| 1. |
- Jarfors, Anders E.W. 1963-, et al.
(författare)
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Feeding and Pore Formation in Semisolid Metal Casting
- 2020
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Ingår i: Metals. - : MDPI. - 2075-4701. ; 10:11
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Tidskriftsartikel (refereegranskat)abstract
- Semisolid casting can provide excellent castings, but the nature of the pore-forming mechanisms has not been properly clarified. In the current communication, it was suggested that hydrogen precipitated during slurry making might have a decisive role in the formation of both gas and shrinkage porosity. Intensive stirring at the end of the slurry making process may act as a degassing step. Without the intense shearing, structures of primary slurry particles form around the hydrogen pores, strongly affecting pore formation and feeding during the intensification stage.
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| 2. |
- Kirabira, J. B., et al.
(författare)
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Properties of super-calendered (SC) paper filled with Mutaka kaolin, Uganda
- 2009
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Ingår i: Paper Technology. - 0306-252X. ; 50:1, s. 11-16
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Tidskriftsartikel (refereegranskat)abstract
- The experts from Makerere University (Mak) and the Royal Institute of Technology (KTH) evaluated three mineral deposits for the production of fireclay refractories in Uganda and found that the Mutaka kaolin deposit in Uganda is of extraordinary quality. Ten tons of raw kaolin was mined at the Mutaka deposit and shipped in a container to STFI-Packforsk, Sweden. The kaolin was first dry sieved in a shaker to remove sand, mica and large particles. The sieved material was mixed with fresh water to a dry content of 15% and hydrocycloned to separate and remove coarse particles. The paper machine trials were carried out at STFI-Packforsk on the EuroFEX paper machine. The results indicate that the potential of exploiting the Mutaka kaolin deposit for paper filling is high. Paper filled with Mutaka clay resulted in a slightly lower opacity, however, with an optimized particles size distribution, this could be improved.
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| 3. |
- Olofsson, A., et al.
(författare)
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Identifying process parameters influencing gear runout
- 2018
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Ingår i: Materialwissenschaft und Werkstofftechnik. - : WILEY-V C H VERLAG GMBH. - 0933-5137 .- 1521-4052. ; 49:7, s. 859-869
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Tidskriftsartikel (refereegranskat)abstract
- The hardening distortions with respect to base body, clutch teeth and helical gears are investigated for a serial-produced main shaft gear of a 20NiCrMoS6-4 steel. The influences of casting geometry, annealing heat treatment and stress relief annealing of blanks, as well as vertical and horizontal loading arrangements during case hardening, are studied. The concentricity, roundness and runout of clutch teeth and helical gears are measured in the soft machined, hardened and hard-machined conditions. The Brinell hardness is measured on blanks obtained from different manufacturing routes showing differences in hardness and scatter. Stress relief annealing lowers the hardness and the scatter for all groups, but has no significant effect on distortions. The case depth, core hardness and surface hardness are measured after hardening. The study shows that the surface hardness correlates with the oil flow measured in the quench tank. The effect of casting geometry is stronger for the clutch teeth compared to the helical gears. For the clutch-teeth roundness and runout, significantly lower values are found for square geometry compared to rectangular. It is also seen that the major part of the runout comes from roundness errors which are mainly induced by the hardening. Horizontal loading reduces roundness errors and runout but produces conical base-bodies with worse backplane flatness.
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| 4. |
- Zhang, Qing, et al.
(författare)
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Effect of Na-based flux on melt quality assessment of 46,000 alloys
- 2023
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Ingår i: Journal of Materials Research and Technology. - : Elsevier. - 2238-7854. ; 27, s. 1830-1842
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Tidskriftsartikel (refereegranskat)abstract
- The influence of Na-Based flux on the melt quality assessment was studied using Density index (DI), bifilm index (BI) and tensile test. The melt was prepared with scrap and ingot with and/or without the addition of Na-based flux. The results show that the addition of Na-based flux decreases the accuracy of the correlation between BI/DI and the hydrogen content due to the increased shrinkage pores. The addition of flux promotes the formation of shrinkage pores by either altering the eutectic solidification behavior or generating more and bigger oxide films which leads to insufficient feeding. Moreover, the addition of flux improves the ductility of specimens by modifying the eutectic phase rather than improving the melt quality.
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| 5. |
- Zhang, Qing, et al.
(författare)
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Four-point bending fatigue behavior of rheocast AlSi7Mg0.3 alloy : Role of the surface liquid segregation
- 2023
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Ingår i: International Journal of Fatigue. - : Elsevier. - 0142-1123 .- 1879-3452. ; 175
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Tidskriftsartikel (refereegranskat)abstract
- The surface liquid segregation (SLS) layer in semisolid casting presents higher hardness than the surface of specimens cast using high-pressure die casting (HPDC). Bending fatigue tests showed that semisolid castings present better fatigue properties at higher stress, and this improvement disappears when the applied stress is lower than a critical load. This is because HPDC and SSM castings share the same surface deformation at low stress. More significant deformation is observed for HPDC castings when the stress exceeds the critical load. The presence of surface defects enlarges the difference in deformation at high stress and reduces the critical load.
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| 6. |
- Zhang, Qing, et al.
(författare)
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On the Role of Stirring on Microstructure and Ductility of Rheocast Al Alloys
- 2021
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Ingår i: JOM. - : Springer Nature. - 1047-4838 .- 1543-1851. ; 73:12, s. 3848-3857
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Tidskriftsartikel (refereegranskat)abstract
- Two alloys containing different Mg contents have been used to study the combined effect of stirring and oxidation on microstructure and ductility. The results show that intensive stirring can sufficiently disperse the α-Al particles and enable better liquid feeding during solidification and consequently reduce the porosity. The morphology of the oxides is determined by the amount of both Mg and stirring. With lower Mg content, the oxides present as oxide films, which can be broken up during stirring. In alloy with higher Mg content, the oxides exist as particles with numerous cracks, and the particle size increases slightly after stirring. In the Magsimal 59 alloy, due to the presence of large clusters of pores in the fracture surface, the influence of the small oxide particles on the ductility is negligible. In contrast, in the 42000 alloy, large oxide films on the fracture surface are correlated with the ductility.
