• 한국식품위생안전성학회지
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• 제26권4호
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• pp.410-416
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• 2011

선식의 품질향상과 위생적인 선식제조에 기초단계인 곡류원료에 위생 상태를 파악하기 위해 선식업체 19곳을 방문하여 선식용 곡류원료 10종류에 대한 일반생균수는 찹쌀 4.8~7.2, 보리 4.8~8.6, 현미 4.6~7.4, 검정콩 4.3~7.1, 검정쌀 4.1~7.1, 검정깨 4.1~6.1, 찰수수 3.1~5.1, 찰조 4.2~5.1, 들깨 3.1~5.1, 율무 3.6~5.2 log(CFU/g)로 검출되었고, Coliform, E. coli은 찹쌀 4.4~2.1, 2.1~3.4, 보리 2.2~4.4, 2.1~3.1, 현미 3.1~3.2, 1.0~2.8, 검정콩 2.3~3.8, 검정쌀 2.1~3.1, 1.0~2.1, 검정깨 2.3~3.6, 찰수수 2.2~2.4, 찰조 2.3~3.2, 들깨 2.3~3.1, 1.0~2.1, 율무 2.2~3.2, 1.0~2.1 log(CFU/g)검출되었으며, B. cereus은 찹쌀 1.0~2.1, 보리 2.1~3.1, 현미 2.4~2.6, 검정쌀 2.1~3.5, 들깨 1.0~2.1 log(CFU/g)로 검출되었다. Sal. spp은 검정깨에서 검출되었고, mold는 보리에서 검출되었다. 제조공정 중 미생물 오염도에 대해 조사한 결과 일반생균수는 입고단계의 경우 5.1~8.5 log(CFU/g)로 검출되었고, 세척 및 증자 공정은 4.4~7.5, 1.0~2.3 log(CFU/g)로 검출되었으며, 냉각, 건조, 방냉, 마쇄, 포장공정에서는 2.4~4.2, 1.0~4.0, 3.4~4.2, 4.3~5.2, 3.3~5.8로 검출되었다. 대장균군는 입고공정에서 1.0~2.01 (CFU/g)로 검출되었고, mold은 입고단계에서 검출되었다. 선식 가공업체의 환경 중 미생 물 결과 일반생균수는 원료탱크 40.2~7.5(CFU/g), 세척기와 건조기는 0.1~2.0, 0.1~3.2(CFU/g)로 검출되었고, 분쇄기, 포장지, 작업실은 3.2~4.0, 2.5~3.0, 3.8~5.2로 검출되었으며, 대장균군은 원료탱크와 분쇄기에서 각각 2.4~4.0, 0.0~4.1 log(CFU/g) 검출되었으며, 대장균은 검출되지 않았다. Mold은 원료탱크와 분쇄기, 작업실에서 검출되었다.

• 폴리머
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• 제36권6호
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• pp.685-692
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• 2012

사출성형공정은 충전, 보압, 냉각, 이형 및 취출 순서로 이루어진다. 이러한 공정 중 보압단계에서 캐비티 내에 가장 큰 압력이 주어진다. 따라서 캐비티 내압은 보압전환 시점과 보압의 크기에 가장 크게 영향을 받는다. 캐비티의 큰 내압은 금형에 큰 응력을 집중시켜 금형을 손상시킬 우려가 있으므로 캐비티 내압을 관찰하고 조절하는 것은 매우 중요하다. 본 연구에서는 이론해석과 실험을 통하여 보압전환 시점과 보압의 크기에 따라 캐비티 내압을 분석하였다. 보압전환 시점이 늦어짐에 따라서 내압이 증가하였다. 또한 보압전환이 늦어지면서 충전시간이 길게 되어 전체적으로 압력을 받는 시간이 길어져 보압 이후 냉각이 끝난 후에도 잔여압력이 존재하였다. 캐비티 내의 압력은 보압크기가 커질수록 비례적으로 증가하는 경향을 보였다. 역시 보압의 크기가 클수록 냉각 후 잔여압력이 증가하였다. 결과적으로 보압전환 시점이 늦고 보압크기가 크면 캐비티 내에 높은 압력이 형성되고 냉각이 끝난 후에도 잔여압력이 존재함을 알 수 있었다. 실험과 해석을 비교해 보았을 때 전체적인 경향은 매우 유사하였으나 해석에서는 잔여압력을 예측하지 못하였다. 캐비티 내압 조절을 위해서는 보압조건의 설정이 중요하며 CAE 해석을 통하여 최적 조건 설정이 가능함을 알 수 있었다.

