Papers by Keyword: Melting

Abstract: This paper deals with the verification of thermoplastic flowing when manufacturing plastic products by injection moulding used in the consumer industry. An analysis was performed by Plastic Insight, which is used for the determination of flow properties of thermoplastic materials. A good knowledge of flow properties of these materials enables a very good starting position for the design of thermoplastic products made by the injection moulding technology [1,2]. The task of this simulation was the comparison of injection parameters of a mould, with and without cooling of channels. Simulated thermoplastic material is used for the manufacture of ribs in washing machine drums. The tested material was polypropylene.

Abstract: This paper summarizes components and phases involved in the cupola melting process, then brings out a composition forecasting model based on the minimum Gibbs energy principle and the equilibria calculation algorithms of multiphase and multicomponent. Besides, the relationship between the melting parameters and the composition of molten iron is set up by using BP neural network based on the idea of indirect constraints. Finally, the paper probes the feasibility of the composition forecasting model with two examples. The application result shows that the prediction with this method can achieve strong practicability and popularization value.

Abstract: Machining operations of cast parts usually generate considerable amounts of waste in the form of chips (usually 3–5% of the casting weight). Traditionally, swarf is sold to scrapers and remelters, but this option is quite expensive because the selling price is roughly 30% of the acquisition price of the commercial 2nd melt raw material. For most aluminium foundries that incorporate machining operations in their products, reusing aluminium chips as raw material for the melting stocks is perhaps the best option as waste management policy in what concerns to economical and technical aspects. Nevertheless, aluminium swarf is a low density product (0.25 kg/dm³) and is usually covered by a thin film of aluminium oxide and machining fluid. Melting such a product without suitable previous preparation leads to very low metal recovery rates, high energy consumption, gases and smoke generation and very low quality of the final product. During the last years, the authors have developed a high efficient and environmentally friend aluminium swarf recycling technique, using direct incorporation in aluminium melts. The influence of processing parameters, namely melt temperature and holding time, melting atmosphere, swarf briquetting pressure and melting charge composition in the metal recovery yield and dross generation was studied and characterized, and the optimal processing parameters were established. The microstructure of the final product obtained in those conditions was evaluated and is also presented. It is shown that the recycling efficiency depends on the swarf conditioning, the melting technique and the melt treatment methodology. Swarf moisture reduction, induction melting under protective atmosphere and a specially developed degassing technique were found the most important factors influencing the recycling process. By using the developed technique, cast ingots with microstructure and sanity similar to commercially available AlSi12Cu1 2nd melt raw material were successfully obtained with minimal dross formation and metal recovery rates around 90%, without using traditional salts and fluxes.

Abstract: During the last years a very significant effort to develop a melting crucible for induction melting of Ti based alloys at competitive cost has been carried out by many researchers, where the authors are included. Results obtained so far have shown that no material accomplishes the melting crucibles two main demands: inertness facing titanium alloys and suitable/enough thermal-shock resistance. Until now, yttrium and calcium oxides were those materials that performed best on what concerns to thermodynamic stability. However, in both cases, crucibles thermal-shock resistance was very poor, and there are references to crucibles that cracked during melting. Besides, calcium oxide reveals manipulation problems, due to its high higroscopicity. This paper concerns to the evaluation of zircon based crucibles with Y₂O₃ inner layer for induction melting of TiAl based alloys. A novel multi layered crucible production technique based in a centrifugally assisted slip casting process followed by a sintering operation is described, and results concerning to crucibles porosity and wall composition and morphology are presented. Crucibles obtained in different processing conditions were used to melt a Ti48Al alloy which was poured in graphite moulds. Experimental results include alloy chemical contamination with residual elements, mainly yttrium and oxygen, microhardness measurement and the presence of yttrium oxide and zircon inclusions in the cast samples. Results concerning to the crucibles behaviour are also presented with particular attention to cracks development. The Y₂O₃ crucible layer was found to suffer some erosion and be slightly dissolved by the molten alloy and the extent of those phenomena depends on the porosity of the layer surface, for fixed experimental melting conditions.

