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Title: The shape forming of flexible chocolate during and after cold extrusion
Author: Chen, Yu Wen
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2007
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Initial work presented in this dissertation on extrusion supports the findings of others with regard to standard die extrusion. In addition, comparisons between ram and screw extrusion results were made and are briefly discussed. In relation to wide sheet extrusion, unusual flow instabilities in the form of central line splitting of the extrudates were observed for the first time, indicating that the chocolate was weak in tension. Solutions for eliminating for flow defects are also presented and mathematical modelling provided insight into the flow mechanism. Post extrusion mechanical characterisation of the extruded chocolate was carried out by means of bending and indentation tests and the effect of processing conditions on the flexibility and hardness of chocolate extrudate was examined. The results showed the presence of a two-stage, post extrusion rehardening process, which was consistent with earlier findings. In terms of stamping, the process itself and the effect of processing variables on the shape formability and surface gloss formation in the chocolate product were established for the first time. Optimal conditions that contributed to the formation of well-defined products with high gloss finish were identified. Product demoulding was also found to be facilitated with the use of a Teflon die. Both the wide sheet extrusion and the stamping process were simulated by numerical models using the finite element codes Forge 3® and 2® respectively. In general, good agreement was achieved between the experimental and numerical results. Moreover, a preliminary, semi-analytical model was proposed to describe the mechanism of surface gloss formation during stamping.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral