into the cooling tank. This Acu-Power conduit pipe is co-extruded - black inside with a thin orange jacket, to designate power cables.
Extrusion of a round metal through a die
A polymer
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic and natural polymers play essential and ubiquitous roles in everyday life. Polymers range from familiar synthetic plastics such as polystyrene to natural biopolymers such as DNA and proteins that are fundamental to biological structure and function. Polymers, both natural and synthetic, are created via polymerization of many small molecules, known as monomers. Their consequently large molecular mass, relative to small molecule compounds, produces unique physical properties including toughness, high elasticity, viscoelasticity, and a tendency to form amorphous and semicrystalline structures rather than crystals.
Appearance of real linear polymer chains as recorded using an atomic force microscope on a surface, under liquid medium. Chain contour length for this polymer is ~204 nm; thickness is ~0.4 nm.
A polyethylene sample that has necked under tension
A plastic item with thirty years of exposure to heat and cold, brake fluid, and sunlight. Notice the discoloration and crazing of the material (compared with replacement item in foreground).
Chlorine attack of acetal resin plumbing joint