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Showing 16 results for Casting

Mehdi Khashei and Mehdi Bijari,
Volume 26, Issue 2 (1-2008)
Abstract

Forecasting models have wide applications in decision making. In the real world, rapid changes normally take place in different areas, specifically in financial markets. Collecting the required data is a main problem for forecasters in such unstable environments. Forecasting methods such as Auto Regressive Integrated Moving Average (ARIMA) models and also Artificial Neural Networks (ANNs) need large amounts of historical data. Although fuzzy forecasting models such as fuzzy regression are suitable metods when the data available is scant, their performance is not satisfactory at times. In this paper, a new Fuzzy Auto Regressive Integrated Moving Average (FARIMA) is presented. The proposed model can be run with less data, so it is more suitable than other models for cases where there are limited data available. The results obtained on exchange rate forecasting reveal the efficiency of the proposed model.
M. Sheikhan and M. E. Kalantari,
Volume 27, Issue 1 (7-2008)
Abstract

This paper tries to estimate the capital investment required for the fixed-telephony network switching equipment as demanded by the fourth national development plan. As a first step, the Cobb-Douglas model is used as a successful demand forecasting model to estimate the demand over the target years. Then, an architectural plan is developed for the fixed-telephony switching network that takes into account the expansion of the existing exchanges as well as the addition of new ones. The number of the required ports in local exchanges, the intercity traffic (including cell phone subscribers), and the required trunks in transit exchanges are then estimated. Two scenarios are used to estimate the investment needed: expanding legacy network (circuit-based), and NGN adoption (a combination of circuit and packet-based networks). Finally, conventional pricelists from different local and foreign suppliers are used to arrive at two total investment estimates: 6,013 billion Rials and 6330 billion Rials for the two mentioned scenarios, respectively.
M. Alizadeh, H. Edris, and A. Shafyei,
Volume 27, Issue 2 (1-2009)
Abstract


M. Meratian, N. Saeidi,
Volume 28, Issue 1 (6-2009)
Abstract

In cast aluminum and its alloys, the microstructure varies under different solidification conditions, causing variations in their mechanical properties. These materials are basically produced in sand and metallic molds or through die casting, each of which is associated with a unique solidification regime with significantly different cooling rates so that the resulting microstructure strongly depends on the casting method used. In the present study, the effects of such important solidification parameters as cooling rate, solidification front velocity, and thermal gradient at the solid-liquid interface on secondary dendrite arm spacing were investigated. By a directional solidification system, the mathematical relation between cooling rate and dendrite spacing was extracted for several commercially important aluminum alloys. A neural network model was trained using the experimental values of cooling rates and secondary dendrite arm spacing. Reliable prediction of these values was made from the trained network and their corresponding diagrams were constructed. A good agreement was found between simulation and experimental values. It is concluded that the neural network constructed in this study can be employed to predict the relationship between cooling rate and dendrite arm spacing, which is difficult, if not iompossible, to accomplish experimentally.
N. Miadi, H. Sarpoolaky, H. Ghassai,
Volume 32, Issue 1 (6-2013)
Abstract

In this study, mullite– irconia composite samples were prepared by reaction sintering of alumina and zircon powder via gel casting process. Gel casting is a new ceramic forming technique. This process is based on the casting of slurry, containing ceramic powder, dispersant and premix monomer solution. To achieve stabilized, high solid loading (80 wt%) and castable slurry, the rheological properties of slurry were optimized. The monomers polymerized the slurry to form gelled specimens. After gelation, the specimens were unmolded, then dried out under controlled condition. Burning out and sintering of the specimens was carried out in the range of 1400-1700°C. Apparent porosity and bulk density of the sintered samples were measured by soaking in water. Crystalline phase evolution and microstructure were determined by XRD and SEM techniques. Results showed that the reaction sintering and mullite formation was completed at 1700°C due to very slow diffusion of Al3+ ions within amorphous silica formed at the decomposition of zircon. The sintered samples at this temperature also showed the lowest apparent porosity (≈ 4%) and the highest bulk density (≈3.40 gr/cm-3).
R. Jamshidi-Alashti, M. Borouni, B. Niroumand,
Volume 32, Issue 2 (12-2013)
Abstract

