O presente trabalho destina-se à discussão sobre o cálculo de vida útil de rolamentos. Mostrando o avanço do processo de cálculo ao longo das décadas até o mais alto grau de desenvolvimento atual. A preocupação do texto é demonstrar de forma simples e objetiva as divergências que existem entre a formulação teórica e a real vida dos rolamentos, no que tange a fadiga de contato. Neste contexto foram realizados testes, em máquina especialmente destinada ao ensaio da fadiga de rolamentos. Variando-se para as duas séries de ensaios, apenas, a temperatura (aproximadamente 85°C e 110°C). Os resultados obtidos indicam que a vida real dos rolamentos apresenta grande divergência se comparada com a vida útil calculada, principalmente, no regime com maior temperatura. Atribui-se a esta disparidade, a ausência de cálculos precisos quanto à correlação da vida útil com o fator l, que é uma forma de se calcular o espaçamento entre as superfícies de contato, e o não emprego do cálculo do fator de carga, na formulação da vida útil de rolamentos. / The present work has the purpose of discussing the life of rolling bearings, describing the evolution of bearing life calculation until its current state of the art. Our focus is to demonstrate, simply and objectively, the inconsistencies occurring between the actual life of rolling bearings and their theoretical fatigue life estimation. For such purpose, tests were developed in a special bearing test rig to assess bearing fatigue. Two test sets were carried out with temperature being the only variation (approximately 85°C and 110°C). Results obtained from these tests suggest that the real life of rolling bearings is indeed very different from calculated bearing life, especially under higher temperature. Such disparity can be attributed to the lack of a precise computation of the relationship between bearing real life and the l factor - which determines the thickness of lubricant separating raceways and balls - as well as to the failure to compute the load factor in bearing life estimation.

Orientador: Sergio Tonini Button / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-04T01:40:40Z (GMT). No. of bitstreams: 1 Gentile_FernandoCesar_D.pdf: 18474234 bytes, checksum: b76313390a0c50a06d4c59b7df69e538 (MD5) Previous issue date: 2004 / Resumo: Neste trabalho foram feitas simulações físicas do processo de Laminação Transversal com Cunha (LTC), também conhecido como Cross Wedge Rolling (CWR), para se analisar a influência da temperatura, da velocidade do processo e das características dos materiais empregados na estabilidade do processo. Para o desenvolvimento deste trabalho foram necessários o projeto e construção de uma bancada de simulação que fosse capaz de laminar peças com variados diâmetros e a diferentes taxas de deformação, e também de um par de ferramentas planas que fosse capaz de fabricar peças isentas de defeitos, segundo os diagramas de estabilidade do processo LTC disponíveis na literatura. Foram utilizados como materiais nas simulações: liga de alumínio, aço ABNT 4140 e aço microligado 48MnV3. A escolha do aço microligado foi baseada nas propriedades necessárias para materiais utilizados na fabricação de eixos escalonados. Para este material, foram feitas medidas da área dos defeitos internos, avaliações da macro e da microestrutura e ensaio de dureza Rockwell C. Os resultados mostraram que o diagrama de estabilidade de Hayama, utilizado para o projeto de ferramentas do processo LTC, não leva em consideração da maneira correta as propriedades do material conformado, já que se obteve diferentes defeitos externos para os diferentes materiais utilizados neste trabalho. Os resultados mostraram também que, para o aço microligado, o aumento da temperatura de processo diminui o tamanho dos defeitos internos, favorece o aumento de grão, o aumento da fração volumétrica de perlita e eleva a dureza, porém, não foi possível neste trabalho a correlação da velocidade de processo (taxa de deformação) com o tamanho do defeito interno e com as microestruturas obtidas / Abstract: ln this work tests were held with the Cross Wedge Rolling (CWR) process to analyze the influence of the process temperature, process speed and properties of the workpiece materiaJson the stability of the process. To perform these tests it was necessary to design and assemble a laboratory CWR equipment flexible enough to manufacture shafts with large ranges of diameters and strain rates, with a pak of flat tools able to roll parts free of defects in accord to stability diagrams found in the literature for CWR process. Three different alloys were tested: a commercial aluminum alloy, ABNT 4140 steel and the microalloyed steel 48MnV3. This microalloyed steel was chosen because of its mechanical properties are similar to those necessary to manufacture stepped shafts. The shafts rolled with this steel were analyzed measuring the internal defects, Rockwell C hardness and perform metallographic analysise valuating their macro and microstructures. Results showed that the Hayama stability diagram, that are used to design CWR tools, are not representative of this process because they do not consider the properties of the workpiece material in the correct way. The results also showed that higher temperatures reduce the probability of internal defects formation, rise the grain size, the perlite volume ftaction and hardness, but no conclusions can be made relating these defects an structures with the variation of the process speed. / Doutorado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica

