• 대한소아치과학회지
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• 제28권2호
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• pp.261-270
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• 2001

본 연구에서는 최근 치과임상에서 이용되고 있는 7종의 복합레진을 시험재료로 선택한 다음 법랑질과 복합레진 충전재가 대합하는 경우의 마모 양상을 조사하기 위해 광중합형 복합레진과 제2소구치 교두를 핀-디스크 구동 방식의 전동식 마모시험기에 고정한 다음 68.6N의 하중을 가한 상태에서 30,000회전시켜 $1.3{\times}10^3m$의 미끄럼 접촉을 가하였다. 마모도를 평가하기 위해 복합레진의 종류에 따른 제2소구치 교두의 수직고경 변화, 시편의 두께 감소와 체적 손실 및 마모시험 전후의 표면을 주사전자현미경으로 관찰하였고, 표면경도가 마모도에 미치는 영향을 평가하기 위해 누프 경도를 측정한 결과, 다음과 같은 결론을 얻었다. 1. 누프 경도는 Spectrum 군에서 70.4로 가장 높고 Heliomolar 군에서 19.8로 가장 낮은 값을 보였으며, Tukey 다중범위검증법에 의해서 각 군 사이의 통계적 유의성을 검증한 결과, Spectrum 군, Z100 군 및 Clearfil AP-X 군을 제외한 나머지 모든 군들 사이에서 상호간에 통계학적으로 유의한 차이를 보였다(p<0.05). 2. 법랑질의 내마모성은 microfill 형인 Heliomolar 군과 대합하는 경우에 가장 높게 나타났으며, 구치부용에서는 구상의 zirconia silica 미세 입자를 복합화한 micro hybrid 형의 Palpique 군에서 가장 높게 나타났다. 3. 복합레진의 연마성 마모에 대한 저항성은 필러의 평균 입경이 작고 미세 필러를 고밀도로 분산시켜 복합화한 hybrid 형 복합레진에서 높게 나타나는 경향을 보였다. 4. 주사전자현미경 관찰 결과, 마모면에서는 필러의 돌출, 마멸과 탈락 및 기질레진의 미세 균열 진전과 표면층의 박리 등이 관찰되었다.

• Journal of Biosystems Engineering
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• 제1권1호
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• pp.15-15
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• 1976

In analyzing the operational characteristics of a rice whitening machine, the internal radial pressure of the machine was measured using strain gage equipment. Changes in cylinder and feed screw configurations, screen type, cylinder speed and counter-pressure levels were examined to determine their impact on the quality and quantity of milled rice and the performance of the machine. The results are summarized as follows: 1. The internal radial pressure in the whitening chamber varied with the surface condition of the grain being processed. During the first or second pass through the machine, pressure was relatively low, reached a maximum after two to three passes with combinations I and II, three to six with combination III and then began to fall. 2. The pitch of the feed screw and the size of the feed gate opening which determine the rate of entry of grain into the whitening chamber, appeared to be the most important factor aff-::cting the degree of radial pressure, quality and quantity of milled rice and the efficiency of the machine. Using a feed screw with a wide pitch (4.8cm), radial pressure was relatively high and head rice recovery ratio \vere quite low. In this case capacity and machine effic?iency were much higher than obtained when using a feed screw with a narrow pitch (2.3cm). Very significant responses in radial pressure, head rice recovery rates and machine capacity were observed with changes in cylinder speed and counter-pressure levels when using the wide pitch feed screw. 3. The characteristics of the screen which surrounds the whitening chamber had an important effect on whitening efficiency. The existence of small protuberances on the original screen resulted in significant increases in both machine capacity and efficiency but without a significant decrease in head rice recovery or development of excessive radial pressure. Further work is required to determine the effects of screen surface conditions and the shape of the cylinderical steel roller on the rate of bran removal, machine efficiency and recovery rates. The size of the slotted perforations 0:1 the screen affects total milled rice recovery. The opening size on the original screen was fabricated to accommodate the round shape of Japonica rice varieties but was not suitable for the more slender Indica type. Milling Indica varieties with this screen resulted in a reduction in total milled rice recovery. 4. An increase in cylinder speed from 380 to 820 rpm produced a positive effect on head rice recovery for all machine combinations at every level of counter-pressure used in the tests. Head rice recovery was considerably lower at 380rpm using a wide screw pitch when compared to the results obtained at speeds from 600 to 820 r.p.m. The effects of cylinder speed On radial pressure, capacity and machine efficiency showed contrasting results, depending on the width of the feed screw pitch. With a narrow feed screw pitch (2.3cm), a direct proportional relationship was observed bet?ween cylinder speed and both radial pressure and machine efficiency. In contrast, using a 4.8 centimeter pitch feed roller produced a series of inverse relationships between the above variables. Based on the results of this study it is recommended when milling Indica type long grain rice varieties that the cylinder speed of the original machine be increased from 500-600 rmp up to a minimum of 800 rpm to obtain a greater abrasive effect between the grain and the screen. The pitch of the feed screw should be also reduced to decr?ease the level of internal radial pressure and to obtain higher machine efficiency and increased quality of milled rice with increased cylinder speeds. Further study on the interaction between cylinder speed and feed screw pitch is recommended. 5. An increase in the counter pressure level produced a negative effect On the head rice recovery with an increase in radial pressure, capacity, and machine efficiency over all combinations and at every level of cylinder speed. 6. Head rice recovery rates were conditioned primarily by the pressure inside the whitening chamber. According to the empirical cha racteristics curve developed in this study, the relationships of head rice recovery ($Y_h$) and machine capacity ($Y_c$/TEX>) to internal radial pressure ($X_p$) followed an inverse quadratic function and a linear function respectively: $$Y_h^\Delta=\frac{1}{{1.4383-0.2951X_p^\ast+0.1425X_p^{\ast\ast}}^2} , (R^2=0.98)$$$$Y_c^\Delta=-305.83+374.37X_p^{\ast\ast}, (R^2=0.88)$$The correlation between capacity and power consumption per unit of brown rice expressed in the following exponential function: $$Y_c^\Delta=1.63Y_c^{-0.7786^\{\ast\ast}, (R^2=0.94)$$These relationships indicate that when radial pressure increases above a certain range (1. 6 to 2.0 kg/$cm^2$ based On the results of the experiment) head ricerecovery decrea?ses in a quadratic relation with a inear increase in capacity but without any decrease in power consump tion per unit of brown rice. On the other hand, if radial pressure is below the range shown above, power consumption increases dramatically with a lin?ear decrease in capacity but without significant increases in head rice recovery. During the operation of a given whitening machine, the optimum radial pressure range or the correct capacity range should be selected by controlling the feed rate and/or counter-pressure keeping in mind the condition of the grain, particulary the hardness. It was observed that the total number of passes is related to radial pessure level, feed rate and counter-pressure level. The higher theradial pressure the fewer num?ber of pass required but with decreased head rice recovery. In particular, when using high feed rates, the total number of passes should be increased to more than three by reducing the counter-pressure level to avoid decreaseases in head rice recovery (less than 65 percent head rice recovery on the basis of brown rice) at every cylinder speed. 7. A rapid rise in grain temperature seemed to have a close relationship with the pressure generated inside the whitening chamber and, subsequently with head rice reco?very rates. The higher the rate of increase, the lower were the resulting head rice recoveries.

