Showing 509 results for in
Babaei R., Varahram N., Davami P., Sabzevarzadeh A.,
Volume 1, Issue 2 (6-2004)
Abstract
In this investigation, α 2-D Finite Volume Method (FVM) with unstructured triangular mesh is developed to simulate the mould filling process. The simulation of fluid flow and track of free surface is based on the Marker And Cell (MAC) technique. This technique has capability ofhandling the arbitrary curved solid boundaries in the casting processes. In order to verify the computational results of the simulation, a thin disk plate with transparent mould was tested. The mould filling process was recorded using a 16mm high-speed camera. Images were analyzed frame by frame, in order to tracking of free surface and filling rate during mould filling. Comparison between the experimental method and the simulation results has shown a good agreement.
Fazel Najafabadi M., Golazar M.a.,
Volume 1, Issue 2 (6-2004)
Abstract
The new in situ method for AI-TiC composite fabrication has been carried out. In this method, fabrication of AI-TiC composite by simultaneous introduction of titanium oxide and carbon into aluminum melt was investigated.. Under the process conditions, titanium and carbon reaction results in titanium carbide whiskers. The salt containing keriolite (Na3AIF6), titanium oxide (TiO2) and graphite used for this purpose. Using Scanning Electron Microscopy (SEM) and X-Ray Diffraction analysis (XRD) the resulted composite was characterized. It was shown that it contains Al as matrix and TiC as the reinforcement. Then, mechanical properties of fabricated composite were examined.
Barzegar Alamdarit B., Ashrafi Zadeh S.n., Ashrafi Zadeh F.,
Volume 1, Issue 2 (6-2004)
Abstract
In the current research, the optimum conditions for the electrolytic deposition of TiO2 coatings on titanium pieces were experimentally investigated. Flat pieces of commercially available titanium with dimensions of 50 x20 x3 mm were used as the anode and cathode electrodes. The coatings were applied on the cathode in an electrolyte solution essentially from water and methanol, containing different amounts of TiCI4, and H202. Coatings of sufficient thickness and adequate adhesion to the substrate were obtained at the optimum conditions of theELD process. The latter conditions were electrode gap distance of 3 cm, TiCl4 concentration of 0.005M, H202 concentration of 0.1 M, current density of 35 mA/cm2, methanol/water volume ratio of 9, and pH of the electrolyte in the vicinity of 1.40. Results of XRD analysis revealed the presence of anatase crystals of titanium oxide in the coated layers, where the deposited coating was treated at some temperatures in the range of 400 to 600°C for a period of at least 2 hours. Scanning electron microscopy (SEM) pictures also confirmed the formation of a uniform coating layer with cracked suiface area. At the optimum conditions of the process coatings with thicknesses of up to 10 flm were easily obtained through the application of one to three deposited layers.
Mirbagheri S.m.h., Ashouri H., Varahram N., Davami P.,
Volume 1, Issue 2 (6-2004)
Abstract
In this investigation a new model was developed to calculate gas pressure at the melt/foam interface (Gap) resulting from foam degradation during mould filling in the Lost Foam Casting (LFC) process. Different aspects of the process, such as foam degradation, gas elimination, transient mass, heat transfer, and permeability of the refractory coating were incorporated into this model. A Computational Fluid Dynamic (CFD) code was developed based on the numerical technique of the SOLution Algorithm- Volume Of Fluid (SOLA- VOF) utilizing model, for the simulation and prediction of the fluid flow in the LFC process. In order to verify the computational results of the simulation, a thin plate of gray iron was poured into a transparentfoam mould. The mould filling process was recorded using a 16mm high-speed camera. Images were analysed frame by frame, in order to measuring foam depolymerization rate and the gap volume during mould filling. Comparison between the experimental method and the simulation results, for the LFC filling sequence, has shown a good agreement.
Sheikh Abdolhossein A., Nili Ahmad Abadi M.,
Volume 1, Issue 3 (9-2004)
Abstract
In the present research influences of different combinations of five types of inoculants and four types of nodularizers on eutectic nucleation in ductile cast iron were studied. The alloys were kept at 1320°C for 0, 5, 10, 15 and 20 min under nitrogen atmosphere. Cooling curves and image analysis were used to characterize the influence of holding time and different combinations of inoculants and nodularizers on the graphite morphologies and eutectic nucleation. When dominant morphology of graphite is spheroidal or flake, by decreasing the different combinations of nodularizers and inoculants fading resistance, temperature of eutectic undercooling decreases. Nevertheless, when there is combination of spheroidal, vermicular and flake graphites temperature of eutectic undercooling increases by reduction of material fading resistance.
