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Processing of Biodegradable Composites
Published in Arbind Prasad, Ashwani Kumar, Kishor Kumar, Biodegradable Composites for Packaging Applications, 2023
Gourhari Chakraborty, Arbind Prasad, Ashwani Kumar
Extrusion is a process that involves forcing molten polymer through a die to create components with a set cross-sectional area, such as tubes and rods. Extrusion is the technique of forcing softened polymer through a die with an opening to produce long products having a consistent cross-section (rods, sheets, pipes, films, and wire insulation coating). Through a hopper, the polymer material in the form of pellets is fed into an extruder. The material is then driven into a die by a feeding screw, turning it into a continuous polymer product. The polymer is softened and melted by heating sources positioned above the barrel. The material’s temperature is controlled by thermocouples. Blown air or a water bath is used to cool the product as it exits the die. Polymer extrusion (unlike metal extrusion) is a continuous operation that lasts as long as feedstock pellets are available [34,35]. Extrusion is primarily used for thermoplastics, but it can also be utilized for elastomers and thermosets. Cross-linking occurs as the material is heated and melted in the extruder.
Viscous and Viscoelastic Dampers
Published in Suhasini Madhekar, Vasant Matsagar, Passive Vibration Control of Structures, 2022
Suhasini Madhekar, Vasant Matsagar
Extrusion is a process in which metal is pushed through a die opening placed in a closed container to mold it in a desired shape. When a polycrystalline metal deforms, its grains are dislocated. Elongation of such grains with large gaps is seen in metal deformation. Further, such metals try to regain their original configurations by the three inter-linked processes, i.e., recovery, recrystallization, and grain growth. Recrystallization is the process of replacing the displaced grains with a fresh set of defect-free grains, until growth of new grains takes place. The temperature at which half of the total recrystallization of grains happens for a period of one hour, is known as recrystallization temperature. Recrystallization temperature differs for various metals; for example, lead has recrystallization temperature well below 20°C. As the recrystallization temperature of lead is very less, compared to other metals, any deformation of lead is simultaneous with the processes of recovery, recrystallization, and grain growth. This property of lead makes it suitable than all other metals as an energy absorber.
Aluminum-Manufacturing Methods
Published in Raghu Echempati, Primer on Automotive Lightweighting Technologies, 2021
Aluminum is the most commonly extruded material and can be extruded when hot (450–500 °C) or cold. There are two main types of extrusion processes: direct extrusion and indirect extrusion (Figures 4.12–4.17). Direct extrusion is the most common extrusion process and is also referred to as forward extrusion. Direct extrusion is the process where a cylindrical billet is placed in a chamber and forced through an extrusion die by a ram. The process is simple; however, the ram must overcome the frictional forces between the billet and the chamber. Indirect extrusion is where the die moves toward the billet and there is no relative motion between the billet and container. In the indirect extrusion process, there is negligible friction between the billet and the container because there is no relative motion between the two. This reduces the pressure of extrusion required in operations that typically have high billet-container friction. Despite this advantage, in indirect extrusion, the die is effectively the ram and is less rigid than a ram used for direct extrusion. This limits the amount of force that can be applied in the indirect extrusion process. Indirect extrusion is also more complicated than direct extrusion. Diagrams of both the extrusion processes as well as the extrusion forces with respect to ram displacement are shown in Figures 4.15 to 4.17.
Influence of single phase NiS nanoparticles as lubricant additive in microscale deformation of copper gear
Published in Australian Journal of Mechanical Engineering, 2023
One further important consideration during micro-extrusion is friction. The size effect and friction coefficient may be greatly reduced in micro-extrusion using surface die coatings (Ghassemali et al. 2013; Krishnans, Cao, and Dohda 2007). Extruded products benefit greatly from using a liquid lubricant, which also helps reduce extrusion force and enhances surface quality. When a lubricant is applied, the load is transferred to the lubricant layer instead of the surfaces themselves. The typical liquid lubricant is driven out of the rough valley of the die orifice as the forming load rises in the micro-extrusion process, increasing friction between the tool and the workpiece. The film’s hydrodynamic pressure may cause the solid surfaces to flex elastically (Wang et al. 2016). Two different NiS concentrations were blended with SAE 20 W-40 motor oil to mitigate these results.
Thermal performance exploration of 3D printed cob
Published in Architectural Science Review, 2019
Mohamed Gomaa, Jim Carfrae, Steve Goodhew, Wassim Jabi, Alejandro Veliz Reyes
This study, on the other hand, has exposed major challenges of cob 3D printing during the early stage of experimentation. Three main challenges were specified: extrusion speed, consistency of extrusion, and continuity of extrusion. Hence, the project team has been developing an innovative bespoke large-scale cob extruder that has improved dramatically the preceding challenges. The new extrusion system is capable of achieving variable high speeds up to 0.3 m/sec, while combining an enhanced cartridges system that allows a continuous extrusion of material. The details of the new system will be introduced as part of a future study. Another line of future studies will focus on establishing a viable business model, utilizing robotically fabricated building components for small-scale building solutions.
Central bursting prediction in axisymmeric extrusion process through dies of any shape
Published in Australian Journal of Mechanical Engineering, 2020
The main factor affecting an extrusion process is the die shape. Therefore, the determination of the specific die shape, which meets the minimum extrusion pressure, is important. In Figure 9, relative extrusion pressure for the streamlined die shape, Equation (43), and the conical die, with the same length, obtained from the upper bound solution are compared with each other. Because streamlined die shape has a smooth transition at the entrance and exit; the extrusion pressure of this curved die is lower than the conical die. It is observed that, for each die shape there is an optimal die length, which minimises the required extrusion pressure. It is seen from the figure that the optimal die length of the streamlined die is smaller than the conical die.