Search Documents

By Renan Oss Giacomelli

The adhesion of multifunctional coatings on soft substrates is of paramount importance in the tribological behavior of this important class of surface treatment. In particular, scratch and indentation tests have been extensively used in order to assess this property. In this paper, the adhesion of a-C:H diamond-like carbon films deposited on nitrided low carbon steel was evaluated by indentation and scratch tests. The coatings were produced by PECVD onto 1020 steel substrates with two different surface finishing: ground (Sq = 0.184 µm) and polished (Sq = 0.002 µm). Indentation tests using a Rockwell diamond indenter were conducted and the adhesion evaluated by measuring the spalling region on images obtained by using optical microscopy. The analysis of the spalling regions produced semi-quantitative results, eliminating the subjective qualitative analysis proposed by the standard method VDI 3198. In addition, scratch tests were performed using the same indenter and a comparison between the two techniques was established.

Jul 31, 2018

By Fernando Nunes da Silva

Wear mechanisms of materials that constitute the equipments and operating parts in the pre-salt area during the production of petroleum and gas can include corrosion, corrosion-cavitation and corrosion-cavitation-erosion. In the laboratory, it is realizable, but at times it is inaccurate to reproduce or visualize some of these mechanisms due to the real complexities caused by hydrodynamic flows, and the physico-chemical and mechanical non-linearities. The main objective of this work was to study coupons of low carbon steel under laboratory conditions, such as corrosive, cavitative-corrosive (CO2) and corrosive-erosive (CO2 + SiO2), in a stirring aqueous saline solution (0 and 5.0 m/s) at two levels of temperature, with bubbling of gas (5.0 L/min) and contaminated with or without (2.5 % mass), by solids particles of SiO2. The surface of the coupons subjected to upstream flow (0° in a cylindrical generatrix of coupon), and downstream flows (180º) were analyzed by profilometry. The measurements of roughness and waviness of all coupons were statistically analysed using Statgraphics® Centurion XVI, at a confidence level of 95% and significant differences observed in some matrices were discussed.

Jul 31, 2018

By Rafael Lioji Kogake

O Alto Forno n° 2 é responsável por cerca de 40% da produção de gusa na CSN. Uma das principais utilidades responsável pela transformação do minério de ferro em gusa é o ar soprado que é fornecido por dois turbo sopradores da Central Termoelétrica n°2. Para que ocorra o processo de transformação do minério é necessário que o ar soprado seja aquecido. Isto é feito através dos regeneradores, os quais aquecem o ar para cerca de 1.300°C. Como cada regenerador tem um tempo de campanha, é necessário fazer a troca do mesmo a cada 1 hora. Nesse momento de mudança de regenerador, uma parte do ar soprado é desviado para o regenerador que está entrando em operação e ainda está vazio. Com isso, há uma perda pontual de produção indesejada, além de causar instabilidade no processo. A solução encontrada para reduzir este problema foi aumentar a vazão de sopro durante o período de troca de regeneradores, garantindo assim uma maior produção e melhor estabilidade do Alto Forno 2. Este trabalho apresenta o estudo do problema em questão, a metodologia utilizada para a sua implementação e os resultados alcançados.

Jul 31, 2018

By Vitor Orlando Ferreira

The efficiency of an apparatus which uses a forced lubrication system, as well as the useful life of its components, is strongly related to the degree of contamination of lubricating oil. The presence of contaminants and the degradation of the oil itself cause it to release substances that fouling of the wall of the pipes. The cleaning and dialysis of the oil pipes, besides prolonging the life of the lubricant reduces wear of the components. There are several methods of cleaning in pipes, the problem is that some have abrasive characteristics, which could damage some types pipes. Among the non-abrasive methods stand the Flushing and Air scouring. Flushing uses the lubricating oil which circulates in temperatures alternating and high speeds, for generating turbulence to perform washing. The Air scouring method uses oil and filtered compressed air, injected into pipe, to generating higher flow, causing the power supply unit with fluid can work with lower power consumption and higher speeds, removing fouling of the pipe. The objective of this research is to evaluate the Reynolds number to correlate with the efficiency of cleaning the pipe. The method applied was the Air scouring and it was verified that the qualitative effects may occur when compared to Flushing. After testing, it was found that the chosen method brings significant changes in flow, and this flow regime varies considerably increasing the Reynolds number.

