Plastic deformation processing extrusion

Plasticity. Slip, the gliding motion of full planes of atoms or partial planes, called dislocation, allows for the deformation processing of polycrystalline metals (forging, extrusion, rolling, swaging, and drawing). Slip occurs much more readily across close-packed planes in close-packed directions. 

It was considered initially that because there is no net tensile stress in a hydrostatic extrusion process it might be possible to impose very large plastic deformations without incurring fracture. It was indeed shown that Rj, of 30 can be imposed in polyethylene comparable to the draw ratios of 30 adiieved in a tensile drawing process, and that both processes are limited by the strain hardening behaviour of the material, which is determined solely by the total plastic strain imposed. This led to an important... 

Keywords Additives, Compounding, Deformation of melts, Extrusion foaming. Flow properties, Influences of processing on properties. Injection molding. Plastic melts, Processing of elastomers and thermosets. Processing of fiber composites. Processing of thermoplastics... 

When a PP is extruded and taken-up at a high draw ratio and crystallized under a high stress and annealed, a lamella-stacked structure is formed. In this structure, the lamellae are oriented perpendicular to the extrusion direction and connected by the tie molecules. When such an extrudate is stretched in the extrusion direction, the lamellae open elastically with the tie molecules working as fixing points. Therefore, after stress removal, the initial shape and structure are restored. Since such a part shows a high elastic recovery after a deformation and the elastic modulus is nearly the same as that of the usually processed article, it is called a Tiard-elastic item. When the hard-elastic film or fiber is drawn beyond the yielding point, plastic deformation occurs, leading to void formation, and a microporous film or fiber can be obtained. 

Plastic deformation of a moldable powder-additive mixture is employed in several forming methods for ceramics. Extrusion of a moist clay-water mixture is used extensively in the traditional ceramics sector for forming components with a regular cross section (e.g., solid and hollow cylinders, tiles, and bricks). The method is also used to form some oxide ceramics for advanced applications (e.g., catalyst supports, capacitor tubes and electrical insulators). A recent development is the repeated co-extrusion of a particle-filled thermoplastic polymer to produce textured microstructures or fine-scale structures. Injection molding of a ceramic-polymer mixture is a potentially useful method for the mass production of small ceramic articles with complex shapes. However, the method has not yet materialized into a significant forming process for ceramics mainly because of two factors ... 

ECMAE controls the deformation process more effectively and the expected result is attained quicker as compared to ECAE. The ECMAE equipment ensures the increase in manycycle extrusion output, a decrease in single deformation intensities for pol5nners of low plasticity, a possibility of providing a strict alternation of intensity values and shear directions for a guided structure forming. This has... 

Extrusion and injection molding are both widely used as shaping processes in particulate technology. This is because, unlike pressing processes, they allow the formation of complex shapes from particulate feed stocks in cost-effective, almost-continuous processes. In addition, the bodies produced by these routes can often be close to their final shape (near net shaped) requiring little finishing. A key element in both processes is the formulation of a plastically deformable body or paste which will flow in a predictable way under an applied pressure gradient and temperature. 

---