• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.199-203
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• 1995

The technology of Semi-Solid Forging (SSF) has been actively developed to fabricate near-net- shape products using light and hardly formable materials, the SSF process is composed of slug heating, forming, compression holding and ejecting step. After forming step in SSF, the slug is compressed during a certain holding time in order to be completely filled in the die cavity and be accelerated in solidification rate. The compression holding time that can affect mechanical properties and shape of products is important to make decision, where it is necessary to find overall hert transfer coefficeient properly which has large effect on heat transfer between slug and die. This paper presents the procedure to predict compression holding time of octaining the final shaped part with information of temperature and solid fraction for a cylindrical slug at compression hoiding step in closed-die compression process using heat transfer analysis considering latent heat by means of finite element method. The influence of the predicted compression hoiding time on mechanical properties of products is finally investigated by experiment.

• Journal of Korean Institute of Industrial Engineers
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• v.30 no.2
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• pp.76-83
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• 2004

This study aimed to empirically investigate perceived discomfort depending upon external load, upper limb postures and their holding time. Discomfort was obtained through an experiment, in which external load, wrist flexion/extension, elbow flexion, shoulder flexion and adduction/abduction were used as experimental variables. The subjects were instructed to hold given postures for 60s and to rate their subjective discomfort scores at 5s, 20s, 40s and 60s by using the free modulus method of magnitude estimation. The results showed that while only external load and elbow flexion were statistically significant at the holding time of 5s at ${\alpha}=0.05$ or 0.10, external load and upper limb postures excluding shoulder adduction/abduction significantly affected discomfort ratings at 20s, 40s and 60s at ${\alpha}=0.01$ or 0.05. Discomfort scores were also significantly different between four posture holding times at ${\alpha}=0.01$. The effects of external load and holding time were much larger than those of upper limb postures. Based on the results of this study, it is recommended that external load and holding time as well as working postures betaken into consideration to precisely quantify postural load in industry.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.2
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• pp.154-161
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• 1998

The effects of melting temperature and holding time on the critical current density($J_c$) of $YBa_2Cu_3O_x$ based superconducting bulk fabricated by MPMG process were investigated. The amount of the formed $Y_2BaCuO_5$ phases increased with the melting temperature. However, the value of critical current density was highest at 1120 $^{\circ}C$. With this proper melting temperature, the effect of holding time on the critical characteristics was also investigated. In the case of Ag addition, the volume of the formed $Y_2BaCuO_5$ phase when the amount of Ag addition was 10 wt% and 20 wt% was observed to be highest at 20 minute and 40 minute respectively. But in the specimen without Ag, volume of $Y_2BaCuO_5$ phase increased as the holding time increased. The proper melting temperature and the holding time obtained were 1120 $^{\circ}C$ and 20 minute. The long holding time was not effective for the $J_c$ improvement as well as the formation of $Y_2BaCuO_5$.

• Proceedings of the Korean Operations and Management Science Society Conference
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• 1998.10a
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• pp.186-189
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• 1998

In this paper, we provide a mathematical formulation to describe the random mobility of users in cellular radio systems. With this, we can also study tile cell sojourn time (CST) distribution as well as the channel holding time (CHT) distribution. The study on user mobility enables to improve the resource management in cellular radio systems. We provide a versatile analysis tool that improves the limit of simplified analyses.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1997.04a
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• pp.597-601
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• 1997

The technology of Semi-Solid Forging(SSF) has been actively developed to fabricate near-net shape products using light and hardly formable materials. Generally, the SSF process is composed of slug heating,forming,compression holding and ejecting step. After forming step in SSF, the slug is comperssed during a certain holding time in order to be completely filled in the die cavity and be accelerated in solidification rate. This paper presents the analysis of temperature,solid fraction and shrinkage at compression holding step for a cylindrical slug,then predicts the solidification time to obtain the final shaped part. Enthalpy-based finite element analysis is performed to solve the heat transfer problem considering phase change in solidification.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.10
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• pp.102-108
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• 1997

The technology of Semi-Solid Forging (SSF) has been actively developed to fabricate near-net- shape products using light and hardly formable materials. Generally, the SSF process is composed of slug heating, forming, compression holding and ejecting step. After forming step in SSF, the slug is compressed during a certain holding time in order to be completely filled in the die cavity and be accelerated in solidification rate. This paper presents the analysis of temperature, solid fraction and shrinkage at compression holding step for a cylindrical slug, then predicts the solidification time to obtain the final shaped part. Enthalpy-based finite element analysis is performed to solve the heat transfer problem considering phase change in solidification.