Kaviani S., Marashi S. P. H.,
Volume 1, Issue 3 (9-2004)
Abstract
The surface condition and microstructure of near stoichiometric (Fe823Ndll.8B5.9) Nd-Fe-B alloy ribbons and the effect of melt spinning parameters were investigated using optical, scanning and transmission electron microscopes (SEM, TEM). The formation of gas pockets on the roll surface of the ribbons during melt spinning can prevent heat transform and result in local coarse grains. The local thickness would also be less in these places and thus perforates preferentially during ion beam milling. Therefore different areas of the sample should be carefully observed in the TEM. Reducing inert gas pressure in the chamber will eliminate the gas pockets. As a general trend, decrease in the ribbon thickness and mean Nd2 Fe14B grain size were observed on increasing the roll speed. By careful adjustment of the melt spinning parameters, the nanostructure will develop. An orientation relationship was found between Nd2 Fe14B and α-Fe precipitates for coarse grain samples melt spun at low roll speed. Dark field image of such grain also shows that some of these α-Fe precipitates have the same orientation. X-ray diffraction evident the development of texture by decreasing the roll speed.
Mir Habibi A.r., Rabiei M., Agha Baba Zadeh R., Moztar Zadeh F., Hesaraki S.,
Volume 1, Issue 3 (9-2004)
Abstract
ZnS : Cu phosphors were prepared by using laboratory grade chemicals through coprecipitating Cu along with ZnS using H2S and thiourea. Photo- and electroluminescence studies indicate that these phosphors have better emission characteristics compared to the phosphors in which activator is externally added. Phosphors with luminescence at ~530nrn were prepared. The difference between the characteristic properties of the samples seems to be due to formation of nanoparticles during the preparation of the samples by different methods.
Bafghi M. Sh., Adeli M., Mohammadi Nikoo H.,
Volume 1, Issue 3 (9-2004)
Abstract
Two commercial methods are used for the production of strontium carbonate:1) Direct conversion of Celsetite to strontium carbonate by hot sodium carbonate,2) Carbothermic reduction of celestite with coal followed by water leaching of strontium sulfide(SrS) and its conversion to strontium carbonate.The present study has been made on the carbothermic reduction of celestite ores of Varamin (Iran) mines. Effects of temperature, time, pellet size, particle size of celestite ore, pellet compactness and type of reducing agent have been studied. In the range of 800-1100°C, reduction rate increases notably with temperature, which may mean that the reduction is predominantly chemical controlled. Activation energy of around 22.5 kcal/mol supports the idea of chemical control mechanism. Further support for this postulation is provided by the following facts:1) Increasing rate with carbon reactivity (graphite, coal, and charcoal)2) Small dependency of rate on pellet compactness.3) Small dependency of rate on pellet size
Javadpour J., Sakhaii K., Masihiyanpour A.a.,
Volume 1, Issue 4 (12-2004)
Abstract
Thin sheets of hydroxyapatite were fabricated by tape casting process. The non-aqueoustape casting formulation was optimized by adjusting the concentration of organic additivesspecially those of binder and plasticizer in the slurry. The optimized slurry was cast on a glasscarrier using a designed laboratory scale doctor blade. Following a binder removal stage, thetapes were sintered at different temperatures in air atmosphere. Heat treatment at 1250 °C led tothe formation of a dense microstructure as was evidenced by the scanning electron microscopy.
Attar E., Babaei R., Homayonifar P., Asgary K., Davami P.,
Volume 1, Issue 4 (12-2004)
Abstract
During mold filling, molten metal can only advance as quickly as the air inside thecavity is expelled. In this work an analytical model describing air flow is developed based on aincompressible flow theory. Air pressure has serious effects upon the filling behaviour such assurface profile and filling time. In this work a new mathematical model is proposed for calculationthe air pressure during the mold filling. A single phase computational fluid dynamic code based onthe SOLA-VOF algorithm used for prediction the fluid flow. Air discharged through the vents ismodelled by ideal gas assumption, conservation of mass equation and Bernoulli law. A newalgorithm was developed to interpolates the air pressure on the surface cell. The creation of airback pressure was correlated with sizes of vents and pouring basin height. In order to verify thecomputational results a series of experimental test was conducted. Comparison between theexperimental data and simulation results has shown a good agreement.