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| 7. |
- Zhang, Qing, et al.
(författare)
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Role of Iron-Rich Phases and Porosity on the Ductility of Rheocast Al-Mg-Si-Alloys
- 2022
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Ingår i: 16th International Conference on Semi-Solid Processing of Alloys and Composites, S2P 2021. - : Trans Tech Publications Ltd. ; , s. 65-70, s. 65-70
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Konferensbidrag (refereegranskat)abstract
- Treatment of the slurry is important during RheoMetalTM casting. In this work, semi-solid slurries were prepared under different stirring intensities, using two types of stirrers: a naked rod (for regular stirring) and a rod with two blades (for intensive stirring). Tensile tests were performed, investigating fracture surfaces, as well as metallographic samples. The results show that intensive stirring produces castings with finer primary particles and a more homogeneous microstructure. On the other hand, more faceted Fe-rich phases are found along the α-Al grains boundary, due to the dissolution of Fe from the stirrers. Moreover, for intensive stirring castings, the porosity found on the fracture surfaces are smaller, while more second (intermetallic) phases, especially Fe-rich phases, are observed. Consequently, the castings with intensive stirring show worse ductility. Finally, a quantitative analysis was made regarding ductility, affected both by porosity and the presence of Fe-rich phases.
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| 8. |
- Ekström, Madeleine, 1984-
(författare)
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Development of a ferritic ductile cast iron for improved life in exhaust applications
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Due to coming emission legislations, the temperature is expected to increase in heavy-duty diesel engines, specifically in the hot-end of the exhaust system affecting components, such as exhaust- and turbo manifolds. Since the current material in the turbo manifold, a ductile cast iron named SiMo51, is operating close to its limits there is a need for material development in order to maintain a high durability of these components. When designing for increased life, many material properties need to be considered, for example, creep-, corrosion- and fatigue resistance. Among these, the present work focuses on the latter two up to 800°C improving the current material by additions of Cr, for corrosion resistance, and Ni, for mechanical properties. The results show improved high-temperature corrosion resistance in air from 0.5 and 1wt% Cr additions resulting in improved barrier layer at the oxide/metal interface. However, during oxidation in exhaust-gases, which is a much more demanding environment compared to air, such improvement could not be observed. Addition of 1wt% Ni was found to increase the fatigue life up to 250°C, resulting from solution strengthening of the ferritic matrix. However, Ni was also found to increase the oxidation rates, as no continuous SiO2-barrier layers were formed in the presence of Ni. Since none of the tested alloys showed improved material properties in exhaust gases at high temperature, it is suggested that the way of improving performance of exhaust manifolds is to move towards austenitic ductile cast irons or cast stainless steels. One alloy showing good high-temperature oxidation properties in exhaust atmospheres is an austenitic cast stainless steel named HK30. This alloy formed adherent oxide scales during oxidation at 900°C in gas mixtures of 5%O2-10%H2O-85%N2 and 5%CO2-10%H2O-85%N2 and in air. In the two latter atmospheres, compact scales of (Cr, Mn)-spinel and Cr2O3 were formed whereas in the atmosphere containing 5%O2 and 10%H2O, the scales were more porous due to increased Fe-oxide formation. Despite the formation of a protective, i.e. compact and adherent, oxide scale on HK30, exposure to exhaust-gas condensate showed a detrimental effect in form of oxide spallation and metal release. Thus, proving the importance of taking exhaust-gas condensation, which may occur during cold-start or upon cooling of the engine, into account when selecting a new material for exhaust manifolds.
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| 9. |
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| 10. |
- Siwale, Workson, et al.
(författare)
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Influence on off-gassing during storage of Scots pine wood pellets produced from sawdust with different extractive contents
- 2022
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Ingår i: Biomass and Bioenergy. - : Elsevier. - 0961-9534 .- 1873-2909. ; 156
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Tidskriftsartikel (refereegranskat)abstract
- Off-gassing and self-heating are the major challenges when it comes to transportation and storage of wood pellets. The heat generated due to self-heating poses a fire risk while off-gassing of toxic gasses such as carbon monoxide (CO) and some volatile organic compounds (VOCs) is an environmental and human health risk. With the increase in production volumes of wood pellets which has subsequently increased the amounts of wood pellets in transportation and storage, there is need to find lasting solutions to off-gassing and self-heating of wood pellets. The objective of this study was to test the off-gassing abilities of Scots pine wood pellets produced from sawdust with varying amounts of extractives. The aim is to come up with raw material pre-treatment measures so as to produce wood pellets that are not liable to off-gassing. Six (6) types of sawdust raw materials namely; fresh pine sawdust (FPS), stored pine sawdust (SPS), sawdust plus pine rosin (PRS), sawdust plus linseed oil (LOS), sawdust plus tall oil (TOS) and acetone extracted sawdust (AES) were used to produce the pellets. The produced pellets were then subjected to off-gassing tests under controlled conditions using the ECOM J2KN analyser. The concentrations of carbon monoxide, carbon dioxide and methane increased with storage time but slowed down towards the end of the nine days test period. The formation of these gasses were largely dependent on the type of extractives present in the raw material and not the total extractive content. The formation of methane started later than the other gases and coincided with the time when residual oxygen was depleted.
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