Hot extrusion

Hot extrusion - Aluminium and magnesium alloys Extrusion - Tliermoplasties Extrusion - Elastomers Cold extrusion... 

The extrusion process requires the use of a lubricant to prevent adhesion of the aluminum to the die and ingot container walls. In hot extrusion, limited amounts of lubricant are applied to the ram and die face or to the billet ends. For cold extrusion, the container walls, billet surfaces, and die orifice must be lubricated with a thin film of viscous or solid lubricant. The lubricant most commonly used in extrusion is graphite in an oil or water base. A less common technique, spraying liquid nitrogen on the billet prior to extrusion, is also used. The nitrogen vaporizes during the extrusion process and acts as a lubricant. 

The alloys are first produced by rapid solidification and are amorphous in nature. They are either directly fabricated as powders, by a process such as high-pressure gas atomisation (HPGA), or by melt-spinning of ribbons, which are subsequently pulverised to form a powder (<150 /im). The powders are then consolidated by hot extrusion between 950-1050°C where the initial amorphous structure breaks down and forms a fine dispersion of stable borides in a ductile Fe-based matrix. 

Hot Extrusion of Shells. A modification of the Ugine-Sejournet hot extrusion process (using glass as lubricant) is used by Scaife Company of Oakmont, Pennsylvania. In this process a complete shell (such as 4.2 inch) can be produced in one piece from a simple billet. Important features of the development are in the substitution of readily available billet stock for seamless steel tubing, a critical material in times of war. Another feature of this process is that it requires about 25% less steel Refs Ordnance, 38, 753 (1954) 2) Iron Age... 

Hot extrusion is a hot-working process that makes use of the deformability of heated metallic materials to shape them. The process is sited for producing barhke and tubular objects. Most metals and alloys can be extruded. 

Use Gage blocks and hot extrusion dies, in powder form as spray-coating material, components for pumps and valves. 

Fig. 1. XRD patterns obtained from the (a) perpendicular and (b) parallel sections to the hot extrusion.

Fig. 3 shows the carrier concentration nc and mobility fi as a function of the hot extrusion temperature. As the hot extrusion temperature is increased, the charge carrier concentration is decreased and the mobility is significantly increased. The significant increase in mobility occurs due to the porosity decrease. 

The variation of Seebeck coefficient a with hot extrusion temperature is shown in Fig. 4. This figure represents that the Seebeck coefficient is increased with increasing the extrusion temperature because of the decrease in carrier concentration. The relationship between the a and nc can be expressed as follows a r-ln nc, where r is the scattering factor [4]. The values of a for the compound hot extruded at 300 and 440 °C are 145.8 and 231.1 fN/K, respectively. The relationship between the electrical resistivity p and hot extrusion... 

Fig. 3. Carrier concentration nc and mobility p as a function of the hot extrusion temperature.

Fig. 4. Variation of Seebeck coefficient a with hot extrusion temperature.

Fig. 5. Relationship between the electrical resistivity p and hot extrusion temperature.

Fig. 6 shows plots of thermal conductivity k vs. hot extrusion temperature. The thermal conductivity is increased with increasing the temperature. The increase in thermal conductivity would be strongly affected by the decrease in porosity. Fig. 7 shows the figure of merit Z of the compound hot extruded at various hot extrusion temperatures. The figure of merit is increased with the extrusion temperature due to the decrease in porosity. The compound hot extruded at 440 °C shows the highest value of Z (Z=2.94x 10 /K). 

Fig. 7. Figure of merit Z of the compound hot extruded at various hot extrusion temperatures. 

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