Jul 31, 2018

By Giuseppe Pintaude

This study aims to evaluate the effect of specimen preparation on the dry sliding wear behavior of CA-6 NM stainless steel. Two different surface finishing manufacturing processes were applied: lapping and metallographic polishing. The wear tests were conducted in reciprocating ball-on-flat system, performed for two loads: 5 or 8 N. For all test conditions, hardmetal ball was employed as counterbody. The surfaces were evaluated using 3D interferometry technique to determine their surface roughness, including texture analysis regarding isotropy. Surface characterization results indicated the presence of texturing and preferential orientation, since the parameter Str was smaller than 0.5 for samples of both the studied conditions. Two distinct levels of isotropy evaluated through Str parameter were achieved: 0.13 for lapping and 0.3 for metallographic polishing process. It is clear from wear tests that the variation of average surface roughness is the key point for tribological behavior of CA-6 NM stainless steel.

Jul 31, 2018

By Rogério Felício dos Santos

Nitriding of metallic materials using electric discharges generated during electric discharge machining (EDM) is a recently developed technique. The aim of this paper was to correlate mechanical properties of a nitrided layer produced in AISI 4140 steel by EDM nitriding with the type and amount of nitrides. A conventional die-sinking EDM equipment and electrolytic copper electrodes were used to generate the electric discharges. The electrolyte was a solution of urea in deionized water. Knoop microhardness profiles assessed the variation of hardness along the nitrided layer, whereas the elastic modulus of this layer was measured using nanoindentation tests. Optical microscopy and X-ray diffraction (XRD) were used to characterize the nitrided surface. The results showed the formation of a nitrided layer containing iron nitrides with average thickness of around 25 µm. The amount of nitrides reduced from the surface towards the centre and these results correlated well with microhardness profiles obtained.

Jul 31, 2018

By Satish V. Kailas

For product sustainability “closing the cycle” is the first requirement. If the materials used in making the product is not replenished at the rate at which it is being extracted, the cycle is open and the product would not be sustainable. This includes the materials used in generating the energy used to make the product, the transportation, use and disposal. If the materials used in a product, that includes lubricants, is one that cannot be replenished, it has to be recycled for the product to be sustainable. The other basic condition for sustainability is the eco-friendliness of the product. It is argued that the present lubricants do not fall in this category. Using the example of cutting oil emulsions we have shown that it is possible to meet the conditions of sustainability in terms of both the material extraction-replenishment cycle and eco-toxicity. Cutting oil emulsions made from coconut oil and natural additives are shown to have superior cutting properties and are completely eco-friendly. It is concluded that products made using these conditions are possible and is a necessity for man to lead a sustainable life. Closing the cycle, with respect to the energy used in the cycle will make the product completely eco-friendly.

Jul 31, 2018

By Manoel Inácio dos Reis Neto

Substituição das atuais lâmpadas de Vapor Metálico/Sódio/Mercúrio de 440 W por lâmpadas com a tecnologia de iluminação através de indução magnética em uma das Salas Fornos da CBA (Companhia Brasileira de Alumínio do grupo Votorantim Metais). As principais vantagens dessa tecnologia são a alta eficiência e o longo ciclo de vida sem significativas depreciações luminosas, diminuindo drasticamente o ciclo de troca e a necessidade de manutenção permanente. Além disso, há uma redução significativa no consumo de energia elétrica de aproximadamente 51% e de 100% no custo de manutenção por um período de 11 anos, contribuindo para a melhoria da eficiência energética da fábrica com uma prática simples e sustentável.

Jul 31, 2018

By Felipe Darabas Rzatki

Polyether ether ketone (PEEK) is a high performance thermoplastic often selected for high temperature tribological applications under chemically aggressive environments. The present work evaluate the tribological behavior of a high performance PEEK composite under ambient and high temperature (30 and 80°C, respectively). The atmosphere was also varied (air or tetrafluorethane). An AMTI tribometer equipped with a hermetic chamber and a heating system was used to carry out sliding tests of PEEK cylinders on 304 stainless steel polished discs (Sq < 10 nm) with reciprocating movement and 175 N normal force. Surfaces roughness analyses were performed with a white light interferometer. As expected, there was a strong influence of temperature on the tribological behavior of the samples tested in ambient atmosphere (25% decrease in friction coefficient associated with a 100% increase in wear rate). On the other hand, samples tested in tetrafluorethane atmosphere showed no significant friction temperature dependence.

