Made available in DSpace on 2014-06-11T19:34:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2004Bitstream added on 2014-06-13T19:47:49Z : No. of bitstreams: 1 padilha_rq_dr_guara.pdf: 4651598 bytes, checksum: 77a7edcf3c2fe16e30e62ec60549c1f8 (MD5) / Universidade Estadual Paulista (UNESP) / Este estudo objetiva analisar a influência da espessura de uma camada intermediária de níquel químico sob cromo duro eletrodepositado no aço de alta resistência, ABNT 4340 (utilizado em trens de pouso de aeronaves), com dureza de 39 HRc e 52 HRc. A análise é realizada por meio de dados obtidos nos ensaios de fadiga por flexão rotativa, das amostras revestidas com cromo duro, com e sem camada intermediária de níquel químico. As espessuras com melhor desempenho foram submetidas a ensaio de fadiga axial, em corpos de prova com e sem entalhe. Os resultados demonstram que a aplicação da camada de níquel químico é benéfica, em todas as espessuras analisadas, porém, há espessura que seu desempenho é ainda melhor. O tema proposto surgiu do interesse da ELEB - Embraer Liebherr Equipamentos do Brasil, em buscar por novas alternativas ou melhorias ao atual revestimento de cromo duro convencional. / The aim of this study is to analyze the effect of the thickness of an intermediate layer of chemical nickel under chromium electroplating on a high resistance steel ABNT 4340 (used in aircrafts landing gears), with hardness of 39 and 52 HRc. The analysis is done through data obtained from rotating bending fatigue tests of samples coated with hard chromium, with and without intermediate layer of chemical nickel. The thickness with better performance are submitted to axial fatigue tests, with and without notch. The results demonstrate that the application of a layer of chemical nickel is beneficial, in all of the analyzed thickness although some thicknesses present even better performance. The proposed work is due to the interest of the Brazilian Company of Aeronautics, Division of Equipments - EMBRAER/ELEB - in searching for new alternatives or improvements to the current coating with conventional hard chromium.

A hard chromium electroplating process is normally used for preventing mechanical and electrical parts such as roller, piston and mold from the harmful environments and giving the good physical properties on the surface such as increased wear resistance, increased hardness, low frictional coefficient as well as good aesthetic look on the surface of workpieces. The problem that often found in this process is the deflected workpieces after plating process due to the low plating performance during a plating period. These deflected workpieces are needed to replating it again. However, the replating method causes a large amount of resource consumptions and increases the production time. To handle this problem, the plating solution temperature is needed to maintain the plating solution temperature at a set point about 50 °C in order to improve the plating performance during the plating period and decrease the occurrence of the deflected workpieces. In this work, the mathematical models are developed to explain the dynamic behavior of the plating solution temperature during the plating time and validated with the real data from a plant. The conventional (PID) controller is applied to this process for the purpose of keeping the plating solution temperature at the set point throughout the plating time. The result demonstrates that the developed mathematical models can be used to explain the dynamic behavior of the plating solution temperature because it gives the good simulation of the plating solution temperature with a slightly different from the real data. Furthermore, the PID controller shows the high control performance for maintaining the plating solution temperature at the set point throughout the plating period with small overshoot at the beginning of every batch.

A presente dissertação tem como objetivo aplicar a metodologia Seis Sigma para a redução dos defeitos de mancha e queima na face das válvulas automotivas, defeitos estes que surgem durante o processo de eletrodeposição de cromo duro da haste das válvulas. A modalidade de pesquisa utilizada foi a pesquisa-ação, justificada pela participação efetiva do autor durante todo processo em estudo. Como resultado da aplicação da metodologia Seis Sigma constatou-se que os defeitos de mancha e queima na face das válvulas acontecem devido ao depósito de cromo na face da válvula durante a etapa de eletrodeposição de cromo duro. A quantidade de válvulas retrabalhadas do Cliente A foi reduzido de 203.970 para 8.483 peças por mês, o que permitiu uma redução de 96% do índice de retrabalho. A mesma análise feita sobre todas as válvulas produzidas pela empresa constata uma redução média do retrabalho de 413.016 peças para 24.027 peças por mês, o que significa uma redução de 96% para 6% do índice de retrabalho devido aos problemas de mancha e queima na face das válvulas. / The present study has as objective to apply the Six Sigma methodology to reduce the defects of spot and burn in the surface of intake and exhaust valves. These defects comes from electrodeposition of hard chromium in the stem of the valves. The modality of used research was to the research-action, justified for the participation accomplishes of the author during all process of implantation. As a result it was identified that the defects of spot and burn in the surface of the valves occur due to the deposit of chromium in the face of valve during the hard chromium electroplating. The amount of reworked valves of the Client A was reduced from 203.970 to 8.483 pieces per month, witch means a reduction of 96% of the reworked pieces. When the same analysis is done on all valves produced by the company is possible to verify an average reduction of rework from 413.016 pieces to 24.027 pieces per month, witch means a rework reduction from 96% to 6% pieces per month.

