Tribology in Metal Working

This thesis focuses on the tribological performance of tool surfaces in two steel working operations, namely wire drawing and hot rolling. In all forming operations dimensions and surface finish of the products are of utmost importance. Forming basically includes three parts – forming conditions excluded – that may be changed; work material, tool and (possibly) lubricant. In the interface between work material and tool, the conditions are very aggressive with – generally or locally – high temperatures and pressures. The surfaces will be worn in various ways and this will change the conditions in the process. Consequently, the surface finish as well as the dimensions of the formed product may change and in the end, the product will not fulfil the requirements of the customer. Therefore, research and development in regard to wear, and consequently tribology, of the forming tools is of great interest. The investigations of wire drawing dies focus on coating adhesion/cohesion, surface characteristics and material transfer onto the coated steel both in laboratory scale as well as in the wire drawing process. Results show that it in wire drawing is possible to enhance the tribological performance of drawing dies by using a lubricant together with a steel substrate coated by a polished, dual-layer coating containing both hard and friction-lowering layers. The investigations of hot rolling work rolls focus on microstructure and hardness as well as cracking- and surface characteristics in both laboratory scale and in the hot strip mill. Results show that an ideal hot work roll material should be made up of a matrix with high hardness and a large amount of complex, hard carbides evenly distributed in the microstructure. The surface failure mechanisms of work rolls are very complex involving plastic deformation, abrasive wear, adhesive wear, mechanical and thermal induced cracking, material transfer and oxidation. This knowledge may be used to develop new tools with higher wear resistance giving better performance, lower costs and lower environmental impact.

Ökat hot och våld i arbetslivet – en följd av förändrade arbetsförhållanden? : En studie utifrån de svenska Arbetsmiljöundersökningarna 1991–2005

Increase in work related violence. A reflection of changes in working conditions? An analysis based on the Swedish Work Environment surveys. Victim surveys from Sweden show that the proportion reporting exposure to work related violence has increased. On the basis of the Swedish Work Environment surveys 1991–2005 this article focuses on the following questions: What kind of situations and working conditions are related to workplace violence? And, has the number of employees exposed to these working conditions increased parallel to the rise of reported workplace violence? Logistic regression analysis shows that some situations and working conditions are indeed related tothe risk of violence. To some extent exposure to these working conditions co-varies with exposure to violence. This result is more prominent for women than for men. Further research is needed to understand how changes in working conditions affect the risk of violence and the development thereof, not least from a gender perspective. Even so, changes in working conditions can not alone explain the increase of reported workplace violence in Sweden during this period. It seems that the influence of changed working conditions offers an interesting complement to criminological theories of broadened definitions and decreasing tolerance against violence in problematizing how an increase in reported workplace violence should and could be understood.