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- Bäckman, Jonas, et al.
(författare)
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Evaluation of filter parameters from direct observations of metal flow in aluminium castings
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The potential in mechanical properties for aluminium casting alloys are in many casting processes not fully utilised. One reason is the defect formation in the casting process. The defects could be oxide films, introduced during mould filling, and pore formation. This investigation has been focused on how the gravity mould filling could be controlled by using filter in the ingate system and the how the pressure drop over the filter can be evaluated.In gravity casting the metal flow velocity usually reaches several metres per second. Direct observations have shown that filters improve mould filling during casting. Additionally, filters cause a pressure loss, which decreases the speed of the metal and gives a smoother filling.In this paper, mould-filling experiments were recorded directly by a video camera through a transparent ceramic glass. Two different types of ceramic filters, reticulated foam filters and extruded filters with 10, 20 and 30 pores per inch and 100 and 300 cells per square inch respectively, were investigated. The influence of active filter area and filter size on the flow reduction has also been investigated. As the casting temperature influences the viscosity of the liquid metal, the pressure loss over the filter was evaluated at various temperatures.Using parameters for calculating flow loss caused by filter can help when designing ingate systems containing filters. The filter parameters can be used in two ways, either to control the speed of the metal or to design the active filter area in a way that the melt flux is not affected. Proper parameters are also important for computer simulations of mould filling. The parameters evaluated from these experiments have been used in computer simulation of mould filling and the results have been compared with experiments.
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- Bäckman, Jonas, et al.
(författare)
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Influence of filter on the mould filling of aluminium melts in vacuum-sealded moulds
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The influence of filters on the mould filling behaviour has been investigated by direct observation experiments. The ingate system was moulded in a vertically parted vacuumsealed sand mould. How the filter in general, and how different filter locations, filter coarseness, active filter area and filter length influence the mould filling has been clarified. The direct observation method is a very powerful way to learn how different ingate system designs and filter conditions affect the mould filling. During mould filling the melt behaviour was recorded by a video camera through a glass wall, from which still images are presented. The general effect of filters is a better filling of the ingate system prior to the filter, and a reduction of the melt velocity, which in turn give smoother filling after the filter. Initially, the downsprue is completely filled at an early stage of the filling due to the back-pressure from the filter. The back-pressure is built up as a result of friction in the filter. An early filling of the downsprue prevents the melt from entraining oxide films or air inclusions. Secondly, the filling of the runner is improved by the use of a filter. The better filling of the runner is mainly an effect of the decreased velocity of the melt. The reduction of the melt velocity results in reduced surface turbulence and less splashing. Reduced surface turbulence and splashing of the melt prevents incorporation of oxide films and air in the melt, which has an overall beneficial effect on the quality of the castings. The location of the filter has been found to play an important role in the filling soundness.
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- Bäckman, Jonas, et al.
(författare)
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Influence of ingate system design on mechanical properties for a cast A1-10Si-0.38Mg alloy
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this work the influence of the ingate system design on the as-cast mechanical properties of an Al-10Si-0.38Mg alloy have been clarified. The Weibull distribution has been seen to describe the spread in mechanical properties very well. The Weibull modulus has therefore been used as a measure of the soundness of an ingate system. Different ingate systems were investigated, including: expanding systems, pressurised systems, systems with and without filter, systems with different designs of the connection between the downsprue and the runner, and systems with and without an additional pocket at the end of the runner. The modification index of the microstructure was also measured in order to investigate if the spread in data is more dependent on the modification index than on the ingate system design. The results showed that a high Weibull modulus is more dependent on the ingate system design than on the modification index of the microstructure. The ultimate tensile strength was not significantly affected by the ingate system design, while the fracture elongation seemed to be more dependent on the melt quality than on the ingate system design. The Weibull modulus indicates that expanding systems are better than pressurised systems, and that the use of a filter in the runner is very beneficial. An additional pocket at the end of the runner has no beneficial effect when using a filter. The connection between the downsprue and the runner should have a rounded bend and the change in cross-section between the downsprue and the runner should be chamfered and not sharp.
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- Bäckman, Jonas, et al.
(författare)
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Mould filling observations of aluminium melts in vacuum-sealed sand moulds
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In order to clarify how the ingate system design influences the mould filling behaviour of aluminium melts in vertically parted vacuum-sealed moulds, some direct observation experiments have been made. A detailed study of how the design of each component in the ingate system affects the mould filling behaviour has been made. The effect of different designs on downsprue-runner connections, runners and end-wall of the runners as well as the effect of wall friction was investigated. The mould filling process was studied through a glass wall and recorded by a video camera. Still images from the videotape are presented and evaluated. The direct observation method has been found to be a very powerful way to follow the melt behaviour during mould filling. To ensure a good filling of the downsprue the melt level in the pouring basin has to be above a certain level from the time when the stopper is removed and during the whole filling sequence. A perpendicular connection between the downsprue and the runner gives a larger flow loss than a rounded type. Due to the larger flow loss the perpendicular connection results in an earlier filling of the downsprue. A tapered runner results in almost simultaneous filling of the specimens compared to a runner with no tapering. On the other hand the tapered runner gives a more divergent melt front which increase the free melt surfaces in contact with air. An additional pocket at the end of the runner has a beneficial effect on the mould filling. A sharp angled pocket is better than a more rounded type. Decreasing the wall thickness increases the flow loss due to wall friction, and causes more significant heat losses.
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- Bäckman, Jonas, et al.
(författare)
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Potential for improved mechanical properties in cast aluminium alloys
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this work is to investigate the potential to improve the mechanical properties of some aluminium alloys, in order to obtain castings with optimum properties. Experiments have been made with pure aluminium, aluminium alloyed with 1% Si and 0,9% Mg and four aluminium cast alloys with 7-12% Si and various amounts of iron, magnesium, copper and manganese. To achieve the best possible solidification, gradient solidification technology of tensile specimen has been used, in order to explore the limits of the mechanical properties in relation to the microstructure. The experiments show that it is not possible to obtain good fracture toughness in alloys with a high iron content. The results also show that many of the aluminium alloys frequently used today are not processed in a way that allows optimal mechanical properties to be achieved. The alloys with a maximum of 0,4% Fe can give 10-23% fracture elongation, depending on other alloying elements such as Si, Mg and Cu. For these alloys it is worthwhile to improve the melt treatment and the casting process to obtain properties close to, or even better than can be achieved in other manufacturing processes. The experiments have given results for both columnar and equiaxed primary solidification structures.
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