Jul 31, 2018

By Luis Armando Espitia

AISI 410 martensitic stainless steel specimens were low temperature plasma nitrided at 400°C in a mixture of 75%N2:25%H2, during 20 h. Active screen technic was used to avoid any edge effect The nitrided case is composed of expanded martensite (a’N) and e-Fe3N iron nitride, whilst chromium nitride precipitation was avoided. Surface hardness reached 1275 HV0.01. The transverse microhardness profile shows a gentle hardness gradient with a NHT nitrided case depth of 28 µm. Nanoindentation tests were carried out in order to assess the hardness (H), the Young modulus (E), the H/E and H3/E2 ratios and the elastic recovery (We) of both nitrided and non-nitrided specimens. The cavitation erosion mass losses were measured as a function of exposure time. The results showed a decrease of 27 times of the mass loss compared to the non-nitride specimens. Wear rate decreased from 2.56 mg/h for the non-nitrided condition to 0.085 mg/h after nitriding. The increment in the elastic recovery and the higher hardness values are responsible for the greater cavitation erosion resistance exhibited by the expanded martensite. Such results showed that low temperature plasma nitriding and the formation of expanded martensite are effective to increase cavitation erosion resistance of AISI 410 stainless steel.

Jul 31, 2018

By Marjorie Benegra

This study aims to compare the wear resistance assessed in rubber wheel abrasion test of nickel aluminide coatings deposited by for Plasma Transferred Arc (PTA) and High Velocity Oxigen Fuel (HVOF) manufacturing, using the same raw material. A nickel aluminide powder was atomized and deposited on 316L steel plate substrate. After deposition, some specimens were submitted to a heat treating (1200 °C for 24 h followed by 760°C for 24 h). The coatings deposited using PTA developed different microstructures due to the incorporation of substrate elements, its performance was better than the HVOF coatings, although their Vickers hardness was similar. After heat treating, a significant variation in hardness and wear resistance was observed. For PTA specimens, there were decrease in hardness of 35%, while for HVOF ones this drop was approximately 20%. Nonetheless, the effect of thermal exposure in wear resistance was quite different: an increase of 21% was observed for HVOF coatings, while a reduction of 20% occurred in PTA ones. Microstructures modifications in PTA coatings were significant for their wear resistance. On the other hand, the reduction of porosity and sintering were responsible for a better performance of heat-treated HVOF coatings.

Jul 31, 2018

By Diogo Tenório dos Santos

This property has been studied to characterize the strength a metallic material exhibits when it is machined so it can be regarded as its typical behaviour. As such, it may even be considered as an intrinsic material property. It is usually measured by an index called Coppini index, which is expressed by the ratio between the removed mass of a cutting tool caused by wear when it is used for machining and its initial one for a certain set of machining parameters. In this investigation, the tests were therefore conducted by an established set of parameters, namely feed rate, cutting and depth rates, in which the same wear mechanism took place in both ferrous alloys: AISI 4140 and AISI 316 steels. They were chosen based upon their increasing ordinary machinability indexes. The initial and final mass of the cutting tool were measured by an analytical scale with 0.01 mg precision. Cylindrical rods of 50-mm diameter were machined and the CI indexes showed a remarkable difference between them: 0.080 for the first steel and 0.049 for the second one, i.e., AISI 316 steel presented better machinability than the first one. It was then possible to conclude that this method presents good results in terms of both reproducibility and adequacy for machine shop conditions and it may be applied in a foreseeable future, mainly for metallic materials that have rather low machinability indices.

Jul 31, 2018

By Tiago Ribeiro Costa

A Praxair é uma das três maiores empresas de gases industriais do mundo, com atuação em mais de 40 países e fortemente atuante na indústria siderúrgica. A Praxair possui experiência para fornecer produtos e serviços para todos os tipos de siderúrgica. Diversas tecnologias desenvolvidas pela Empresa, como o CoJet® (sistema para injeção de jato coerente de oxigênio em fornos elétricos e conversores), Slag Splashing (espalhamento de escória nas paredes de conversores, aumentando a vida útil dos refratários), AOD (processo para produção de aços especiais) e outros, encontram-se em operação comercial atualmente em diferentes partes do mundo. No Brasil, a PRAXAIR é a controladora da White Martins, maior empresa de gases industriais da América do Sul, presente em nove países do continente. Seu portfólio inclui gases atmosféricos, produção de gás carbônico, acetileno, hidrogênio, gases especiais e medicinais, misturas para soldagem, cilindros de aço sem costura, equipamentos para aplicação, transporte e armazenamento de gases. A empresa também opera uma unidade para liquefação de gás natural. Além de tecnologias e processos, a White Martins também pode fornecer soluções e equipamentos para medição, controle e injeção de gases, atendendo às rígidas normas de segurança e padrões de qualidade. O Objetivo deste trabalho é apresentar e discutir sobre a solução para o fornecimento de mistura para atmosfera de fornos de tratamento térmico através de um painel misturador de gases hidrogênio e nitrogênio. Será discutida a operação do equipamento e abordadas às características construtivas.