Karaminezhaad M., Maghsoudi A.a., Nozhati R., Sakhaei A.,
Volume 1, Issue 4 (12-2004)
Abstract
A large number of reinforced concrete structures subjected to chloride ions. Two basicapproaches for preventing corrosion of reinforcing steel embedded in concrete are: Increasing theconsolidation of concrete and using different coating on rebars. In present research steel rebarsare coated in different ways: a) 40 µm of zinc electroplated on steel rebar b) Zinc powder withepoxy paste (zinc rich). The rebars were placed in a macrocell design according to ASTM G109-92. Concrete operations were done with mixture designs of high and normal strength concrete.The results show corrosion decrease of zinc coated rebars.
Akbar Zadeh A., Salari M.,
Volume 1, Issue 4 (12-2004)
Abstract
AA3004 alloy is widely used in can making. The major concern in the production of canbodies is earing, which develop by high planar anisotropy of rolled sheet. Balance ofrecrystallisation and rolling textures together with a uniform and fine grain microstructure canminimize the earing. The effects of finish rolling temperature (FRT) on planar anisotropy,microstructure, texture development and mechanical properties of sheet have been analyzedIncreasing the FRT resulted in promotion of cube and G texture in hot rolled sheet. Lower |ΔR| ofthe final sheet with higher FRY, i.e. the lower planar anisotropy, is accompained with a balance ofrolling and recrystallisation orientations.
Mirfakhraee B., Eshraghi H., Sar Poulaki H.,
Volume 2, Issue 1 (3-2005)
Abstract
Effect of MgO addition on reaction sintering of aluminium titanate was investigated using equimolar Al2O3 and TiO2 after firing the samples at 1400 C for four hours. Results showed that MgO addition enhanced the sintering process by magnesium aluminates formation, which led to lower porosity and improved densification of the samples. Physical and mechanical properties showed that samples containing 5 wt% MgO was the optimum composition.
Aneziris C.g., Borzov D., Schmidt G.,
Volume 2, Issue 1 (3-2005)
Abstract
Improved structures of MgO carbon bonded materials due to new binder systems and due to the application of electrical currents during operation have been achieved for advanced applications in the secondary metallurgy and during near net shape metal casting.
Yahosseini M.r.s., Simchi A., Varahram N., Davami P.,
Volume 2, Issue 1 (3-2005)
Abstract
In the present work, a model was proposed to predict the thermal history during rapid solidification (RS) of metal droplets in the gas atomization process. The classical theory of heterogeneous nucleation was based on Newtonian heat flow and enthalpy method. Solving the governing numerical equations by the finite difference method (FDM) gave up the opportunity of analyzing the temperature-time history of the droplets during cooling in the RS process. Here, cooling in the liquid state, nucleation and recalescence, segregated solidification, eutectic solidification and cooling in the solid state were considered. To verify the model, the gas atomization of Al-4.5% Cu alloy was studied and the results were compared with the Shukla's model [1]. Convincing agreement was obtained between the predicted undercoolings and the experimental results reported previously.
Pakshir M., Amini R.,
Volume 2, Issue 1 (3-2005)
Abstract
Anodes are critical component of cathodic protection systems. As part of this effort, three different anodes were tested in a cathodic protection system that was designed and constructed to prevent further corrosion of reinforced concrete. This anodic system includes an electrically conductive coating composition applied in fluid form over an outer surface of the concrete mix. The composition further includes a predetermined amount of electrically conductive carbon material (coke, carbon black, graphite) uniformly distributed in the epoxy resin (as a binder) whereby the coating composition has a predetermined value of resistively. This investigation attempts to find the best type and optimum content of conductive carbon filler in poxy coating, to ensure optimal anode working parameters for marine environments (basically marine and sewer environments) and if any of the coating systems tested in this study excel over the other. In this study, electric and electrochemical parameters of three layer (with average coating thickness of 300µm) coke-epoxy, carbon black-epoxy and graphite-epoxy conducting paints (with different amount of filler) have been determined during long-term anodic polarization (70 days) in a seawater solution. During this test, on the basis of impedance measurements, the electrical resistances of these coatings have been calculated every 14 days. if conductive paints exhibit good electric and electrochemical stability, they will be attractive for cathodic protection of reinforced concrete.
