• Title, Summary, Keyword: hardness

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Experimental Studies on the Improving Surface Hardness of Dental Stone (치과용(齒科用) 경석고(硬石膏) 의 표면경도(表面硬度) 강화(强化)에 관(關)한 실험적(實驗的) 연구(硏究))

  • Kim, Chang-Whe
    • The Journal of Korean Academy of Prosthodontics
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    • v.9 no.1
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    • pp.23-27
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    • 1969
  • The purpose of this studies is to determine the surface hardness of dental stone and to investigate the methods which increase the surface hardness of dental stone using the dissolved solution of various synthetic resin, the obtained results of hardness value calculated Rockwell Hardness Number by means of Rockwell Hardness Tester. 1) In this experiment, 10% polystyrene dissolved in 100cc amylacetate is excellent solution which provides the surface hardness of dental stone after setting of specimen, and there is no effective way that stone specimen is immersed into polystyrene in amylacetate, polystyrene in benzene and polystyrene in butylacetate above 1 hour. 2) When the stone specimen is immersed into acrylic resin in benzene and melamin resin in amylacetate at least 1 hour to 3 hours, the hardening effect of stone surface is valuable. 3) The stone specimen immersing into urea resin in butylacetate, the surface hardness of the stone specimen decreased within 1 hour, but increased after 3 houre. 4) For the separating medium, the easyfoil is superior to the olive oil in the aspect of improving the hardening effect of the immersed specimen.

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The Effect of Test Variables on the Accuracy of Equo-Tip Hardness (Equo-Tip 경도값에 미치는 실험변수의 영향)

  • Nahm, S.H.;Jeon, S.B.;Kim, J.J.
    • Journal of the Korean Society for Heat Treatment
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    • v.3 no.2
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    • pp.32-36
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    • 1990
  • For the accurate measurements of hardness in a material, it is necessary to have a thorough understanding of the effects of test variables on the accuracy of hardness value. For the rebound hardness test, major test variables are the radius of hammer ball tip, type of backing materials, size and roughness of the specimen. In this study, effects of these variables on Equo-Tip hardness value were investigated. Hardness measurements were carried out using WC balls with various sizes of worn-ot zone. The sample materials chosen for the experiments were commercial standard hardness blocks and SM45C steel bars subjected to either normalization or quench and temper treatments. As backing materials, aluminum, steel and rubber plates were used in all the experiments. Experimental results show that for the accurate measurements of Equo-tip hardness, it is necessary to use the hammer ball with a worn-out zone parameter of less than 0.23, and the recommended minimum thickness and width of the specimen are 25mm and 70mm, respectively. Further for the surface preparation, the specimens need to be polished with an emery paper of No. 400 or finer, and for the backing matrials, it is recommended to use steels or rubbers.

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Prediction of the % Hardness Curve of Cellulose Acetate Mono Filters (셀룰로오스 아세테이트 모노 필터의 경도 예측)

  • Kim Jong-Yeol;Kim Soo-Ho;Shin Chang-Ho;Park Jin-Won;Lim Sung-Jin;Kim Chung-Ryul;Rhee Moon-Soo
    • Journal of the Korean Society of Tobacco Science
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    • v.28 no.1
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    • pp.43-50
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    • 2006
  • The objective of the present study is to induct the regression equation for the hardness prediction of cellulose acetate filter which was manufactured by the domestic cellulose acetate tow manufacturer. As a result of our study, the hardness of filter was increased with increasing the plasticizer content and packing density as major factors affecting to the filter hardness. As a result which was obtained by the three dimensional response surface methodology in STATISTIC A program, the hardness prediction value well fitted with experiment result on the high plasticizer content. To make up for the this equation, the new modified fraction of solid factors which was contained the mono denier factor was introduced to the hardness prediction equation, and this third regression equation which was sufficient for the wide plasticizer content, was obtained by the three dimensional response surface methodology in STATISTICA. This results indicated that the third regression equation which was obtained this study was applicable for the hardness prediction of cellulose acetate filter which was manufactured by the domestic cellulose acetate tow manufacturer.

