Results of Rctk residual strength tests are presented for samples of moulding sands prepared with a stable content of soluble sodium silicate binding agents of different WB structure indicator values, hardened in the ester process. The test temperature range was 300°C to 1000°C, with 100°C steps. A notable relation between the WB structure indicator values and Rctk residual strength of moulding sand samples was observed. Moulding sands prepared with soluble sodium silicate with low values of WB structure indicator < 1.4 have more advantageous properties related to removing cores from castings and castings from moulds, in the mould heating temperature range from approx. 600°C to approx. 900°C, compared to similar properties when using soluble sodium silicate with a WB structure indicator of ≥ 1.4.
Keywords: moulding sand, soluble sodium silicate, colloidal structure, residual strength,
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Izabela Krzak, Krzysztof Jaśkowiec, Adam Tchórz, Łukasz Boroń
The purpose of this paper is to evaluate the internal structure of alloys similar to AlSi9Mg (EN AC-43300), made with the counter-gravity low-pressure air-melted process (CLA) and with the gravity casting process. The X-ray computed tomography (CT) examination method was combined with structural and mechanical testing for a qualitative evaluation of the castings produced with these processes. The structural discontinuities in CLA and gravity castings were investigated by studying the imaging made with an industrial-grade CT scanner manufactured by Phoenix X-ray. The examples of images are shown on selected cross-sections (2D) and by 3D visualisation. The CT examination proved to be insufficient for a qualitative comparison of castings produced with different techniques; hence a microstructural examination was carried out under an optical microscope and a static tensile test was completed on the samples at ambient temperature.
Keywords: counter-gravity low-pressure air-melted casting (CLA), X-ray computed tomography (CT), structural discontinuities,
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Wojciech Leśniewski, Piotr Wieliczko, Marcin Małysza
This paper presents the results of work on the determination of actual molten metal flow in a mould during centrifugal casting in the SuperCast induction vacuum furnace manufactured by Linn HighTherm. The centrifugal casting process uses the effect of centrifugal force on the flow of liquid metal in the mould with a resulting increase of the liquid and solidifying metal pressure. At the mould rotational speed of 250 rpm and the mould distance of 0.2 m from the rotation axis, the centrifugal force acting on the liquid metal is 14 times higher than the force of gravity. Despite a high force, misruns of unexplained origin have been found in castings from centrifugal induction furnaces. Here the action of gravity is insignificant to the flow of metal within the rotating mould. When casting in centrifugal forces, a certain amount of metal remains on the crucible surface, indicative of a minimum two forces present and acting on the liquid metal during the process. One is the centrifugal force, which prompts the flow of metal in parallel to the radius vector of the rotating mould. The sense of the other force is directed perpendicularly to the radius vector direction, as suggested by the residues of solidified metal in the crucible spout. A specially designed geometry of the casting system has been used in a series of experiments to observe the way in which the flow and casting filling occur. The analysis of produced results suggests that the inclusion of the Coriolis force in the computer-aided simulation of non-inertial reference systems explains the metal flow during centrifugal pouring. The computer calculations have proven the results of the said experiments.
Keywords: centrifugal casting, computer simulation, Flow-3D, wax models, centrifugal force, Coriolis force,
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