Dehghanian C., Saremi M., Mohammadi Sabet M.,
Volume 2, Issue 1 (3-2005)
Abstract
The synergistic behavior of molybdate and phosphate ions in mitigating the corrosion of mild steel in simulated cooling water was evaluated performing potentiodynamic polarization and impedance spectroscopy tests. Phosphate and molybdate showed a synergistic effect on corrosion inhibition of steel in simulated cooling water. The observed reduction in anodic and cathodic current densities could be the consequence of incorporation of both phosphate and molybdate ions in forming a protective layer on the surface. The charge transfer resistance of the protective layer formed on steel surface was much greater in presence of both ions in solution than that when each inhibitor used alone.
Kharazi Y.h.k., Divandari M.,
Volume 2, Issue 1 (3-2005)
Abstract
The mold-filling behavior in the casting of aluminum alloy (A413) using lost foam casting (LFC) was explored. The effects of gate numbers, type of gating and casting thickness on the filling behavior were evaluated. Although, unlike convectional casting process, the gating system showed little effect onfilling ability, casting thickness created a greater effect on the mold filling. In contrast with convectional casting process, the mold filling seems to be controlled by castinggeometry as a consequence of combined influence of heat and mass transfer. The melt used to enter from the first gate instead of last gate which is in contrast with convectional casting process.
Mehryab A., Arabi H., Tamizifar M., Seyedein S.h., Razazi M.a.,
Volume 2, Issue 1 (3-2005)
Abstract
In this research, the mechanism of joining three sheets of metals, i.e. brass-steel-brass, by cold roll welding process has been studied. For this purpose, the two surfaces of steel sheets were roughened with stainless steel wire brush by different amounts, then the brass sheets were put on both sides of the steel sheets, before they were subjected to cold roll process. During rolling, peaks of the asperities on the surfaces of the steel sheet were pressurized, i.e. deformed, much more than that of trough. Hence, more hardening due to formation of higher dislocation density in the peaks regions were detected in comparison to the trough regions. Therefore, due to the differences in the amounts of work hardening occurred during cold rolling in the peaks & trough of the scratches and also due to the nature of the rough surfaces of the steel sheets, which causes the smooth surface of soft brass sheets laied over the rough surface of the steel sheet to be shappend according to the profile of the steel sheet scratches during cold rolling, mechanical locking occurred at the interface of brass & steel sheets. In addition, while the extrusion of brass took place through cracks within the surface of hardend peaks and metal bonding occurred on the contact points of the brass sheet & the vergin steel. Therefore, it seems two mechanisms were in operation is making a suitable joining between the sheets. One was a locking mechanism due to the roughness of the steel sheets & the other was bonding mechanism due to the bonding between the peak points of the scratches &soft brass surface. The strength of the bonded points in the interface were later increased by annealing the composite, so that by annealing the samples within the 500-900°C range for aperiod of 1 1/2 hr the interface strength increase substantially. The results of peeling test indicated that the interface strength of the samples annealed at 700°C or more increased so much that the brass sheet toms during peeling & the fracture did not pass through the interface.
Paydar M.h., Fadaei R., Shariat M.h.,
Volume 2, Issue 2 (6-2005)
Abstract
Copper coated SiC powders having three different amounts of copper, in the range of 20-60 wt%, were prepared via electroless coating process. The produced composite powders were uniaxially cold compressed and sintered at different temperatures and times under protective atmosphere. It was found that composite Cu/SiC powders and a relatively dense copper matrix composite with a uniform distribution of SiC reinforcing particles imbedded in copper matrix can be fabricated via electroless coating method followed by conventional cold pressing and sintering process. The results also show that SiC particles have a poor wettability with copper and so liquid phase sintering of the Cu/SiC composite powders did not enhance densification of the samples. Regarding this fact, optimum sintering temperatures, which depends on copper content, was determined to be in the range of 1050-1080?C.
