• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1998.03a
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• pp.107-112
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• 1998

The semi-solid materials(SSMs) fabricated under electric-magnetic stirring condition are necessary to be applicated in the thixoforging process. The optimal reheating conditions to thixoforging process were investigated with changing the reheating time, holding time, reheating temperatures, capacity, and adiabatic material size. In the case of solid fraction fs=50%, the microstructure of SSM (specimen size:d76X 190) at the condition of the first reheating time 4min, holding time lrnin and reheating temperature 350%, the second reheating time 3min, holding time 3min and reheating temperature 575C, the thlrd reheating time lmin, holding time 2min and reheating temperature 584'C, capacity Q=8.398KW, and adiabatic material size 53mm is obtained with globular microstructure and finest.

• Journal of the Korean Society of Food Science and Nutrition
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• v.25 no.3
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• pp.504-512
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• 1996

Changes in quality of cooked rice after microwave reheating were evaluated. Ceramic coated microwave oven reduced a reheating time(1 min). Storage temperature, storage time and microwave reheating did not affect the color value of cooked rice after microwave reheating. Hardness of cooked rice after microwave reheating decreased in frozen storage treatment. Photomicrographs of cross-section of cooked rice after microwave reheating showed restoration of starch. Effect of storage temperature and time were not significant in appearance, aroma, taste and texture of cooked rice after microwave reheating for sensory evaluation test.

• International Journal of Precision Engineering and Manufacturing
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• v.4 no.2
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• pp.49-56
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• 2003

As semi-solid forging (SSF) is compared with conventional casting such as gravity die-casting and squeeze casting, the product without inner defects can be obtained from semi-solid forming and globular microstructure as well. Generally, SSF consists of reheating, forging, and ejecting processes. In the reheating process, the materials are heated up to the temperature between the solidus and liquidus line at which the materials exists in the form of liquid-solid mixture. The process variables such as reheating time, reheating temperature, reheating holding time, and induction heating power has large effect on the quality of the reheated billets. It is difficult to consider all the variables at the same time for predicting the quality. In this paper, Taguchi method, regression analysis and neural network were applied to analyze the relationship between processing conditions and solid fraction. A356 alloy was used for the present study, and the learning data were extracted from the reheating experiments. Results by neural network were in good agreement with those by experiment. Polynominal regression analysis was formulated using the test data from neural network. Optimum processing condition was calculated to minimize the grain size and solid fraction standard deviation or to maximize the specimen temperature average. Discussion is given about reheating process of row material and results are presented with regard to accurate process variables fur proper solid fraction, specimen temperature and grain size.

• Korean Journal of Food Science and Technology
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• v.28 no.3
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• pp.528-537
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• 1996

Qualify changes of microwave-reheated cooked rice aseptic-packaged with different lid materials and oxygen absorbers were determined during storage at $20^{\circ}C,\;30^{\circ}C$ and $40^{\circ}C$. Springiness cohesiveness and adhesiveness increased as storage temperature increased, while gumminess and hardness decreased. Lid materials oxygen absorbers, and storage temperatures showed no significant effect on the textural properties of cooked rice after microwave reheating. Degree of gelatinization was increased as storage temperature increased and was restored after microwave reheating. Scanning electron micrograph showed that the surface of cooked rice became rough and hollowed after microwave reheating for 1.5 min, indicating starch was regelatinized, while there was no difference with respect to lid materials. Photomicrographs of the cross-section of aseptic-Packaged cooked rice showed that a compact and solid structure increased and retrogradation occured in starch as storage temperature decreased, while a compact and solid structure was decreased and starch was regelatinized after microwave reheating.

• Corrosion Science and Technology
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• v.6 no.4
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• pp.193-197
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• 2007

It is well known that the development of Advanced High Strength Steels (AHSS) is very important for the automotive industry in order to improve fuel efficiency and the reduction of material costs. However, it is particularly difficult to improve the surface quality of AHSS because the high amount of Si, Al, Mn and Ti etc. in AHSS promote selective oxidation, resulting in surface defects. The reheating process in the hot strip mill would cause severe oxidation because it is carried out at elevated temperatures under aggressive environments. In this study a reheating furnace simulator was developed to investigate oxidation phenomena in the reheating process. The environmental gas for the reheating furnace was made by burning coke oven gas with air in the simulator. The air/fuel ratio is precisely controlled by MFC. Ti oxides are easily formed on grain boundaries and Mn and Si oxides are usually formed in inner grains near the steel surface with a small round shape.

