• Journal of the Korean Ceramic Society
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• v.52 no.6
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• pp.403-409
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• 2015

Porous alumina ceramics are involved in many industrial applications due to the exceptional properties of these products. This study addresses the preparation of porous alumina ceramics using hollow microspheres as a pore-forming agent and slip casting as a green-body-forming technique. A uniform distribution of pores is a basic requirement of a porous material. This study investigates three different slurry systems, i.e., as-prepared alumina slurry, alumina slurry electrostatically dispersed by hydrochloric acid (HCl), and slurry dispersed by the commercial dispersant 'Darvan C-N'. At a low viscosity, the hollow microspheres in the slurry tend to float, which causes a non-uniform pore distribution. To avoid this phenomenon, the viscosity of the slurry was increased to the extent that the movement of hollow microspheres ceased in the slurry. As a result, a uniform pore distribution was achieved.

• Journal of the Korean Society for Heat Treatment
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• v.32 no.2
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• pp.68-73
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• 2019

${\alpha}$-titanium alloy has a relatively low heat treatment characteristic and it is mainly subjected to heat treatment for residual stress, recovery or dynamic recrystallization. In this study, commercially pure titanium hollow castings was fabricated by gravity casting. Heat treatments were carried out at $750^{\circ}C$, $850^{\circ}C$ and $950^{\circ}C$ to investigate the effect of post-heat treatment on microstructure and mechanical properties. Beta-transus temperature ($T_{\beta}$) was about $913^{\circ}C$, and equiaxed microstructure was shown at temperature below $T_{\beta}$ and lath-type microstructure at temperature above $T_{\beta}$. Microstructure and mechanical properties did not show any significant difference in the direction of solidification for titanium hollow billet, so it can be seen that it was a well-made material for extrusion process. The optimum heat treatment condition of hollow billet castings for the seamless tube production was $850^{\circ}C$, 4 hr, FC, indicating a combination of equiaxed microstructure and appropriate mechanical properties.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.6
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• pp.1-6
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• 2010

Aluminum rear lower arm is designed for luxury sedan and manufactured by hollow sand casting in the present study. Here we present the relationship between local microstructure and coupon tensile test in the rear lower arm. The characteristics of the local tensile deformation are supposed to be dependent upon Si distribution and DAS (dendrite arm spacing). Si distribution affects the yield strength and DAS affects the elongation of local area in the part, respectively.

• Journal of the Korea Concrete Institute
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• v.13 no.2
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• pp.87-92
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• 2001

Until now, disposal of casting foundry fly ash generally depends on reclamation. This is the great loss from a point of view saving of resources and utilizing industrial wastes. Therefore, a study on the use of fly ash as a substitute material for construction is necessary in order to utilize industrial wastes, to reduce cost of production, to improve quality in producing concrete products, and to protect environment from pollution. In this study, concrete products(hollow concrete block and concrete brick) using casting foundry fly ash as a substitute materials for cement, are produced. And experiments are conducted based on Korean Industrial Standards. Finally, the used methods of casting foundry fly ash as a substitute materials in industry are presented.

• Computers and Concrete
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• v.21 no.2
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• pp.117-126
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• 2018

This research investigate the behavior of reinforced normal and lightweight aggregate concrete hollow core slabs with different core shapes, shear span to effective depth (a/d). The experimental work includes testing seven reinforced concrete slabs under two vertical line loads. The dimensions of slab specimens were (1.1 m) length, (0.6 m) width and (0.12 m) thickness. The maximum reduction in weight due to aggregate type was (19.28%) and due to cross section (square and circular) cores was (17.37 and 13.64%) respectively. The test results showed that the decrease of shear span to effective depth ratio from 2.9 to 1.9 for lightweight aggregate solid slab cause an increase in ultimate load by (29.06%) and increase in the deflection value at ultimate load or the ultimate deflection by (17.79%). The use of lightweight aggregate concrete in casting solid slabs give a reduction in weight by (19.28%) and in the first cracking and ultimate loads by (16.37%) and (5%) respectively for constant (a/d=2.9).The use of lightweight aggregate concrete in casting hollow circular core slabs with constant (a/d=2.9) (reduction in weight 32.92%) decrease the cracking and ultimate loads by (12%) and (5.18%) respectively with respect to the solid slab. These slab specimens were analyzed numerically by using the finite element computer program ANSYS. Good agreements in terms of behavior, cracking load (load at first visible crack) and ultimate load (maximum value of testing load) was obtained between finite element analysis and experimental test results.

