• Resources Recycling
• /
• v.13 no.5
• /
• pp.23-27
• /
• 2004

In this study, experimental work was performed to mold tensile specimens by using the injection molding machine. Melt temperature, mold temperature and the mixed ratio of recycled resin were selected as processing parameters for studying the effect of those conditions on the shrinkage, weight, absorption, and tensile strength of molded parts. As a result, the shrinkage was increased according to the higher mold and melt temperature and it was more sensitive to the change of mold temperature. On the other hand, the weight of molded parts was decreased due to the increment of mold and melt temperature. Tensile strength was increased with mold and melt temperature, and it was also easy to change by mold temperature.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1997.04a
• /
• pp.337-341
• /
• 1997

The purpare of this research is to develope a FEM program for analyzing solidification processes of axisymmetic casting, considering phase changes and the contact between the metal and mold. Temperture recovery method is employed for considering the phase changes releasing the latent heat. A gap element is employed for modeling the interface between the model and metal in finding deformed shapes. In order to verify the developed program, an axisymmetric aluminum casting processes is simulated. Temperature distribution, phase front position, and shrinkaga and porosity creation are compared with measurement, FIDAP results, and ANSYS results, and good agreements are examined.

• Journal of Korea Foundry Society
• /
• v.23 no.1
• /
• pp.40-46
• /
• 2003

Semisolid forming requires alloys with non-dendritic microstructure of the thixotropy. Recently, low pouring temperture method without stirring, i.e. liquidus casting has been found out new fabrication method of the semisolid metals. Effects of melt superheat and mold conditions on the globulization of primary Al of $AlSi_7Mg$ alloy were investigated in gravity casting process without stirring. The microstructures of primary Al as function of melt superheat and mold temperature show globular, rosette and dendritic shapes. The conditions for globular microstructure of primary Al were low melt superheat < 35 K and low mold temperature < 500 K. The thermal conditions for globular microstructure of primary Al were undercooled melt at early solidification stages and slow cooling < 0.6 K/s. It was found that the initial microstructure was maintained throughout the solidification and the globules of primary Al can be obtained by high nucleation of fine and spherical nuclei due to enhanced undercooling of melt.

• Journal of Technologic Dentistry
• /
• v.34 no.2
• /
• pp.75-81
• /
• 2012

Purpose: All ceramic crown, made from zirconia instead of metal for core material, is recognized the best esthetical prosthesis. Recently, high-priced zirconia blocks and expensive CAD/CAM machines come into use for making zirconia core. In this study, slip casting process is adapted to evaluate the possibility of the recycling the remained parts of zirconia block after machining. Methods: Remained zirconia blocks were reduced to powders with zirconia mortar, and screened with 180 mesh sieve. Passed powders were ball milled under various conditions to obtain the optimum zirconia slip for casting. Solid casting method was used for casting the specimens with plaster mold. Formed specimens were dried and biscuit fired at $1,000^{\circ}C$ for 1 hour. Biscuit fired specimens were finished with exact shape of square pillar. Finished specimens were fired from $1,200^{\circ}C$ to $1,550^{\circ}C$ at $50^{\circ}C$ intervals for 1 hour. Linear shrinkage, apparent porosity, water absorption, bulk density, and flexural strength were tested. Microstructures were observed by SEM. Results: Above examinations indicated that the optimum firing temperture was $1,500^{\circ}C$, and when fired at this temperature for 1 hour, apparent porosity was 0% and flexural strength was 680MPa. SEM photomicrographs showed uniform 200~300nm grain size, which is equal with microcture of sintered commercial zirconia block. when compare 24% linear shrinkage of cast specimen with 20% linear shrinkage of CAD/CAM machined block, it was estimated that the size controlling of cast core was not so difficult. Conclusion: According to the all of this experimental results, the cast zirconia core produced from the remained parts of zirconia block was possible to use for all ceramic denture.