The increasing demand for more readily bio-degradable, renewable and non-toxic environmentally adaptive lubricants with a lower degree of bioaccumulation has escalated the investigation of water-based lubricants as the potential alternatives for conventional mineral-based oils. Water is an excellent environmentally adapted lubricant; however, it is a low viscous fluid and holds downsides of having corrosive nature and extremely low pressure-viscosity coefficient leading to insufficient load-carrying capacity. These shortcomings make pure water a poor choice for operations involving high load and low speed, for instance, within hydropower applications. Therefore, the choice of appropriate modifiers and additives is crucial to improve the viscosity, friction-reducing performance and anti-wear properties of water as a base lubricant. Appropriate selection and combination of bearing materials also significantly improve the tribological performance of the lubricants. In the presented work, tribological behavior of polyvinylpyrrolidone (PVP) and poly(sodium 4-styrenesulfonate) (PSS) thickening agents with water as a base fluid in the lubrication of pure UHMWPE and SCF reinforced UHMWPE bearing materials has been investigated individually under reciprocating tribometer. The results showed that both PVP and PSS are excellent viscosity modifiers. PVP exhibited excellent friction-reducing and anti-wear performance, while PSS revealed increased wear rates with an insignificant reduction of friction coefficients. This study aims to explore the potential for using newly developed water-based lubricants in the replacement of traditional mineral-based lubricants for hydropower turbine bearings.

Achieving sustainable lubrication by using environmentally friendly formulated lubricants has became an essential component of the transition process from fossil-powered vehicles to electrified transportation. Mixtures, or aqueous solutions of molecules such as polyhydroxy alcohols, and glycols usually known as green lubricants make it possible to achieve low friction coefficients under different lubrication conditions, which constitutes a potential alternative to improve the tribological performance of moving parts in automotive systems, at the same time that the environmental requirements are satisfied. There is a need to improve the protection against mild-wear and micropitting offered by green-lubricants before consider using them in the transmission gear box of battery electric vehicles BEVs, where their low shear-stress resistance can potentially help to improve the vehicle efficiency. Therefore, this research work aims to gain understanding of the tribological behaviour of rolling-sliding elements under glycerol-based lubrication, with focus on assessing the influence of different glycerol-based lubricant formulations on the wear modes associated to rolling contact fatigue such as micropitting, and macropitting.  Micropitting tests were carried out by using a micropitting rig, with a roller on ring planetary configuration. The evolution of microcracks, and micropitting was studied for several glycerol-based lubricants at different slide-to-roll ratios (SRRs) 5-30%, and different load contact conditions 1.5-2.5 GPa. A comparison against a fully formulated transmission oil has been performed. A relationship between the surface damage morphology and the operating conditions has been established. The lubrication regimes of DLC coated contacts and uncoated contacts in presence of glycerol-based lubricants were investigated through the construction of 3D friction maps, and Stribeck curves in a wide range of rolling speeds, and SRR testing conditions. The capability of two different DLC coating systems to prevent micropitting onset due to rolling contact fatigue in presence of glycerol-based lubricants was studied: Cr/a-WC:H/a-C:H and a-C:Cr.  Under mixed-lubrication regime it was found that a reduction up to 51% of friction can be achieved by using glycerol-based lubricants compared to a commercial transmission oil. The initial low friction coefficients at low contact cycles was attributed to the low pressure-viscosity coefficient of the glycerol-based lubricants. Friction was even further reduced with the increasing contact cycles since glycerol aqueous solutions were found to promote mild-wear, causing a smoothing of the surface asperities and therefore an enhancement of the hydrodynamic effect due a higher lambda ratio (Λ), making possible to trigger superlubricity in the contact. Surface micro-cracking was found to decrease at low SRR values under glycerol-based lubrication contrasted to the contacts lubricated with a fully formulated transmission oil. Once microcracks were nucleated, micropitting progressed faster in the contacts lubricated with glycerol-based lubricants, while micropitting was null or significantly delayed in presence of transmission oil. With the increasing SRR surface microcracks density and micropitting was found to became higher. The reduction of microcracks density with a glycerol-glycol based lubricant was attributed to the adsorption of long glycol molecules on the steel surface that avoid the direct interaction between asperities. The faster micropitting progression was attributed to the presence of dissolved water in the contact. Thin DLC a-C:Cr coatings were shown to significantly mitigate the penetration of surface initiated pits into the steel substrate, which was translated in a lower volume loss. Local micro-delamination was found to be the main reason behind coating failure in presence of glycerol-based lubricants, as a result, pitting took place on the steel exposed areas.

