Study of surface evolution in the wheel-rail interface

This paper aims to trace surface evolution in the wheel-rail interface using data obtained from a twin-disc testing machine and the surface replication technique. Changes in the surface profile of the rail testing disc are explicitly analysed according to the wear mechanism, which helps elaborate a better understanding of the attrition of asperities during the wearing-in process of surface modification. The surface profile amplitude was seen to decrease during the initial running-in phase of the experiment cycle, and after reaching a saturation value, the profile amplitude then increased. Ultimately the results show that grinding will roughen the rail surface and the wheel-rail contact conditions will then remove this surface damage to some saturation value of the profile height. The variation in the rail surface profile beyond this point is then only dependant on the contact conditions which exist between the wheel and rail during normal operation.

Experimental studies on the performance of rail joints with modified wheel/railhead contact

Rail joints are provided with a gap to account for thermal movement and to maintain electrical insulation for the control of signals and/or broken rail detection circuits. The gap in the rail joint is regarded as a source of significant problems for the rail industry since it leads to a very short rail service life compared with other track components due to the various, and difficult to predict, failure modes – thus increasing the risk for train operations. Many attempts to improve the life of rail joints have led to a large number of patents around the world; notable attempts include strengthening through larger-sized joint bars, an increased number of bolts and the use of high yield materials. Unfortunately, no design to date has shown the ability to prolong the life of the rail joints to values close to those for continuously welded rail (CWR). This paper reports the results of a fundamental study that has revealed that the wheel contact at the free edge of the railhead is a major problem since it generates a singularity in the contact pressure and railhead stresses. A design was therefore developed using an optimisation framework that prevents wheel contact at the railhead edge. Finite element modelling of the design has shown that the contact pressure and railhead stress singularities are eliminated, thus increasing the potential to work as effectively as a CWR that does not have a geometric gap. An experimental validation of the finite element results is presented through an innovative non-contact measurement of strains. Some practical issues related to grinding rails to the optimal design are also discussed.

Roughness generated in surface grinding of metals

When a metal is surface ground the roughness generated is the summation of a function of the wheel roughness and the roughness due to wheel attrition and damage to the workpiece. We identify this function here as a maximum em,elope profile, which is fractal within certain cut off wavelengths determined by the dressing conditions of the wheel. Estimating the global displacement of the binder-grit-workpiece system from the maximum envelope power spectra, we determine the plastic indentation of the workpiece at characteristic length scales using simple contact-mechanical calculation. The estimated roughness corresponds well with that recorded experimentally for hard steel, copper; titanium and aluminium.

Influência da velocidade de avanço do rebolo nos danos de aços endurecidos retificados

A tendência mundial é o aumento da produtividade e da produção de peças cada vez mais sofisticadas, com elevado grau de tolerância geométrica, dimensional, com bom acabamento superficial, com baixo custo. A retificação é responsável pelo acabamento final no processo de usinagem de um material. No entanto, danos gerados nesta fase de produção comprometem todos os recursos utilizados nas fases anteriores. Grande parte dos problemas ocorridos na retificação deve-se à enorme temperatura gerada pelo processo devido às condições de usinagem. Atribui-se à velocidade de avanço, que está diretamente relacionada com a produtividade, os danos ocorridos na retificação, ficando esta variável limitada até valores que não proporcione danos. Neste trabalho, através da variação da velocidade de avanço no processo de retificação cilíndrica externa do aço ABNT D6, racionalizando a aplicação de dois fluidos de corte e usando um rebolo superabrasivo de CBN (nitreto de boro cúbico) com ligante vitrificado, avaliou-se a influência da velocidade de avanço nos danos superficiais de aços endurecidos. Os resultados permitiram concluir que a velocidade de avanço associada a uma eficiente refrigeração e lubrificação, não provocou danos térmicos (queima, trincas, tensões de tração) ao material. Tensões residuais e a rugosidade do material retificado apresentaram uma correlação com as condições de usinagem. O trabalho concluiu ser capaz um aumento dos índices de produtividade sem provocar danos nos componentes retificados.

The minimum quantity of lubricant (MQL) technique in the surface grinding of steel

This research aimed to analyze the viability of the minimum quantity of lubricant (MQL) technique towards different methods of lubri-refrigeration in surface grinding of steel, considering process quality, wheel life and the viability of using cutting fluids The proposal methods were the conventional (abundant fluid flow), the minimum quantity lubrication (MQL) and the optimized method with Webster nozzle (rounded) This analysis was carried out in equal machining conditions, through the assessment of variables such as grinding force, surface roughness, G ratio (volume of removed material/volume of wheel wear), and microhardness The results showed the possibility of improvement of the grinding process Besides, there is the opportunity for production of high quality workpieces with lower costs The MQL technique showed efficiency in machining with lower depths of cut The optimized method with Webster nozzle applies the fluid in a rational way, without considerable waste Hence, the results show that industry can rationalize and optimize the application of cutting fluids, avoiding inappropriate disposal, inadequate use and consequently environment pollution

The behaviour of resin-bond diamond wheels in the grinding of advanced ceramics

Results are reported of the behaviour of the plane tangential grinding process using diamond grinding wheels. Grinding performance is analysed in terms of the wear behaviour of the wheel in the grinding of ceramic. Discussion of the results concentrates on the wear mechanism of the diamond wheel and the process of material removal.

Estudo da predição da circularidade e rugosidade de peças retificadas utilizando as redes neurais artificiais

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estudo comparativo entre a lubri-refrigeração convencional e a MQL no processo de retificação cilíndrica externa de mergulho

Pós-graduação em Engenharia Mecânica - FEB

Proposta de uma máquina para processo de abrasão baseado na combinação de algumas características da lapidação e retificação

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Análise da influência da velocidade de mergulho na retificação de aços endurecidos utilizando refrigeração otimizada

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Evaluation of different methods of cooling-lubrication in cylindrical grinding of advanced ceramic dip

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)