• 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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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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A Study on the Heat Treatment Effect of SCM Series Gear (SCM계 기어의 열처리 효과에 관한 연구)

  • Ahn, Min-Ju;Ahn, In-Hyo;Zhang, Qi;Lyu, Sung-Ki
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.10 no.2
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    • pp.84-89
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    • 2011
  • This paper studied the carburizing of chromium molybdenum steel which the heat treatment effect of gear geometric tolerance, OPD, Runout, the surface hardness, the maximum hardness, the core hardness and the bending fatigue strength were investigated. Firstly, the deformation is observed, and the results of circularity, squareness, OPD and Runout of SCM822, SCM425, and SCM415 are obtained in order. Secondly, in order to investigate the gear hardness, the surface hardness, the maximum hardness and the core hardness of SCM822, SCM425, and SCM415 are obtained; and the surface hardness of SCM822 is about 10% higher than SCM415's, and about 3% higher than SCM425's. Thirdly, the fatigue strength of SCM822 is about 10% higher than SCM415's, and about 7% higher than SCM425's in the fatigue test results. At last, for the purpose of the minimum deformation of heat treatment, and also the improvement of fatigue strength, the best gear material is SCM822 in this test.

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 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.

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.

The Effect of Midsole Hardness of Running Shoe on Fatigue of Lower Extremity Muscles and Impact Force (런닝화의 미드솔 경도가 하지 근육의 피로와 충격력에 미치는 영향)

  • Kim, Eonho;Lim, Kyuchan;Cho, Seunghyun;Lee, Kikwang
    • Korean Journal of Sport Biomechanics
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    • v.29 no.3
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    • pp.167-172
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    • 2019
  • Objective: The aim of this study was to investigate the effect of midsole hardness of running shoe on muscle fatigue and impact force during distance running. Method: Ten healthy college recreational runners who were performing distance running at least three times a week participated in this experiment. They were asked to run for 15 minutes in the treadmill at 10 km/h with running shoes having three different types of midsole hardness (Soft, Medium, Hard). EMG signal and insole pressure were collected during the first and last one minute for each running trials. Data were analyzed using a one-way analysis of variance (ANOVA) with repeated measures. Results: Midsole hardness did not affect the consistency of stride length. For the median frequency of the EMG signal, only VL was affected by midsole hardness; that of medium was greater than other midsoles (p<.05). The loading rate of impact forces increased by midsole hardness (p<.01). Conclusion: Although soft midsole could attenuate impact forces at heel contact, it might have a negative effect on the fatigue of muscle which could decelerate the body after heel contact. Therefore, it is necessary to select the optimum hardness of midsole carefully for both reduction impact forces and muscle fatigue.

Characteristics of Hardness and Wear-Resistance of Plasma-Nitrided and Nitrocarburized Carbon Steels (플라즈마질화 및 침질탄화처리한 탄소강의 경도와 내마모특성)

  • Kim, M.K.;Jung, B.H.;Park, H.S.;Lee, B.C.;Shin, S.H.;Lee, J.S.
    • Journal of the Korean Society for Heat Treatment
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    • v.12 no.2
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    • pp.166-173
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    • 1999
  • Commercial carbon steels containing 0.2~0.55 wt.----C were plasma-nitrided or plasma nitrocarburized at $550^{\circ}C$ for 21.6Ks using $H_2-N_2$ or $H_2-N_2$-CO mixed gas respectively. The characteristics of hardening and wear-resistance of each treatment were studied and compared. And also microstructure of nitrided layer and nitrides formed in compound layer near surface were studied. All plasma-nitrided steels investigated showed remarkable increase of surface hardness with the increase of carbon content. But nitrocarburized steels resulted in higher surface-hardness than plasma-nitrided steels, which means that nitrocarburized has higher surface-hardening effect. Plasma-nitrided steels showed hardness increase in through-thickness direction near surface. And also nitrocarburized steels showed similar hardness distribution in through-thickness direction to that of plasma-nitrided steel. However, nitrocarburized steels had higher cross-sectional maximum-hardness than plasma-nitrided steels as much as 100Hv. Wear test showed that the amount of specific wear was reduced by both plasma-nitriding and nitrocarburized, showing that the amount of specific wear was not related to the hardness. But non-treated specimen showed that the amount of specific wear was related to the hardness.

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