Recently, the present working environment tends to be reconsidered with high interest in the environmental problem. Especially, air pollution by generating metallic fume during the progress of cutting and welling is the unavoidable issue for labor health. For settling this matter, it is necessary to design the suitable ventilation system that is desirable to be generally composed of large scaled equipments with high efficiency due to big capacity of a fabrication shop. However, the physical property and movement characteristic of fume as minute particles have not been grasped accurately even now.
In this paper, with a view to establishing the ventilation system with perfect control of fume flow, the transportation phenomena on fume, that are assumed minute particles to be gas-phase in turbulent flow by driving vent fans, would be clarified using experimental means and numerical calculation. The experimental simulations of fume diffusion using smoke generator in the three dimensional models of fabrication shop are executed with the appropriate similarity law. And the experimental result of fume flow shows considerably good agreement with the calculated data using two-layers Zone model on the diffusion state of heat and fume. Furthermore, the relation between the ventilation system and the fume transportation state in a fabrication shop is investigated evidently using experimental data.

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With a recent tend to take high interest in the environmental problem and the acquisition of ISO 14001 standard, the time has come to reconsider the present working environment. Especially, air pollution by metallic fume from the progress of cutting and welling is an unavoidable issue for labor health. For settling this matter, it is necessary to design a highly efficient ventilation system that is generally composed of large-scale equipments due to big capacity of the fabrication shop. However, the physical property and movement characteristic of the fume, which is composed by minute particles in different sizes, have not been grasped accurately even now.
In this paper, for establishing efficient ventilation system to control the fume flow, the transportation characteristic of fumes is studied by assuming the fume as a turbulent buoyant gas-phase flow. Three-dimensional numerical simulation on a part of a fabrication shop in some cases are carried out using k-ε model and SIMPLE algorithm to investigate the tendency of forming stagnant fume areas where advection effect on turbulent gas flow is weak. Furthermore, laboratory experiments on fume diffusion, in which pigmented salt waters are used in quasi-two dimensional models of a fabrication shop under an appropriate similarity law, are executed. A two-dimensional numerical simulation is also made and the predicted fume flow shows considerably good agreement with the experimental observation.

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As a recent tendency to take high interest in the environmental problem, the time has come to reconsider the present working environment. Especially, air pollution caused by the generated metallic fume during the progress of cutting and welding in a fabrication shop is a hygienic issue for labor health. For settling this matter, it is necessary to take the pollution-control measures that are desirable to conform to the diffusing aspect of metallic fume in a fabrication shop. However, the physical property and movement characteristic of fume as minute particles have not been grasped accurately even now.
For the purpose of improving the working environment in a fabrication shop, the measurements of distributional concentration and particle size of metallic fume at N/C cutting line, sub-assembly line and cubic block manufacturing line in two shipyards were carried out. Moreover, the turbulent diffusion state of fume corresponding to measurement conditions, in which it has tendency to form those stagnant in absence of advection effect on turbulent gas flow, was numerically analyzed by using k-ε model based on SIMPLE algorithm. As the results, the prediction of fume diffusion shows considerably good agreement with the measurement data. Then, the relation between the ventilation system and the fume transportation state on the working site is investigated evidently using experimental data and calculated data, for establishing the ventilation system with efficient control of fume flow.

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Air pollution caused by the generated metallic fume during the progress of welding in a fabrication shop is one of unavoidable issues for labor health. Especially, a worker is likely to be exposed to high concentration of welding fume in semi-enclosed spaces such as cubic blocks under construction. For setting to cope with the pollution-control, it is necessary to take suitable measures considering the diffusing aspect of welding fume in a cubic block. However, this issue has the problem in which a ventilating way for purging fume should not disturb the welding arc and the shielding gas.
In collaboration with the measurements of distributional concentration of welding fume during manufacture of cubic block, the turbulent diffusing aspect of fume is numerically analyzed using the viscous eddy model in the condition of various ventilation systems and the way of low fume generation. Then, the effect of the measures for decreasing fume concentration on the working site in cubic block is investigated evidently on the base of calculated results.

