|Dewi Idamayanti||Department of Foundry Engineering, Politeknik Manufaktur Bandung, Jl. Kanayakan No.21 Bandung 40135, West Java, Indonesia|
|Wiwik Purwadi||Department of Foundry Engineering, Politeknik Manufaktur Bandung, Jl. Kanayakan No.21 Bandung 40135, West Java, Indonesia|
|Beny Bandanadjaja||Department of Foundry Engineering, Politeknik Manufaktur Bandung, Jl. Kanayakan No.21 Bandung 40135, West Java, Indonesia|
This research examines the suitability of rice husk waste as an exothermic material for a riser sleeve for use in steel casting production. Exothermic sleeves are used in the steel casting process to compensate for shrinkage of the steel during solidification. Commonly, the exothermic sleeve consists of fuel materials, fillers, and binders. Rice husk waste has potential for use as a fuel material in the exothermic sleeve due to its high calorific value. For this study, rice husk waste was ground to gain a particle size of 60 mesh and then mixed with organic binders of 12wt%, 15wt%, and 18wt%. A H-sleeve was then formed by hand pressing, followed by drying. A series of quantitative tests were carried out to analyze the performance of the rice husk as an exothermic material. These include measurement of modulus extension factor (MEF) and the cooling rate of the steel casting within the liquidus-solidus temperature range. The test results show that the rice husk sleeve mixed with 12wt% of binder extended the solidification time from 273 seconds to up to 511 seconds within the desired temperature range. Furthermore, the best MEF of 1.69 was achieved using the rice husk riser sleeve. This meets the standard MEF value of an exothermic sleeve.
Exothermic sleeve; Modulus extension factor; Rice husk; Riser sleeve; Steel casting
Exothermic riser sleeves are feeding aids used in steel casting to prevent the molten steel from shrinking during solidification. They perform better than silica sand risers (conventional risers) in increasing feeding efficiency and minimizing the riser size (Brown, 2000; Miki, 2002). One riser sleeve manufacturer reports that the use of an exothermic riser sleeve can enhance the casting yield by 74.47–91.80% (Schäfer, 2011). According to many references (Auderheide et al., 1999; Miki, 2002; Schäfer, 2011), exothermic riser sleeves consist of fuels (i.e., oxidizable metals or exothermic materials), fillers (i.e., sand or metal oxides), and binders (i.e., resin or water glass). In order for an exothermic riser sleeve to produce a high casting yield, certain parameters must be considered, such as the heat resistance of the fuel material in the exothermic sleeve, which should readily ignite at 600oC (Williams et al., 2015; Dafiqurrohman et al., 2016); the density of the exothermic sleeve, which should be low as porosity produces higher insulation (Miki, 2002); and the ash content after the material is burned (Rao, 2013). These properties are required to keep the retardation of temperature fall during steel solidification. In our previous studies (Idamayanti et al., 2015; Purwadi et al., 2016), we investigated an exothermic riser sleeve manufactured from aluminium slag and red mud waste. The results of these studies confirmed that the synergy of these materials resulted in excellent characteristics due to their exothermic and insulating behavior.
However, our previous studies revealed several problems, including limited raw materials and a complicated sleeve fabrication process. To solve these problems, substitute materials were studied based on their thermal properties. One study reported on an experiment in which rice husk was used as the primary material to produce a top riser sleeve to prevent heat loss from the mold (Rao, 2013). This showed the potential of rice husk for use in a riser sleeve. Currently, rice husk is not widely used in the foundry industry, despite its abundance as biomass waste in Indonesia (Gibran et al., 2018). It is a source of renewable energy and, due to its high calorific value (Lim et al., 2012), is promising as an exothermic material. Thus, this study aimed to utilize rice husk waste as a material for an exothermic riser sleeve. Rice husk has a remarkably higher heating value (15.84 MJ/kg) (Lim et al., 2012) than commercial exothermic sleeves (250–850 kJ/kg) (Williams et al., 2015). Burned rice husk produces combustion residues that contain SiO2 (91.42%), K2O (3.71%), CaO (3.21%), Al2O3 (0.78%), and small amounts of other metal oxides (Maiti et al., 2006), all of which can act as insulators. As well as being affordable and having slow oxidation properties, rice husk is one of the carbonaceous materials with anti-piping characteristics (Rao, 2013). Based on previous studies, it can be concluded that rice husk is a potential material for exothermic sleeves with its excellent physical properties (Maiti et al., 2006), effective insulating potential due to the amorphous structure of residual silica, and the high porosity of its ash residues (Wang et al., 2016a); (Tiwari and Pradhan, 2017). It is easy to form into briquettes with a low binder of 2–4% (Maiti et al., 2006) and is an eco-friendly product with very low emissions (Unrean et al., 2018).
Hence, this research focuses on the use of rice husk waste as an exothermic material for a riser sleeve in steel casting. Its suitability as a riser sleeve was determined quantitatively by testing the modulus extension factor (MEF) and measuring the cooling rate to observe the thermal behavior of the rice husk sleeve. Furthermore, the simulation was calculated to predict its feeding efficiency in steel casting. The physical properties of the rice husk sleeve, such as its bulk density and compressive strength, were also investigated.
Rice husk waste has significant potential for use as a material for a riser sleeve feeding system in steel casting. The MEF calculation generates an MEF value of 1.69, based on which the rice husk sleeve can be classified as an exothermic sleeve. With a binder content of 12wt%, the rice husk sleeve had good formability, a sufficient compressive strength of 6.9 kg/cm2, and excellent temperature retardation of during GX60Cr15 solidification. The solidification time of molten metal in the rice husk sleeve can be extended to 511 seconds, which is higher than that of the sand riser (215 seconds). Furthermore, the feeding efficiency of the rice husk sleeve can be increased to approximately 67.58%. In terms of compliance, the main characteristics of the rice husk sleeve comply with the standard specifications of IS 15865:2009 for an exothermic sleeve. Hence, the rice husk sleeve is recommended for use in a feeding system for steel casting, where it has the potential to replace existing commercial exothermic sleeves and enhance the value of rice husk waste.
The authors acknowledge POLMAN-Bandung for providing financial support under the Polman research project. We also thank the foundry department for providing facilities.
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