Analysis of Sliding Wear Properties for Aluminum Alloy According to the Hardness Values of the Mating Tool Steel (알루미늄 합금의 미끄럼마모 특성에 미치는 상대재 경도의 영향)

  • Lee, Han-Young;Cho, Yong-Jae;Kim, Tae-Jun;Park, Won-Kyu
    • Tribology and Lubricants
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    • v.26 no.2
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    • pp.105-110
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    • 2010
  • In order to investigate the wear behavior of aluminum alloy depended on different hardness of the mating tool steel, sliding wear tests were conducted. It was found that the wear characteristics pattern of aluminum alloy for sliding speed was not affected by the hardness of the mating tool steel. However, the effects of the hardness of the mating tool steel exhibited only in relatively low sliding speed ranges. At these ranges, the wear rate of aluminum alloy decreased when increasing the hardness of the mating tool steel. This was attributed by the fact that $Al_2O_3$ particles released from the aluminum worn surface were crushed and embedded on the mating worn surface with high hardness level. At the high sliding speed ranges, wear of aluminum alloy was hardly occurred by the formation of thick $Al_2O_3$ film on the worn surface, regardless of the hardness of the mating tool steel.

Effects of Mo, V addition on Linear Thermal Expansion Coefficient and Hardness of Low Thermal Expansion Cast Steel (주강계 저열팽창 주조합금의 열팽창 계수와 경도에 미치는 Mo, V 첨가의 영향)

  • Kim, Young-Han;Yoon, Eui-Park;Moon, Byoung-Moon;Hong, Young-Myung
    • Journal of Korea Foundry Society
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    • v.18 no.5
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    • pp.467-473
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    • 1998
  • For enhancing the mechanical properties of LTE (low thermal expansion) cast steel, systematic researches have been carried out. The effects of alloying elements such as vanadium, molybdenum and carbon on the hardness and linear thermal expansion coefficient were investigated. In the range of $0.5{\sim}2.3\;wt%$ carbon, addition of 1.73 wt% carbon caused hardness increase due to the formation of eutectic carbide having high hardness but over the range of 1.73 wt% carbon, hardness was decreased. Thermal expansion coefficient increases with carbon contents. In the LTE cast steel containing 0.6 wt% carbon, hardness increased up to 1.96 wt% vanadium addition. But over the range of 1.96 wt% vanadium hardness was decreased by coarse eutectic carbide. Thermal expansion coefficient of LTE cast steel containing 0.6 wt%carbon moderately increased with increasing vanadium contents. There was no significant variation of hardness and thermal expansion coefficient according to molybdenum content in LTE cast steel.

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Surface Properties of Fancy Veneer Overlaid Medium Density Fiberboard by Coating (도장처리에 의한 무늬단판 오버레이 MDF의 표면물성)

  • Kim, Jong-In;Park, Jong-Young;Doh, Geum-Hyun;Joung, Doo-Jin;Park, Sang-Bum
    • Journal of the Korea Furniture Society
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    • v.18 no.1
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    • pp.13-19
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    • 2007
  • The influences of coating on oak veneer overlaid Medium Density Fiberboard (MDF) were evaluated. The hardness of 9mm-MDF by hardness test were increased about 28% with coating on MDF and the more increased hardness of 31% with oak veneer overlaid MDF. The hardness of veneer overlaid MDF increased with increment of the veneer thickness and that of overlaid MDF showed the higher hardness compared to non-overlaid MDF. The optimum moisture content in terms of the hardness of panels MDF was in the range of 7% to 10% and the hardness was decreased with increasing of the moisture content. Any cracks were not overlaid coated on the MDF but the cracks were observed on the overlaid MDF after Soak under Vacuum Dry 10-cycle. The thicker veneer-overlaid MDF showed more cracks.

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Analysis of Sliding Wear Behavior of Mild Steel According to Hardness of Dissimilar Mating Materials (이종 상대재 경도에 따른 철강재료의 미끄럼 마모 특성 해석)

  • Lee, Han-Young
    • Tribology and Lubricants
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    • v.32 no.6
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    • pp.195-200
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    • 2016
  • This study examines the wear behavior of mild steel pins mated against alloyed tool steel discs in a pin-on-disc type sliding test machine and provides specific clarification regarding the effects of disc hardness on the wear behavior of a mating mild steel pin. The analysis confirms these effects through the observation of differences in the wear rates of the mild steel pins at low sliding speed ranges. These differences occur even though the hardness of the mating disc does not affect the wear characteristic curve patterns for the sliding speeds, regardless of the wear regime. In the running-in wear regime, increasing the hardness of the mating disc results in a decrease in the wear rates of the mild steel pins at low sliding speed ranges. However, in the steady-state wear region, the wear rate of a pin mated against the 42DISC is greater than the wear rate of a pin mated against the 30DISC, which has a lower hardness value. This means that the tribochemical reactivity of the mating disc, which is based on hardness value, influences the wear behavior of mild steel at low sliding speed ranges. In particular, oxides with higher oxygen contents, such as $Fe_2O_3$ oxides, form predominantly on the worn surface of the 42DISC. On the contrary, the wear behavior of mild steel pins at high sliding speed ranges is nearly unaffected by the hardness of the mating disc.

