Journal of Japan Foundry Engineering Society
Online ISSN : 2185-5374
Print ISSN : 1342-0429
ISSN-L : 1342-0429
Volume 82, Issue 2
Displaying 1-5 of 5 articles from this issue
  • Shuxin Dong, Yasushi Iwata, Hiroshi Hohjo, Hiroaki Iwahori, Takashi Ya ...
    2010 Volume 82 Issue 2 Pages 79-85
    Published: February 25, 2010
    Released on J-STAGE: April 21, 2015
    JOURNAL FREE ACCESS
      The occurrence mechanism and the occurrence criterion of cracks in shell molds during aluminum alloy casting were elucidated. Cylindrical shell molds made of silica sand break easily when filled with aluminum alloy melt. The breaking mechanism can be considered as follows. The immediate inner surface of the shell mold undergoes rapid temperature rise from sudden heating by the melt and attempts to expand. This thermal expansion is restrained by the other part of the mold that is still low in temperature. Consequently, compressive stress in the area near the inner surface and tensile stress in the area near the outer surface develop respectively, causing the shell mold to break when the tensile stress exceeds the tensile strength of the shell mold. With some parts of the cylindrical shell mold cut to a thinner thickness, a large tensile stress occurs at the outer surface of the thinner part and a crack is formed in a shorter time after aluminum alloy melt has filled. The criterion for the occurrence of cracks in shell molds can be described by the fracture stress-effective volume relation based on the Weibull's statistical method, which is utilized for the strength evaluation of brittle materials. The fracture stress-effective volume relation of the present shell mold was derived from tensile test results to predict the occurrence of cracks in shell molds.
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  • Naoto Shiraki, Toshitake Kanno
    2010 Volume 82 Issue 2 Pages 86-91
    Published: February 25, 2010
    Released on J-STAGE: April 21, 2015
    JOURNAL FREE ACCESS
      The purpose of this study is to investigate the effects of the distribution of graphite nodules on characteristics of fatigue crack propagation in spheroidal graphite cast iron where carbon content and the distribution of graphite nodules are changed. As specimens, spheroidal graphite cast irons with 3.0, 3.2, 3.4, 3.6 and 3.8mass% carbon content were produced respectively (C3.0%, C3.2%, C3.4%, C3.6% and C3.8% material). The mean diameter of the graphite nodules decreases as the carbon content increases, and the number of graphite nodules per unit area increases. The fatigue crack propagation test was conformed to ASTM standards. Stress ratio R was 0.1, and the specimen used was the 1CT type of 12.5mm in thickness. The test was carried out at room temperature atr the humidity of 40%. The relationship between the characteristics of fatigue crack propagation and crack closure produced on the fracture surface was also investigated.
      Threshold stress intensity factor range, ΔKth was almost constant in C3.0 to C3.6% materials, but in the C3.8% material in which the graphite was close to each other, ΔKth decreased. In all materials, fatigue crack propagated connecting the graphite nodules. In the C3.8% material, the spacing between graphite nodules was small. Therefore, fatigue crack propagation rate increased in comparison with other materials, thereby decreasing the ΔKth of the C3.8% material as a result.
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  • Shuji Tada, Hiroyuki Nakayama, Toshiyuki Nishio, Keizo Kobayashi
    2010 Volume 82 Issue 2 Pages 92-96
    Published: February 25, 2010
    Released on J-STAGE: April 21, 2015
    JOURNAL FREE ACCESS
      Several frozen molds were produced from various types of sand, and the effects of sand characteristics such as material, grain size, and grain shape on the cooling behavior of lead-free bismuth bronze cast into the frozen maids were examined. Basically, the frozen mold enabled lead-free bismuth bronze to provide faster cooling rates compared with conventional green sand molds. In addition, the cooling potential of frozen mold was improved by the following sand particle properties; higher thermal conductivity, greater grain size, and spherical shapeness. Based on the above results, a heat transfer model in the frozen mold was developed. In the frozen mold, ice near the mold surface contacting molten metal thaws immediately, and changes to vapor just after pouring which then blows out from the mold removing the heat from the casting. Finally, the casting is cooled down through the heat transfer between sand particles when water disappears in the mold. This model suggests that it is important for the frozen mold to have good air permeability to enhance its ability as a cold source. A finer structure was successfully produced in the lead-free bismuth bronze casting by using a frozen mold consisting of coarse spherical alumina grain, which provides the fastest cooling rate to castings.
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  • Hiroyuki Nakayama, Toshiyuki Nishio, Keizo Kobayashi
    2010 Volume 82 Issue 2 Pages 97-102
    Published: February 25, 2010
    Released on J-STAGE: April 21, 2015
    JOURNAL FREE ACCESS
      Behavior of bismuth in the solidification process of lead-free bronze and effects of bismuth on the mechanical properties of the castings were studied. Bismuth existed at the finally solidified area in the bronze, and filled pores produced by the shrinkage of the bronze. During solidification, the bronze expanded according to the expansion of the bismuth. This volume expansion remarkedly appeared when the amount of bismuth addition exceeded that of pores. The tensile strength of the bronze decreased with increasing bismuth content due to the local stress around the bismuth in the casting. The decrease in tensile strength by bismuth addition reduced by the refinement of the bismuth size, because the decrease in the bismuth size reduces the stress field in the vicinity of the bismuth.
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