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- Bergquist, Bjarne
(author)
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New insights into influencing variables of water atomization of iron
- 1999
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In: Powder Metallurgy. - : Informa UK Limited. - 0032-5899 .- 1743-2901. ; 42:4, s. 331-343
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Journal article (peer-reviewed)abstract
- Trace amounts of surfactants have an acute influence on measured surface tension of melts and may influence viscosity. A water atomisation experiment was performed to investigate if variations of these elements could affect quality. Effects of water pressure, melt superheat, and sulphur content, iron scrap oxygen content, and aluminium content were studied. Responses studied were particle size distribution, apparent density, flow, powder chemistry, morphology, green density, and dimensional change. A large sulphur addition reduced the particle size, as a result of a reduction of surface tension, but the largest effect came from changing water pressure. Higher water pressures also resulted in powders with lower apparent density, lower flowrate, and reduced swelling during sintering. An empirical water atomisation model is proposed. Aluminium additions reduced the powder size standard deviation and increased the carbon content of the powder. A reduced powder size standard deviation was seen also for melts with raised superheating.
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| 2. |
- Bergquist, Bjarne
(author)
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Statistical approaches to PM steel process improvements
- 1999
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Doctoral thesis (other academic/artistic)abstract
- Increased performance:cost ratios for PM steel components is vital if current growth rate of market shares of such components versus competing technology is to be sustained. Both performance and cost of components are affected by variation of component properties. This work focuses on variation; where major variation sources lie and measures to circumvent problems that could be taken.A design-of-experiments approach was used to identify the most important green compact variations and interactions of a Fe-P alloy. The results show that the highest impact energies are obtained for high green densities, and without graphite addition. It is concluded that sintered density is the reason for the observed impact energies. Variation sources controlling phosphorus content and added graphite content are of concern since they affect the dimensional stability. Prospects for a robust sintering operation of same alloy is investigated. The objective is to find a setting of the variables investigated to maintain high tensile strength and proof stress without loss of dimensional stability, tensile elongation or impact energy. In the study, an endothermic sintering atmosphere was better for the robustness of the tested properties. A mechanism for the occasionally brittle behavior of the system is concluded to be loss of grain boundary cohesion due to decarburization.Possibilities for improved particle size distribution of water atomized powder are studied experimentally and by simulations. The most important variable for all studied responses is water pressure. Higher melt temperatures reduce particle size due to decreased viscosity. Large sulfur additions reduce particle size and this is an effect of reduced surface tension. Narrower size distributions were obtained for powder atomized with aluminum additions and for increased melt temperatures. A model for particle size for water atomization is presented and used in simulations.
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| 5. |
- Mellström, Ulf, 1959-
(author)
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Engineering lives : Technology, time and space in a male-centred world
- 1995
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Doctoral thesis (other academic/artistic)abstract
- This thesis deals with engineers. It is an ethnographic study of the life organisation for seventeen engineers with Master's degrees working at two different workplaces, Automobile Inc. and Microchips Inc. The study is based on participant observation and life-history interviews. It is a study of work, careers and life-paths among thirteen men and four women. Underlying question of this study are what makes sense to these people and how meaning is constructed in their lives as engineers.The thesis consists of two parts. In the first part, situated activities and social practices of the two engineering workplaces are focused on. It examines how meaning is produced, reproduced, and socially organised in two engineering microcultures - in short, how technical work is socially constructed under various conditions.In the second part, the lives of the seventeen engineers are presented. Their life-paths are examined through a series of questions such as; Are there any common formative life expedences in the lives of these seventeen engineers? What is their relation to technology and education in the early years of life? How do one relate to family background and "significant others"? How do these engineers present and understand themselves through the reconstruction of their lives in relation to career and gender? What meaning is given to the occupational career in the organisation of life? How are occupational careers in engineering performed?The basic theoretical position in this study is an interactionist one. The most important concepts of the study's first part are microculture, time, space and different forms of everyday interaction. In the study's second part the concepts of perspectives, horizon, socialisation, and career are used to point out individual experiences of culture.
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| 8. |
- Svensson, Olof
(author)
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Nonadmissible convergence in symmetric spaces
- 1996
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In: Journal für die Reine und Angewandte Mathematik. - : Walter de Gruyter GmbH. - 0075-4102 .- 1435-5345. ; :472, s. 53-68
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Journal article (peer-reviewed)abstract
- In the disc (or half-plane, or half-space) the well-known Fatou theorem says that the Poisson integral of an $L^1$-function has non-tangential boundary limits a.e. J. Marcinkiewicz and A. Zygmund cleared up the corresponding situation in products of discs (or half-spaces), introducing the notions of restricted and unrestricted non-tangential convergence. For general Riemannian symmetric spaces the corresponding notions ("restricted and unrestricted admissible convergence") have also been found, and the classical results generalized, some time ago. In 1984 A. Nagel and E. M. Stein investigated again the half-space case and found that the convergence theorem could be proved for slightly larger than nontangential approach domains (the exact description is too technical to state here). The subject of the present paper is to extend this investigation to general Riemannian symmetric spaces. The notion of restricted admissible convergence (which is the natural one for $L^1$-functions) is appropriately extended and the convergence theorem proved in a way which seems to be the final word on the subject. Unrestricted convergence (which goes with $L^p$ functions, $p>1$) is also discussed and a theorem proved, but only in the case of one particular example of a space of rank two. The proofs display considerable virtuosity in the application of real-variable methods.
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