Abstract: Melting TiAl based alloys in ceramic crucibles often leads to chemical contamination, alloy heterogeneity and non-metallic inclusions. The severity of such phenomena usually depends on the nature of crucible materials, the melting stock composition and the melting parameters, namely superheating time and temperature and melting pressure. Among the referred drawbacks, Al loss during melting is a critical aspect, as its concentration in TiAl based alloys has a very strong effect in their mechanical properties. Although a few studies of critical factors affecting the evaporation behaviour of Al during electron beam and induction skull melting of Ti-Al alloys had been carried out, until now no information was released on this subject for the ceramic crucible induction melting process. In this work a Ti-48Al alloy was induction melted in a zircon crucible with Y₂O₃ inner layer, using 50 and 100 °C superheating temperatures and 0, 60 and 90 second holding times, and poured into a graphite mould. The effect of different temperature/time combinations in the alloy composition, Al loss by evaporation and extent of the metal/crucible interaction was studied for different melting pressures. Al loss was found to increase significantly for melting pressures below around 10^-1 mbar, at a rate that increases as melting pressure decreases, until a maximum rate is reached, remaining constant for lower pressure levels. Metal/crucible interaction increased directly with the melting pressure and superheating time, leading to alloy contamination with yttrium and oxygen. For the experimental set-up and conditions used on this work, optimal superheating time/pressure combinations that lead to acceptable alloy composition and sanity have been identified.

Abstract: The RheoMetal process (previously called the Rapid S- and RSF- process) is a novel method to produce cost effective, high quality, semisolid slurries for component casting. The RheoMetal process uses an Enthalpy Exchange Material (EEM) as cooling agent to absorb heat and produce a slurry. Critical process parameters to create a slurry by robust melting of the EEM are alloy content, stirring speed, EEM to melt ratio, EEM temperature, EEM microstructural characteristics and melt superheat. In this paper, the melting sequence and melting rate of the EEM was studied experimentally. The effect of EEM composition, as well as superheat, on evolution of shape and dimension of the EEM during stirring was investigated. Initial material freezing onto the EEM was observed, followed by a stationary phase with subsequent gradual melting of the EEM. It was shown that the characteristics of freeze-on layer were strongly correlated to melt superheat, EEM temperature, as well as material composition, hence also has significant influence on the melting sequence.

Abstract: In this paper, the technology of melting in induction furnaces with ceramic crucibles was used for production of TiAl-based Ti-47Al-2W-0.5Si alloy. Due to high reactivity of liquid titanium alloys, the melting process was conducted in special crucibles made of stabilised ceramic materials resistant to the aggressive action of these alloys. When characterising the chemical composition and microstructure of Ti-47Al-2W-0.5Si alloy melted in different ceramic crucibles, problems accompanying the melting process were described and conditions for making an alloy with satisfactory purity were determined.

Abstract: Analyzed the melting process of iron base which contacted tightly with boron slag, established the boriding melting dynamical model of iron base and calculated the melting rate of pure iron. The melting rate of pure iron is not only decided by heat transfer rate, but also related to the mass transfer rate of boron. With the resolving of the model, we can know that the melting rate of pure iron is 3.41mm/min, and melting time is 15 min. When the speed of heating is high, the melting rate is mainly decided by diffusion.

Abstract: The laser beam machining uses the effects generated at the impact of the workpiece surface with a laser beam that has adequate energetically and spatial - temporal characteristics. It is known that, as result of the laser beam impact with the workpiece material, local chemical and physical effects are signalized. In order to study such effects and simultaneously the technological possibilities of laser beam equipment, some experimental researches were developed on an Ytterbium fiber laser equipment of 300 W. Movements of the laser spot along established trajectories were ensured, changing the sizes of the machining parameters. The influence exerted by the machining parameters and by the materials characteristics on the material removal from the test piece was highlighted. The surface layer modifications were also studied.

Abstract: The objective of the present study was to melt and cast AA2195 alloy in Vacuum Induction Melting (VIM) under dynamic inert atmosphere. These billets were homogenized and subsequently hot forged and rolled to sheets. The products in the form of sheets were subjected to T8 (Solution Treatment +WQ+CW+Aging) temper condition. Mechanical properties were evaluated at room temperature and correlated with microstructure. Highest mechanical properties obtained in T87 temper have been reported.