Application of ceramic reinforcements is one of the effective and well-known ways to refine the microstructure of brittle metals such as magnesium. In this research, the influence of nano/micro particles of zirconia on the microstructure of cast AZ91 alloy was studied. At the first stage, nano and micro ZrO2 powders were blended through mechanical alloying procedure. In five specimens, the total amount of nano and micro reinforcements in the final mixture was fixed at 5 wt%, whereas their ratio was varied. Two other composites were also produced using 5wt% of nano or micro particles of zirconia. These powder mixtures were then stirred in the molten AZ91 at 650C by vortex method and finally cast in a sand mold at 615C. For comparison, two monolithic castings including a conventionally cast specimen and a super heat-treated sample were also cast. The average grain sizes for all composites were decreased with respect to both monolithic castings. The best results in terms of grain size and microstructure improvement were obtained for AZ91/5wt% nano ZrO2 composite with remarkable improvement in comparison with monolithic castings.
M. Rahmani, K. Janghorban , S. Otroj,
Volume 33, Issue 1 (7-2014)
Abstract

In this study, the effect of different amounts of Y2O3 on the properties of mullite-zirconia composites was investigated. For this purpose, these composites were fabricated by reaction-sintering of alumina and zircon as raw materials. Besides, the slip casting method was used for forming these composites, and sintering process was carried out at 1600 °C. Then, the physical and mechanical properties, phase composition and the microstructure of these composites were investigated. The results showed that yittria addition up to 0.5 wt.% has no effect on the properties of these composites. Besides, addition of more than 0.5 wt.% yittria formed solid solution with zirconia grains and led to stabilization of tetragonal zirconia phase and increasing of its amount. Hence, yittria addition increases the hardness and bending strength of composite by stabilizing tetragonal zirconia phase and then, decreasing the micro-crack formation during zirconia phase transformation. As results show, addition of 0.75 wt.% yittria leads to a considerable increase in the bending strength.
L. Akbarshahi, H. Sarpoolaki, H. Ghassai,
Volume 33, Issue 1 (7-2014)
Abstract

In this research according to unique properties of fused silica and Its numerous applications fused silica parts with 77% by weight solid loading formed by gel casting. Rheological behavior of the slurry and sintering conditions were optimized. Sample sintered at optimum conditions has bulk density of 1.71 g/cm3, open porosity of 18.13%, water absorption of 10.60%, linear shrinkage after firing of 3.5%, closed porosity of 1.09% and relative density of 78.80%. Its thermal expansion coefficient in range of room temperature to 1000 ◦C has been measured 0.4432×10-6 1/ . Results showed that With increasing temperature and time In addition to the increased vscous flow, Crystallization also extend. Finally sintered at high temperature and short time for an instance with the lowest overall high crystallinity and density, were found suitable
M. Rahmani, K.janghorban, S. Otroj,
Volume 33, Issue 2 (3-2015)
Abstract

In this study, the effect of different amounts of Y2O3 on the properties of mullite-zirconia composites was investigated. For this purpose, these composites were fabricated by reaction-sintering of alumina and zircon as raw materials. Besides, the slip casting method was used for forming these composites, and sintering process was carried out at 1600 °C. Then, the physical and mechanical properties, phase composition and the microstructure of these composites were investigated. The results showed that yittria addition up to 0.5 wt.% has no effect on the properties of these composites. Besides, addition of more than 0.5 wt.% yittria formed solid solution with zirconia grains and led to stabilization of tetragonal zirconia phase and increasing of its amount. Hence, yittria addition increases the hardness and bending strength of composite by stabilizing tetragonal zirconia phase and then, decreasing the micro-crack formation during zirconia phase transformation. As results show, addition of 0.75 wt.% yittria leads to a considerable increase in the bending strength
A. Samadi, M. Ghayebloo ,
Volume 34, Issue 2 (7-2015)
Abstract