• 한국주조공학회지
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• 제17권6호
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• pp.592-597
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• 1997

The microstructure and tensile properties of Mg-Zn-Ca and Mg-Zn-Mn-Ca alloys have been investigated. The alloys were obtained by melting in a low carbon crucible coated with boron nitride under an Ar gas atmosphere to prevent oxidation and combustion. The Mg alloy melt was cast into the metallic mold at room temperature, and cooling part was located at the bottom of mold. The phase formed during solidification of the Mg-Zn-(Mn) alloys containing 0.5%Ca is $Ca_2Mg_6Zn_3$. The yield strength and ultimate tensile strength of the alloys increased with increasing Zn content, but the ductility did not change with increasing Zn content. The addition of Mn improves the yield strength and ultimate tensile strength of the alloys, but the ductility did not change. Tensile fracture of the alloys revealed brittle failure, with cracking along the $Ca_2Mg_6Zn_3$ phase. The variation of stress with strain obeyed the relationship of the ${\sigma}=K{\varepsilon}^n$.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 추계학술대회 논문집
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• pp.1059-1063
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• 2005

Development of a feed drive-system with high speed, positioning accuracy and thrust has been an important issue in modern automation systems and machine tools. Linear motors can be used as an efficient system to achieve such technical demands. By eliminating mechanical transmission mechanisms such as ball screw or rack-pinion, much higher speeds and greater acceleration can be achieved without backlash or excessive friction. However, due to great power loss and magnetic attraction of the linear motors heating and deflection problems occur. Therefore, it is necessary to design strong structure, cooling device with high efficiency and light weight construction in designing stage of linear motors. This paper presents an investigation into a structural design of linear motor system. In this research, a new concept of moving table with high stiffness and of cooling plate is also introduced. Structure analyses are performed by using a commercial code ANSYS in order to evaluate the design safety.

• 한국기계가공학회지
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• 제15권3호
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• pp.130-134
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• 2016

Due to the need for advanced technologies in the automotive industry, the demand for lighter and safer vehicles has increased. Even though various nonferrous metals, like Aluminum, Magnesium and also Carbon Fiber Reinforced Plastic (CFRP), have been implemented in the automotive industry, a lot of technical research and development is still focused on ferrous metals. In particular, the market volume of High Strength Steel (HSS) parts and Ultra High Strength Steel (UHSS) by hot press forming parts has expanded significantly in all countries' automotive industries. A new tool steel, High Thermal-Conductivity Tool Steel (HTCS), for stamping punches and dies has been developed and introduced by Rovalma Company (Spain), and it is able to support better productivity and quality during hot press forming. The HTCS punches and dies could help to reduce cycle time due to their high thermal conductivity, one of the major factors in hot press forming operation. In this study, test dies were manufactured in order to verify the high thermal conductivity of HTCS material compared to SKD6. In addition, thermal deformation was inspected after the heating and cooling process of hot press forming. After heating and cooling, the test dies were measured by a 3D scanner and compared with the original geometry. The results showed that the thermal deformation and distortion were very small even though the cooling time was reduced by 2 seconds.

