Extrusion machines force or pull unformed material into alignment guides and shaped dies to produce lengths of stock forms and cross-sectional shapes. They are used mainly in the plastics, metals, and composite-forming industries. Extrusion machines are also used in automotive, aerospace, and construction applications. The basic parts of an extruder include a tubular barrel, a revolving screw, and a ram or plunger within the barrel. An extruder also has a hopper at one end from which the material to be extruded is fed to the screw, ram, or plunger. A die at the opposite end is used for shaping the extruded mass. Extrusion machinery that can cut extruded materials into short or long intervals is also available.
There are many different types of extrusion machines. Often, suppliers categorize products by the material extruded or the extrusion technology. For example, plastic extruders are designed to shape plastic materials in pipe extrusion, profile extrusion, and sheet extrusion applications. Thermoplastic extrusion machines and rubber extrusion machines are also available. In terms of extrusion technology, there are two basic types: hot and cold. Hot extrusion machines form plastic, rubber, metal, or composite products from raw materials that have been preheated. Cold extrusion machines do not. Some hot extruders also provide hot spinning, the forming of metal parts from a flat, rotating disk that applies controlled pressure to one side and causes the metal to flow against a rotating male form.
Selecting extrusion machines requires an analysis of extruder screws, barrels, and tips. Screw materials include high-carbon, high-chrome, and proprietary tool steels. Nitriding, chrome plating, and carbide coating are common surface treatments for extruder screws. Extruder barrels are also made of tool steels, but often with wear-resistant or corrosion-resistant liners. There are four types of screw tips for extrusion machines: three-piece, four-piece, locking ring, and free flow. In plastics processing applications, extruder screws must provide consistent feeding, uniform melting, steady pumping, and homogenous mixing action. Screw section lengths, flight depth, flight pitch, length-to-diameter ratio, and radius are also important specifications to consider when selecting these components for rubber extrusion machinery, plastic extrusion machinery, and metal extrusion machinery.