To evaluate the effect of inoculant addition on functionally graded microstructure of centrifugally cast Al-Mg2Si composites, two cylinders of Al-13.8 wt.% Mg2Si with and without the addition of 1 wt.% Al-5Ti-B inoculant were cast in a vertical centrifugal casting machine. The chemical composition, microstructures and microstructural phases of the different radial sections of the cast cylinders were studied using induction coupled plasma (ICP) method, optical/scanning electron microscopes, and X-ray diffractometry, respectively. The results showed that in the inoculant content cylinder, owing to the prevailing thermal regime as well as the specific mode of eutectic solidification in this composite, the titanium and boron compounds were segregated towards the middle layer of the cylinder and caused the formation of primary Mg2Si particles and non-eutectic Al () in this layer. In addition, due to the effect of centrifugal force during solidification, a higher volume fraction of the light primary Mg2Si particles, according to Stocks law, was segregated towards the inner layer of the cast cylinders.
M. Sarvari, M. Divandari,
Volume 35, Issue 2 (9-2016)
Abstract

In this study, centrifugal casting process was used for producing Al/Mg bimetal. Molten Mg was poured at 700 oC, with 1.5 and 3 melt-to-solid volume ratio (Vm/Vs) into the 450 oC preheated solid Al rotating at 800, 1200, 1600 and 2000 rpm. Castings were kept inside the centrifuged casting machine and cooled down to 150 oC. Investigating the effect of melt-to-solid volume ratio showed that increasing volume ratio from 1.5 to 3 results in diminishing metallurgical bonding in Al/Mg interface, because the force of contraction overcomes the resultant force acted on the interface. The results of study by scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) showed that bimetal compounds of Al3Mg2, Al12Mg17 and δ+Al12Mg17 eutectic structure (δ is the solid solution of Mg in Al) are formed in the interface. Atomic force microscopy (AFM) image of Al surface showed that the surface was rough in atomic dimentions, which can result in the formation of gas pores in the interface.


S. Tavassoli, M. Abbasi, R. Tahavvori,
Volume 35, Issue 2 (9-2016)
Abstract

The purpose of this article is to study the formation of intermetallic compounds (IMCs) at the interface of Al/Cu bimetal produced by compound casting of molten Al in solid copper tubes. The mechanism of the intermetallic compounds formations at the interface, the effects of molten aluminum pouring temperature and solid copper tubes preheating tempreture, were investigated on the IMCs type and thickness and Al/Cu interface microstructures were characterized by optical microscope (OM) and electron probe micro-analyzer (EPMA). Results show that the interface consists of three main layers, where Layer (I) is α-Al/Al2Cu eutectic structure, layer (II) is intermetal of Al2Cu and layer (III) constituites several intermetallic compounds such as AlCu, Al3Cu4, Al2Cu3 and Al4Cu9. Considering the components of hypereutectic melt at the interface, initially layer (II) was formed by θ phase nucleation and growth mechanism, then layer (I) was formed by Al and Cu dissolving and solidification. Finally layer (III) was formed by solid-state phase diffusion. Raising molten Al temperature and preheating solid Cu leads to increase of the intermetallic compounds thickness at interface which consequently increases the specific electrical resistance and decreases the Al/Cu bond strength. From experimental results it seems that the bond strength is affected by the thicknesses of layer II and III.