Development of an Automatic Soil Hardness Measuring System Mountable on Agricultural Tractors (트랙터 부착형 자동 토양경도 측정 시스템 개발)

  • 이현동;김기대;김찬수;김성환
    • Journal of Biosystems Engineering
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    • v.27 no.6
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    • pp.537-546
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    • 2002
  • In this study an automatic soil hardness measuring system mountable on agricultural tractors was developed to improve the accuracy of manual soil hardness testers by a constant penetrating rate, right direction of the cone-penetrometer and the isolation of vibration from the operator. This was necessary to supply similar experimental condition for performance test of new model and comparative experiment. The results of the study are summaried as follows; 1. The system consisted of a sensing part of soil hardness, a driving part of the measuring system and an attaching part between the tractor and the measuring system. 2. The allowable limit value of the system developed was set to 392N to protect from breaking the serve motor and the coupling used in this system. 3. The driving shaft penetrated into soil by 0.3m to measure soil hardness. The soil hardness was measured at the depth of 0.3m from the soil surface but the penetrating work was stopped and the driving shaft was pulled out to protect the system when the value of the soil hardness was too big on foreign substances like stones or straws. 4. Two values measured by automatic measuring system developed in this research and manual penetrometer were compared by statistics hypothesis testing method. When two people measured the soil hardness at the depth of 0.1 and 0.15m by manual cone penetrometer, there was no relationship between two values by two people but the values at the same depths by automatic measuring system developed showed similarity. The automatic system, therefore, developed in this research was proper for measuring soil hardness.

Effects os Cold Drawing Ratio on the Hardness of Inconel 718 Wire (Inconel 718 선재의 경도에 미치는 냉간신선가공의영향)

  • Jeong, Yong-Kwon;Jo, Chang-Yong;Jung, Byong-Ho;Kim, In-Bae
    • Korean Journal of Materials Research
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    • v.8 no.4
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    • pp.354-358
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    • 1998
  • Effect of cold drawing ratio and aging time on the hardness of lnconel 718 wire aged at 11l6K were investi¬gated by hardness measurement and scanning & transmission electron microscopy. Hardness which was 245Hv in as¬solution treated condition increased very rapidly to 450Hv as cold drawing ratio increased to 50%. The hardness in the early stage of aging was increased by the precipitation of $\gamma^{'}$ and $\gamma^{'}$ phases and after the peak hardness, the hardness was decreased by the transformation of $\gamma^{'}$ phase to $\delta$ phase. The time to reach peak hardness during aging appeared to be reduced with the increase of cold drawing ratio, and those times were 30, 10, and 5 minutes for 0, 30 and 50% cold drawn materials, respectively. For the 50% cold drawn material. $\gamma^{'}$ and $\gamma^{'}$ were precipitated by aging for 5 minutes at 1116K. The hardness in the same material was largely decreased under the initial hardness by the recrystallization.

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Hardness and microstructural changes by cooling rate and holding time during porcelain firing of a multi-purpose dental gold alloy (다목적용 치과용 금합금의 소성 시 냉각속도와 계류시간에 따른 경도와 미세구조의 변화)

  • Cho, Mi-Hyang
    • The Journal of Korean Academy of Dental Technology
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    • v.33 no.4
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    • pp.271-281
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    • 2011
  • Purpose: The aim of this study is to investigate the changes in hardness and microstructure of a dental multipurpose alloy after simulated complete firing with controlled cooling rate and holding time by characterizing the changes in hardness and microstructure after simulated firing with various cooling rates and holding times. Methods: Before hardness testing, the specimens were solution treated and then were rapidly quenched into ice brine. The specimens were completely fired in furnace. Hardness measurements were made using a Vickers microhardness tester. The specimens were examined at 15 kV using a field emission scanning electron microscope. Results: The maximum hardness value was obtained at stage 0 after simulated firing with various cooling rates (quick cooling, stage 0, stage 1, stage 2, stage 3). By the repetitive firing, the hardness of the tested alloy decreased gradually. By holding the specimen at $500^{\circ}C$ for 10-20min after simulated firing, the hardness increased apparently. However, to hold the alloy for long periods of time in the relatively high temperature after simulated firing resulted in the formation of thick oxidation layer. The oxide film formed on the surface of the alloy after simulated complete firing with controlled cooling rate, which was mainly composed of O and Zn. Conclusion: It is reasonable to hold the alloy at $500^{\circ}C$ for 10-20min after complete firing in other to improve the final hardness of the alloy.