The thesis deals with technology of hot-rolled profiles, describing total summary of principles and conditions this process is based on. There is a draft of a calibration of profile, the application of which is subsequently verified through a numerical simulation. Futher in the thesis also was verified the mechanical properties of applied construction steel S355J2 through the up-setting test and compared the results with the used material model in the simulation software Simufact Forming. Then, the test rolling of the calibrated profile was carried out. As a next step, the dimensions of the rolled bars were compared with the results of the simulation, on the basis of which the applicability and suitability of the simulation in the future development of other profiles was verified and evaluated.

The aim of this thesis is a construction concept of tyre rolling resistance measuring device. The first part deals with the rolling resistance. It describes its causes, its influential factors and it also includes rolling resistance identification methods. The second part deals with construction design of the rolling resistance measuring device itself. It contains stress analysis, and fatigue analyses as well. It includes selection of transducers used for tyre rolling resistance measuring and also measurement error analyses. The last part focuses on estimated financial requirements connected with producing and assembling the designed measuring device.

This research is about a costly problem in the automotive industry due to tool fracture during the splines cold rolling of steel shafts. The objective is to study the cause of this failure and propose solutions that can be implemented in the workshop.The writing starts with a brief introduction of the companies involved in shafts production and problem solving. It introduces the cold rolling process and its advantages on splines manufacturing, and it goes through relevant material and process characteristics that help to determine the cause of tool fracture.In order to understand the process failure and production flow, it has been necessary to build up an Ishikawa diagram with possible tool fracture causes. After collecting and analysing the data about the machine tool, cold rolling process and work-piece and rolling tool materials, tests and experiments have been done.It has been considered that there is a rolling tool fatigue that causes tool fracture. Beside tool fracture, two more problems with production flow instability and the right side rolling tool have been detected. Testing the material hardness of the work-piece has shown continuous hardness fluctuations from the supplier. Rolling tool misalignment has been measured by using a vernier caliper measurement device. Rolling tools material hardness analysis shows that tool is very hard and it is possible to use a tougher material which responds better to cyclic loads.Leax has tried to solve the problem by testing another lubrication and tool coatings. A modal analysis test has been performed in order to find the natural frequency of the work-piece which possibly may lead to vibration and over loading one of the rolling tools.The conclusion that has been reached is that main cause of fracture is rolling tool fatigue due to cyclic loads and it is important to use other rolling tool material. The other two detected problems, production flow instability and rigth side rolling tool fracture, should be considered as a part of the problem in order to significantly increase tools life and stabilize production flow rate.

WE43 magnesium foils (thickness ≤ 200 μm) were successfully produced via hot rolling. The initially extruded material was heat treated at 450 °C for 2 h to achieve a more homogenous microstructure. Afterwards the sheets were hot rolled at 480 °C in two to five rolling passes to achieve a thickness less than 200 μm and finally heat treated (T5 and T6 heat treatment). Microstructural und texture evolution after foil rolling and the final heat treatment were investigated and the resulting mechanical properties were also evaluated. Therefore, the samples were quenched directly after foil rolling and the final heat treatment. The foil rolling led depending on the number of the rolling passes either to a deformation microstructure (two and three passes) or globular grains (four and five passes).

WE43 magnesium foils (thickness ≤ 200 μm) were successfully produced via hot rolling. The initially extruded material was heat treated at 450 °C for 2 h to achieve a more homogenous microstructure. Afterwards the sheets were hot rolled at 480 °C in two to five rolling passes to achieve a thickness less than 200 μm and finally heat treated (T5 and T6 heat treatment). Microstructural und texture evolution after foil rolling and the final heat treatment were investigated and the resulting mechanical properties were also evaluated. Therefore, the samples were quenched directly after foil rolling and the final heat treatment. The foil rolling led depending on the number of the rolling passes either to a deformation microstructure (two and three passes) or globular grains (four and five passes).