G. Kafili, B. Movahedi, M. Milani,
Volume 36, Issue 3 (11-2017)
Abstract

In this study, Spark Plasma Sintering (SPS)  of both slip casted and powder specimens of alumina/ yttria core-shell nanocomposite were utilized for fabricating transparent Yttrium Aluminum Garnet (YAG) ceramics. Phase evolution, optical transmittance and the microstructure of sintered samples were compared. In slip casting process, Dolapix CE64 was used as a dispersant for preparing the stable aqueous slurry of this nanocomposite powder. The effect of Dolapix concentration and pH value on the stability of the suspension was described, and the viscosity diagrams were investigated at different pH value and different weight percents of Dolapix. The rheological behavior of the nanocomposite powder slipped at 60-70 wt% solid loading was studied by measuring their viscosity and shear stress as a function of shear rate of the slurry. The results showed that, the suspension has a minimum viscosity at pH of 10 by addition of 2.5 wt% Dolapix. Also, the slurry with solid loading of 60 wt% showed the Newtonian behavior and this rheological behavior was preserved even above this solid loading values. Slip casting technique caused the uniform size and pores distribution as well as eliminating large pores in the green body. Consequently, transparent YAG ceramic with 60% optical transmittance was achieved after SPS process of slip casted green body which was much higher than that of nanocomposite powder, i.e. about 30% at the same sintering conditions.
 


M. Haghshenas Gorgani, M. Mirkazemi, F. Golestanifard,
Volume 37, Issue 4 (3-2019)
Abstract

In this research, the rheological behavior and stability of suspensions containing Si3N4, Al2O3, Y2O3 and starch were investigated in order to use them in the starch consolidation casting of porous silicon nitride. Dolapix CE64 was used as the dispersant. Then, the effect of some parameters such as Si3N4 surface oxidation, dispersant content, solid loading and starch content on the viscosity and rheological behavior of Si3N4-starch slurry was determined. Surface oxidation of Si3N4 powder at 800°C for 2 hours reduced the viscosity of the slurry, effectively. The best dispersant content was 0.4 wt. %, relative to ceramic powders. Slurries containing 30 to 40 vol. % and 7.5 to 25 vol. % starch, relative to total solid loading, had the suitable viscosity and the sufficient stability for casting by the starch consolidation method.

M. Rajabi, M. Shahmiri, M. Ghanbari,
Volume 37, Issue 4 (3-2019)
Abstract

In this study, the effects of boron (B) and zirconium (Zr) on the microstructure and mechanical properties of Fe3Al-based alloys were investigated. Cylindrical samples were produced using a vacuum induction melting furnace (VIM); consequently, the melt was cast into a metallic mold. The microstructure, phase identification, tensile and compressive mechanical properties and fractography of the samples were investigated. Upon microstructural observation, it was found that the alloys microstucture was denderitic and the precipitated phases were mostly present between interdendritic regions. Addition of B and Zr to the alloys resulted in the formation of boride precipitates and Laves phases. The results, therefore, showed that Zr had the most pronounced effect on the mechanical properties because of the formation of Laves phases. Fractographic studies of alloys also revealed that the brittle fracture was dominant between the samples.

H. Hadian, M. Haddad Sabzevar , M. Mazinani,
Volume 39, Issue 4 (2-2021)
Abstract

In this research, effect of swarf addition on the microstructure of die cast aluminum A380 alloy and the possibility of altering the alloy structure in the metallic die has been studied. The microstructure mainly consists of the α-phase, eutectic, intermetallic compounds and porosity. Since the alloy solidifies under non-equilibrium conditions, the Scheil equation with exact amount of equilibrium distribution, analyzed by SEM-Line scan around an intermetallic phase at different mixing times as well as governing equations of thermal analysis, was used to calculate the solid weight fraction. Finally, using the thermal flux analysis in the crucible, a scientific prediction on the optimal amount of swarf addition, mixing time and temperature, was made. The shape factor at an optimum temperature of 590 °C was measured as 0.643. According to the optical microscope images of the die cast samples, the addition method (adding it to the floor or to the surface) and increasing the injection temperature have a significant effect on the solid weight fraction, morphology of the α-phases and final microstructure of the alloy.
 


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