• Journal of Biosystems Engineering
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• 제1권1호
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• pp.17-48
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• 1976

In analyzing the operational characteristics of a rice whitening machine, the internal radial pressure of the machine was measured using strain gage equipment. Changes in cylinder and feed screw configurations, screen type, cylinder speed and counter-pressure levels were examined to determine their impact on the quality and quantity of milled rice and the performance of the machine. The results are summarized as follows: 1. The internal radial pressure in the whitening chamber varied with the surface condition of the grain being processed. During the first or second pass through the machine, pressure was relatively low, reached a maximum after two to three passes with combinations I and II, three to six with combination III and then began to fall. 2. The pitch of the feed screw and the size of the feed gate opening which determine the rate of entry of grain into the whitening chamber, appeared to be the most important factor aff-::cting the degree of radial pressure, quality and quantity of milled rice and the efficiency of the machine. Using a feed screw with a wide pitch (4.8cm), radial pressure was relatively high and head rice recovery ratio \vere quite low. In this case capacity and machine effic\ulcorneriency were much higher than obtained when using a feed screw with a narrow pitch (2.3cm). Very significant responses in radial pressure, head rice recovery rates and machine capacity were observed with changes in cylinder speed and counter-pressure levels when using the wide pitch feed screw. 3. The characteristics of the screen which surrounds the whitening chamber had an important effect on whitening efficiency. The existence of small protuberances on the original screen resulted in significant increases in both machine capacity and efficiency but without a significant decrease in head rice recovery or development of excessive radial pressure. Further work is required to determine the effects of screen surface conditions and the shape of the cylinderical steel roller on the rate of bran removal, machine efficiency and recovery rates. The size of the slotted perforations 0:1 the screen affects total milled rice recovery. The opening size on the original screen was fabricated to accommodate the round shape of Japonica rice varieties but was not suitable for the more slender Indica type. Milling Indica varieties with this screen resulted in a reduction in total milled rice recovery. 4. An increase in cylinder speed from 380 to 820 rpm produced a positive effect on head rice recovery for all machine combinations at every level of counter-pressure used in the tests. Head rice recovery was considerably lower at 380rpm using a wide screw pitch when compared to the results obtained at speeds from 600 to 820 r.p.m. The effects of cylinder speed On radial pressure, capacity and machine efficiency showed contrasting results, depending on the width of the feed screw pitch. With a narrow feed screw pitch (2.3cm), a direct proportional relationship was observed bet\ulcornerween cylinder speed and both radial pressure and machine efficiency. In contrast, using a 4.8 centimeter pitch feed roller produced a series of inverse relationships between the above variables. Based on the results of this study it is recommended when milling Indica type long grain rice varieties that the cylinder speed of the original machine be increased from 500-600 rmp up to a minimum of 800 rpm to obtain a greater abrasive effect between the grain and the screen. The pitch of the feed screw should be also reduced to decr\ulcornerease the level of internal radial pressure and to obtain higher machine efficiency and increased quality of milled rice with increased cylinder speeds. Further study on the interaction between cylinder speed and feed screw pitch is recommended. 5. An increase in the counter pressure level produced a negative effect On the head rice recovery with an increase in radial pressure, capacity, and machine efficiency over all combinations and at every level of cylinder speed. 6. Head rice recovery rates were conditioned primarily by the pressure inside the whitening chamber. According to the empirical cha racteristics curve developed in this study, the relationships of head rice recovery ($Y_h$) and machine capacity ($Y_c$/TEX>) to internal radial pressure ($X_p$) followed an inverse quadratic function and a linear function respectively: $$Y_h^\Delta=\frac{1}{{1.4383-0.2951X_p^\ast+0.1425X_p^{\ast\ast}}^2} , (R^2=0.98)$$ $$Y_c^\Delta=-305.83+374.37X_p^{\ast\ast}, (R^2=0.88)$$ The correlation between capacity and power consumption per unit of brown rice expressed in the following exponential function: $$Y_c^\Delta=1.63Y_c^{-0.7786^\{\ast\ast}, (R^2=0.94)$$ These relationships indicate that when radial pressure increases above a certain range (1. 6 to 2.0 kg/$cm^2$ based On the results of the experiment) head ricerecovery decrea\ulcornerses in a quadratic relation with a inear increase in capacity but without any decrease in power consump tion per unit of brown rice. On the other hand, if radial pressure is below the range shown above, power consumption increases dramatically with a lin\ulcornerear decrease in capacity but without significant increases in head rice recovery. During the operation of a given whitening machine, the optimum radial pressure range or the correct capacity range should be selected by controlling the feed rate and/or counter-pressure keeping in mind the condition of the grain, particulary the hardness. It was observed that the total number of passes is related to radial pessure level, feed rate and counter-pressure level. The higher theradial pressure the fewer num\ulcornerber of pass required but with decreased head rice recovery. In particular, when using high feed rates, the total number of passes should be increased to more than three by reducing the counter-pressure level to avoid decreaseases in head rice recovery (less than 65 percent head rice recovery on the basis of brown rice) at every cylinder speed. 7. A rapid rise in grain temperature seemed to have a close relationship with the pressure generated inside the whitening chamber and, subsequently with head rice reco\ulcornervery rates. The higher the rate of increase, the lower were the resulting head rice recoveries.