• Korean journal of food and cookery science
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• v.5 no.2
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• pp.35-41
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• 1989

This study was written to assess microbilogical quality by passage of time and holding method after making foods, by means of evaluating time, temperature and microbiological quality during vairous phases in product flow of hard-boiled mackerel served by an industry feeding operation for 500 persons a day, measuring pH & Aw and analyzing factors affecting nicrobiological growth conditions. The results were as fallows: 1. According to phases in product flow of hard-boiled mackerel, it showed 4.9 hours of mean of needed time, $27.5^{\circ}C$ of room temperature, 4.8~5.7 of pH value and 0.95~0.98 of Aw. these conditions were suitable for microbiological growth, and the phases with potential hygienic danger were pre-preparation and assembly & service. 2. As for holding methods and passage of time, holding as steam table was more effective than holding at room temperature as time past. 3. Food poisoning bacteria were not dectected from phases in product flow of hard-boiled mackerel.

• Journal of Korea Foundry Society
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• v.30 no.5
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• pp.161-166
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• 2010

In this examination, the effect of Sr addition and holding time on microstructure of Al-10.5wt%Si-2wt%Cu secondary die-casting alloy was investigated. Degree of undercooling was improved with increasing the Sr content in this alloy. Up to 0.02wt%Sr addition, acicular and lamellar eutectic structure was observed in the microstructure. Meanwhile, the eutectic Si was modified toward the fine fibrous form by increasing Sr content with more than 0.03wt% and holding time of the melt. The well- modified alloys showed decreased eutectic silicon size from 3.25 ${\mu}m$ to less than 0.8 ${\mu}m$. From these results, the optimal strontium content and holding time were identified on the Al-10.5wt%Si-2wt%Cu secondary die-casting alloy.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1997.11a
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• pp.356-359
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• 1997

The Effects of different melting temperature and holding time in the melting temperature on J$\sub$c/ of YBa$_2$Cu$_3$O$\sub$x/ based superconducting bulk using MPMG process were investigated. the value of critical current density was the largest at l120$^{\circ}C$, the melting temperature which is appointed to the mid point of (Y$_2$BaCuO$\sub$5/ + Liquid)region. With the melting temperature in which the value of J$\sub$c/ is the largest, J$\sub$c/ was again measured to see whether the holding time at this proper melting temperature has the effect on the critical characteristics. From the result above it was concluded that the melting temperature and holding time were important to improve the J$\sub$c/ and the formation of the Y$_2$BaCuO$\sub$5/. In this paper, the melting temperature obtained was l120$^{\circ}C$ and propel holding time could be obtained as 20 minute and the more holding time was not effective in the J$\sub$c/ improvement as well as the formation of Y$_2$BaCuO$\sub$5/.

• Korean journal of food and cookery science
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• v.4 no.2
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• pp.71-79
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• 1988

This study is written to look into microbiological quality by passage of time and holding methods after making foods, by means of evaluating time, temperature and microbiological quality during various phases in product flow of cold soybean noodles serviced by an industry feeding operation for 500 persons a day, measuring pH & Aw and analyzing factors affecting microbiological growth conditions. The results were as follows: 1. According to phases in product flow of cold soybean noodles, it showed 15.6 hours of mean of needed time, $24.2^{\circ}C$ of room temperature, 5.1~7.6 of pH value & 0.95~0.98 of Aw except dry noodles. These conditions were good for multipling of microbe, and the phases with potential sanitary danger were ingredient, pre-preparation, holding before assembly and service and assembly & service. 2. As for holding methods and passage of time, holding at cold table was more effective than holding at room temperature as time past. 3. As for equipments using for making food, dipper, basket, kitchen board & kitchen towel showed high microbiological value in total aerobic plate counts and kitchen towel and stainless-steel were showed high microbioloical value in coliform counts. 4. E. coli, food poisoning bacteria was detected from barrel filled with soybean soup and also soybean itself.