Strip casting is a new method of producing metal matrix composites. Two-roll melt dragged processing (TRMD-ing) and single-roll melt dragged processing (SRMD-ing) methods were used to study the manufacture of 2-mm-thick composite strips by using PbSn (≈ 11.3 g/cm3) eutectic alloy matrix reinforced with iron (≈ 7.86 g/cm3) powder (≈ 70 μm) at a rate of 0.3 m/s. The metallic powder stored in the feed hopper (≈ 90 g) was pushed during the pouring operation of the cast alloy (≈ 4 kg) at 260 oC on the cooling slope to produce a mixture of metallic slurry and particles to feed the nozzle to be dragged by the lower roll. Various surface defects occurred during processing, such as the failure of the powder particle to be embedded in the matrix by SRMD-ing with and without stirrer into the nozzle, and the rolling up of the strip into the nozzle by TRMD-ing. Graphite nanoparticles formed inside the α-Pb grain revealed a complicate eutectic structure in both the processing methods. The colloidal graphite used to coat the crucible, cooling slope, and nozzle could act as a nucleation agent for preferential centre segregation in the α-Pb grain. This suggests that the graphite nanoparticles functioned as nucleation points in the lead-rich α phase. Thus, another type of composite was formed in the presence of graphite nanoparticles within the lead-rich α-phase surrounded by β-Sn. An electron probe microanalysis and scanning electronic microscopy were used to investigate the composition and distribution and identify the different phases. Several types of particulate reinforcements may be added to the matrix to obtain composites for mechanical, electronic, and magnetic applications using these technologies.
Continuous metal matrix composite strip casting (MMCS-ing) composed of six 0.3-mm diameter annealed bare copper wires in a eutectic SnPb matrix was manufactured by a two-roll melt dragged processing (TRMD-ing) method at a rate of 0.3 m/s. The wires were dragged through a semisolid pool with a fibre contact time of approximately 0.2 s. The required gap between rolls to thixoforge the semisolid material around the wire filaments was approximately 1.4 mm. A successful continuous composite strip casting was achieved with a notably good degree of wire alignment. No cracks were observed at the copper wire/matrix interface. However, regions of porosity occurred in the matrix; their possible formation mechanisms are discussed. The solidification structure of the matrix was analysed, and the analysis results indicated the formation of small globular grains measuring approximately 3 μm in diameter. The specimens were evaluated for their tensile properties and compared with the rule of mixtures. The surface fracture analysis indicated a good matrix/fibre union. MMCS-ing is an economically viable process and has significant advantages over other metal matrix composite (MMC) fabrication methods.
Al–Si A413 treated and untreated alloys were cast and poured at approximately 720 oC, 700 oC, and 680 oC in a cooling slope to obtain the semisolid material feeding the ceramic nozzle (150 cm3) at the lower roll (single-roll melt-dragged processing)—this drags the metallic slurry via the chill/columnar layers at a rate of 0.2 m/s, forming a molten-metal strip with a thickness of 2 mm and width 45 mm, approximately. The untreated alloy poured at 720 oC formed coarse structures of α-Al dendrites, as well as a coarse eutectic of Al–Si and microshrinking on the surface of the casting strip facing the atmosphere. The Al–Si 413 alloy poured at 680 oC and treated with Al5Ti1B (0.1%) led to microstructural refinement, resulting in α-Al globular structures, the absence of microporosities on the surface facing the atmosphere, and a finer and more homogeneous distribution of the eutectic grains with smaller Si particles. The AlTiB master alloys are not used as a grain refiner in Al–Si alloys because of Si poisoning. This subject is discussed in this paper. The addition of the inoculant and 0.2% of the Al–Si eutectic morphology modifying agent (Al–10%Sr) refined both the α-Al and eutectic phases more efficiently in the cast strip poured at 700 oC and 680 oC. This suggests that the inoculant did not interfere with the action of the modifying agent. As a result, molten metal strips of higher mechanical strengths and ductilities were obtained.
The design and performance of an effusion cell used to deposit low melting point metals under UHV conditions is described. A novel feature of the cell is a transfer rod and pretreatment chamber that allow for the rapid loading and retrieval of crucibles containing low melting point source elements. This feature of our cell makes it ideal for depositing the highly reactive alkali metals. The performance of the effusion cell is evaluated for the deposition of the metal potassium.
No panorama atual, onde o mercado é notadamente competitivo, cada vez mais as empresas necessitam buscar melhorias em seus processos, visando produzir com qualidade, suprir o esperado pelos clientes, reduzir custos e manter o negócio lucrativo. A utilização de auditorias de processos vai de encontro a este propósito, visto que o uso correto desta ferramenta permite verificar a eficácia e a eficiência dos processos produtivos, e conduzi-los a possíveis melhorias e a solução das não conformidades encontradas entre as especificações de processo, realização das tarefas, procedimentos operacionais, organização, 5S, treinamento operacional, entre outros. Esse artigo tem como objetivo mostrar, por meio de uma pesquisa descritiva apoiada em uma revisão bibliográfica, o modo de trabalho de uma empresa metalúrgica que começou a utilizar as auditorias de processos como ferramenta de apoio a melhoria contínua do processo de fundição. Os principais resultados obtidos comprovaram a eficácia desta ferramenta, colaborando para o desenvolvimento de uma cultura empresarial focada em qualidade, além de auxiliar na redução dos custos e contribuir para o alcance das metas de produção da empresa.
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