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Volume 25, Issue 7
Displaying 1-6 of 6 articles from this issue
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Tohru Takeda, Kazumi Minagawa1978 Volume 25 Issue 7 Pages 213-218
Published: November 25, 1978
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSMolten copper was atomized by using a conical water jet in air and nitrogen to examine effects of atmosphere on properties of powders. With increasing water pressure of more than 100 kg/cm2, geometrical standard deviation σg for particle size distribution increases in nitrogen, but does not change in air. Oxygen contents of powders atomized in nitrogen and air are 0.04 and 0.12 wt%, respectively. Particles are composed of lots of fine spheres which may come to a critical size in the breakup of droplets. The relationship between critical size d and surface tension γ is given by dair/dN2=γair/γN2=0.89. Atomizing at the temperature range of 1200-1270°C under a water pressure of 135 kg/cm2 with a flow-rate of 320 1/min in nitrogen atmosphere, the apparent density attains a minimum, as low as 2.0 g/cm3 for 145/200 mesh powder, and σg a maximum. Compactibility of this kind of powder is improved by annealing at 500-600°C for 1 hr. in hydrogen. Compacts pressed at 1 t/cm2 show a density ratio of 65% and a rattler's value of 1.5%.View full abstractDownload PDF (2558K) -
Kiyoaki Akechi, Zenshiro Hara, Tetsuo Sakai, Masao Itabashi1978 Volume 25 Issue 7 Pages 219-222
Published: November 25, 1978
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe sintering process of iron powder during flash resistance-sintering was analyzed on the basis of temperature and electric-resistance changes of the compacts. The temperature change for very short time was estimated from the power input value at every moment. The estimated temperature was compared to the compact surface temperature measured by an infrascope, and it was confirmed that the difference between both the temperatures was rather small, and decreased with an increase of set-up current level. From the analysis, it was shown that in the resistance-sintering of metal powder, heat generated at an early stage is mostly due to the contact resistance, between particles, and its fraction decreases as the sintering time proceeds. The rate of decrease depends upon the properties of the metal powder and resistance-sintering conditions.View full abstractDownload PDF (2557K) -
Kazuhiko Majima, Tatsuro Isomoto, Hiroyasu Mitani1978 Volume 25 Issue 7 Pages 223-228
Published: November 25, 1978
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSIn this experiment, we tried the production of Al-19.6 wt% Si alloy powders having structures frozen by an extremely rapid cooling velocity, and examined its sintering characteristics by means of dilatometric method.
The results obtained were as follows:
(1) From the relationship between the dendrite arm spacing and its cooling rate, it was assumed that molten drops of Al-19.6 wt%Si alloy was frozen into powders with the cooling rate of about 6×105°C/see, and showed the structure of well defined primary Si, the size of about 1μm.
(2) The Al-19.6 wt%Si alloy powder compacts showed fairly good sintering charactersitics from about 560°C during heating process, and the size of primary Si was of only 5 Fpm even after the sintering at 570°C for 1 hr.View full abstractDownload PDF (4386K) -
Yoji Awano, Michio Watanabe, Atsushi Danno, Kazuhiko Ito, Takashi Kimu ...1978 Volume 25 Issue 7 Pages 229-235
Published: November 25, 1978
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSIn order to study whether transient cracks can be re-welded in P/M forging, ring specimens machined from closed-upset 4600-0.37%C preforms with re-sealed cracks but no traces in the circumference were subjected to a squeezing test and an observation of microstructures and fracture surfaces. The factors influencing re-welding of transient cracks were also investigated in tension test of P/M forged Fe and Fe-0.50%C preforms with previously drilled holes of 0.5 or 1 mm diameter, instead of unintentional transient cracks.
It was found that some transient cracks had been re-welded, in consideration of the facts that radial crushing strength of closed-upset specimens with no traces of visible cracks was nearly equal to or larger than that of hot coined ones and the SEM of the fracture surfaces showed a dimple pattern. The drill holes in Fe specimens did not re-welded owing to surface oxidation. Addition of 0.50%C eliminated the deleterious effect of drill holes on the tensile properties. It was also confirmed from the observation of microstructures and fracture surfaces that the drill holes in the specimens had been re-welded. Alloying of carbon in preforms was found to play an important role in re-welding.View full abstractDownload PDF (6045K) -
Hiroshi Yamamoto, Toranosuke Kawaguchi, Mitsuru Nagakura1978 Volume 25 Issue 7 Pages 236-241
Published: November 25, 1978
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSMany reports have been issued about ferrite permanent magnets as well as their magnetism. limiting in Ba and Sr system ferrites.
The present experiment has been carried out to investigate the optimum condition for preparing isotropic Ca ferrite magnets having the best magnetic and physical properties. Compositions were chosen according to the fomula (CaO⋅nFe2O3)100-x(La2O3)x and (CaO1-ySrOy⋅6Fe2O3)97 (La2O3)3, where x was varied between 0 and 4.0, n was varied between 5.5 and 6.25, and y was varied between 0 and 1.0.
The results are as follows; 1) The best magnetic properties of (CaO⋅nFe2O3)100-x(La2O3)x compounds were obtained in n=6 and x=3.2) To obtain magnets having (BH)max more than 1.0 MG⋅e, semi-sintering at the temperature above 1200°C is required. 3) Curie temperature of (CaO⋅6Fe2O3)100-x(La2O3)x compounds increases with the increase of x value. 4) The magnetic properties of (CaO1-ySrOy⋅6Fe2O3)97(La2O3)3 magnet are improved by substitution of SrO for CaO.View full abstractDownload PDF (2825K) -
Hiroshi Yamamoto, Toranosuke Kawaguchi, Mitsuru Nagakura, Yasuhito Kob ...1978 Volume 25 Issue 7 Pages 242-248
Published: November 25, 1978
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSThe present experiment was carried out to investigate the effect of SrO substitution on magnetic and physical properties of anisotropic calcium ferrite magnets. Compositions were chosen according to the formula (CaO1-ySrOy⋅6Fe2O3)97(La2O3)3, where y was varried between 0 and 1.0.
The results are summarized in the following; The magnetic properties of (CaO1-ySrOy⋅6Fe2O3)97(La2O3)3 magnets were apparently improved by substitution of SrO for a part of component oxides. Moreover coercive force Curie temperature, anisotropy constant and anisotropy filed increased with the increase ofy value. Ca-Sr system ferrite magnets having the value of (BH)max. 3.5-3.9 MG⋅Oe could be prepared by the conventional manufacturing technique.View full abstractDownload PDF (2839K)
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