The global shift towards sustainable practices extends across various domains, including energy generation. Wind energy, a cornerstone of this transition, relies heavily on the efficient operation of wind turbines. This study investigates the impact of contaminants on the longevity and performance of blade bearings in wind turbines. Under real-world conditions, blade bearings frequently operate in suboptimal lubrication environments, attacked by contaminants like wear particles and water. This research, conducted in collaboration with Vattenfall R&D, aims to focus on the specific effects of these contaminants.  Through comprehensive literature reviews and tribological tests, the study evaluates the load in rolling elements, examines the contact conditions between raceways and rollers, and determines the effects of contaminants on wear volume. Findings indicate that most pitch movements in blade bearings are limited to small angles, influencing lubrication requirements and wear patterns. Chloride-based EP additives, probably inactive due to insufficient activation temperatures, show potential for hydrolysis-induced corrosion.  Wear tests suggest that used grease may perform better under certain conditions compared to fresh grease, highlighting the complexity of lubricant performance. Long-term tribological tests show that FUCHS LUBRITECH GLEITMO 585K exhibits better wear resistance compared to Shell Rhodina BBZ in test conditions.  The study underscores the importance of proper lubrication and contamination management in extending blade bearing life. Recommendations include regular grease monitoring and analysis, understanding tribo-corrosion effects, and improving seal compatibility to enhance overall bearing reliability.

Metal on metal wear at high sliding speeds and high contact pressures results in the melting of one or both of the sliding solid bodies due to heat generated at the contact interface. Understanding the influence of sliding speeds, contact pressures and material properties on wear rates is important in developing predictive models for designing more efficient and effective engineering system components. Typical engineering applications subjected to these extreme conditions include ultrahigh speed machining, rocket sleds, large caliber cannon, and electromagnetic launchers. Sliding speeds on the order of 1,000 m/s and contact pressures in excess of 100 MPa are common in these applications and difficult to replicate in a laboratory environment. A unique wedge experiment using a minor caliber electromagnetic launcher has been developed and implemented to characterize wear deposition of a 6061-T6 aluminum sliding body on several different guider materials of varying mechanical and thermal properties at sliding speeds from 0 – 1,200 m/s and contact pressures from 100 – 225 MPa. Optical microscopy and 3D profilometry were used to characterize and quantify the slider wear. Three distinct wear regions, plasticity dominated, severe plastic deformation and melt lubrication were observed. Test results provided evidence that the aluminum slider contact interface was molten. Modeling of the experimental wear data showed a dependence on pressure and velocity and guider material properties, density and specific heat. A predictive wear model was developed for the melt lubrication region as a tool for designing components subjected to similar operating conditions.

<p>У раду је извршено триболошко истраживање у области граничног<br />подмазивања које се јавља на примарним деловима вентила у<br />системима природног гаса. Истраживања су извршена етапно, у<br />реалним и, лабораторијским условима, користећи савремене методе<br />триболошких експерименталних истраживања. Извршена је замена<br />могућим оптималним материјалима трибо парова у односу на реалне<br />ефектуиране материјале вентила. Креирана су нова мазива за област<br />граничног подмазивања у односу на инострана и извршено је<br />упоређивање по више критеријума. Статистичка, металографска,<br />хемијска и физичка испитивања трибо парова су извршена и<br />упоређивана.</p> / <p>U radu je izvršeno tribološko istraživanje u oblasti graničnog<br />podmazivanja koje se javlja na primarnim delovima ventila u<br />sistemima prirodnog gasa. Istraživanja su izvršena etapno, u<br />realnim i, laboratorijskim uslovima, koristeći savremene metode<br />triboloških eksperimentalnih istraživanja. Izvršena je zamena<br />mogućim optimalnim materijalima tribo parova u odnosu na realne<br />efektuirane materijale ventila. Kreirana su nova maziva za oblast<br />graničnog podmazivanja u odnosu na inostrana i izvršeno je<br />upoređivanje po više kriterijuma. Statistička, metalografska,<br />hemijska i fizička ispitivanja tribo parova su izvršena i<br />upoređivana.</p> / <p>In this paper an experimental tribological research was carried out at the field<br />of boundary lubrication wich appear on primary parts of valves in systems of<br />natural gas. Research was carried out in stages, at the real conditions and in<br />the laboratory, using modern methods of experimental research of wear.<br />Replacement of materials was made with possible optimized tribo pairs in<br />relation to the real effectuated materials of valve. The new lubricants were<br />created for boundary lubrication regime with respect to foreign and<br />comparison was made through more criteria. Statistical, metallographic,<br />chemical and physical test were performed with tribo pairs and compared.</p>

