Analise dos parametros de torneamento de aços endurecidos

Orientador: Nivaldo Lemos CupiniDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Enge nharia MecanicaResumo: Com as recentes melhorias em máquinas operatrizes e em materiais para ferramentas, a usinagem de materiais duros tem ganhado bastante interesse. Uma das metas mais importantes é a substituição da retificação pelo torneamento em operações de acabamento. Neste trabalho, estudou-se algumas características do torneamento de aços endurecidos (ABNT 52100 e ABNT M2), usando ferramentas cerâmicas e de PCBN. Vários experimentos foram delineados com objetivo de analisar o comportamento da rugosidade superficial, das componentes da força de usinagem e da potência de corte. Além disso, observou-se a deterioração da ferramenta e o tipo de cavaco formado. Encontrou-se que o torneamento de aços endurecidos é possível do ponto de vista tecnológico. O nível de rugosidade superficial obtido é similar ao do processo de retificação.Abstract: Nowadays, with machine and tool material developments, there has been great interest on machining of hard materials. The most important target is to replace grinding by turning in finishing operations. In this work, some characteristics of hardened-steel turning (AISI 52100 and AISI H2), using ceramic and PCBN tools were studied. Experimental sets were designed to analyse surface roughness, cutting forces and cutting power behavior. Furthermore, tool deterioration and chip type were observed. It was found that turning of hardened steels is possible from technological point of view. The surface roughness is similar to that obtained in grinding processes.MestradoMestre em Engenharia Mecânic

Proposta de uma metodologia para construção de um modulo especialista dirigido a escolha das condições de corte

Orientador: Nivaldo Lemos CoppiniTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecanicaResumo: A determinação das condições de usinagem raramente tem sido contemplada como um problema de planejamento, e, portanto, integrada às outras etapas. Observa-se que essa determinação vem sendo tratada isoladamente, como um problema de pesquisa operacional (otimização de uma função objetivo) ou como uma simples consulta a um banco de dados. Em muitas situações, ela é deixada a cargo de um operador experiente. O objetivo deste trabalho foi formalizar uma metodologia para construção de uma ferramenta computacional que permita a um especialista humano gerar um sistema para enfrentar esse problema. A presente metodologia tem um caráter generalista, permitindo ao usuário obter um sistema que contenha sua experiência pessoal e seja dirigido pelo e para um determinado chão-de-fábrica. Para atingir esse objetivo empregou-se as seguintes técnicas: propagação de restrições, raciocínio baseado em casos e raciocínio qualitativo-causal. A metodologia proposta já se encontra na forma de um protótipo implementando em VISUAL-BASIC e COMMON LISP; sendo possível a construção de um Módulo Especialista para escolha das condições de corte paralelamente às outras etapas do planejamento da usinagemAbstract: The selection of cutting conditions is an important task in the machining planning. It affects time, cost, quality and always yields undesirable side-effects as excessive tool wear and large cutting forces. However, there is a few attempt to integrate it in the automated process planning systems. Probably, because there is no theoretic models to allow theirs values to be selected. The presence of experimented personnel remains necessary to choose the initial conditions and change them when something goes wrong at the shop fIoor. The purpose ofthis research is an attempt to face this problem. A very general methodology was proposed. Constrain propagation, similarity evaluation and qualitative-causal models were the techniques employed to formalize this proposal. Constraints were used as a medium forcommunication among hierarchical levels of variables. Similarity coefficients were fundamental to retrieve past experience from a case base. The causal dependency between variables were expressed using qualitative relations, which allowed to adapted the retrieved case to satisfy the most important constraint. The current methodology - implemented using VISUAL-BASIC and COMMON LISP - permits an Expert Module to be tailored to a very specific shop fIoor and the choice of cutting variables can be made concurrently with the others planning tasksDoutoradoMateriais e Processos de FabricaçãoDoutor em Engenharia Mecânic

Genotoxic effect induced by dried nicotiana tabacum leaves from tobacco barns (kiln-houses) in chinese hamster lung fibroblast cells (V79)

Nicotiana tabacum is the most cultivated tobacco species in the state of Rio Grande do Sul, Brazil. Workers who handle the plant are exposed to the leaf components during the harvesting process and when separating and classifying the dried leaves. In addition to nicotine, after the drying process, other components may be found including tobacco-specific nitrosamines, polycyclic aromatic hydrocarbons, as well as pesticides residues. The objective of this study was to examine the genotoxicity attributed to the aqueous extract of dried tobacco leaves obtained from tobacco barns using Chinese hamster lung fibroblast cells (V79) as a model system by employing alkaline comet assay, micronucleus (MN) and Ames test. MTT assay was used to assess cytotoxicity and establish concentrations for this study. Data demonstrated cell viability > 85% for concentrations of 0.625–5 mg/ml while the comet assay indicated a significant increase in DNA damage at all concentrations tested. A significant elevation of MN and nuclear buds (NBUD) was found for 5 mg/ml compared to control and other dry tobacco leaves concentrations (0.625–2.5 mg/ml). Mutagenicity was not found using the Salmonella/Microsome test (TA98, TA100, and TA102 strains) with and without metabolic activation. The concentration of inorganic elements was determined employing the PIXE technique, and 13 inorganic elements were detected. Using CG/MS nicotine amounts present were 1.56 mg/g dry tobacco leaf powder. Due to the observed genotoxicity in V79 cells, more investigations are needed to protect the health of tobacco workers exposed daily to this complex mixture of toxic substances present in dry tobacco leaves

Evaluation of the cytotoxic and genotoxic effects of Sida planicaulis Cav extract using human neuroblastoma cell line SH-SY5Y

Sida planicaulis is a weed thought to have originated in Brazil, where it is present in abundant quantities, but also this plant is also found in south-central Florida, Indian Ocean Islands, and the Pacific Islands. Sida planicaulis produces neurotoxicity that adversely affects livestock breeding with heavy animal losses and consequent negative impact on Brazil’s economy. The aim of this study was to determine the chemical profile, cytotoxic and genotoxic effects of ethanolic extracts of S. planicaulis collected in winter (leaf extract) and summer (leaf extract and leaf + flower extract) using an in vitro model of human neuroblastoma cell line SH-SY5Y. Phytochemical screening demonstrated the presence of alkaloids, flavonoids, and apolar compounds. Rutin, quercetin, and swainsonine were detected by HPLC and GC/MS, respectively. Phosphorus, potassium, iron, and zinc were the inorganic elements found. Extracts produced cytotoxicity at all concentrations tested (7–4,000 μg/ml) as evidenced by the colorimetric assay [3-(4,5-dimethyl-thiazol-2-yl) −2,5-diphenyltetrazolium bromide (MTT)]. Based upon the alkaline comet assay extracts were found to induce genotoxicity at concentrations ranging from 0.437 to 7 μg/ml. DNA damage produced by extracts was affirmed using a modified comet assay with the enzymes Endo III and FPG in a concentration dependent manner. Further, enzyme-modified comet assay showed both oxidized purines and pyrimidines, and consequently oxidative stress was related to genomic instability and cell death. Data suggest that low concentrations of ethanolic extracts of S. planicaulis (different seasons) induced increased DNA damage related to oxidative stress and chemical composition