Tire tread health is essential for safe operation of a passenger vehicle. Worn out tires significantly increases the risk of traffic accidents and hydroplaning. This thesis investigates the possibility to detect tire tread wear by estimating the effective rolling radius of a tire. The effective rolling radius of a tire is affected by several different factors. As to not confuse change in external factors with actual tire tread wear, there is therefore a need to compensate the effective rolling radius to nominal conditions, to make sure that the change in compensated rolling radius is only due to the tire tread wear. This raises the questions: how can the effective rolling radius be estimated? Can it be compensated with respect to external factors? The behavior of the tire changes between different tire models. This is because different models uses different materials, patterns, internal structure etc. This raises an additional question. Can a compensation model with the same parameter values be used in all vehicles of the same type no matter the tires of the vehicle, or is there a need for an adaptive compensation model that adapts the parameters to the current tire? This thesis investigates how the estimation of the tires effective rolling radius can be improved by estimating the velocity using sensor fusion between GPS- and IMU-signals. This was done using an Extended Kalman Filter. Furthermore, this thesis proposes different ways of compensating a tires effective rolling radius with respect to external factors and compares these methods with each other to obtain the most efficient compensation method. After finding an appropriate compensation method, further investigations regarding the need of adaptivity between tires was performed to find out if the compensation factors can be used on the same vehicle model with different tire sets. Ultimately, the investigations showed that the estimation of the effective rolling radius of a tire using sensor fusion was not fruitful due to limitations set by the IMU. If the vehicle had been equipped with a 6-axis IMU instead of a 3-axis IMU, this method might be feasible. The method that directly calculates the effective rolling radius from GPS-velocity and wheel speed gave a more accurate rolling radius signal. The compensation of the effective rolling radius can be achieved with respect to velocity, tire pressure and tire temperature. The most advantageous compensation method proposed in this thesis was a polynomial compensation model. Lastly, when investigating the need of adaptive compensation factors it was found that these compensation factors needs to be adaptive between tire sets.

A nonlinear finite element model of the hot and cold rolling processes has been developed for flat rolling stock with rectangular cross section. This model can be used to analyze the flat rolling of cold and hot steel rectangular strips under a series of different parameters, providing the rolling designer with a tool that he can use to understand the behavior of the steel as it flows through the different passes. The models developed, take into account all of the non-linearities present in the rolling problem: material, geometric, boundary, and heat transfer. A coupled thermal-mechanical analysis approach is used to account for the coupling between the mechanical and thermal phenomena resulting from the pressure-dependent thermal contact resistance between the steel slab and the steel rolls. The model predicts the equivalent stress, equivalent plastic strain, maximum strain rate, equivalent total strain, slab temperature increase, increase in roll temperature, strip length increase, slab thickness % reduction (draft), and strip's velocity increase, for both the cold and hot rolling processes. The FE model results are an improvement over the results obtained through the classical theory of rolling. The model also demonstrates the role that contact, plastic heat generation and friction generated heat plays in the rolling process. The analysis performed shows that the steel in cold rolling can be accurately modeled using the elastic-plastic (solid Prandtl-Reuss) formulation, with a von Mises yield surface, the Praguer kinematic hardening rule, and the Ramberg-Osgood hardening material model. The FE models also demonstrate that the steel in hot rolling can be modeled using the rigid-viscoplastic (flow Levy-Mises) formulation, with a von Mises yield surface, and Shida's material model for high temperature steel where the flow stress is a function of the strain, strain rate, and the temperature. Other important contributions of this work are the demonstration that in cold rolling, plane sections do not remain plane as the classic theory of rolling assumes. As a consequence, the actual displacements, velocity, and stress distributions in the workpiece are compared to and shown to be an improvement over the distributions derived from the classical theory. Finally, the stress distribution in the rolls during the cold rolling process is found, and shown to be analogous to the stress distribution of the Hertz contact problem. / Master of Science

Ways of rolling tubes on a continuous rolling mill considered in the work. Overview of three-roll continuous rolling mills are given. Technology for the production of pipes for pipe unit with 3 roller stand continuous mill developed. The geometric model of the process by scanning the tube sheet is constructed. Determination of the amount of deformation is made. Kinematically possible velocity field is constructed. Examples of calculations of a table rolling and modes of compression on a continuous three-roll mill is shown. / В работе рассмотрены способы прокатки труб на непрерывном стане, проведен обзор трехвалковых оправочных станов. Приведена технология производства труб на ТПА с 3-х валковой клетью непрерывного стана. Построена геометрическая модель обжатия путем развертки трубы в лист и проведено определение размера очага деформации. Построено кинематически-возможное поле скоростей. Приведены примеры расчетов таблицы прокатки и режимов обжатия на непрерывном трехвалковом стане.