Jul 31, 2018

By Salete Martins Alves

The future lubricants must be more environmentally adapted, with a higher level of performance lower total life cycle, cost than currently used lubricants. Environmental friendly, the biodegradable alternatives are available for a large variety of mineral oil based lubricants. Vegetable oils are the major source of these base fluids, although they have lower thermal and oxidation stability and even worse low-temperature behavior than mineral oil. These physical and chemical properties can be improved by chemical modification. The aim of this study was to evaluate physicochemical properties and film formation from modified vegetable oils. The vegetable oil was chemically modified by epoxidation reaction with acetic and formic acid using sunflower oils. Viscosity, iodine value, density, acidity value and thermal stability were determined for epoxidized oils. The film formation was analyzed using a HFRR tribometer. The results showed that epoxidized vegetable oils had excellent properties to be used as lubricant, and their tribological performance is higher than mineral oil.

Jul 31, 2018

By Eduardo Dominguez Trindade

Lubricant oils are subjected to reciprocating movement in the piston ring/cylinder tribocouple of automotive engines. In this kind of movement, the relative speed oscillates between zero and a maximum, and therefore the lubrication regime goes from boundary to hydrodynamic. Tribotests are widely used in laboratories to hint at the friction developed in these systems. In the present work, a SRV tribometer was used to evaluate the friction behaviour of lubricant oils under reciprocating movement up to 60 Hz. A high acquisition rate allowed the analysis of data inside each reciprocating cycle. Both a pure base oil and a fully formulated lubricant were used. Changes in the contact pressure, viscosity and speed were seen to influence friction, which was correlated to the relative thickness predicted by Hamrock-Dowson equation. While some observed characteristics were typical consequences of the Stribeck curve, other effects were also observed, such as the occurrence of seizure at high reciprocating frequency. A lower boundary coefficient of friction due to additive package in the formulated oil was also observed. The results allow a better understanding of friction in reciprocating cycles and can be used to evaluate the performance of oils and surfaces in laboratory prior to engine testing.

Jul 31, 2018

By Nigel Marx

In order to understand (and ultimately to predict) the friction reduction resulting from the use of polymer solutions, the rheological properties of model polymer solutions have been measured over a wide range of shear rates. Both temporary and permanent shear thinning have been observed. By using base fluids of different viscosities it has been shown that permanent shear thinning depends more closely on the shear stress experienced by the fluid than on the strain rate. Hydrodynamic measurements have been made on the polymer solutions using a compliant ball on flat lubricated contact that operates in isoviscous-elastic conditions. The measured friction values can only be predicted with reasonable accuracy if the measured shear thinning properties of the lubricant are taken into account in the hydrodynamic model.

Jul 31, 2018

By Valdicleide Silva Mello

Nowadays the biodiesel use is obligate in Brazil, in order to reduce the emissions of fuel burn. However, it is important to analyze which percentage of biodiesel is necessary to keep or improve the lubricant action of fuel for diesel engine, as well which kind of biodiesel give better performance. Therefore, this work aims to analyze the parameters that keep the lubricant action of biofuels, by using the Box-Behnken design type to optimize them. In this design was evaluated the input parameters: the type of the biodiesel (soybean, sunflower and palm), the concentration (5%, 20% and 100%) and the temperature of contact (25°C, 40°C and 60°C). The analyzed output parameters were the percentage of film formation, coefficient of friction, wear scar diameter (WSD) of ball, these output parameters were obtained by HFRR tribometer and they were analyzed applying response surface methodology. With this methodology was possible to determine the simultaneous influence and the interactions between two or more independent variables investigated. The response surfaces generated for the coefficients of friction, WSD, film formation showed a higher lubricant action for higher levels of concentration of biodiesel. An increase in lubricant action was found to high and intermediate temperature.

