| 1. |
- 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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| 2. |
- Bäckman, Jonas, et al.
(författare)
-
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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| 3. |
- Bäckman, Jonas, et al.
(författare)
-
Mould filling observations of aluminium melts in vacuum-sealed sand moulds
- 1999
-
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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