Ultra high molecular weight polyethylene (UHMWPE) is a polymer commonly used in various applications, particularly in hip joint replacements. Despite its good performance, it is susceptible to oxidation degradation, which can be mitigated with the addition of vitamin E, and to excessive wear against metal countersurfaces, which can potentially be improved with the addition of nanoparticles. In this work, sixteen newly developed UHMWPE nanocomposites with different nanofillers (multi-walled carbon nanotubes, graphene oxide and nanodiamonds), blended with and without vitamin E, and both irradiation crosslinked and non-crosslinked were studied. Thermomechanical characterisation (dynamic mechanical analysis and thermogravimetric analysis) and tribological pin-on-disc testing showed that both nanofillers and the addition of vitamin E ensured improved the performance of the nanocomposites compared to the virgin UHMWPE. Vitamin E improved the oxidative and thermal stability of UHMWPE, decreased the wear and increased the coefficient of friction. The nanoparticle reinforcements contributed to improved thermal stability to some degree and decreased the wear. Crosslinking was also shown to result in improved thermomechanical performance, although it appears that the addition of vitamin E inhibits the crosslinking process.

No description available.

Neste trabalho, foi investigado o comportamento tribológico dos pares cerâmicos aluminanitreto de silício no deslizamento em água e em uma suspensão de sílica coloidal em água (hidrosol). O objetivo foi verificar a possibilidade de atingir um coeficiente de atrito da ordem de unidades de milésimos, aqui chamado de ultra-baixo coeficiente de atrito (UBCA), verificar se a mudança do meio, de água para hidrosol, diminui o running-in do coeficiente de atrito, e verificar o efeito da variação da rugosidade inicial da alumina no comportamento do atrito. Os ensaios foram realizados na configuração de teste esferasobre- disco, no qual a esfera foi de nitreto de silício e o disco de alumina, sob carga normal de 54 N e velocidade de 1 m/s. A água utilizada nos ensaios foi destilada e deionizada, e a sílica coloidal amorfa, hidrofílica, sem porosidade e de tamanho médio de partícula de 12 nm foi a Aerosil® 200, e o hidrosol foi preparado com pH 8,5 num eletrólito de NaCl de 1 mM. A esfera de nitreto de silício, adquirida comercialmente, e a alumina, sinterizada em laboratório, foram caracterizadas quanto a densidade, as fases foram determinadas por difração de raios X, microscopia eletrônica de varedura (MEV) observada em amostras ceramográficas atacadas. Algumas propriedades mecânicas como dureza, módulo de elasticidade e tenacidade à fratura foram determinadas. Duas condições de rugosidade dos discos de alumina foram utilizadas nos ensaios tribológicos, 350 nm e 10 nm RMS. Em todos os ensaios, em água, em hidrosol e independentemente da rugosidade inicial do disco o coeficiente de atrito no regime permanente apresentou pequena dispersão de valores de 0,002 a 0,006, e não foi possível estabelecer diferença entre elas. A menor rugosidade do disco de alumina acarretou menor desgaste e menor período de running-in de coeficiente de atrito, tanto em água quanto em hidrosol. Os ensaios em meio de hidrosol acarretaram menor desgaste das cerâmicas e apresentaram menor running-in de coeficiente de atrito, comparados aos ensaios com água. O disco de alumina apresentou menor desgaste do que a esfera de nitreto de silício, em todas as condições estudadas. Com a análise das perdas volumétricas, da rugosidade final das superfícies desgastadas, das curvas de coeficiente de atrito e das espessuras mínimas de filme lubrificante, calculadas com uso de modelo da literatura, foi possível relacionar a diminuição do desgaste e do running-in de coeficiente de atrito em meio de hidrosol, com a presença da sílica na superfície ou próxima dela. / In this work, the tribological behavior of the alumina-silicon nitride couple was investigated under water and hydrosol (colloidal silica suspensions in water) lubricated sliding. The purposes were to study how an ultra-low friction coefficient can be achieved and to analyze the effects of the environment, lubricant and alumina roughness changes on the friction behavior. Ball-on-disk tests with a normal load of 54 N and a sliding speed of 1 m/s were carried out, using a silicon nitride ball and an alumina disk. The water used as lubricant was distilled and deionized. The silica was amorphous colloidal and hydrophilic, without porous and with a 12 nm medium particle diameter, commercially named Aerosil ® 200. The hydrosol was obtained with a pH value of 8,5 and a 1mM NaCl electrolyte. To estimate the minimum film thickness, formed during the lubricated sliding tests, a theory model was used. The commercial silicon nitride balls and the alumina disks, which were conformed and sintered in laboratory, were characterized by density, X-ray diffraction and scanning electron microscopy measurements. The mechanical properties such as hardness, Young modulus and fracture toughness were determined. The friction coefficient values obtained in the steady state regime showed low standard deviations (0,002 to 0,006) under all conditions. A shorter period of running-in was observed with the lower disk roughness, both in water and hydrosol lubrication. The hydrosol lubricated sliding produced a lower wear and friction running-in comparing with the tests under water lubrication. The alumina disk always showed lower wear than the silicon nitride ball. The volume loss, friction coefficients, worn surfaces roughness and minimum film thickness results suggest that the wear and friction coefficient running-in decrease was caused by the presence of silica on the sliding surfaces or on the near surface regions.