Jul 31, 2018

By Milson de Andrade Júnior

A central termoelétrica número 1 (CTE#1) da Companhia Siderúrgica Nacional possui duas caldeiras em operação denominadas 8 e 9 com capacidade total de produção de vapor de 200 Toneladas por hora. Estas caldeiras fornecem vapor para os turbo geradores e turbo sopradores da CTE#1, além de vapor de processo para a Usina Presidente Vargas (UPV). As caldeiras entraram em operação em 1982/83 e seus sistemas de controle e instrumentação eram totalmente pneumáticos. Ao longo do tempo foi surgindo dificuldades para reposição e manutenção dos componentes pneumáticos, motivo pelo qual se iniciaram os estudos para substituição deste sistema. Em 2009 teve início um projeto para substituição do controle pneumático por um controle microprocessado feito por PLC redundante trabalhando com um supervisório scada e para substituição das malhas de instrumentação pneumática por instrumentação em rede fieldbus. A substituição completa dos componentes pneumáticos foi concluída em 2012. O novo sistema implantado trouxe diversas melhorias na performance, confiabilidade, segurança operacional e ergonomia. Este trabalho apresenta as causas que motivaram o projeto em questão, a metodologia utilizada para a sua implantação e os resultados alcançados com a aplicação de tecnologia moderna para controle e instrumentação de caldeiras.

Jul 31, 2018

By Lis Nunes Soares

A qualidade de fabricação de tubos de aço sem costura está relacionada ao processo de tratamento térmico. O controle do comportamento dos fornos industriais de tratamento térmico é de grande importância de modo a garantir a qualidade do produto. É necessário conhecer os parâmetros de operação dos fornos, assim como suas influências nas variáveis de processo. Este estudo avaliou as extensões do efeito do tipo de alinhamento dos tubos no interior do forno nas temperaturas dos canais de fumaça, temperatura do forno, temperatura do tubo, pressão interna do forno, demanda dos queimadores e consumo de gás natural. Diferentes alinhamentos podem impactar no escoamento da massa de gás queimado dentro do forno e consequentemente ter um efeito nas variáveis de processo avaliadas. Para determinar o tipo de alinhamento mais adequado do ponto de vista da qualidade do material final e da melhor eficiência energética, testes foram realizados durante uma corrida em um forno de austenização, na qual se alternou entre os diferentes tipos de alinhamento, medindo-se as variáveis de processo estudadas. Os resultados foram analisados utilizando-se técnicas estatísticas, como ANOVA. Ao final observou-se que certos parâmetros são impactados pelo tipo de alinhamento do tubo, sobretudo a temperatura de fumos e pressão interna no forno. As variações foram relativamente pequenas, principalmente pelo fato da principal variável controladora do processo, a temperatura do forno, possuir uma dinâmica de resposta lenta.

Jul 31, 2018

By João Luiz do Vale

In standard wear tests, such as pin on disk (ASTM-G99) or block on ring (ASTM-G77), the apparatus simulates conditions that are often different from a machine element real application. Therefore, for an accurate investigation of a tribological application, it is essential to test the real condition in which there are similarities as: geometry, contact details, force application mode, materials, among others. It emphasizes that for studies involving polymeric materials it becomes extremely relevant. Thus, the Laboratory of Surfaces and Contact (LASC) at UTFPR developed an apparatus for sliding bearing on shaft test. In that equipment, loads are applied by a dead-weight system and the frictional force is measured on a load cell. The apparatus operating ranges for load added to the dead weight system and rotation shaft are from 0.2 to 5.0 kgf and from 260 to 3500 rpm, respectively. This paper presents a detailed evaluation of such apparatus, which includes free-body diagrams analysis and a deduction to obtain an equation for the kinetic friction coefficient. Also, the standard measurement uncertainties of a caliper, an electronic scale, and a cell load were determined. It was verified that the kinetic friction coefficient equation is dependent on the apparatus geometry, the applied load, and the frictional force value. Additionally, through the statistical significance analysis it was concluded that some terms in the equation were not significant. Finally, through the application of the error propagation theory in the kinetic friction coefficient equation, the standard measurement uncertainty of the apparatus which showed a value nearby 0.002 along the operating range of the apparatus was obtained.

Jul 31, 2018