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Volume 32, Issue 11
Displaying 1-5 of 5 articles from this issue
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Midori Otani1963 Volume 32 Issue 11 Pages 1031-1039
Published: November 25, 1963
Released on J-STAGE: August 05, 2011
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Tetsugoro Muramoto1963 Volume 32 Issue 11 Pages 1040-1046
Published: November 25, 1963
Released on J-STAGE: August 05, 2011
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Keizo Ishizaki1963 Volume 32 Issue 11 Pages 1047-1053
Published: November 25, 1963
Released on J-STAGE: August 05, 2011
JOURNAL FREE ACCESSFor the measurement of surface tension by the conventional drop weight method, the wettability of the rod to a liquid drop is not taken into account. When, however, the contact angle is comparatively great and the rod is less wettable to the liquid the wettablity of the rod is naturally expected to have an influence on the falling phenomenon of the drop
When the soap bubble, whose contact angle is 90 degrees, is adhering to the apex of a cone, whose base angle is a, the adhesive force F of the bubble to the cone is expressed by
πdγcosα-1/4⋅πd2P=F (1)
where d; diameter of contact circle of soap bubble
γ; surface tension of soap bubble
P; internal pressure of soap bubble
Assuming P is constant, F and d can be expressed as a quadratic curve, with F attaining a maximum under the following condition,
Fmax=πdγ/2⋅cosα (2)
When the soap bubble is exposed to a wind, the adhesive force F will increase against the wind pressure with a decrease of diameter d up to the above value ; but when d becomes smaller than the above value, F will begin to diminish until the bubble will be fast blown off from the apex of the cone. At Fmax, one of the principal values of curvature near the contact line becomes zero.
If this is applied to a molten droplet adhering to a cone, whose base angle is β, with contact angle θ0, the following equation can be obtained:
Fmax=πdγ/2⋅sin(β+θ0) (3)
The point of zero curvature in the profile of the droplet under gravity corresponds to an inflection point of the curve. In the case of a very small droplet adhering to a relatively big cone, the droplet grows up until the horizontal circle intersecting the inflection point coincides with the contact circle of the droplet, when gravity is equal to adhesive force of the droplet.
It was suggested that a possible change of the melting tip of the electrode from flat to conical profile might be an influencial factor in the transfer transition mechanism of droplet from drop to spray in MIG weldingView full abstractDownload PDF (2929K) -
Takashi Nakamura, Masanobu Hamasaki, Sadao Obokata1963 Volume 32 Issue 11 Pages 1054-1058
Published: November 25, 1963
Released on J-STAGE: August 05, 2011
JOURNAL FREE ACCESSGenerally, in spot welding of galvanized sheet, it is believed that better conditions than in welding of bare sheet are necessary, and that bare sheet sometime requires 300-400% of welding current.
We think that the difficulty of resistance welding of galvanized sheet is due to the reduction of the current density, by which the heat generation was decreased. As the cause, the following two can be considered:
i) Microscopically enlard area depending on softness of zinc coating. This means less contact resistance.
ii) Macroscopically enlarged area by spreading of fused zinc depending on the low melting point. On the basis of such consideration and some experimental demonstration, we could succeed in getting reliable weld even under lower class welding conditions, by using a low inertia holder. (See Table 3 and Fig. 11)
However, as the number of welding spots increases, nugget gradually becomes hard to form owing to the pick-up of zinc coating (even in such a case considerable shear strength can be obtained).
To prevent such pick-up, it is necessary to dress the electrode tips about every 1000 spots.View full abstractDownload PDF (1827K) -
Haruyoshi Suzuki, Michio Inagaki, Toyoaki Bada1963 Volume 32 Issue 11 Pages 1059-1072
Published: November 25, 1963
Released on J-STAGE: August 05, 2011
JOURNAL FREE ACCESSIn this report, the continuation of authors' first report, various types of austenitic, martensitic and ferritic stainless steels were studied by RPI hot ductility test, the effects of working method upon the hot ductility were investigated about wrought round bars and rolled plates of austenitic stainless steels, and the effects of austenite grain size on the hot ductility were also studied. The following results were obtained.
(1) It was found that the hot ductility during the cooling portion of thermal cycle is, in general, higher in rolled plates than in wrought round bars.
In the 347 type stainless steels, the effect of working method on the hot ductility is remarkable, and it appears that this is one of the characteristic of these 347 type stainless steels. It was also found that the variation of hot ductility depending on the change is large in this steel.
(2) The hot ductility measured at 1200°C to 1300°C during the cooling portion was the best in a 16-8-2 Cr-Ni-Mo alloy among various austenite stainless steels, followed by 316 type, 304L type, 304 type and 347 type in that order, the lowest value being given by 310 type. It was found by metallographic observation that the decrease of hot ductility of these austenitic stainless steels was due to the embrittlement caused by the partial liquation of grain boundary din heating up to 1340°C.
(3) The behaviours of ferritic stainless steel 430 type and martensite stainless steel 410 type were quite different from that of austenitic ones.
These steels did not show the embrittlement caused by liquation of grain boundary which occurred in austenitic stainless steel, since their melting points were much higher. Therefore, the decrease of hot ductility during cooling portion may be attributable to the growth of grains. In general, these steels showed good hot ductility, and it appears that the weld cracking of these steels may not be hot cracking but low temperature cracking due to martensitic transformation.
(4) It was found by the RPI hot ductility test that the weldability of some austenitic stainless steels could be improved by the refinement of grain size and the steels with large grains inclined to suffer from more weld cracking.View full abstractDownload PDF (15448K)
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