Made available in DSpace on 2014-06-11T19:31:04Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-09-28Bitstream added on 2014-06-13T20:41:15Z : No. of bitstreams: 1 fernandes_ub_dr_bauru.pdf: 2660962 bytes, checksum: fc9e67e750b58c50d6c4a294d57f31a5 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A operação de retificação cilíndrica interna de precisão tem sido empregada na fabricação de componentes de responsabilidade na indústria metal-mecânica em geral. As modernas retificadoras CNC aprimoraram este processo no que diz respeito ao posicionamento e à rigidez do sistema máquina-peça-ferramenta, possibilitando a obtenção de peças de elevada precisão com baixos valores de tolerâncias dimensionais. Todavia, tem-se observado nos últimos anos uma crescente conscientização quanto à toxidade dos fluidos de corte empregados na lubrificação e refrigeração da peça. Paralelamente, criou-se nos últimos anos uma rígida legislação, visando evitar uma depredação desenfreada do meio ambiente. Diante de tal conjuntura, as indústrias iniciaram uma busca a métodos alternativos de lubri-refrigeração que empregassem menores quantidades. Dentre todas as técnicas existentes à de Mínima Quantidade de Lubrificação (MQL) vem ganhando cada vez mais destaque. Tal técnica pode ser entendida como um elo de ligação entre os métodos de lubri-refrigeração convencional e a usinagem a seco. Pretende-se ainda avaliar o desempenho de um novo bocal de aspersão de fluido de corte, baseando-se no modelo desenvolvido por Webster , adequado a operação de retificação cilíndrica interna. Logo, tem-se neste trabalho, o intuito de associar estas novas tendências por meio do estudo do comportamento da operação de retificação cilíndrica interna de mergulho a alta velocidade no processo de acabamento de um aço endurecido, utilizando-se a técnica de Mínima Quantidade de Lubrificação (MQL), o modelo otimizado e ainda o modelo convencional.A análise dos dados que servirão para a avaliação dos métodos de lubri-refrigeração empregados será feita por meio dos valores de rugosidade , desvio de circularidade , micro-estrutura e micro-dureza . Espera-se, com este... / Plunge cylindrical grinding has been widely employed in the manufacture of components by the metal and mechanical industry in general. Modern CNC grinding machines improve this process in terms of the positioning and rigidity of the machine-workpiece-tool system, allowing for the fabrication of high precision workpieces with low dimensional deviations. However, over the last few years, increasing awareness has been shown regarding the toxicity of the cutting fluids employed in the lubrication and cooling of the workpiece. Concomitantly, increasingly strict legislation has been passed in recent years, aiming to prevent inrestrained destruction of the environment. This situation has prompted the industry to seek alternative lubrication and cooling methods that use lower quantities of fluids. Among the existing techniques, the Minimum Quantity Lubrication (MQL) method has gained increasing prominence. This technique can be considered a combination of the conventional cooling and dry grinding methods. An evaluation was made of the performance of a new cutting fluid dispersion nozzle, based on Webster's model, suitable for the plunge cylindrical grinding operation. The purpose of this work is to examine these new trends in a study of the behavior of highrotation plunge cylindrical grinding in the finishing operation of hardened steel, using the MQL technique, the optimized nozzle model, and the conventional model. The lubrication and cooling methods employed here are evaluated based on an analysis of the roughness, circularity deviation, microstructure, and microhardness data. The results of this study le to the conclusion that the optimized lubrication and cooling method provide the best results and that the MQL system in cylindrical grinding produced unsatisfactory results, requiring further studies aimed at solving the problems that were identified.