• Korean journal of food and cookery science
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• v.11 no.5
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• pp.494-502
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• 1995

The study was conducted to evaluate the characteristics of Nuhbiani qualities with the different cooking, reheating methods and storage conditions. Cooking and reheating methods were used with pan, microwave and their combinations. Precooked samples were stored for 0, 1, 4, 7, 15 days in the refrigerator and for 15, 30 days in the freezer. TBA value, shear value by rheometer and sensory attributes in rancidity, hardness, juiciness and overall acceptability were measured. There was no significant difference between cooking, reheating methods in TBA values. Lower values in TBA were noted in the Nuhbiani of frozen storage as compared with that of refrigerated storage. There is a tendency that TBA values were increased as the storage time extended during the refrigeration. Shear values were more increased by microwave cooking and microwave reheating than other methods showing harder texture. Results from sensory evaluation of rancidity, hardness, juiciness and overall acceptability show that there were no significant differences between storage methods, among storage periods and cooking, reheating methods.

• Transactions of Materials Processing
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• v.11 no.2
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• pp.155-164
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• 2002

One of the important steps on semi-solid forming Is the reheating process of raw materials to the semi-solid state. This Process is not only necessary to achieve the required SSM billet state, but also to contro1 the microstructure of the billet. In reheating process, the globule size is determined by the holding time of last heating stage. Therefore, some experiments to investigate the relationship between the mechanical properties and the holding time in the last heating stage was performed. The alloys used in this experiment were 357, 319 and A390 alloys. The experiments of reheating were performed by using an Induction heating system with the capacity of 50kw. This paper shows the evolution of the microstructure according to the holding time of last reheating stage. Furthermore, to evaluate the effect of globule size controlled by holding time in last heating stage uniaxial tension test was performed. The strain-stress curves were plotted according to the holding time.

• Transactions of Materials Processing
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• v.8 no.5
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• pp.437-448
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• 1999

The reheating of the billet in the semi-solid state as quickly and homogeneously as possible is one of the most imposrtant parts. To obtain a fine globular microstructure in cross section of billet, the optimal design of the induction coil for variation of alloys and specimen sizes is necessary. For the thixo-forging process the construction of the reheating data base is very important, because the reheating conditions are different for variation of SSM and billet sizes. So in this study, the optimal coil design of A356 (ALTHIX) and Aι2024 with d×ι=60×90 (mm) to obtain the globular microstructure is theoretically proposed. The suitability of an optimal coil design will be demonstrated by reheating experiments. Finally, the thixoformability of an arbitrarily shaped product is evaluated by its forming variables. The defects and mechanical properties are also investigated.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.2
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• pp.114-125
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• 2002

As semi-solid forging (SSF) is compared with conventional easting such as gravity die-easting and squeeze casting, the product without inner defects can be obtained from semi-solid forming and globular microstructure as well. Generally speaking. SSF consists of reheating, forging, ejecting precesses. In the reheating process, the materials are heated up to the temperature between the solidus and liquidus line at which the materials exists in the form of liquid-solid mixture. The process variables such as reheating time, reheating temperature, reheating holding time, and induction heating power have much effect on the quality of the reheated billets. It is difficult to consider all the variables at the same time when predicting the quality. In this paper, Taguchi method, regression analysis and neural network were applied to analyze the relationship between processing conditions and solid fraction. A356 alloy was used for the present study, and the learning data were extracted by the reheating experiments. Results by neural network were on good agreement with those by experiment. Polynominal regression analysis was formulated by using the test data from neural network. Optimum processing condition was calculated to minimize the grain size, solid fraction standard deviation, otherwise, to maximize the specimen temperature average. In this time, discussion is liven about reheating process of row material and results are presented with regard to accurate process variables for proper solid fraction, specimen temperature and grain size.

• Transactions of Materials Processing
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• v.32 no.5
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• pp.239-246
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• 2023

To reduce the forming load due to the temperature drop, during the hot forging process, a reheating hot forging process design is required that to repeat heating and forging. However, if the critical strain required for recrystallization is not induced during forging and grain growth becomes dominant due to the reduction in dislocation density due to repeated heating, the mechanical properties may deteriorate. Therefore, in this study, Inconel 706 alloy was applied, and the grain refinement behavior was comparatively analyzed according to the number of reheating times and effective strain during reheating hot forging process. Reheating was carried out with a total compression rate of 40% up to 4 times. The Inconel 706 compression test specimens heated once showed finer grains as the effective strain increased due to the dynamic recrystallization phenomenon. However, as the number of heating increases, grain refinement was observed even in a low effective strain distribution of 0.43 due to static recrystallization during reheating. Moreover, grain growth occurs at a relatively low effective strain of 0.43 when the number of reheating is four or more. Therefore, it was effective to apply an effective strain of 0.43 or more during hot forging to Inconel 706 in order to induce crystallization through grain refinement and improve the properties of forged products. In addition, we could notice that up to three reheating times condition was appropriate to prevent grain growth and maintain fine grain size.