Yes / In a hard chromium electroplating process, a heat exchanger is employed to remove the heat produced from the high current intensity in an electroplating bath. Normally, a conventional U shape heat exchanger is installed in the bath but it provides low heat removal. Thus, this study designs a novel W serpentine shape heat exchanger with identical heat transfer area to the conventional one for increasing heat removal performance. The performance of the heat exchange is tested with various flow velocities in a cross-section in range of 1.6 to 2.4 m·s− 1. Mathematical models of this process have been formulated in order to simulate and evaluate the heat exchanger performance. The results show that the developed models give a good prediction of the plating solution and cooling water temperature and the novel heat exchanger provides better results at any flow velocity. In addition, the W serpentine shape heat exchanger has been implemented in a real hard chromium electroplating plant. Actual data collected have shown that the new design gives higher heat removal performance compared with the U shape heat exchanger with identical heat transfer area; it removes more heat out of the process than the conventional one of about 23%.

Ce travail de thèse s’inscrit dans un projet de grande envergure piloté par l’IRT M2P, intitulé « Hard Chrome by Trivalent Chromium » qui regroupe 15 partenaires industriels et 2 partenaires académiques. L’objectif principal est de substituer les composés du chrome hexavalent par des électrolytes à base de chrome trivalent dans les procédés de chromage « dur », en réponse à l’application du règlement européen REACH en septembre 2017, même si des demandes d’autorisations temporaires sont en cours. Dans le cadre de cette thèse, des études électrochimiques ont été réalisées sur des bains commercial et synthétique. Celles-ci ont conduit au choix d’un matériau jouant le rôle d’anode, à une meilleure compréhension des mécanismes mis en jeu et de ce fait à une optimisation des conditions d’utilisation du bain commercial. D’autre part, une étude approfondie des courbes transitoires permet de mieux appréhender le comportement des électrolytes de chrome trivalent vis-à-vis des courants pulsés. Ainsi, un plan d’expérience sur les paramètres des pulses avec pour sortie de multiples caractérisations des dépôts de chrome montre que les courants pulsés influent sur plusieurs propriétés telles que : la teneur en carbone, la structure cristalline, la microdureté, la morphologie de surface et la microfissuration. Grâce au traitement des données issues du plan d’expériences, l’optimisation des paramètres de polarisation aboutit à l’élaboration de séquences de pulses optimisées. L’utilisation de celles-ci, employées seules ou en combinaison avec d’autres séquences de pulses issues également du plan d’expériences, aboutit à l’obtention de dépôts de chrome trivalent dont les propriétés sont modulables en fonction des paramètres procédés. Dans l’optique de la mise en place d’une nouvelle stratégie de choix des paramètres de l’impulsion anodique, un dispositif permettant la mesure du pH local en fonction des séquences et à proximité immédiate de la surface a été élaboré. Les premières tendances confirment les modes d’action des courants pulsés, et les choix qui ont été faits pour l’optimisation. / This thesis work is part of an ambitious project handled by IRT M2P, named “Hard Chrome by Trivalent Chromium” which gathers 15 industrials partners but also 2 academic partners. The main objective is to substitute the hexavalent chromium compounds in hard chromium electroplating process before there ban by European instances (REACH, ECHA) in September 2017, excepted for those authorized. As part of this thesis, electrochemical studies were realized on commercial and synthetic baths. Thanks to this studies, a material has been chosen to act as an anode for the making of the trivalent chromium coatings ; furthermore, the utilization conditions of the commercial bath has been optimized. Moreover, another study based on transient curves allows a better comprehension of the behaviour of the trivalent chromium electrolytes regarding pulsed current. This work permitted the elaboration of pulse sequences in the form of an experimental design. The realization and characterization of trivalent chromium coatings as a part of the experimental design show that pulsed current have an effect on several properties of the coatings such as carbon content, crystalline structure, microhardness, surface morphologies an microcracking. Thanks to the analyses of the results from the experimental design, an optimization of pulsed current has been made to obtain optimized pulse sequences. The utilization of those pulse sequences, used alone or combine with some pulse sequences of the experimental design lead to the elaboration of trivalent chromium coatings which properties are adjustables depending on the set parameters of the process. To further optimize the properties of the coatings, the basis of an analysis tool based on local pH measurements are developed; this analysis tool must make it possible to select the most interesting pulse sequences for the realization of trivalent chromium coatings.