Resumo: No processo de retificação e utilização de fluidos de corte é uma maneira de implementar a qualidade final ao processo, pois os fluidos têm como finalidade a lubrificação na área de contato entre a peça e ferramenta e a refrigeração das superfícies, assim evitando danificações na superfície da peça. Com isso, a utilização de fluidos de corte tem sido constantemente estudada, visando diminuir a utilização deste, pois a utilização de fluidos de corte tem seus problemas. O custo do produto final aumenta consideravelmente com o uso de fluidos de corte no processo de retificação, além de que os fluidos de corte são substâncias tóxicas e nocivas tanto às pessoas quanto ao meio ambiente. Portanto indústrias, universidades e centro de pesquisas são levados a pesquisar métodos alternativos menos prejudiciais ao meio ambiente. Dentre as alternativas surge e técnica da mínima quantidade de lubrificante (MQL), que também tem suas desvantagens, como por exemplo, a formação de uma borra de óleo na superfície de corte do rebolo, o que gera uma rugosidade maior na peça. Porém, visando minimizar esse problema podem ser usados jatos de ar comprimido incidindo na superfície de corte do rebolo, com o objetivo de limpar a superfície de corte do rebolo, com o objetivo de limpar a superfície do rebolo. Dessa forma, avaliou-se a eficiência desse sistema de ar comprimido para a limpeza e pôde-se verificar que, a utilização da limpeza juntamente com a técnica do MQL, torna-se viável, pois de uma maneira geral a técnica do MQL com limpeza obteve melhores resultados na qualidade da peça e desgaste da ferramenta, em relação ao MQL sem limpeza. A limpeza com um ângulo tangente à superfície do rebolo foi a condição de limpeza que obteve melhores resultados para a limpeza o que comprova que a melhoria na técnica do... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In grinding process the use of cutting fluids is a way to implement the final quality of the process because the fluids are intended for the lubrication in the contact area between the work piece, the tool and the cooling of the surfaces avoiding damages on the work piece surface. However, the use of cutting fluids has been constantly studied in order to reduce its use since this practice brings a lot of problems about. The final product cost increases considerably along with the use of cuting fluids in gringing process, besides those substances are toxic and harmful to people and to the environment as well. Therefore, industries, universities and research center have been taken as sites for investigating less harmfulll alternative methods to the environment. Among such alternatives comes up of minimum quantify of lubricant technique (MQL), which also has some disadvantages, such as the formation of oil sludge on the cut surface of the wheel, which creates a greater surface roughness on the work piece. However, in order to minimize this problem compressed air jets can be used focusing on the cut surface of the wheel, in order to clean it. Thus, we could evaluated the effectiveness of that compressed air system used for cleaning, and it was possible to observe that the use of cleaning with the MQL technique is feasible because from a general view the use of the MQL technique in the cleaning process showed better results in the quality of the work piece and wornout of the tool comparing to the to the MQL with no cleaning. The cleaning with a tangent angle to the surface of the wheel was the condition of cleanliness that showed better results for the cleanliness which proves that the improvements for the MQL techniques does not lead to significant results compared to the conventional technique. However, the MQL technique with cleanliness has its... (Complete abstract click electronic access below) / Orientador: Eduardo Carlos Bianchi / Coorientador: Anselmo Eduardo Diniz / Banca: Carlos Elias da Silva Junior / Banca: Celso Naves de Souza / Mestre