The Science Definition of Extrusion
A large number of applications of special extrusion technologies, such as powder extrusion and composite extrusion (Al-clad steel wire and low-temperature superconducting materials); In March 1956, a U.S. patent was filed for a «hot metal extrusion process.» Patent US3156043 A describes that a number of important benefits can be obtained by hot extrusion of ferrous and non-ferrous metals and alloys when an extruder billet changes its physical properties in response to physical forces by heating it to a temperature below the critical melting point. [3] Hot extrusion occurs above room temperature, but below the material`s recrystallization temperature, temperatures range from 800 to 1800 °F (424 to 975 °C). It is typically used to achieve the right balance between required forces, ductility and final extrusion properties. [4] Extrusion is the most commonly used secondary processing method for MMC, where a billet of MMC is first placed in an extrusion chamber with a die at the end and a piston at the other end. By applying a force, the billet undergoes a gradual reduction of the surface area by the relatively narrow tool to obtain long profiles with constant cross-section, which are determined by the geometry of the tool. Fig. 16 shows three types of extrusion, namely direct, conventional and hydrostatic. In direct extrusion, there is a dead zone near the die where extruded materials cannot flow. In conventional extrusion, the die is modified to minimize the dead zone, but the conical die generates matrix friction more easily than that of a flat die, resulting in higher strain stress at the MMC/matrix interface, which can lead to fractures of the material such as serrated edges. To solve the problem of dead zone and material discontinuities, hydrostatic extrusion is proposed by performing extrusion in a high-pressure fluid.
Due to the minimized contact surface between the material and the tool, an almost hydrostatic state and minimal friction effect in the billet can be achieved in this high-pressure fluid. When Portia received this extrusion verdict, she turned to her poet for financial compensation. The extrusion process is generally economical when it produces between several kilograms (pounds) and several tons, depending on the extruded material. There is a transition point where profiling becomes more economical. For example, some steels become more economical to roll if they produce more than 20,000 kg (50,000 lb). [2] In general, high-temperature extrusion is used for the production of ready-to-eat snacks, while cold extrusion is used for the production of pasta and related products for subsequent cooking and consumption. Processed products have low humidity and therefore a much longer shelf life and offer consumers variety and convenience. Back of the cube.
The wall thickness of the extrusion is 3 mm (0.12 inches). The design of an extrusion profile has a significant impact on the ease with which it can be extruded. The maximum size of an extrusion is determined by finding the smallest circle that fits around the cross-section, this is called a circumscriptive circle. This diameter, in turn, controls the size of the tool needed, which ultimately determines whether the workpiece fits into a particular press. For example, a larger press can process circuits 60 cm (24 inches) in diameter for aluminum and 55 cm (22 inches) in diameter for steel and titanium. [1] Direct extrusion and downstream extrusion are widely used in the manufacture of pipe structures, and the extrusion process called combined or integrated extrusion has also been developed. Integrated extrusion is a combination of two or three direct extrusion, rearward extrusion and radial extrusion processes (Matsumoto et al., 2014; Hwang et al., 2005). Three important factors must be critically controlled during extrusion. These include: (1) extrusion ratio, (2) extrusion temperature, and (3) extrusion speed. These factors can significantly affect the mechanical performance of final extruded MMCs. Wang et al. (2011) and Tun and Gupta (2008) found that the distribution of reinforcements, whether micron-SiC particles or nano-Y2O3 particles in Mg matrix composites, can be improved when the extrusion ratio is increased.
In addition, increasing the extrusion ratio of nano-Y2O3/Mg composites produced by PM also reduced porosity as well as refined grains, resulting in improved mechanical properties. The extrusion temperature has a strong influence on the dynamic recrystallization (DRX) of the metal matrix during extrusion. If the extrusion temperature is too low, the XRD process is not complete, resulting in many large grains after extrusion, however, a high extrusion temperature would induce significant grain size growth, which has been demonstrated in micron-SiC-reinforced AZ91 alloy composites (Wang et al., 2011). Extrusion speed can also affect the final mechanical properties of MMCs. Sun et al. (2018) investigated the effects of extrusion velocity on the mechanical properties and microstructure of SiCp/AZ91 composite. They showed that a reduction in extrusion speed (from 1.0 mm/s to 0.01 mm/s) could significantly improve yield strength (YS) and tensile strength (UTS), mainly due to grain refining and precipitation in phase Mg17Al12. However, ductility decreased significantly, which also limited the use of this material. In addition, some researchers have focused on optimizing the parameters of the extrusion nozzle. For example, Huang et al. (2016) investigated the effects of extrusion matrix angle on the microstructure and properties of composites (TiB + TiC)/Ti6Al4V in situ of the Ti matrix.
They stated that tensile strength and ductility were reduced when the angle of the extrusion tools increased from 45° to 75°, and suggested that the optimal angle of the extrusion tools be less than 60°. Cold extrusion takes place at or near room temperature. The advantages of this hot extrusion over hot extrusion are no oxidation, higher resistance due to cold deformation, tighter tolerances, better surface finish, and fast extrusion speeds when the material is exposed to hot brevity. [1] Friction extrusion was invented at the Welding Institute in the UK and patented in 1991. Originally, it was primarily designed as a process for producing homogeneous microstructures and particle distributions in metal matrix composites. [5] Friction extrusion differs from conventional extrusion in that the load (billet or other precursor) rotates relative to the extrusion nozzle. An extrusion force is applied to press the load against the die. In practice, the cube or load can rotate or be counter-rotating. The relative rotational motion between the load and the die has several significant effects on the process. First, the relative motion in the plane of rotation leads to large shear stresses, resulting in plastic deformation in the filler layer in contact with and near the die.
This plastic deformation is dissipated by recovery and recrystallization processes, resulting in significant heating of the deformation load. Due to strain heating, friction extrusion usually does not require auxiliaries to preheat the load, which can result in a more energy-efficient process. Second, the large plastic deformation in the relative rotational motion range can promote solid-state welding of powders or other finely dispersed precursors such as flakes and chips and effectively enhance the load before extrusion (friction consolidation). [6] Extrusion coating is the process of applying a thin adhesive film made of plastic material to a non-plastic continuous substrate such as paper, cardboard or film. The process is similar to extrusion of cold roll films. A high melting temperature is used with a downward splitting nozzle to create a low-viscosity melting path that adheres to the substrate. If necessary, the substrate can be pre-treated to improve adhesion. The tape is directed against the surface of the substrate between a pressure roller and a cooling roller immediately before entering the pinch. The thickness of the layer is determined by the extrusion speed and the line speed of the substrate. The cooling roller controls the surface quality of the coating. Extrusion coatings are usually applied in thin films up to 0.005 mm.
Plastic extrusion typically uses plastic chips or pellets, which are usually dried to expel moisture into a hopper before going to the feed screw. The polymer resin is heated by a combination of heating elements and shear heating of the extrusion screw to the molten state. The screw, or screws as in twin-screw extrusion, pushes the resin through a die and shapes the resin into the desired shape. The extrudate is cooled and solidified when pulled through the die or water tank. A «puller» (called «puller» in the United States) is used to create tension on the extrusion line, which is essential for the overall quality of the extrudate. Granulators can also generate this tension while pulling extruded strands for cutting. The trigger of the track must ensure smooth traction; Otherwise, there will be deviations in cutting lengths or deformed products. In some cases (such as fiber-reinforced tubes), the extrudate is sucked through a very long die in a process called pultrusion.