• Journal of the Korean Ceramic Society
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• v.48 no.1
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• pp.74-79
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• 2011

The pore generation technology using GHM (Glass Hollow Microsphere) was studied in order to reduce the weights of porcelain. In this study, we verify the property of modified slurry by adding GHM. The modified slurry was prepared by adding 1.0~2.5 wt%(K1), 1.0~6.0 wt%(K37) of GHM to the slurry for porcelain. The slurry viscosity were stable inside a content range of 1.0~2.5 wt%(K1), 1.0~6.0 wt%(K37). However, the viscosity of modified slurry increased more than 3.0 wt%(K1) and 6.5 wt%(K37). The formed specimen by slip casting was fired at $1229^{\circ}C$, $1254^{\circ}C$. As the amount of GHM content increased, the weight decreased and the addition of 1.0~2.5 wt%(K1), 1.0~6.0 wt%(K37) of GHM resulted in a weight drop of 30%(K1) and 25(K37). However, when the GHM content increased, the strength decreases over 70%. This is caused by the presence of a large volume of surface defects (pores) and defects from the agglomeration of GHM.

• Proceedings of the Membrane Society of Korea Conference
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• 1995.04a
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• pp.26-27
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• 1995

Most of synthetic polymeric membranes used in ultrafiltration, reverse osmosis and microfiltration processes are prepared by phase inversion(or phase separation) technique. In this technique, a homogeneous polymer solution is cast into thin film or hollow fiber shape and then immersed into a nonsolvent coagulant bath. The exchange of solvent and nonsolvent across the interface between casting solution and coagu!ant can make the casting solution phase-separate and form a membrane with a symmetric or asymmetric structure. Because of importance of this technique in membrane field, many investigations have been dedicated to elucidate the mechanism of membrane formation by phase inversion technique.[1-10] These investigation have suggested that the structure formation and permeation properties of phase inversion membrane depend on the variables such as the nature and content of casting solution and coagulant, temperature of casting solution and coagulant, and the diffusional exchange rate of solvent and nonsolvent etc. which can be related to the thermodynamic and kinetic properties of the casting system. The variables such as the nature and content of casting solution can also be the important factor affecting the structure formation and permeation property of the phase inversion membrane.

• Journal of the Korean Ceramic Society
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• v.40 no.12
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• pp.1159-1164
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• 2003

Two processing routes (i.e., the gel casting and polymer preform routes) using polymer beads were studied to fabricate porous ceramics with a cellular structure. The gel casting route, comprising the gel casting of a ceramic slurry mixed with polymer beads, was found to be inadequate to produce porous ceramic bodies with a interconnected pore structure, due to complete coating of the slurry on the polymer beads, which left just isolated pores in the final sintered bodies. The polymer preform route, involving the infiltration of a polymer beads preform with the ceramic slurry, successfully produced porous ceramics with a highly interconnected network of spherical pores. The pore size of 250-300 $\mu\textrm{m}$ was demonstrated and the porosity ranged from 82 to 86%. This process is advantageous to control the pore size because it is determined by the sizes of polymer beads used. Another feature is the avoidance of hollow skeleton, giving a high strength.

• Journal of Korea Foundry Society
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• v.18 no.4
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• pp.325-333
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• 1998

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.5
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• pp.111-117
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• 2020

Centrifugal casting is suitable for producing hollow-products using centrifugal force. Bush type metal bearings are the key parts that facilitate the rotational movement of various machinery. Metal bearings produced by conventional centrifugal casting machines show rotational imbalance. Therefore, after injecting a large amount of material, the product's precision is secured in the secondary processing. Rotational imbalance is caused by the force acting on the rotary disc plate. In order to minimize rotational imbalance, NASTRAN was used for the optimal design and structural analysis. It was concluded that the rotating plate of the conventional centrifugal casting machine should be prevented from tilting. For this purpose, the location & thickness of the stiffeners were obtained through the optimum design. In the conventional centrifugal casting machine, both ends of the product are lower in temperature than the center part, so internal stress occurs. This solves this problem by inserting a heating coil into the rotating plate.