• 암석학회지
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• 제21권2호
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• pp.263-275
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• 2012

경기육괴 중부인 포천지역과 양주지역에는 국내 주요 암석자원의 하나인 대보 흑운모화강암이 각각 분포한다. 이 연구의 주 목적은 상기한 두 지역의 흑운모화강암류의 입도, 암색, 광물조성, 물성 및 열극체계 등의 고유한 특성을 밝히는 데 있다. 포천지역의 흑운모화강암(PG)는 조립질과 담회색, 양주지역의 흑운모화강암(YG)은 중립질-조립질과 회색-담회색으로 대표된다. 구성광물의 모우드에서 주성분인 석영+알칼리장석+사장석은 PG에서, 부성분인 흑운모는 YG에서 증가하며, 이러한 광물함유량 차이로 인하여 PG가 YG보다 밝은 회백색을 띠게 된다. 물성 변화 및 특성에서, 비중은 PG보다 YG에서 약간 증가하며 이러한 차이는 전자보다 후자에서 주성분 광물에 비해 높은 비중을 갖는 흑운모의 함량 증가로 볼 수 있다. PG와 YG의 흡수율과 공극률은 0.33%와 0.86%를 가져 동일한 값을 각각 보여준다. 물성간의 상관도에서, 공극률 대 비중은 완만한 부의 경향, 공극률 대 흡수율은 뚜렷한 정의 경향을 보여준다. 압축 및 인장강도는 PG가 1,775 $kg/cm^2$ 와 87 $kg/cm^2$ 그리고 YG가 1,647 $kg/cm^2$와 79 $kg/cm^2$를 각각 가져 모두 PG에서 증가한다. 이러한 강도특성은 내재하는 암석조직에 기인될 수 있다. 마모경도는 PG에서 약간 증가하며, 이러한 마모특성은 다른 주성분 광물에 비하여 보다 높은 경도를 갖는 석영의 함량증가에 기인될 수 있다. 한편 포천 및 양주지역에서 발달하는 단열 조의 방향성에 대하여 국내 중생대 화강암류에서 발달하는 수직 결의 방향성과 비교하였다. 중첩도를 통하여, 단열 조와 상기한 수직 결 사이의 분포형태가 부합된다는 사실은 국내의 중생대 화강암류에 내재하는 미세균열 계는 경기육괴 중부의 대보 흑운모화강암류에서도 발달함을 시사한다. 상기한 두 지역간의 단열형태 특성을 보여주는 도면에서, PG에서는 규격석 그리고 YG에서는 비규격석이 보다 많이 산출될 잠재성이 있다.