• 한국산학기술학회논문지
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• 제12권3호
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• pp.1051-1057
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• 2011

최근 개발된 GMP공정의 활용으로 디지털 카메라, 광저장기기, 각종 전자기기 등의 광응용 기기에서 비구면 유리렌즈가 폭넓게 활용되고 있다. GMP공정은 복잡한 형상의 유리렌즈를 정밀하면서도 경제적으로 생산할 수 있다. 본 연구에서는 다구치 실험계획법을 이용하여 순차이송형 GMP공정에서 비구면 유리렌즈의 성형 조건을 최적화 하였다. 냉각 1단계에서의 압력과 온도, 시간을 3가지 주요 공정변수로 정하였으며, 3캐비티 금형을 이용하여 실험한 결과 순차이송형 유리렌즈 성형공정에서 냉각시간이 비구면 유리렌즈의 형상정밀도(PV)에 가장 큰 영향을 미치는 것을 알 수 있었다.

• Tribology and Lubricants
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• 제8권1호
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• pp.70-77
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• 1992

Al-Pb-Si bearing alloys were produced by a forced stirring method and a rapid solidification process to study wear properties of bearing alloys. A homogeneous distribution of Pb particles in Al matrix could be obtained by means of the forced stirring and the rapid cooling during the casting. The wear properties of bearing alloys were tested by a pin-on-disc wear tester. The change in microstructure according to the alloy manufacturing variables was observed by the backscattered electron images. Al-Pb and Al-Si binary alloys showed a transition from mild to severe wear. The transition was not found in Al-Pb-Si ternary alloys. It could be concluded that the lubricatioin effect of Pb and the strengthening effect of Si in the ternary alloys enhanced the bearing properties. A Al-25%Pb-13%Si alloy showed the lowest coefficient of friction in this experiment. It indicated that the optimum concentration of alloy was 25% Pb and 13% Si when the forced stirring of melt and water-cooled-copper-mold solidification were adopted.

• 한국주조공학회지
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• 제9권1호
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• pp.39-48
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• 1989

A basic three dimensional thermal model has been developed to simulate the solidification sequence for gravity die casting process. The finite difference method was used to analyze the solidification process during all the casting cycles. The prediction of die temperature in the quasi-steady state was analyzed by the boundary element method. The influence of die cooling on the heat flow in the cast/mold system was also investigated. Predictions of the computer simulation on temperature profiles and location of shrinkage defects were in good agreement with those observed in experimental die castings. Models of computer simulation which is developed by this work can be useful for the design and process control of die casting.

• 대한기계학회논문집B
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• 제25권10호
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• pp.1337-1345
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• 2001

Numerical investigation is made to study the effects of thermosolutal convection on the formation of macrosegregation in a Pb-Sn alloy solidification process in a two dimensional confined rectangluar mold. The basic equations are sovled using the Contrinum Model theory with the SIMPE algorithm during the solidification process. In addition, to track the liquid-solid interface with time variations, the moving boundary condition was adopted and moving irregular interface shapes were treated with the time-dependent, boundary-fitted coordinate system. As the temperature reduces from the liquidus to the solidus, the liquid concentration of Sn, the lighter constituent, increases. Then the buoyancy-driven flow due to temperature and liquid composition gradients occurs in the mushy region and forms the complicated macrosegregation maps. belated to this phenomena, effects on the macrosegregation formation depending on the cooling condition and gravity values are examined.

• Journal of Mechanical Science and Technology
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• 제17권6호
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• pp.896-905
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• 2003

A linear motor has many advantages next to conventional feed mechanisms: high transitional speed and acceleration, high control performance, and good positioning accuracy at high speed. Through the omission of a power transfer element, the linear motor shows no wear and no backlash, has a long lifetime, and is easy to assemble. A disadvantage of the linear motor is low efficiency and resultant high-temperature rise in itself and neighboring structures during operation. This paper presents the thermal behavior of the linear motor as a feed mechanism in machine tools. To improve the thermal behavior, an insulation layer is used. By placing the insulation layer between the primary part and the machine table, both the temperature difference and the temperature fluctuation in the machine table due to a varying motor load are reduced.