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In a previous paper, it was clarified that the welding fume produced during arc welding with coated electrode can be converted to the value measured by the filter paper method by multiplying the correction factor 2 measured with the digital dust indicator irrespective of the electrode or the weldment.
In this report, similar experiments were performed in other cases. The results obtained are as follows.
(1) The value of fume density which is produced during semi-automatic carbon-dioxide and non-gas shielded arc welding was obtained by the filter paper method and the indication of digital dust indicator.
There is a proportional relationship similar to that of arc welding with coated electrode and not influenced by the weldment.
(2) It is possible to obtain the same accurate value of welding fume density as that obtained by the filter paper method by multiplying the correction factor 5 to the corresponding value measured with digital dust indicator in semi-automatic carbon-dioxide arc welding and the correction factor 3 in case of semi-automatic non-gas shielded arc welding.
(3) Welding fume is mainly composed of Fe, and Mn, and the collected welding fume in the actual welding site was quantitatively analyzed, obtaining some representative oxides, that is, 49.2% Fe₂O₃ and 7.2% MnO.
(4) Based on these experimental results, it is possible to easily assess a working environment if the fume density in the actual welding sit is measured, and the measured value is compared with the permissible fume density prescribed by the Welding Engineering Standard (WES 9004-1976) ofJapan.

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The production of fumes during brazing is a well-known phenomenon. One of the most important problems associate with such fumes is cadmium due to this element's hazardous nature.
In the present work, the behavior of cadmium fumes during brazing was closely examined for BAg-1 and BAg-3, the typical silver filler metals containing cadmium.
The conclusions drawn from the experiments conducted are as follows:
1) The amount of fumes produced by either BAg-1 or BAg-3 was found to increase as the heating temperature increased when the optimum brazing temperature range was exceeded. This phenomenon can well be explained by the secondary electron images obtained by EPMA.
2) For the both types of filler metals, the cadmium contents of the fumes produced remained as low as less than 0.80% and 0.70% for BAg-1 and BAg-3, respectively, when brazing was conducted at a heating temperature within the optimum temperature range. When this range was exceeded, however, the cadmium content of the fumes increased as the temperature increased.
3) For this experimental device, so long as the heating temperature was kept within the optimum brazing temperature range, Cd concentration of fumes in the air can be controlled less than the WES (9007) control limit. When this range was exceeded, however, the fume concentration surpassed the WES limit by an amount which increased in proportion to the temperature employed.

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The heat source of resistance brazing is electric resistance heating. Therefore the same principles as those for other resistance welding are considered to be applied. However the mechanism of heating and the correlation between the brazing conditions and the strength of brazed joint are less known. It is interesting to investigate the problems of brazing process from the view point of resistance welding process. The authors made small braze area on lap joint specimens similar to resistance spot welding, then tested and analyzed the effects and correlation between elements of resistance brazing condition comparing with those for resistance spot welding. Thus the following fundamental data has been obtained.
The behavior of resistance brazing is very similar to that of resistance spot welding. The correlation between the elements of condition has similar characteristics. The strength of braze increases in proportion to brazing current and brazing time. When the increase rate is saturated, fusion zone similar to nugget of spot weeding is formed. When this phenomenon appears, the strength per a unit area decreases rapidly. And the base metal is heat affected.
Resistance brazing is operated relatively easily, and strength obtained is stable and reliable with optimum schedules.
The voltage drop characteristics at the brazed area observed with an oscillograph is vrey similar to that of resistance spot welding. By analyzing it, it becomes possible to choose appropriate conditions of brazing and control the operation.
The choice of electrode is important. Carbon graphite is of low cost, but has the following shortcoming. The magnitude of current varies remarkably depending on its size, especially decreases exponentially with increase in the thickness.
The surface of material to be brazed and electrode sticks to each other owing to temperature increase before the current duration to obtain the maximum tensile shear load is reached, which. causes a problem in practical operation.

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