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The Influence of Segregation Phenomena on Quality of Product in Extrusion Process

Skorulski G., Piwnik J., Baranowski P.

Archives of Foundry Engineering

2010

Vol. 10, iss. 3 spec.

251--254

The segregation phenomena and formation of agglomerate have the basic influence on structure of the final product. The aim of this work is analyzing the phenomena of segregation in semi-solid extrusion process, using several kind of substitute materials, which can simulate the thixotrophic fluid behavior and displacement of solid particles. The experimental researches are made to investigation of segregation in the near-wall layers and the formation of agglomerate. Especially, the distribution of the solid particles at the end of extrusion process have been taken into consideration. Theoretical criteria describe the critical value of the energy liberated at the surfaces by the action of forces depends on the temperature, the pressure, the yield stress and the physical state and degree of intimacy of the contacting surfaces. The theory has been tested experimentally using a silicon polymer as a substitute material. Experimental stand with a Plexiglass die was prepared, such that the velocity fields at the surfaces could be observed and measured during plastic flow, allowing the empirical coefficients in the mathematical formulation to be estimated. On the basis of the theory and experiment an optimal die chamber was designed for a die with a complex shape.

Modelling of semi-liquid aluminium flow in extrusion with temperature effect

Skorulski G., Piwnik J.

Archives of Foundry Engineering

2007

Vol. 7, iss. 2

25-30

During thixoforming, when the material is in the semi-liquid state, it exhibits thixotropic properties, i.e. the unsupported material remains stiff and holds its shape so it can be readily handled, but rapidly thins and flows like a liquid when sheared. It is this behaviour that is the key to the thixoforming process where material flows as a semi-liquid slurry into a die, as in conventional die-casting. Modelling the influence of the temperature distribution heterogeneity on deformation mechanisms during extrusion of the aluminium alloys in semi-liquid phase, the way of preparing samples and experimental technique has been analysed in the following work. There were made an analysis on the influence of the possible temperature distribution in recipient obtained during heating it on the extrusion process proceedings. The conclusions concerning stability of the process and appearing during it deformation mechanisms had been drawn on the ground of the received results. The plasticine and rape oil have been choosen as a substitute materials. Some kind of different variants have been investigated used a special experimental stand. The results of the tests presented below prove that the proposed technique can provide valuable insight into the material flow during deformation of aluminium alloys in the semi-liquid state and thus can give some guidance concerning the desirable temperature distribution within the workpiece.